Integration of Membrane

Integration of Membrane Filtration Into Water Treatment Systems

Subject Area:High-Quality Water


©2006 AwwaRF. All Rights Reserved.

About the Awwa Research Foundation

The Awwa Research Foundation (AwwaRF) is a member-supported, international, nonprofit organization that sponsors research to enable water utilities, public health agencies, and other professionals to provide safe and affordable drinking water to consumers.

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Prepared by:Jonathan R. Pressdee, Srinivas Veerapaneni, Holly L. Shorney-Darby, and Jonathan A. ClementBlack & Veatch Corporation8400 Ward Parkway, Kansas City, MO 64114and

Jan Peter Van der HoekAmsterdam Water SupplyArlandaweg 88, 1043 EX Amsterdam, The Netherlands

Jointly sponsored by:Awwa Research Foundation6666 West Quincy Avenue, Denver, CO 80235-3098and

U.S. Department of the Interior, Bureau of Reclamation Technical Service Center, Water Resources Research Laboratory, Denver, CO 80225

Published by:


DISCLAIMER

This study was jointly funded by the Awwa Research Foundation (AwwaRF) and the U.S. Bureau of Reclamation (Reclamation) under Cooperative Agreement No. 00FC810253. AwwaRF and Reclamation assume no responsibility for the content of the research study reported in this publication or for the opinions or statements of fact expressed

in the report. The mention of trade names for commercial products does not represent or imply the approval or endorsement of either AwwaRF or Reclamation. This report is presented solely for informational purposes.

Copyright © 2006by Awwa Research Foundation

All Rights Reserved

Printed in the U.S.A.


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CONTENTS LIST OF TABLES.................................................................................................................... vii LIST OF FIGURES .................................................................................................................. xi FOREWORD ............................................................................................................................ xiii ACKNOWLEDGMENTS ........................................................................................................ xv EXECUTIVE SUMMARY ...................................................................................................... xvii CHAPTER 1: INTRODUCTION............................................................................................ 1 Definition of Membrane Integration............................................................................. 1 Objectives ..................................................................................................................... 1 Reasons for Membrane Integration............................................................................... 2 Overview of This Manual and the Decision Tool......................................................... 2 CHAPTER 2: CASE STUDIES OF MEMBRANE INTEGRATION .................................... 5 Introduction .................................................................................................................. 5 Case Studies of MF/UF Integration .............................................................................. 5 Bendigo WTP, Australia................................................................................... 5 Ennerdale WTP, UK ......................................................................................... 14 San Patricio WTP, Texas, USA ........................................................................ 19 Columbia Heights WTP, Minneapolis, Minnesota, USA................................. 30 Chaparral WTP, Scottsdale, Arizona, USA...................................................... 38 Clay Lane WTP, England, UK ......................................................................... 47 Bexar Metropolitan Water System (Bexar Met) WTP, Texas, USA................ 54 Inverness WTP, Scotland, UK.......................................................................... 62 Choa Chu Kang WTP, Singapore ..................................................................... 68 Case Studies of NF/RO Integration .............................................................................. 72 Méry-sur-Oise WTP, France............................................................................. 72 Heemskerk WTP, The Netherlands .................................................................. 76 Torreele Facility, Belgium................................................................................ 80 Pilot Evaluations of Membrane Integration.................................................................. 88 Monroe WTP, Bloomington, Indiana, USA ..................................................... 88 Fort Thomas WTP, Kentucky, USA................................................................. 94 A Case Study of a Utility Considering Membrane Integration..................................... 101 Richard Miller WTP, Cincinnati, Ohio, USA................................................... 101 CHAPTER 3: ISSUES OF MEMBRANE INTEGRATION................................................... 111 Choosing the Right Membrane System ........................................................................ 111 Pilot Testing ...................................................................................................... 119


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Membrane Integrity ...................................................................................................... 123 Membrane Warranty ........................................................................................ 125 Residuals Treatment and Disposal................................................................................ 125 Public Involvement ....................................................................................................... 127 Procurement .................................................................................................................. 127 Municipal Procurement..................................................................................... 128 Private Company Procurement ......................................................................... 129 Operation and Maintenance Needs ............................................................................... 129 Fiber Repair ...................................................................................................... 130 Costs ........................................................................................................................... 131 Installation and Commissioning ................................................................................... 135 Preservative Rinsing ......................................................................................... 136 Wetting of Membrane ....................................................................................... 136 Recommendations to Utilities Considering Membrane Filtration ................................ 136 CHAPTER 4: DECISION TOOL............................................................................................ 139 Overview of the Decision Tool..................................................................................... 139 New Facility...................................................................................................... 139 Retrofitting an Existing Facility........................................................................ 140 CHAPTER 5: CONCLUSIONS AND RECOMMENDATIONS........................................... 143 Conclusions................................................................................................................... 143 Recommendations......................................................................................................... 144 Piloting.............................................................................................................. 144 Planning ............................................................................................................ 144 Design ............................................................................................................... 144 Operation and Maintenance .............................................................................. 145 APPENDIX A: REASONS FOR MEMBRANE INTEGRATION ........................................ 147 APPENDIX B: TECHNICAL ISSUES OF MEMBRANE INTEGRATION......................... 161 APPENDIX C: AwwaRF PROJECTS RELATED TO MEMBRANE INTEGRATION....... 211 APPENDIX D: OPERATIONAL DEFINITIONS.................................................................. 213 APPENDIX E: NOTES FROM MEMBRANE INTEGRATION WORKSHOP ................... 217 APPENDIX F: UTILITY QUESTIONNAIRE FORM ........................................................... 235 REFERENCES ......................................................................................................................... 261 ABBREVIATIONS .................................................................................................................. 275


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TABLES 2.1 Summary of participating membrane integration utilities ............................................ 6 2.2 Summary of the Bendigo WTP, Australia .................................................................... 9 2.3 Typical water quality parameters at the Bendigo WTP................................................ 10 2.4 Summary of the Ennerdale WTP, UK .......................................................................... 15 2.5 Summary of the District’s Plant C................................................................................ 20 2.6 Typical water quality of the Nueces River, which feeds the District’s membrane

treatment plant (Plant C)................................................................................... 21 2.7 Design criteria for pretreatment at the District’s membrane plant (Plant C)................ 22 2.8 Description of Pall membrane modules at the District’s Plant C ................................. 23 2.9 Summary of TMP after CIPs at the District’s Plant C.................................................. 25 2.10 Instrumentation at the District’s Plant C....................................................................... 26 2.11 Evaluated bids for the District’s membrane system at Plant C..................................... 28 2.12 Construction costs for the District’s Plant C................................................................. 28 2.13 Operating costs for 2002 at the District’s Plant C ........................................................ 29 2.14 Summary of the Columbia Heights WTP, Minneapolis, Minnesota, USA .................. 30 2.15 Raw water quality of the Mississippi River.................................................................. 31 2.16 Membrane feed water quality at MWW Columbia Heights WTP................................ 32 2.17 Characteristics of the X-Flow membranes installed in Columbia Heights WTP ......... 33 2.18 Summary of the Chaparral WTP, Scottsdale, Arizona, USA ....................................... 39 2.19 Summary of SRP canal raw water quality during pilot trials ....................................... 45 2.20 Summary of the Clay Lane WTP, England, UK........................................................... 48 2.21 Summary of the Bexar Met WTP, Texas, USA............................................................ 55 2.22 Raw water quality for the Bexar Met MF facility......................................................... 56


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2.23 Settled water quality at the Bexar Met facility ............................................................. 57 2.24 Characteristics of the Aquasource membrane modules at Bexar Met .......................... 58 2.25 Monthly operating costs for Bexar Met Aquasource WTP .......................................... 61 2.26 Summary of the Inverness WTP, Scotland, UK ........................................................... 63 2.27 Feed water quality to the Inverness WTP (January 1, 2000, to

December 31, 2000).......................................................................................... 64 2.28 Summary of the Choa Chu Kang WTP, Singapore ...................................................... 69 2.29 Membrane pilot plant characteristics CCK WTP, Singapore ....................................... 70 2.30 Summary of the Méry-sur-Oise WTP, France.............................................................. 73 2.31 Summary of the Heemskerk WTP, The Netherlands.................................................... 76 2.32 Summary of the Torreele facility, Belgium .................................................................. 80 2.33 Water quality at IWVA’s Torreele facility ................................................................... 82 2.34 Infiltration water quality standards for the Torreele facility......................................... 87 2.35 Raw and finished water quality at the Monroe WTP, Bloomington, Indiana, USA..... 89 2.36 Treatment components of the existing conventional Monroe WTP, Bloomington, Indiana, USA..................................................................................................... 90 2.37 Settled water quality at the Monroe WTP (May 2000 to April 2001) .......................... 91 2.38 Ohio River raw water quality (1999 to 2000)............................................................... 95 2.39 Summary of the existing facilities at the Fort Thomas WTP........................................ 96 2.40 Fort Thomas finished water quality data (1999 to 2000).............................................. 97 2.41 Fort Thomas distribution system water quality data (1999) ......................................... 97 2.42 Summary water quality for the Richard Miller WTP, Cincinnati, Ohio, USA............. 102 2.43 Turbidity and endospore data throughout the Richard Miller WTP,

Cincinnati, Ohio, USA...................................................................................... 103


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3.1 Summary of lessons learned from the literature review ............................................... 112 3.2 Summary of lessons learned from the participating utilities ........................................ 114 3.3 Reasons for membrane integration for the participating utilities.................................. 119 3.4 Integrity test failures and fiber repairs for Manitowoc Public Utilities ........................ 130 3.5 Factors to be considered in estimating costs of membrane systems............................. 132 3.6 A comparison of O&M costs for a conventional versus MF full-scale plant ............... 132 3.7 Impact of water treatment plant upgrades on water rates for the MWW...................... 133 3.8 Costs for membrane filtration plants of the participating utilities ................................ 134 3.9 Recommendations by participating utilities.................................................................. 136



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FIGURES 2.1 Process flow diagram for Bendigo WTP, Australia...................................................... 10 2.2 Process flow diagram for the Ennerdale WTP, UK...................................................... 16 2.3 Process flow diagram for the District’s Plant C, Texas, USA...................................... 22 2.4 Process flow diagram for the MWW Columbia Heights WTP, Minnesota, USA........ 32 2.5 Process flow diagram for the pilot plant for the Chaparral WTP, Arizona, USA ........ 42 2.6 Process flow diagram for the full-scale Chaparral WTP, Arizona, USA ..................... 46 2.7 Process flow diagram for the Clay Lane WTP, England, UK ...................................... 49 2.8 Process flow diagram for the Bexar Met WTP, Texas, USA ....................................... 56 2.9 Process flow diagram for the Inverness WTP, Scotland, UK....................................... 65 2.10 Process flow diagram for the CCK WTP, Singapore ................................................... 71 2.11 Process flow diagram for the Méry-sur-Oise WTP, France ......................................... 74 2.12 Process flow diagram for the Heemskerk WTP, The Netherlands ............................... 78 2.13 Location of the Torreele facility and surrounding geology .......................................... 81 2.14 Process flow diagram for the Torreele facility, Belgium.............................................. 82 2.15 Process flow diagram for the pilot plant at the Monroe WTP, Indiana, USA .............. 91 2.16 Process flow diagram for the pilot plant at the Fort Thomas WTP,

Kentucky, USA................................................................................................. 98 2.17 Process flow diagram for the Richard Miller WTP, Greater Cincinnati Water

Works, Ohio, USA............................................................................................ 102 2.18 Decision tool introduction page .................................................................................... 105 2.19 Decision tool retrofitting existing facility options page ............................................... 106 2.20 Decision tool process flow diagram recommendations ................................................ 107 2.21 Decision tool process recommendations and discussion .............................................. 108


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2.22 Decision tool discussion of issues of integration recommendations (part 1)................ 109 2.23 Decision tool discussion of issues of integration recommendations (part 2)................ 110 3.1 Membrane system capital costs as reported by utilities................................................ 135


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FOREWORD

The Awwa Research Foundation (AwwaRF) is a nonprofit corporation that is dedicated to the implementation of a research effort to help utilities respond to regulatory requirements and traditional high-priority concerns of the industry. The research agenda is developed through a process of consultation with subscribers and drinking water professionals. Under the umbrella of a Strategic Research Plan, the Research Advisory Council prioritizes the suggested projects based upon current and future needs, applicability, and past work; the recommendations are forwarded to the Board of Trustees for final selection. The foundation also sponsors research projects through the unsolicited proposal process; the Collaborative Research, Research Applications, and Tailored Collaboration programs; and various joint research efforts with organizations such as the U.S. Environmental Protection Agency, the U.S. Bureau of Reclamation, and the Association of California Water Agencies.

This publication is a result of one of these sponsored studies, and it is hoped that its findings will be applied in communities throughout the world. The following report serves not only as a means of communicating the results of the water industry’s centralized research program but also as a tool to enlist the further support of the nonmember utilities and individuals.

Projects are managed closely from their inception to the final report by the foundation’s staff and large cadre of volunteers who willingly contribute their time and expertise. The foundation serves a planning and management function and awards contracts to other institutions such as water utilities, universities, and engineering firms. The funding for this research effort comes primarily from the Subscription Program, through which water utilities subscribe to the research program and make an annual payment proportionate to the volume of water they deliver and consultants and manufacturers subscribe based on their annual billings. The program offers a cost-effective and fair method for funding research in the public interest.

A broad spectrum of water supply issues is addressed by the foundation’s research agenda: resources, treatment and operations, distribution and storage, water quality and analysis, toxicology, economics, and management. The ultimate purpose of the coordinated effort is to assist water suppliers to provide the highest possible quality of water economically and reliably. The true benefits are realized when the results are implemented at the utility level. The foundation’s trustees are pleased to offer this publication as a contribution toward that end. Walter J. Bishop Robert C. Renner, P.E. Chair, Board of Trustees Executive Director Awwa Research Foundation Awwa Research Foundation



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ACKNOWLEDGMENTS The authors of this report wish to thank the following water utilities for their cooperation and participation in this project:

Minneapolis Water Works, Minneapolis, Minnesota Intermunicipal Water Company of the Furnes Region, Belgium Three Valleys Water Company, Hertfordshire, United Kingdom United Utilities PLC, Warrington, United Kingdom Scottish Water, United Kingdom Amsterdam Water Supply, The Netherlands Veolia Environmental, Paris, France City of Scottsdale, Arizona Bendigo region of Victoria, Australia Bexar Met Water System, Texas City of Bloomington Utilities, Indiana Northern Kentucky Water District, Kentucky San Patricio Municipal Water District, Texas PWN, The Netherlands Public Utilities Board, Singapore Cincinnati Water Works, Ohio We are also extremely appreciative of the support and encouragement from the Project

Advisory Committee - Peter Hillis (United Utilities); Adam Kramer, Director (Minneapolis Water Works); Gene Koontz, senior vice president (Gannett Fleming); and Michelle Chapman (U.S. Bureau of Reclamation). We also wish to thank Kim Linton, senior account manager (AwwaRF), for her support and advice throughout this project.

The authors of this report would like to acknowledge the contribution of Mr. Emmanuel VanHoutte for the Torreele Water Treatment Plant case study for Intermunicipal Water Company of the Furnes Region, Belgium.

The authors also wish to acknowledge the technical assistance of Gayla Fecher, Liia Hakk, Kara Richter, and Tamara Mannon.



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EXECUTIVE SUMMARY Membrane filtration for drinking water treatment has increased dramatically over the past decade. As drinking water regulations become more stringent, and the availability of high-quality water sources declines, membranes will continue to be an important process alternative for water utilities. Membranes are being installed for many reasons including regulatory compliance, treating challenging waters, asset renewal to replace media filters, protection against degrading water quality in the watershed, in particular disinfectant resistant pathogens, and as a compact and modular treatment process that can fit within limited space and still meet treatment goals. Integration of membrane filtration processes presents many challenges that are not just related to technical considerations. Political, managerial, operational, and maintenance considerations are also necessary to ensure successful integration of membrane filtration systems.

RESEARCH OBJECTIVES

The objective of this project was to examine the process and design implications associated with the integration of membranes into existing water treatment plants and process schemes. The aims of this research were specifically to:

1. Examine why membrane filtration technologies are being integrated into drinking water systems around the world.

2. Perform a detailed and focused literature review detailing experiences with membrane integration including pilot, demonstration and full-scale projects.

3. Report on the design challenges, operational issues, and performance based on experience from utilities, either those which are operating and maintaining membrane filtration systems or planning to install membrane filtration technology in the future.

4. Develop a simple decision-making tool to assist users in selecting the most appropriate membrane technology to treat a given contaminant in the feed water.

5. Capture information gained from the literature review and utility interviews into a fully comprehensive report to assist future users considering membrane systems.

Utility interviews form the backbone of this research. Detailed interviews were held with

over 14 utilities that have experience with membrane systems. The utilities range from the largest drinking water membrane filtration facilities, to smaller plants which treat challenging water. Pilot-scale experience is also included in this research. Membrane technologies covered include microfiltration (MF), ultrafiltration (UF), nanofiltration (NF), and reverse osmosis (RO). Both configurations (i.e., encased and submerged) of the low-pressure membrane technologies were included in this study. Where experience was particularly of interest, follow-up interviews were conducted to gain the best perspectives. Participation by utilities from four continents has brought together diverse experience from Europe, America, Asia, and Australia illustrating the use of membranes to meet treated water quality goals for various constituents on parameters.


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LESSONS LEARNED

Following this Executive Summary, Tables E.1 and E.2 summarize lessons learned during membrane integration projects from the literature review and from the participating utility interviews, respectively. Many of the integration challenges faced by utilities can be prepared for, avoided, or effectively managed by reviewing the lessons learned from this study.

CONCLUSIONS

This study concludes that membrane integration has been successful at both small and large scale water treatment facilities. The main issues associated with membrane integration that were identified in this study, include:

1. Meeting regulatory compliance within a limited time period, particularly for Cryptosporidium removal in the United Kingdom (UK), could impact overall project schedule.

2. Changing water quality and its impact on membrane fouling. 3. Pretreatment influences and impacts of changing water quality on downstream

membrane processes. 4. Maintaining integrity and minimizing fiber breakage with MF/UF processes. 5. Waste or concentrate disposal, due to local limitations on discharge. Finer filtration

by membranes results in waste volumes that are larger than those generated by conventional filtration processes.

6. Translation from pilot- to full-scale installation. 7. Integrating operation of the membrane system with the existing plant processes. 8. Predicting staffing levels. 9. Anticipating training needs for new operators. 10. Achieving regulatory approval. 11. Hydraulic considerations, such as surge issues and flow balancing, throughout the

facility. 12. Preventing flow bottlenecks in integrated systems.

RECOMMENDATIONS

After review of the existing literature and discussions with utilities, the following recommendations for successful membrane integration are suggested:

Pilot Testing

The following recommendations are made for pilot testing of membranes:

1. Pilot test challenging waters thoroughly, by testing through all anticipated water quality changes (e.g., seasonal) and keep pilot plant operational settings as close to those used in the full-scale design as possible.

2. Perform a detailed analysis of the feed water quality to identify all contaminants and potential foulants. Anticipate likely foulants and develop chemical cleaning regimes to target these fouling compounds.


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3. Involve operation and maintenance (O&M) staff during the piloting exercise so that they gain familiarity with the process.

4. Involve regulators through the pilot protocol and testing phases of the piloting program, even if not mandatory, to ease the transition to full-scale implementation and to gain acceptance of the technology.

5. Consider retaining the pilot plant or constructing a small-scale unit for conducting off-line testing once the full-scale plant is operational. This allows testing of alternative chemical cleaning regimes, alternative membrane formulations, and optimization of set points without risk to the full-scale plant.

Planning

The following suggestions are made for membrane integration planning:

1. Involve citizens through meetings, newsletters, and citizens’ advisory groups to generate interest in the project and potentially improve public relations.

2. Talk with other utilities that have installed membranes and learn from their experiences.

3. Go to conferences to understand the issues of membrane integration and discuss these issues with other utilities.

4. Include the costs for piloting in the development of costs for the facility. 5. Meet with regulators to discuss pilot plant test protocol and log removal credit

criteria.

Design

The following areas were identified as design recommendations for successful membrane plant operation:

1. Size the washwater recovery processes with sufficient capacity to avoid creating bottlenecks. If using recovery processes, pilot beforehand to check design criteria. This is particularly important when using membrane filters for processing washwater.

2. Allow for flexible chemical cleaning regimes, and provide space for additional chemical storage and dosing systems. Also, consider provision for cleaning systems even if not specifically required by the membrane system installed.

3. Minimize hydraulic shock by: a. Ensuring sufficient backpressures are maintained through the system for

permeate, concentrate, backwash (BW), and chemical cleaning piping. b. Provide smooth pump start and stop sequences. c. Perform hydraulic analysis and consider all failure modes, including power

failure. 4. Consider the hydraulic gradient and make best use of available head to minimize

pumping costs. 5. Select a design flux that provides not only cost effective treatment, but also stable

operations. 6. Allow sufficient time during commissioning to wet the membranes, fix broken fibers,

and handle/discard preservative solutions.


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Operation and Maintenance

O&M recommendations are as follows:

1. Ensure operational staff has good process training to better understand water chemistry effects upon membrane performance.

2. Involve O&M staff during the piloting, design and construction phase so that they become familiar with the technology well in advance of handover.

3. To optimize handling of fiber repair, O-ring and seal replacement and membrane replacement:

a. Consider contracting these routine tasks if efficiency savings can be demonstrated.

b. Consider purchase of additional vacuum test equipment to speed up the detection of leaks and confirm successful membrane repair.

FUTURE RESEARCH

As membrane filtration technologies are being implemented to treat a wider variety of feed waters, more research is needed to evaluate various design and operation aspects of integration. The largest utilities interviewed as part of this study are approaching 100 million gallons per day (mgd) [378 million liters per day (ML/d)], and membrane technologies are being challenged on an unprecedented scale. The largest plants treat surface waters that can vary significantly in their composition and present challenges to MF and UF processes. How these membrane plants cope with varying water quality conditions over time would be of the utmost interest and follow up interviews should be considered. It should be noted that most large membrane systems have been in operation for less than five years and, for the most part, are still within the original warranty periods. Whether the membrane systems meet these warranty terms or exceed operational life will be interesting to record. Alterations to chemical cleaning regimes to adapt to changing water quality conditions and to optimize membrane filtration processes, particularly in regard to optimizing energy costs, should also be researched. Fiber breakage rates continue to be of concern with several of the utilities interviewed. Modifications to either the system or membrane formulation and their success in reducing breakage rates should also be reviewed as part of any additional study.

In summary, the additional research needs to include:

1. Evaluating the impact of variable and difficult-to-treat surface water on membrane performance.

2. Monitoring the performance of chemical cleaning over a long period of operation. 3. Observe and record fiber breakage rates as a function of average operational flux and

type and frequency of chemical cleans.

OVERVIEW OF THIS MANUAL AND THE DECISION TOOL

This manual is broadly divided into three parts – case studies for 14 utilities that have investigated or implemented integration of membranes into their treatment processes, a discussion of the issues associated with membrane integration, and a computer-based decision tool.


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Chapter 1 is an introduction to the project, and Chapter 2 summarizes the experience of 14 utilities that have investigated or implemented the integration of membranes into their treatment process to various degrees. Information on issues such as planning, regulatory approval, financing, design, pilot studies, procurement, and operational experiences is documented. In addition, the use of the decision tool is illustrated using one utility’s treatment goals. Chapter 3 is a discussion of the issues associated with membrane integration, Chapter 4 gives an overview of the computer-based decision tool, and Chapter 5 summarizes major findings of this study and makes recommendations.

Information compiled from the literature review, interviews with utility personnel, discussions with the project team, members of the Project Advisory Committee, and leading experts from the membrane filtration industry was used to develop of the decision tool model. The main objective of the decision tool model is to identify potential options for integration of membranes with other water treatment processes, either at an existing facility or at a new facility, to meet treatment goals.

There are six appendices in this report. Appendices A and B are reviews of the drivers for membrane integration, including a regulatory review, and a literature review that focuses on issues related to membrane integration, respectively. Appendix C is a list of other relevant AwwaRF reports. Appendix D includes definitions and equations for common membrane-operating parameters. Appendix E is a summary of the workshop that was held as part of this project, and Appendix F is the survey form that was used during the utility interviews.


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Table E.1 Summary of lessons learned from the literature review

Category Lesson Learned • Impurities in chemicals (i.e., coagulant, antiscalant, etc.) can contribute

to fouling of MF/UF and NF/RO. • The potential of naturally-organic compounds to foul membranes is site

specific, with both low- and high-molecular weight organics contributing to fouling at different sites.

• Certain polymers (e.g., cationic) will cause fouling of MF/UF membranes if used during pretreatment and their use should be verified with membrane suppliers prior to feeding these polymers upstream of membranes. Residual polymer in the recycled decant from residuals treatment has been less problematic, but the potential exists for polymer-enhanced fouling.

• Prepare cleaning solutions with softened or demineralized water for MF/UF and NF/RO systems.

• On-line monitoring of oxygen uptake has shown potential for predicting biofouling of membranes.

• Computer models and artificial neural networks are, in general, good indicators of membrane performance.

Fouling

• Algae in source water can significantly impact a membrane water treatment plant (WTP) by clogging pre-strainers, clogging membrane fibers, and secreting polymeric compounds onto the membrane surface. To combat these problems, automatic backwashing pre-strainers are recommended.

Pretreatment • Pretreatment ahead of MF/UF membranes has been shown to lengthen the time between cleanings, reduce feed water quality variability, and allow sustained operation at higher fluxes.

• Certain pretreatment processes ahead of NF/RO can inadvertently contribute to fouling. For example, residual aluminum can react with silicates to create nucleation sites for inorganic scaling.

• MF/UF can provide a lower silt density index (SDI) than conventional treatment upstream of NF/RO; however, fouling of NF/RO can still be problematic.

• Bank filtration can be effective pretreatment to NF/RO. • Allowing oxidants to contact RO membranes can cause increased salt

passage through the affected membrane. The magnitude of this effect depends on the membrane material, the concentration of oxidant, and duration of exposure.

• Oxidation upstream of NF/RO membranes can change the characteristics of any organic compounds present and increase the fouling potential of the feed water.

(continued)


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Table E.1 (Continued) Category Lesson Learned

• The extreme water quality characteristics must be considered during MF/UF and NF/RO design. For example, during a drought year, higher-than-usual sulfide concentrations caused premature fouling of NF/RO membranes.

• The flux for secondary MF/UF that treats BW water is typically much lower (e.g., up to 75 percent lower) than the flux of the primary MF/UF units.

• The concentration of contaminants (e.g., heavy metals) in MF/UF BW can be concentrated to higher levels than BW from conventional filters, and this can result in higher costs for disposal.

• Some utilities in the (United States of America) USA are collecting data for regulatory agencies to justify sending filtrate from a secondary MF/UF unit to distribution.

• Some utilities are recycling untreated BW water to the head of the treatment plant where solids are removed in a pretreatment process.

BW

• Rigorous integrity testing and fiber repair is not always deemed necessary for secondary membrane systems, but this must be confirmed with the presiding regulatory agency.

Reuse • Using MF/UF and NF/RO membranes for treating wastewater can be challenging due to variable water quality, the potential for biological fouling, inorganic fouling, and algal blooms.

• Retrofitting existing filter beds or process basins requires a thorough investigation of feasible alternatives to identify the most cost-effective system. If membranes are being installed for pathogen removal to achieve a specified level of disinfection, adding other alternatives to the existing facility, such as ozone, may be less costly than adding MF/UF.

• Utilities have installed additional membrane filtration capacity to minimize any risk of lower-than-expected production and allow for flexibility in plant operation. This additional capacity can also help maintain production during periods with unusual water quality, such as higher-than-expected turbidity.

• Multiple barriers of disinfection, by both chemical inactivation as well as physical removal, are required by most regulatory agencies, and MF/UF membranes often serve as a physical barrier that is supplemented with chemical disinfection.

• The flow pattern and hydraulic mixing provided by submerged MF/UF systems can yield a high baffling factor for achieving chemical disinfection within the membrane process, if necessary.

Design

• NF/RO currently do not receive pathogen removal credits by regulatory agencies in the USA, although research has shown that NF/RO membranes can achieve > 5.5-log removal. Other countries, such as The Netherlands, grant removal credits to NF/RO systems for viruses.

(continued)


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Table E.1 (Continued)

Category Lesson Learned • The decision to use UF rather than MF is sometimes dictated by the need

for higher virus rejection by UF. However, when using MF/UF for filtration, both can achieve greater than 4-log removal of Cryptosporidium and Giardia, and virus inactivation can usually be achieved with low dosages of commonly used disinfectants, such as chlorine

• Turbidity removal requirements for membrane versus media filter WTPs can be different even though both treatment trains are at the same facility. This has occurred in Canada, but no such facilities have been identified in the USA.

• If there is insufficient time to evaluate MF/UF or NF/RO with pilot testing before design, a conservative flux is typically used to lower the risk of fouling.

• Wetting of a new membrane is usually required at start-up, and this generally requires an extended soak in manufacturer-recommended chemicals during start-up.

• Frequent and sudden flow changes in some of the pressurized, or encased, MF/UF systems can result in enough physical vibration to cause structural fatigue over time

Table E.2 Summary of lessons learned from the participating utilities

Category Lesson Learned Drivers for Integration

• Most of the participating utilities installed MF/UF to meet more stringent water quality regulations or contractual requirements, particularly for maintaining low-filtered water turbidity, and as a barrier for waters impaired by Cryptosporidium and/or Giardia. Limited land space was identified by Scottsdale as a primary driver for MF/UF at their Chaparral WTP.

• Primary reasons for installing or investigating NF/RO integration by participating utilities were to remove dissolved contaminants or constituents, such as pesticides, organics, DBP (disinfection byproduct) precursors, and trace metals. The European utilities also indicated that improving the taste of the water by NF/RO was a reason for installation.

• Reuse is another key driver for membrane integration. The Torreele facility in Belgium, with UF and RO, has been a membrane integration success and is recharging up to 1.8 mgd.

(continued)


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Table E.2 (Continued) Category Lesson Learned

Pilot Testing • All of the participating utilities conducted pilot tests, and some continued the pilot evaluations during commissioning and after WTP operation commenced. The extended pilot studies have resulted in improved cleaning regimes for flux recovery and have identified the impact of different operating procedures [i.e., coagulants, backwashing intervals, chemically-enhanced backwashes (CEBWs)] on sustainable operation. Also, other water quality issues have been identified by pilot testing (e.g., the need for taste and odor control at the Bendigo WTP).

• Some regulatory agencies require pilot testing of MF/UF as alternative filtration technologies prior to approval for a full-scale facility. Both San Patricio and Bexar Met conducted pilot trials to meet these requirements in Texas.

• Oxidant-tolerant membranes proved essential for San Patricio, which experiences very warm water conditions in the summer. Chlorine is needed to control microbial growth. Pilot testing had identified the potential for microbial fouling of non-oxidant-tolerant membranes.

• The potential benefits of long-term pilot trials can not be overstated. For example, Columbia Heights and Scottsdale experienced a fouling event during the final phase of pilot testing, and this identified the need for flexible cleaning regimes at these facilities. At the Inverness facility, extended pilot testing allowed for optimization of the CEBWs, which improved the plant recovery from the contractual requirement of 98 percent to over 99 percent.

• Many of the participating utilities are actively involved in the research and development of their membrane systems. For example, the Heemskerk, Méry-sur-Oise, and Bexar Met facilities have test fibers and/or modules to help membrane vendors and operators gain information on long-term operation of new products. Méry-sur-Oise continues to research cleaning regimes, including different temperatures for the chemicals, to improve flux recovery of NF membranes.

Fiber Breakage

• One UK utility reported a high rate of UF filter breakage due to operation at the upper range of acceptable transmembrane pressure (TMP) for the membrane. Specialized equipment was developed to streamline the repair procedures to help minimize the required staff time for fiber repair.

• In a large facility, the number of broken fibers is typically a low percentage of the total number of fibers, yet it should be recognized that fiber repair is an off-line activity that is labor intensive. Some utilities contract broken fiber identification and repair to membrane vendors or other contractors.

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Category Lesson Learned • The number of broken fibers experienced at a facility can be a sensitive

or confidential topic due to membrane warranty implications; however, several of the participating utilities shared information about their rate of fiber breakage. Some have experienced few fiber breaks since start-up (e.g., San Patricio, Ennerdale), whereas others have experienced a higher rate of fiber breaks (Clay Lane).

Design • The Bendigo facility was designed with a detention basin downstream of the MF cells to account for variations in filtrate flow due to backwashing and tank filling/emptying. This basin helps maintain constant flow to downstream processes.

• During the winter when demands are low, all cells of the Bendigo plant are operated at decreased flux rather than taking them out of service, which would require preservation and/or a maintenance regime.

• Maintaining adequate heating in the building is necessary to prevent freezing of the membranes, especially when some of the racks or cells are removed from service during the winter.

• Extra membrane capacity was included in the initial construction of the San Patricio WTP and this allowed for flexible operation of the facility and helped ensure that production targets could be met.

• Strainers are installed upstream of membranes (MF/UF or NF/RO) to protect the membranes from foreign materials, even when there is extensive pretreatment upstream of the membranes (e.g., Columbia Heights WTP, Clay Lane, Méry-sur-Oise). Also, strainers can capture solids that pass through the pretreatment processes (e.g., excessive iron-salt coagulant solids that occasionally are found in strainers at Bexar Met).

• Allowing for flexible computer programming options of routine functions, such as backwashing intervals, durations, and flow rates, is recommended to optimize treatment over time.

Integrity Testing

• Air bubbles in particle counters are a common problem among the participating utilities.

• Most MF/UF utilities perform daily integrity tests that are typically pressure decay tests (PDTs), and often monitor both turbidity and particle counts in the filtrate of each cell/basin/rack and for the combined filter effluent. Utilities in countries other than the USA tend to perform integrity tests less frequently (e.g., weekly), and often use particle counts as a measure of integrity (Heemskerk and Inverness). Inverness also uses spiked integrity tests (SIMs) every three days as a second means of integrity testing.

• Heemskerk staff monitors the integrity of the RO units with on-line sulfate monitoring.

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Category Lesson Learned • Keeping a detailed log of pinned fibers helps maintain accurate

calculations of system performance at the Bendigo facility. • Misaligned O-rings were reported by Bendigo and Inverness as

occasional causes for integrity testing failures. At the Bendigo facility, particle counting did not detect the problem.

BW • In an effort to minimize discharges from the plant, the Ennerdale facility recycles as much of the primary and secondary BW flow as possible. The total dissolved solids (TDS) of these recycle streams (including neutralized chemicals) must be carefully monitored because high TDS concentrations can impair the sludge thickening process.

• Because the BW process will concentrate solids, including those that may contain contaminants such as arsenic, disposal options may be more costly than expected. For Scottsdale’s Chaparral WTP, initial plans were to dispose BW to the sewer; however, the high cost for disposal and implications with arsenic in the solids led to on-site treatment of solids by clarification and centrifuge dewatering.

• Ennerdale, Inverness, and Clay Lane use secondary membranes to treat BW water. At the Ennerdale and Inverness facilities, the filtrate from secondary units is delivered into distribution. The flux of the secondary units is generally 40 to 50 percent lower than the flux of the primary units.

Commissioning • When bringing the new MF/UF plant on-line, recognize the impact on pressure within the distribution system. At Ennerdale, the entire MF plant was brought into service at once to minimize disruption to the distribution system.

• Sufficient time needs to be allocated for pinning fibers and wetting of the membrane fibers during commissioning.

Operations • Several of the participating utilities contract maintenance and fiber repair work to the membrane suppliers. Their services are used for tasks ranging from guidance on clean-in-place (CIP) scheduling, BW interval, broken fiber location, and fiber repair.

• As utilities gain experience with membrane operation, it is likely that some will petition state regulatory agencies to allow operation at a higher flux to increase capacity. The San Patricio Municipal Water District has petitioned its State regulatory agency to increase production from 7.8 mgd to 8.4 mgd, which is an eight percent increase.

• When water demand decreases in the winter, San Patricio and Bendigo both elect to operate all membrane modules at a reduced flux rather than remove racks or cells from service. This eliminates the need to preserve and monitor off-line trains.

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Category Lesson Learned • Some facilities have required an increased level of staffing after

membrane integration (e.g., Clay Lane), whereas others have maintained similar staffing levels after installation. Many of the facilities are unmanned during the evening hours.

• At the Torreele reuse facility, biofouling was found to be more difficult to predict and control than inorganic fouling. Chloramination is used to help control biofouling of the RO membranes. Monitoring the pre-filter upstream of the RO membranes is also a good indicator of biofouling.

CIPs • Depending on the chemicals used for CIPs, some facilities (e.g., San Patricio, Clay Lane) are able to re-use chemical batches for multiple CIPs. The acid and caustic CIP wastes are also routinely neutralized without additional chemicals.

• Some facilities rely on full CIPs for flux maintenance (e.g., Chaparral WTP, Ennerdale, Bexar Met) whereas others (e.g., Columbia Heights, Heemskerk) use CEBWs to extend the time between CIPs.


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CHAPTER 1 INTRODUCTION

The use of membrane filtration for drinking water treatment has increased considerably over the past 15 years. Initially, membranes were implemented predominantly in smaller plants (less than 1 mgd; 3.7 ML/d) with minimal pre- and post-treatment to treat relatively high quality source water. As the technology matured, and with recent advances in membrane production, the cost has become competitive with conventional processes. Now membrane technology is being implemented in plants treating greater than 100 mgd (370 ML/d). In addition, increasingly stringent drinking water regulations, and declining quality of available source water also are creating rapid growth in the use of membranes to treat more challenging water sources. Many utilities are integrating membrane processes with other treatment processes to meet multiple treatment goals.

Despite the wide implementation of membrane processes in treating various water sources around the world, practical information on issues associated with various aspects of their implementation is not readily available. In particular, issues associated with the integration of membranes with other treatment processes have not been previously investigated. With a sufficient number of plants now in operation worldwide, using various membrane types to treat different source waters, this is an appropriate time to take advantage of lessons learned and knowledge gained through membrane applications for water treatment. To that extent, this report focuses on gathering and consolidating information currently available in the literature regarding integration of membrane processes with other treatment processes. In addition, information gathered on key implementation issues including planning, design, procurement, regulatory issues, construction, and operation is presented.

DEFINITION OF MEMBRANE INTEGRATION

Membrane integration refers to the installation of the membrane filtration process into a water treatment system, either in addition to an existing system or as an entirely new treatment plant. The membrane processes included in this study consist of MF, UF, NF, and RO.

OBJECTIVES

This project was undertaken with the following objectives:

1. To examine the reasons why membrane treatment is gaining popularity with drinking water utilities around the world.

2. To review the literature and the experience gained from pilot-, demonstration- and full-scale membrane integration projects.

3. To report on the design issues, operational challenges, costs, and performance of membrane filter installations studied.

4. To develop a simple decision-making computer tool that will illustrate the potential use of membranes with other processes to achieve treatment goals.


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REASONS FOR MEMBRANE INTEGRATION

According to a survey conducted by United States Environmental Protection Agency (USEPA) (2001), the principal reasons for integrating MF/UF membranes are:

1. Compliance with existing and future regulations (with compliance being facilitated by using membrane filtration).

2. Providing an absolute barrier to protozoan cysts and bacteria (and in some cases, a significant level of virus removal by UF).

3. Improving operating efficiency through automation and ability to treat water of variable quality.

4. Using a smaller land area for the plant in comparison with a conventional filtration system.

5. Providing an additional barrier against hazards to public health. 6. Lowering both capital costs and O&M costs (in comparison with other technologies). 7. Providing a barrier for unfiltered systems that may lose unfiltered status. 8. Providing pretreatment preceding NF or RO. 9. Bolstering consumer confidence in water quality.

The main reason for installing NF and RO is to remove a dissolved contaminant or contaminants from water. Examples of these contaminants are dissolved salts or salinity, pesticides, and total organic carbon (TOC). The most commonly cited reason for implementing membrane filtration has been to meet or exceed current and future regulatory requirements, and for MF/UF particularly the removal of particles, pathogens, and organics. However, because membrane technology has become cost competitive with conventional processes, as well as with some high rate processes, there are other factors such as elimination of operator error and smaller site requirements that are making it more attractive to water purveyors. These issues are discussed in more detail in Appendix A of this report. Drinking water regulations and guidelines established in different countries worldwide have the common goal of protecting public health by maintaining the quality of their drinking water at an acceptable level. The regulations pertaining to membrane integration are reviewed and discussed in Appendix A. In general, the USA and UK have existing or pending regulations that focus on treatment for turbidity and Cryptosporidium removal, whereas other countries use turbidity as a surrogate for treatment targets. These regulations are driving more utilities to consider membranes for compliance.

OVERVIEW OF THIS MANUAL AND THE DECISION TOOL

This manual is broadly divided into three parts – case studies for 14 utilities that have investigated or implemented integration of membranes into their treatment processes, a discussion of the issues associated with membrane integration, and a computer-based decision tool.

Chapter 2 summarizes the experience of 14 utilities that have investigated or implemented the integration of membranes into their treatment process to various degrees. Information on issues such as planning, regulatory approval, financing, design, pilot studies,


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procurement, and operational experiences is documented. In addition, the use of the decision tool is illustrated using one utility’s treatment goals.

Chapter 3 is a discussion of the issues associated with membrane integration, Chapter 4 gives an overview of the computer-based decision tool, and Chapter 5 summarizes major findings of this study and makes recommendations.

Information compiled from the literature review, interviews with utility personnel, discussions with the project team, members of the Project Advisory Committee, and leading experts from the membrane filtration industry was used to develop of the decision tool model. The main objective of the decision tool model is to identify potential options for integration of membranes with other water treatment processes, either at an existing facility or at a new facility, to meet treatment goals.

There are six appendices in this report. Appendices A and B are reviews of the drivers for membrane integration, including a regulatory review, and a literature review that focuses on issues related to membrane integration, respectively. Appendix C is a list of other relevant AwwaRF reports. Appendix D includes definitions and equations for common membrane-operating parameters. Appendix E is a summary of the workshop that was held as part of this project, and Appendix F is the survey form that was used during the utility interviews.



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CHAPTER 2 CASE STUDIES OF MEMBRANE INTEGRATION

INTRODUCTION Twelve utilities were interviewed to gain insight into the issues of membrane integration into full-scale WTPs. For most, membrane integration has been a success with minimal challenges. Many of the utilities used pilot testing to verify performance before and sometimes after design and construction of the full-scale facility. The findings of pilot-scale tests of membrane integration for two additional utilities are also included as case studies. One found that membrane integration would be costly and possibly difficult to maintain based on pilot evaluations, and opted to not integrate membranes.

The participating utilities were selected to provide a broad array of membrane and source water types. Table 2.1 summarizes the (1) technology that is employed, (2) plant capacity, (3) year of construction, where applicable, (4) pretreatment processes, and (5) specific issues that were experienced by the utility.

In this chapter, the integration experience of each utility is summarized individually. Background information about the reason(s) for membrane integration is presented, and operating conditions are summarized. Any unique issues or challenges are also discussed, and descriptions of any pilot studies are also included. A synopsis of these utility integration experiences is provided in Chapter 3.

A case study of one utility that is considering membrane integration is also provided. The background and treatment objectives for this utility are first described, and then the decision tool is used to generate options for membrane integration. CASE STUDIES OF MF/UF INTEGRATION

Bendigo WTP, Australia

The Bendigo WTP uses MF to treat surface water. This is a full-scale installation that has been operating since 2002. A summary of the Bendigo WTP is shown in Table 2.2.

Background

The Coliban Water Aqua Project (i.e., Aqua 2000) is a build-own-operate-transfer (BOOT) project awarded to Veolia Water for the design, construction, and 25-year operation of three water treatment plants in the Bendigo region of Victoria, Australia. Aqua 2000 includes three WTPs: (1) Bendigo (33.3 mgd; 126 ML/d), (2) Castlemaine (4.75 mgd; 18 ML/d), and (3) Kyneton (2.1 mgd; 7.8 ML/d). Each of these treatment plants has MF followed by ozone and biological activated carbon (BAC). This utility interview will focus on the Bendigo facility, which uses USFilter’s submerged MF system. Castlemaine and Kyneton use USFilter’s cartridge, or pressurized, MF system.

The Bendigo facility completed commissioning in May 2002, and began delivering water to distribution in June 2002.


Table 2.1 Summary of participating membrane integration utilities

Plant Water source Membrane technology

Membrane supplier

Plant capacity

Year constructed Pre- and post-treatment Key issues

Bendigo, Australia

Surface water, reservoir, upland source

MF Memcor CMF-S

33 mgd 126 ML/d

2002 Aluminum chlorohydrate (ACH) coagulation, lime and carbon dioxide (CO2) Post ozone and granular activated carbon (GAC)

Optimized organic removal, pH control

Ennerdale, UK Surface water, lake, upland

MF Memcor CMF

16 mgd 59 ML/d

1999 30 micrometer (µm) drum screen

Algae, limited volumetric discharge permit. Cryptosporidium protection.

San Patricio, Texas

River 60% Reservoir 40%

MF Pall 7.8 mgd 30 ML/d

2000 Coagulation and clarification

TOC, Reduced flux operation at low flow, pipe material compatibility

Columbia Heights, Minneapolis, Minnesota

River, direct abstraction

UF Norit 70 mgd 275 ML/d

2005 Lime softening, powdered activated carbon (PAC), ferric chloride coagulation, and clarification

Variable quality source, alkalinity changes, variable organic composition, cold water

Chaparral WTP, Scottsdale, Arizona

Canal UF Zenon 500D 30 mgd 114 ML/d

2005 Ferric coagulation

Post GAC

Algae, arsenic, solids disposal deterioration

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Table 2.1 (Continued) Plant

Water source Membrane technology

Membrane supplier

Plant capacity

Year constructed

Pre- and post-treatment Key issues

Clay Lane, UK Groundwater UF Norit 42 mgd 160 ML/d

2001 Ozone and GAC pretreatment.

Limited volumetric discharge permit. Fiber breakage detection. Cryptosporidium reduction.

Bexar Met, Texas

Reservoir, river fed

UF Aquasource 9 mgd 34 ML/d

2000 Superpulsator clarification. PAC and pH correction provision.

Pre-filter clogging. Instrument calibration.

Inverness, UK

Blend from two lochs or lake sources

UF Norit 9.1 mgd 35 ML/d

2002 80 µm drum strainers, ferric coagulation.

Color removal using direct filtration. Cryptosporidium protection.

CCK, Singapore

Reservoir blend from three sources

UF Zenon 1000 48 mgd 182 ML/d

2006 – 2007 Pulsator clarifiers pretreatment, and chlorine post-disinfection.

Algae, aquatic invertebrates, TOC removal. Siphon arrangement.

Méry-sur-Oise, France

River, direct abstraction

NF Dow Filmtec 37 mgd 140 ML/d

1999 Ballasted flocculation, ozone, PAC, dual media filtration. Post ultraviolet (UV) disinfection.

Turbid water source. TOC reduction, lower chlorine demand.

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Table 2.1 (Continued)

Plant Water source Membrane technology

Membrane supplier

Plant capacity

Year constructed

Pre- and post-treatment Key issues

Heemskerk, The Netherlands

Lake UF and RO Norit UF Hydranautics RO

16 mgd 60 ML/d

2000 Coagulation, clarification and sand filtration.

Salinity reduction. UF fiber breakage.

Torreele WTP, Belgium

Wastewater effluent, aquifer recharge

UF and RO UF – Zenon 500C RO – Dow

1.8 mgd 6.8 ML/d

2002 Pre-screening, chloramination, antiscalent. Post UV disinfection.

Biofouling control, scaling.

Monroe WTP Bloomington, Indiana

Reservoir Pilot study MF and UF

N/A – pilot study N/A – pilot study

Plant not built

Pilot tests run with and without pretreatment. Pretreatment comprised coagulation and clarification.

TOC renewal, temperature variations.

Fort Thomas WTP, Kentucky

Reservoir Pilot study NF and RO

N/A – pilot study N/A – pilot study

Plant not built

Pre-chlorination, coagulation, clarification, filtration and dechlorination.

DBP precursor removal, fouling.

Greater Cincinnati Water Richard Miller WTP, Ohio

Direct river abstraction

Desk study with

decision tool

MF/UF Not supplier specific.

Study only Primary sedimentation, PAC, secondary sedimentation, sand filtration, GAC.

Cryptosporidium concern due to nature of watershed and direct abstraction.

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Table 2.2

Summary of the Bendigo WTP, Australia Status of project Start-up in 2002 Capacity 33.3 mgd: 126 ML/d Source water Surface;-aqueduct/reservoirs Pretreatment ACH coagulation Type of membrane USFilter - submerged MF Design flux 35.2 gfd; 60 lmh Pilot testing Yes, 1998-1999, pretreatment

versus direct filtration Integrity testing Daily PDTs Main driver for integration

Low finished water turbidity requirements

Source Water

The raw water originates in the mountains and is collected and stored in three reservoirs. The raw water flows from these reservoirs through about 43 miles [70 kilometers (km)] of aqueduct to the Sandhurst Reservoir then to the WTP. This water is used for drinking water supply as well as for irrigation along the aqueduct system. Additionally, raw water may be obtained from Lake Eppalock, which is a recreational reservoir.

The storage reservoir that supplies the Bendigo facility has a capacity of 1,850 million gallons (MG) [7,000 million liters (ML)]. The source water is soft and unbuffered, and can contain moderately high concentrations of TOC (Table 2.3). The temperature can be as low as 43°F (degrees Fahrenheit) [6°C (degrees Celsius)].

Description of Treatment Plant

The process flow diagram is shown in Figure 2.1. Pretreatment. Raw water is pre-screened with rotating screens that have pore openings of 3 millimeter (mm) to remove debris and the broad-leaf weeds that grow in the reservoir. The water is dosed with lime and CO2 for buffering and corrosion protection. An ACH coagulant is then added [5 to 6 milligrams per liter (mg/L)] for the coagulation of color, metals, particles, and organics. The targeted pH range is between 6.8 and 7.0. A three-minute contact time (at design flow) is provided to allow micro-floc development prior to membrane filtration.


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Table 2.3 Typical water quality parameters at the Bendigo WTP

Raw water Post CMF-S BAC filtered Turbidity nephelometric turbidity units (NTU‡)

0.9 – 2.4 0.012 0.05

Particles (cnt/ml;2-5µm) 8000 0 - 3 (online)

35 – 45 (grab sample)

True color (CU§) 10 – 22 5 -12 ( at 10 mg/L ACH)

2 – 3

Aluminum (mg/L) 0.060 - 0.2 0.03 - 0.04 (at 10 mg/L ACH)

0.04

Iron (mg/L) 0.080 – 0.120 <0.05 <0.05 Manganese (mg/L) 0.01 – 0.094 <0.1 <0.1 Dissolved organic carbon (DOC) (mg/L)

5.4 – 6.2 4- 4.5 (at 10 mg/L ACH)

2.0 – 2.8 (50 – 60% removal)

TTHM*† (µg/L) 360 98 23 HAA5* (µg/L) 120 54 30 Bromate (µg/L) - - <10

* TTHM and HAA5 formation using simulated distribution system method. † Raw water TTHM is from formation potential testing conditions. ‡ Nephelometric turbidity units (NTU) § Color unit (CU)

Primary Membranes. The water flows by gravity to the submerged membrane plant. The Bendigo facility has eight cells and each contains 576 submerged membrane modules. The membrane modules are mounted in a clover arrangement. The permeate passes through the MF membrane, which as a nominal pore size of 0.2 µm, by use of one suction pump per basin.

3 Raw Water Reservoirs

Pretreatment

Lime ACHCO2

Aqueduct

SupernatantCleaning Waste

Neutralization Tank

Ozone

Static Mixer

6 BAC Filters

To Sewer

Cl2NH3

LimeFI

DirtyBackwash

ACH

ThickenerTo Sewer

Drying Beds

Filter to Waste

Figure 2.1 Process flow diagram for the Bendigo WTP, Australia

Distribution3 Raw Water Reservoirs

Pretreatment

Lime ACHCO2

Aqueduct

SupernatantCleaning Waste

Neutralization Tank

Ozone

Static Mixer

6 BAC Filters

To Sewer

Cl2NH3

LimeFI

DirtyBackwash

ACH

ThickenerTo Sewer

Drying Beds

Filter to Waste

Figure 2.1 Process flow diagram for the Bendigo WTP, Australia

Distribution


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The design flux rate is 35.2 gallons per square foot per day (gfd) [60 liters per square meters per hours (lmh)], which is based on seven cells in operation, which equates to a total membrane area of 1,541,220 square feet (ft2) [143,236 square meters (m2)]. An eighth cell was added to help stabilize the flow from the membrane cells to the downstream ozone contactors. The plant achieves an overall recovery of about 95 percent. Post-treatment. Ozone and BAC are used downstream of the membranes to control taste and odor as well as to remove additional organics and algal toxins from the filtered water. These post-treatment processes also produce a more biologically stable finished water, the benefits of which include less regrowth in the distribution system and a lower disinfectant demand.

Ozone is generated at the Bendigo facility using liquid oxygen. Ozone is injected into static mixers upstream of the ozone contactor. The ozone contactor has three compartments and provides five minutes of contact time at design flow.

The six BAC filters house coal-based GAC. The empty bed contact time (EBCT) is eight minutes and the filters are backwashed with air, followed by air and water, and finally by water. They are equipped with a filter-to-waste system.

BAC filtered water is dosed with chlorine and then ammonia to provide a chloramine residual. This disinfectant is used to meet the total trihalomethanes (TTHM) and the regulated five haloacetic acids [dibromo-, dichloro-, monochloro-, monobromo-, and trichloro-acetic acid (HAA5)] standards of 0.08 mg/L and 0.06 mg/L, respectively. Lime is also added for corrosion control and fluoride is added for dental protection.

An 11-MG (42-ML) clearwell is used to supply the gravity distribution system. A summary of the WTP’s water quality data is shown in Table 2.3.

Backwashing and cleaning. Two types of waste are generated at the Bendigo facility (1) BW water from the membrane cells and the BAC, and (2) chemical cleaning waste. Backwashes are conducted per cell at a frequency of every 30 minutes. Both air and water are used for each BW. Permeate from the membrane system is stored in a holding tank to supply BW flow for the membranes.

The plant was designed with an extra basin to better balance flow to the downstream ozone contactors. The backwashing operations are designed such that after a basin backwashes, the entire contents of the basin are drained to waste. The basin is then filled with feed water and remains off-line until the next basin begins backwashing. The time period of non-operation is less than 10 minutes.

BW water from the membranes and BAC filters is re-coagulated using ACH in a circular clarifier. The supernatant is recycled and introduced upstream of lime addition in the main process train. The target turbidity of this supernatant stream is <5 NTU, and it is typically <1 NTU. The sludge is discharged to drying beds, and any sludge bed filtrate is recycled to the thickener.

No polymer is added to the BW treatment at the Bendigo facility; however, for the past five months, a polymer has been applied to a similar treatment for BW water at the Castlemaine Water Treatment Works (WTW) to improve the turbidity. Staff monitors closely the membrane characteristics and post-clean recovery at this plant to determine any impacts of polymer carry-over on the pressurized membranes at that location. To date there has been no detrimental performance of the membranes associated with polymer use in the thickener.

CIPs are performed every four weeks. During the winter, low demand allows for longer soaking periods of up to 16 hours, but during the summer the soaking period is two hours in acid


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at pH 1.95 followed by two hours in caustic, at 52 milli-Siemens (mS), measured by conductivity probe.

Membrane cleaning chemicals are neutralized and removed via sewer. Cleaning waste and sludge are the only waste flows from the treatment plant. All other flows are recycled.

Control and Operating Philosophy

The current philosophy is to maintain the current program of operating all eight basins concurrently. During the winter of 2002, when the demand was lower, all eight basins were in operation, however, the flux was decreased and cleaning times extended.

Staff

The plant is operated with a day shift crew consisting of a manager, a chemist, and four operators. There is a call-out system for after hours. These operators also perform basic maintenance and calibration of instruments. External contractors are used for other plant maintenance as well as the supervisory control and data acquisition (SCADA) and programmable logic control (PLC) system.

Pilot Plant

Two phases of pilot trials were conducted for the Coliban Water Authority. The first stage operated from May 1998 until February 1999. During this trial, the use of an upstream clarifier versus direct dosing of coagulant was evaluated. Direct dosing of ACH at 20 mg/L was not found to significantly hinder operations. The cleaning interval and design flux was also established. One advantage of pilot testing was that the need for long-term taste and odor control was identified.

After the award of the contract, a more comprehensive pilot program, which is referred to as the Process Verification Plan (PVP) was conducted in parallel with the detailed design. This second phase of pilot testing began in October of 1999 and will be operated in the future as a research and development tool. Several aspects of treatment have been evaluated during the PVP. These include:

1. A comparison of an adsorption clarifier and a ballasted flocculation clarifier for

coagulation upstream of the MF. 2. The effect of polymer carryover on the MF. 3. The cleaning regime for the MF. 4. The design parameters for downstream ozone and BAC.

Design details from the PVP provided the basis for life cycle cost evaluation of PAC

addition versus ozone and BAC. Ozone and BAC proved to be less expensive and more reliable for taste and odor control. This option also offered other benefits for organics and pesticide removal.

The PVP helped to determine and refine critical process parameters as well as to test various analytical instruments and chemicals that could be used in the full-scale plant. The PVP


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continues to operate periodically as a tool for training plant operators and evaluating different cleaning regimes and coagulant dosages.

The cost of the pilot plant, including the building and testing, was $423,000 (AUS$750,000; 0.564 conversion factor).

Instrumentation

The water quality and quantity are measured at numerous locations within each of the WTPs. Parameters that are monitored include online particle counting and turbidity for each of the eight basins.

Interface points are also monitored. Interface points are defined as places in the system where the water is transferred from the contractor (i.e., Veolia) to the client (i.e., Coliban Water Authority). An additional monitoring location is the first customer in the distribution system. Each of the interface points are monitored continuously for chlorine residual, pressure, flow, pH, and color, and daily microbiological samples.

Integrity Testing

The integrity of the system is verified with on-line particle counting and daily PDTs. The frequency of integrity testing was a contractual requirement, and not prescribed by the Australian Drinking Water Guidelines (ADWG).

On occasion, staff have observed a higher-than-expected particle count [e.g., 1 to 2 counts per milliliter (mL)] in the permeate. PDTs have verified the integrity of the system, and the increase in particle counts is attributed to air bubbles in the sampling lines after the cell is backwashed. Significant monetary penalties are incurred if the particle count exceeds 10 counts per mL, thus any possible error of on-line particle counting needs to be corrected. Staff has investigated automated valves that will minimize air gaps and bubbles in the sample line to the particle counter.

Results from the PDT are used to calculate the log removal for the plant. The BOOT contract requires greater than 4-log removal. The plant achieves greater than 4.5-log removal.

Staff believes that the PDT is a better indicator of system integrity than particle counting. During commissioning, a PDT indicated a problem with one of the cells even though the particle counts were low (i.e., less than 1 count per mL). Investigations of each module showed that one of the O-rings was not installed properly. The O-ring installation was corrected, the PDT was successfully repeated, and maintenance instructions were modified to ensure the problem could not reoccur.

Operation to Date

The Bendigo facility has been operating well since the system began supplying water in July 2002. The operators alter the ACH dose and coagulation pH to achieve optimum turbidity and organics removal. Methods to improve membrane cleaning regimes are also being investigated. Operators keep a detailed log of all membrane fibers that are pinned. Maintaining a thorough record of the non-operational fibers will assist with performance calculations at the plant.


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Cost

Confidentiality agreements between Veolia and the client prevent the publication of capital and O&M costs for the Bendigo facility.

Influence of Regulators

The contract had water quality targets that have been adopted from the USA and European Union (EU) drinking water standards. These targets were more stringent than the 1996 ADWG, and these targets were a main driver for membrane integration.

Planning Issues

No significant planning issues emerged during this project. The plant is located in a rural area, just outside the suburbs of Bendigo, which has a population of about 100,000.

Recommendations to Other Utilities

Pilot testing was recommended to identify the flux and cleaning regime for the source water to be filtered. The Bendigo facility is equipped with a permanent pilot plant to allow future testing of operations like cleaning regimes. Allowing enough time to complete pinning of non-functional fibers during commissioning was one recommendation for utilities planning membrane integration. The submerged membrane modules are not able to be tested in the factory as for pressurized systems, and during commissioning, the membrane modules have to be tested and some fibers pinned. Also time is required to ensure the membranes are adequately wetted. Detailed logs of all chemical batches and dilutions are recommended to make sure that CIPs are performed at the correct concentrations. If on-line instruments, such as conductivity probes, are used to control the strength of the chemical solutions, they must be calibrated and maintained, otherwise the CIPs may be incomplete.

Main Drivers for Membrane Integration

The water quality requirements for the Bendigo facility were mandated by the contractual documents, which followed water quality regulations from the USA and EU. The turbidity requirement for the permeate was <0.1 NTU, 95 percent of the time, with an absolute maximum limit of 1.0 NTU. Penalties are imposed if turbidity readings are greater than 0.1 NTU or for changes in turbidity of more than 0.2 NTU. The particle count standard requires that no more than 10 particles per ml in the 2- to 5-µm range, 95 percent of the time, can be detected. These strict limits for turbidity and particles required a process with consistent water quality, and MF was selected to meet these performance standards and protect against Cryptosporidium and Giardia.

Ennerdale WTP, UK

The Ennerdale WTP uses MF to treat a surface water supply. This plant has been in operation since 1999. A summary of the Ennerdale WTP is in Table 2.4.


15

Table 2.4

Summary of the Ennerdale WTP, UK Status of project Start-up in 1999 Capacity 16 mgd; 59 ML/d Source water Surface, Lake Ennerdale Pretreatment Strainers Types of membrane Memcor CMF-9010C Cartridge MF Design flux 94 gfd; 160 lmh Pilot testing 1993-1994; three different membrane

systems Integrity testing Weekly PDTs Main driver for integration Cryptosporidium removal

Background

In 1993, the West Cumbria region of northern England experienced a Cryptosporidium outbreak that led to a 63 confirmed cases of Cryptosporidiosis. Water supplies in this region are historically of good quality (i.e., low turbidity and low color), and existing treatment for many facilities comprise micro-straining and chlorine disinfection. North West Water evaluated the performance of WTPs in West Cumbria and determined that several systems, including the Ennerdale WTP, required improved particle removal to safeguard the public against further incidences of Cryptosporidium. The existing WTP at Ennerdale included extraction from Lake Ennerdale, followed by micro-straining with 30 μm pore-size rotating drum strainers, followed by chlorination. This facility is located in the beautiful and pristine Lake District National Park. Farming is the major industry in the area and sheep graze on the surrounding pastures and hillsides. The location is a remote, rural setting with no access to a sewer system. As a result, the facility has almost a zero discharge. All major flows are recycled, except for the micro-strainer BW, and solids are hauled off site by tanker truck. The Ennerdale WTP serves 60,000 customers.

Source Water

The source of supply is Ennerdale Lake, which is a shallow lake subject to algal blooms in the summer and elevated turbidity in the winter. The winter runoff results in some sand being caught in the intake. The average turbidity entering the plant is about 0.2 NTU, and it can sometimes peak at 0.9 NTU.


The new Ennerdale WTP was commissioned in 1999 with a design flow range of 1.3 to 16 mgd (5 to 59 ML/d). There are no plans to expand the WTP because the plant currently has excess capacity for the service area. This is a result the closure of a chemical plant that used to require as much as 6.6 mgd (25 ML/d).


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The plant was constructed as a design-build project with two main contracts: USFilter Memcor for the membrane equipment and Tilbury Douglas as the general contractor. Bechtel were the consulting engineers.

A process flow diagram is shown in Figure 2.2. Pretreatment. The intake in Lake Ennerdale is located about 3.3 feet (ft) [1 meter (m)] above the lake bed, and typically has 13.2 ft (4 m) of head from the overflow weir in the lake.

Lake water is fed by gravity to three rotating drum strainers (30 μm; Beaudrey, France). These existing strainers are finer than those typically specified for the Memcor MF process. They are washed with a high-pressure jet spray, which increases as the differential pressure builds with continued use. BW water is pumped either back to a fish pass or to the River Ehen, which flows into Lake Ennerdale. Water from the micro-strainers is pumped to the MF system. Primary Membranes. Two pumps supply the membrane systems at 30 pounds per square inch (psi), (2 bar) pressure. The Ennerdale WTP is equipped with 17 primary MF units (Memcor CMF-9010C) that operate at a flux of 64.8 to 94.3 gfd (110 to 160 lmh) at 36 to 61°F (2 to 16 C), respectively. These membranes were provided with a five-year warranty.

Extra piping and valves have been installed so that two of the primary units can be used as secondary units for the purposes of wash water recovery, if necessary.

Figure 2.2 Process flow diagram for the Ennerdale WTP, UK

Trucks Hauling Off-Site

River Ehen

3 Micro-Strainers

BackwashNaOH Orthophosphate

Supply

Neutralization Tank

Dirty Backwash Tank

Secondary BackwashTank

SludgeThickener

Supernatant

Control Valves

Lake Ennerdale

NaOH H2SO4

Permeate

FNaOCl

SecondaryMFs

CIP Waste

CIP Wash

Permeate

Strainer

StorageTank

Recycle

MemcorMF

Contact Basin

Back-wash

Figure 2.2 Process flow diagram for the Ennerdale WTP, UK


River Ehen

3 Micro-Strainers

BackwashNaOH Orthophosphate

Supply

Neutralization Tank

Dirty Backwash Tank

Secondary BackwashTank

SludgeThickener

Supernatant

Control Valves

Lake Ennerdale

NaOH H2SO4

Permeate

FNaOCl

SecondaryMFs

CIP Waste

CIP Wash

Permeate

Strainer

StorageTank

Recycle

MemcorMF

Contact Basin

Back-wash


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No specific membrane preservation techniques have been used at the facility. Maintaining adequate heating within the building is critical to preventing freezing conditions when units are out of service. Post-treatment. Sodium hypochlorite (NaOCl) and fluoride are added to permeate as it enters the existing chlorine contact tank. The pH is typically between four and five, and sodium hydroxide is used to adjust the final pH to 8.0 for corrosion control. Orthophosphate is also added to the finished water for corrosion control. Secondary membranes. There are two secondary MF units (Memcor CMF-9010C) that operate at approximately 36.5 to 58.9 gfd (62 to 100 lmh) at 36 to 61°F (2 to 16°C), respectively. Secondary membrane units are used to treat the BW water from the primary units. The secondary units are backwashed every 30 minutes using the air/wash BW. The BW from the secondary units flows to a receiving tank [9,250 gallons; 35 cubic meters (m3)]. Backwashing and Cleaning. The primary units are backwashed every 60 minutes for about three minutes with a water and air BW sequence. BW flows to a primary receiving tank (660,500 gallons; 50 m3). It is then pumped to a secondary membrane filtration process.

An automated CIP system utilizes two percent sodium hydroxide for a three-hour soak. This is performed about every 10 days. CIP waste is neutralized with sulfuric acid to a pH of 6.5 to 7.5. No CIPs are performed on weekends or holidays, so that staff can be present to monitor the performance and resulting conductivity. The CIP solution is heated to 104oF (40oC) to improve the efficiency of the procedure.

Sulfuric acid CIPs are conducted at pH 1.5 only about once every three months, due to the low mineral content of the raw water. Efforts are made to minimize sulfuric acid CIPs, because neutralization of the CIP waste elevates the conductivity in the secondary BW tank significantly, which feeds the sludge thickeners. When sulfuric acid CIPs are performed, waste streams are sometimes removed from site by tanker, rather than combining them with flow in the thickeners. This is because high conductivity in the thickeners impairs the thickening process. The maximum allowable conductivity to enter the thickeners is 700 mS.

Under normal operations, the conductivity of the water increases by less than 10 percent; however, the conductivity in the secondary treatment system is typically near 120 mS, but it is then diluted by the raw water, which has a conductivity near 25 mS.

Hydrogen peroxide biocide CIPs can also be conducted; thus far, only annual peroxide CIPs have been necessary. Sludge Treatment. Two sludge thickeners treat the BW from the secondary MF units to about two percent solids. Polyaluminum chloride (PACl) is added to achieve a pH of 6.1. The goal of four percent solids has been difficult to achieve, due to the impact of conductivity on the blanket stability within the thickener. There is a feed point for polymer addition at the inlet to the thickeners; however, it has not been used as the impact of any residual polymer carry-over to the secondary units is not known. About 2,600 gallons (10 m3) of sludge is produced per week during average conditions at 8 mgd (30 ML/d). This is stored on site and hauled away by truck to a licensed disposal site. The supernatant from the sludge thickeners is returned to the BW tank and is treated by the secondary MF units.


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Staff

The plant is manned with operators on eight-hour shifts. Weekends, evenings, and holidays are covered by telemetry and a 24-hour call-out rotation.

Pilot Plant

In 1993 and 1994, pilot testing was conducted using three different membrane systems: Acumem, Aquasource, and Memcor. The Acumem system was operated for about 18 months, and the Aquasource and Memcor units operated for about six months. The pilot tests were conducted to allow vendors to develop design data for bidding the full-scale plant. Memcor’s bid was ultimately selected.

Currently, there are no pilot plant units on site. Because there is extra capacity at the plant, there are discussions about challenging one of the units with sustained higher flux rates over a 12-month period to test the durability of the system.

Instrumentation

The raw water is monitored for pH, turbidity, and conductivity. The feed water to the MF units is monitored for particle counts, turbidity, and conductivity. There are conductivity monitors on the filtrate of each unit. The common filtrate stream is monitored for turbidity, particle counts, fluoride, and chlorine. The Ennerdale WTP petitioned to discontinue the Drinking Water Inspectorate (DWI) required continuous Cryptosporidium monitoring. The equipment is still available for use, and will only be used if the MF plant is bypassed. If a bypass occurs, a boil order notice will be issued.

Integrity Testing

Weekly PDTs are manually initiated on both the primary and secondary units. The pressure at the start and end of the PDT is recorded for each unit, and if the pressure difference exceeds 1.3 psi [9.0 kilo Pascal (kPa)], the unit is taken out of service. This pressure decay target was established to maintain 4-log Cryptosporidium removal in the system. A Memcor technician is then called to site to perform sonic mapping on the unit to identify which of the 90 membrane modules on the unit is compromised. The compromised membrane cartridge is isolated by manually closing inlet and outlet valves, and the unit is returned to service. When about 10 percent of the plant’s capacity is isolated and out of service, a subcontractor is hired to perform immersion testing to identify and pin the compromised fibers. This approach has proved more cost effective than calling in the subcontractor for single module replacement. During the immersion test, air is applied to the filtrate portal of the module, and air bubbles are visually observed.

Operation to Date

The plant has operated very well since its commissioning in 1999. Memcor has been retained on a maintenance contract and provides guidance on CIP, BW, and production


19

operations for both the primary and secondary units. Memcor have also been retained to handle service calls for sonic mapping of compromised membrane modules.

Planning Issues

The Ennerdale WTP is located in the Lake District National Park. The Planning Board had strict requirements for the new facility. The exterior architecture was selected to blend into the rural landscape. The buildings are single story with stone facing, and have a slate roof. When the new intake was constructed, a tunnel boring machine was used to minimize any disturbance to natural vegetation in the area. Tunneling immediately adjacent to the lake was performed manually by a qualified team of excavation specialists. Truck traffic is limited to two loads per day to and from the facility. This restriction presents challenges for chemical deliveries and sludge and waste removal activities at the plant. This facility is a critical source of supply in the area, and is prone to heavy snowfall events in the winter. As a result, the site is equipped with 21,000 gallons [80,000 liters (L)] of diesel fuel to allow three days operation if the power supply is terminated and the site is inaccessible to traffic.


When the membrane equipment was installed, the driving head of the existing WTP was broken. This required careful coordination between distribution pumping needs and production. Ennerdale staff chose to bring the entire plant into service as opposed to a staged start up sequence, and although this change over was successful, it was recommended that a detailed plan be prepared to enable a smooth transition.

The plant has observed a slight decrease in the chlorine demand at Ennerdale; however, the corresponding cost savings is not deemed significant. They have, however, received a few complaints about chlorine taste, but that may be associated with pipe replacement projects.

Membrane plants are often visited by staff from other utilities, school groups, politicians, and community groups. The administration building contains a small classroom that can accommodate about 24 people. It houses a process schematic, a map of the service area, dissected membrane modules, and literature for visitors.

San Patricio WTP, Texas, USA

The San Patricio Municipal Water District (District) treats a surface water with clarification and MF. The WTP has been in operation since 2000. Table 2.5 summarizes the District’s WTP, which is referred to as Plant C.

Background

In the past, San Patricio County, which is in the southern part of Texas, depended on groundwater for potable water supply. As a result, the salinity of the available groundwater has steadily increased rendering the groundwater unusable as a potable supply. This led to the formation of the San Patricio Municipal Water District, which treats and delivers surface water. The District now operates two conventional surface WTPs as well as a new membrane treatment facility.


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Table 2.5

Summary of the District’s Plant C Status of project Start-up in 2000 Capacity 7.8 mgd; 30 ML/d Source water Surface, reservoir Pretreatment Chlorine dioxide, alum coagulation,

sedimentation Type of membrane Pall MF (Microza USV-6203) Design flux 58 gfd; 99 lmh Pilot testing Required by primary agency, three

membrane systems evaluated Integrity testing Daily PDTs Main driver for integration Giardia and Cryptosporidium removal

Plant A is a 9 mgd (34 ML/d) conventional WTP consisting of coagulation, flocculation,

sedimentation and mixed media filtration. Plant B is a 6 mgd (23 ML/d) WTP and it supplies non-potable water to one of the District’s industrial customers. The treatment train includes coagulation, flocculation, plate settlers, an upflow clarifier, and mixed media filter units.

By the mid-1990s, the District recognized the need for additional drinking water capacity to meet the potable water demand. The District constructed of a new plant, Plant C, which utilizes membrane filtration.

Source Water

The source water for Plants A, B, and C is the Nueces River water and Lake Texana surface water. The District has historically drawn surface water from the Nueces River at Calallen, Texas using a pump station, which has four raw water pumps at the river and an intermediate booster pump station. To increase the District’s capacity, the District constructed a new 36-inch pipeline to draw water from the Mary Rhodes Pipeline which brings water from Lake Texana. The supply lines from these two sources merge at a blending station and a 42-inch pipe carries the water the final seven miles to the WTPs. Currently the blend ratio is approximately 60 percent from the Nueces River water and 40 percent from Lake Texana. The District is also executing a project to achieve an equal blend of the two sources.

The water from both sources is delivered to a 192-MG (730-ML) reservoir. The reservoir is an earthen embankment that is 135 ft (41 m) wide at the base, 16 ft (4.8 m) tall and approximately one mile in length. When at capacity, the depth of water is 16 ft (4.8 m) with a water surface area of 38 acres. Due to its large storage capacity and resulting detention time, the reservoir partially clarifies the water.

Typical raw water quality parameters are listed in Table 2.6. In general, the water is characterized by high turbidity, a high TOC concentration, moderate-to-high hardness, and high alkalinity. Giardia and Cryptosporidium have not been detected in the raw water to the plant. Algae content is a concern most of the year due to the high temperatures that are prevalent most of the year at this location. Because of the high organic content, the DBP formation potential is high.


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Table 2.6 Typical water quality of the Nueces River, which feeds

the District’s membrane treatment plant (Plant C) Parameter Range of Values Turbidity (NTU) 20 - 200 Hardness (mg/L as CaCO3

*) 150 – 250 Alkalinity (mg/L as CaCO3

*) 100 – 200 Temperature (ºC) 10 – 27 TOC (mg/L) 5 - 8 *calcium carbonate (CaCO3)


The treatment at Plant C consists of conventional pretreatment (i.e., coagulation, flocculation, and sedimentation) and membrane filtration. The membranes are housed in a pre-engineered building with dimensions of 129 ft by 243 ft (39 by 74 m). The membranes occupy 1681 ft2 (156 m²) of the building. Approximately 3,914 ft2 (364 m²) is available for future expansion. A detailed description of each process of the treatment train is presented, and the process flow diagram is shown in Figure 2.3. Pretreatment. Algal growth in the reservoir is controlled through application of copper sulfate at 0.48 mg/L. The water from the reservoir flows by gravity to Plants A, B, and C. Approximately 1.5 mg/L chlorine dioxide is added just upstream of the rapid mix to control algae and biological growth.

The District is satisfied with the performance of their existing conventional treatment plant (Plant A), which has been in operation for more than 30 years. As a result, the pretreatment that is upstream of membranes in Plant C was designed to match that of Plant A. The following information on the rapid mix, flocculation, coagulation, and sedimentation is for both Plants A and C.

The pretreatment consists of two trains, with each train having one rapid mix basin, two flocculation basins, two sedimentation basins, and one wet well. The design criteria for these basins are listed in Table 2.7.

Water from the rapid mix basins enters the flocculation basins through inlet distribution troughs. Water from the flocculation basins flows to the sedimentation basins through a slotted, poured-in-place concrete wall. The sedimentation basins are not equipped with any sludge collector devices. The basins are designed with sloped bottoms and sludge collection hoppers to facilitate gravity sludge withdrawal. The sludge hopper bottoms are sloped at four percent to allow sludge conveyance to the drain sump. All four sedimentation basins drain to one sump. The sludge is pumped via an 8-inch pipeline to three areas for land application at the plant.


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Table 2.7

Design criteria for pretreatment at the District’s membrane plant (Plant C)

Equipment Parameter Chemical feed Coagulant Liquid alum, 50 percent by weight Dosage range 40 – 100 mg/L Rapid mix Number of basins 2 Flow rate per basin 4 mgd (15 ML/d) Detention time 27 seconds Mixing Intensity 615 1/second Mixer type Mechanical Mixer Coagulation/flocculation Number of basins 4 Coagulant Alum Flow rate (each) 2 mgd (7.6 ML/d) Detention time 47 minutes Velocity 0.01 foot per second Flocculator mechanism Walking beam Velocity gradient 60 1/second at 70 ºF Max. paddle speed 1.6 fps Sedimentation basins Number of basins 4 Flow rate (each) 2 mgd (7.6 ML/d) Detention time 4.3 hours Velocity 0.46 foot per minute (2.4 x 10-3 m/s)

Flocculation SedimentationBasin

Clearwell

Chlorine Dioxide

Lake TexanaNueces River

Backwash andCleaning Waste

ChlorineAmmoniaOrthophosphateFluoride

Sludge to Land Application

To Industrial WTP forNon-Potable Water

Production

To Distribution

Figure 2.3 Process flow diagram for the District’s Plant C, Texas, USA

Alum

MF

12 MGReservoir

Rapid MixReservoir

Flocculation SedimentationBasin

Clearwell

Chlorine Dioxide

Lake TexanaNueces River

Backwash andCleaning Waste

ChlorineAmmoniaOrthophosphateFluoride

Sludge to Land Application

To Industrial WTP forNon-Potable Water

Production

To Distribution

Figure 2.3 Process flow diagram for the District’s Plant C, Texas, USA

Alum

MF

12 MGReservoir

Rapid MixReservoir


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Clarified water from the sedimentation basins flows to two common pump wetwells from which water is drawn for further treatment with membranes at Plant C.

Through use of alum, the plant achieves 40 to 50 percent of TOC removal and 70 to 80 percent of arsenic removal, when it is present in the supply. Primary Membranes. Based on pilot testing (which is described later) and competitive bidding, a Pall membrane filtration system was selected for installation in Plant C.

The membrane filtration system consists of six trains, each with 50 membrane modules, resulting in total membrane area of 26,900 ft2 (2,500 m2) per train. The description of the membrane modules is provided in Table 2.8. The design net flux is 58 gfd (99 lmh) at 68ºF (20ºC), thus, operation at the design net flux would yield a total production capacity of 9.36 mgd (35.4 ML/d) with all trains in service, and 7.8 mgd (29.5 ML/d) with one train out of service. Based on this design, the plant is currently rated at 7.8 mgd (29.5 ML/d). The District is currently in the design phase of expanding the WTP to 11.3 mgd by adding 20 modules to each rack. The District works closely with the Texas Commission on Environmental Quality (TCEQ), the state regulatory agency on membrane related issues. The total recovery of the membrane system is from 94 to 96 percent.

Table 2.8 Description of Pall membrane modules at the

District’s Plant C Criterion Value Module model number Microza MF module USV-6203 Dimensions of module 6-inch-diameter (15 mm) by 80

inch (203 mm) long Active membrane area (feed surface) 538 ft2 (50 m²) based on outside

diameter Nominal pore size (µm) 0.1 μm Membrane material PVdF Membrane configuration Hollow fiber,

Outside-to-inside flow Membrane hydrophobicity/ Hydrophilicity

Hydrophobic

Membrane charge Neutral to negative Standard testing pH 5 - 7 Standard testing temperature (ºC) 5 - 40 Maximum allowable operating pressure

40 psi (2.7 bar)

Allowable operating pH range 1 - 10 Allowable cleaning pH range 1 - 12 Chlorine tolerance Up to 5,000 mg/L


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Currently, the production from the membrane plant is between 6 to 7.8 mgd (23 to

30 ML/d). Even though at times, the production is below the design capacity, all trains are operated below design flux to meet the current demand. The current demand could be met by operating fewer trains; however, operation of all trains eliminates the issues associated with having one or more trains offline. For example, the off-line trains would need to be occasionally flushed to prevent biological growth and to avoid drying of the membranes.

The system is designed to operate in a cross-flow mode with 10 percent of the feed flow recycled to the feed water; however, because, the plant is currently operated below design flux, the recycle flow has been reduced to less than five percent of the feed flow, and staff has even operated without recycle. Post-treatment. Chlorine is added at a dose of 1 mg/L to the membrane filtrate. The membrane filtrate flows to a clearwell through a 140-foot (42.7 m), 54-inch (1.4 m) diameter pipe. The contact time in the pipe provides the necessary 3-log virus inactivation for Plant C. The chlorine residual at the entrance to the clearwell is approximately 0.4 mg/L. Chlorine and liquid ammonia are added to achieve a chloramine residual of 4 mg/L. Zinc orthophosphate and fluoride are also added at doses of approximately 0.11 mg/L and 0.50 mg/L, respectively. Backwashing and cleaning. Each train was originally designed to BW after filtering 20,000 gallons (76 m³) of water. Plant C is now operating at near the design capacity and flux, and each unit is backwashed after filtering 30,000 gallons (114 m³). Two types of backwashes are performed: (1) one by reversing the flow (i.e., reverse flush BW), followed by a chlorine soak period; and (2) the other uses air scrub with a reverse flush BW.

The reverse flush BW involves pumping filtrate water in the reverse direction for 45 seconds at a flow rate of 1,000 gallons per minute (gpm) [63 liters per second (l/s)] per train. The system is then soaked in a 30 mg/L chlorine solution for approximately 45 seconds. The system is then flushed with filtrate and returned to service. The BW solution is sent to the 12-MG (45 ML) reservoir that supplies Plant B, which produces clarified water for non-potable, industrial use.

The air scour and reverse flush BW is performed during every other BW. Compressed air is introduced into the system during BW to scour deposits from the membrane surface. The air flow during air scour is 250 cubic feet per minute (cfm) and lasts 30 seconds.

The procedures for backwashing have been modified. The current BW procedure involves reverse flushing for 45 seconds, with no chlorine soak phase, followed by the air scour reverse flush BW for 90 seconds.

The pilot study indicated that a CIP would be required once every six months. The CIP procedure involves draining each train of the feed water and circulating a 25-percent caustic solution for 60 minutes. The caustic solution is then drained and the system is rinsed with filtrate. A two-percent citric acid solution is then circulated through the system for 60 minutes. The system is then rinsed with filtrate and returned to service.

The caustic and acid solutions are reused twice. Neutralization of these two solutions is achieved by mixing them together. The neutralized waste is blended with rinse water and this flow is conveyed to a 12 MG (45 ML) reservoir that supplies Plant B, which is for non-potable production.


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CIP procedures for each train require approximately four hours of down time. The current practice is to use the cleaning solutions to clean two trains consecutively, before neutralizing and discharging them.

The membrane plant operated for eleven months before the first CIP was performed. Since this initial CIP, additional CIPs have been performed at approximately 6-month intervals. To evaluate the effectiveness of CIP, the operators record the TMP of all trains during production of 100 gpm (6.3 l/s) instantaneous filtrate flow per train. The TMP values during start-up and after each CIP are shown in Table 2.9.

It appears that the performance of almost all the trains, expressed as TMP required to produce 100 gpm (6.3 l/s) per train has improved since start-up. The TMP values stabilized after the second CIP (i.e., after 17 months of operation), and the reason for this is not clear. Secondary Membranes. There are no secondary membranes at this facility. The disposal of BW water and other waste streams is discussed below.

Staff

The plant has one operator on duty at all times, and this operator works a 12-hour shift. The operator monitors and operates all three of the District’s WTPs, as well as remote pumping, mixing, storage, and delivery facilities. The membrane plant is typically monitored and controlled from the central operator station at Plant A. The operator walks through the facility three or four times per shift to perform a visual and auditory check and to fill day tanks, verify chemical feed pump rates, and check tank levels. All operators are trained to perform CIPs and can also provide services as a backup to chief operator. Typically, one CIP is performed for two trains per shift allowing reuse of cleaning chemicals. Other personnel at the District’s plants include one full-time laboratory chemist and two management staff.

Table 2.9

Summary of TMP after CIPs at the District’s Plant C* TMP after CIP

Train At start-up

11 months after start-up



A 1.22 -- 0.73 0.82 B 1.31 1.16 0.97 1.03 C -- 0.99 0.76 0.66 D -- 0.92 0.68 0.81 E 0.85 1.05 0.97 0.81 F -- 0.92 0.68 0.81

Average 1.13 1.01 0.80 0.89 * TMP measured after CIP at 100 gpm instantaneous filtrate flow and normalized to 77ºF (25ºC).


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Pilot Plant

The District is under the jurisdiction of TCEQ. The TCEQ regulations require a licensed professional engineer to perform pilot evaluations of non-conventional systems such as membrane filtration. The regulations also require pilot testing for a period of at least 90 days.

The District invited several vendors for pilot testing and three vendors responded (1) Pall, (2) Hydranautics, and (3) US Filter. The pilot testing was conducted during the months of March through July of 1998. The feed water for the membrane pilot units was clarified water from the sedimentation basin at Plant A.

In general, all three membrane filtration systems performed acceptably during the pilot study. No significant differences in treated water quality were observed. One of the membranes was not resistant to oxidants and had some operational difficulties because there was a chlorine residual in the clarified water.

Plant staff operated the pilot units. Their exposure to the membrane units during the evaluation helped to alleviate their concerns regarding a new treatment process.

Based on the pilot results, design fluxes for each membrane system were determined and used for the bidding process, which is described later in this section.

Instrumentation

The plant process control and data acquisition is conducted using GE Fanuc PLC. The human machine interface equipment consists of Windows NT Intellution Fix 32 SCADA. Each train has a small PLC to allow independent control. Table 2.10 lists the instrumentation used at Plant C.

Table 2.10

Instrumentation at the District’s Plant C Stream Instrument Type Raw water Turbidity pH Temperature After rapid mix Chlorine residual pH After sedimentation Chlorine residual pH Temperature Membrane feed Pressure Flow Membrane filtrate Turbidity

(one per train) Flow Particle counters Upstream of clearwell Chlorine residual


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Integrity Testing

PDTs are used at this facility. PDTs are automatically performed on each membrane rack every 24 hours. The PDT involves stopping the feed flow and injecting air to replace the water in the fibers. Once the water is displaced, the pressure is increased to 24 psi (1.63 bar) and the air supply is shutoff. The decrease in pressure over nine minutes is measured. A decrease in excess of 0.3 psi [20 millibar (mbar)] triggers an alarm. If the decrease in pressure is less than 0.3 psi (20 mbar), the unit is returned to service. For decay greater than 0.3 psi (20 mbar), a manual integrity test is performed and if the unit fails again, it is taken out of service to determine the cause of failure. So far, four fiber breaks have occurred since start-up. During start-up, however, three broken fibers were detected and repaired.

Operation to Date

In general, the plant has performed very well and has required little maintenance. As discussed above, the frequency of CIP is very low and only four broken fibers have been detected since the start-up. The non-routine maintenance operations and equipment modifications performed are listed below:

1. Perforated polyvinyl chloride (PVC) pipe flange breakage, which was traced to improperly adjusted control valve operating speed.

2. Reverse flush system filtrate pump addition to boost pressure on filtrate used for backwashing.

3. Caustic pump for CIP solution to reduce time required. 4. Level sensors in chemical feed systems were replaced with a different model because

the original sensors failed. 5. Flow metering devices were supplemented with redundant paddle wheel meters to

backup ultrasonic meters in critical locations. 6. Occasional air binding at the membrane feed pump has yet to be remedied.

Cost

The three membrane vendors that participated in the pilot test were allowed to bid. The bids were received in September 1998, and the evaluated bid results are listed in Table 2.11. The warranty for the membranes was seven years.

Based on the evaluated bid costs in Table 2.11, the Pall system was selected for full-scale implementation. The costs of Table 2.11 were actually lower than expected, and as a result, the District was able to increase the installed capacity to 7.8 mgd (29.5 ML/d).

The project was completed using five principal contractors and two professional design teams. The costs were audited internally. The construction costs are listed in Table 2.12. These costs include an 840,000-gallon storage and pumping facility. The costs do not include fiscal agent fees, land costs, legal fees, or staff time.


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Table 2.11

Evaluated bids for District’s membrane system at Plant C Pall Memcor Hydranautics

Total base bid for 5.2 mgd $2,274,200 $2,161,500 $3,095,000 Annual payment (6%, 20 yrs) $200,184 $345,400 $257,548 Annual operating cost $407,442 $643,493 $445,997 Capital and operating cost ($/1,000 gallons)

$0.215

$0.323

$0.235

Table 2.12

Construction costs for the District’s Plant C Contract Design Firm Contractor Award Date Final Cost MF process equipment (7.8 mgd)

Malcolm Pirnie, Inc.

Pall Corp. 10/6/1998 $2,791,200

Flocculation, settling, and storage


H&S Construction

10/13/1998 $2,878,500

Process assembly and startup


H&S Construction

3/9/1999 $3,288,700

Plant building Roots Foster Architect

Bracco Construction

1/12/99 $956,300

High service pumps Malcolm Pirnie, Inc.

Odessa Pumps

12/15/1998 $38,400

Total equipment and construction cost

-- -- -- $9,953,100

Engineering and architectural services

-- -- -- $1,438,800

Inspection -- -- -- $102,000 Testing -- -- -- $71,000 Total construction cost

-- -- -- $11,564,900

Operating costs for the year 2002 are listed in Table 2.13.


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Table 2.13 Operating costs for 2002 at the District’s Plant C

Category Annual Cost Payroll and related items $111,226 Maintenance and repair services $79,824 Chemicals $153,502 Electricity (including high service pump station)

$88,432

Membrane replacement fund $180,000 Plant insurance $27,424 O&M reserve fund $33,300 Lab equipment and telephone $4,414 Total operating costs $678,121

Planning Issues

The planning for Plant C involved process selection as well as cooperation with a local industrial user to help fund the construction. The District needed to provide additional water to a new industrial user and also to increase its capacity of potable water supply to meet growing demand. Several treatment scenarios were considered to meet the objectives of the industrial customer as well as drinking water standards. While conventional treatment was considered, due to increasingly stringent regulations, the District was willing to consider membrane filtration even if it would cost up to 15 percent more than conventional treatment. In addition, the consistently high-quality filtrate from the membrane filtration plant would also meet the industrial customers’ requirements.

The industrial customer agreed to fund a portion of the total capital cost, and the level of funding was proportional to the volume of water that would be supplied to the user. The District’s board approved the plan for a new membrane plant unanimously. The construction cost was below the estimate, and the District returned part of the funding to the industrial customer that supported the project.


The plant staff offered the following recommendations to other utilities based on their experience:

1. Provide adequate space for pilot testing of multiple units. 2. Oxidant-tolerant membranes may be necessary for treating surface water in warmer

regions where biological activity could be high. 3. “Tight” specifications are recommended and a good evaluation procedure should be

developed in the contract documents (e.g., life cycle cost analyses). 4. The procurement of membrane equipment by a separate contract worked well for the

District and is a recommended approach. 5. The level of experience of the design team is an important consideration for any

project.


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6. PVC piping should not be used where vibrations or shock loading is anticipated. 7. The startup of their plant progressed very well, primarily due to the good planning,

continued assistance from the design team, and adequate time and resources allocated by the membrane manufacturer.

Columbia Heights WTP, Minneapolis, Minnesota, USA

The Columbia Heights WTP is a softening plant with UF. The plant should be operational in autumn 2005. A summary of the facility is in Table 2.14.

Background

The Minneapolis Water Works (MWW) supplies water to businesses and residents of the city of Minneapolis and surrounding suburbs. This utility operates multiple facilities – a 165-mgd softening WTP and a 120-mgd conventional filtration WTP located in Fridley and a 70-mgd plant in Columbia Heights. In addition to the Columbia Heights membrane WTP, a 95-mgd membrane WTP is planned for the Fridley location. Drawing water directly from the Mississippi River has posed many challenges over the years due to rapid changes in water quality, particularly during the spring when snow melts in the watershed. In the mid 1990s the MWW embarked on an ambitious program to improve treatment to meet increasingly stringent regulations and also to replace obsolete infrastructure that was becoming expensive to maintain. A number of different technologies were reviewed to meet these challenges, including:

• Ozone and GAC adsorption • UV irradiation • MF and UF

Following pilot testing, extensive bench-scale experiments and a value engineering study,

UF was selected as the most appropriate technology to meet the MWW’s criteria at an acceptable cost. Design commenced for the 70-mgd facility for the Columbia Heights WTP in January, 2001 and the plant will be in service in autumn 2005. At the time of writing, it will be the largest drinking water UF plant in North America and amongst the largest in the world.

Table 2.14 Summary of the Columbia Heights WTP, Minneapolis, Minnesota

Status of project Start-up in autumn 2005 Capacity 70 mgd: 265 ML/d Source water Surface, Mississippi River Pretreatment Softening, recarbonation, FeCl3 coagulation,

sedimentation Type of membrane Ionics, X-Flow UF Design flux 57 gfd; 97 lmh Pilot testing Extensive phases for multiple membrane systems Integrity testing Daily water displacement test Main driver for integration

Microbial risk inherent to watershed


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Source Water

Raw water is abstracted directly from the Mississippi River. Minneapolis is approximately 200 miles south of the headwaters at Lake Itasca. The river receives numerous discharges in the watershed, including agricultural run-off, power plant cooling water, and effluent from wastewater treatment plants (WWTPs). These threats have driven improvements to the treatment plant over the years. Typical raw water values are presented in Table 2.15.

Description of Treatment Plant Pretreatment. Water is abstracted with a raw water lift station located near the banks of the Mississippi River. PAC is added to the raw water with potassium permanganate, which is used intermittently depending on water quality. Water is fed to lime precipitators into which alum is also dosed. Additional PAC is added immediately after lime softening. Softened water is recarbonated in two chambers. One chamber feeds the Fridley Filtration Plant, the other chamber supplies a pumping station for lifting softened water to the Columbia Heights Membrane Filtration Plant. A process flow diagram is shown in Figure 2.4.

Re-carbonated water is then subjected to further coagulation and flocculation treatment with the addition of ferric chloride. Six horizontal flow sedimentation basins are provided in three hydraulically-connected pairs. Chlorine and ammonia are also added with the coagulant as part of the disinfection process. The water quality of the feed supply to the membrane filtration process is summarized in Table 2.16.

Sludge from the sedimentation basins is manually removed once per year during annual maintenance activities. Sludge is transported to a dewatering facility which uses thickeners and centrifuges. Primary Membranes. Five, variable frequency feed pumps, four duty one common standby, feed four trains of membrane units. Each train comprises nine UF membrane units, each with a capacity of 2.2 mgd (8.3 ML/d) operating at a design flux of 57 gfd (97 lmh). Feed water to each membrane unit is pre-filtered through automatic BW strainers (i.e., four duty, one common standby) with 150 µm mesh. The strainers are of a candle-filter design and are washed periodically via a rotating wash arm. Strainers remain in service during backwashing. Each wash of the strainer takes approximately two minutes.

Table 2.15 Raw water quality of the Mississippi River

Parameter Average Maximum Minimum pH 8.3 8.9 7.7 Hardness, mg/L as CaCO3 170 236 89 Temperature, oC 11.7 30.7 0 Turbidity, NTU 9.8 52.5 1.5 TOC, mg/L 10 15 8 Color (CU) 40 115 17 TDS, mg/L 150 200 80


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The membrane units are manufactured by Ionics, Inc. and use UF membrane cartridges

manufactured by X-Flow, a Dutch membrane manufacturing company. The membranes are described in Table 2.17. Each membrane unit has 28 pressure vessels (PVs) similar to those used in RO systems and they are 28 feet in length. Each PV contains four membrane modules which are connected in series. By-pass channels within each module allow for even flow distribution throughout the PV. Filtrate is used for backwashing the membrane units. Fluoride and polyphosphate are added downstream of the BW water supply draw-off location. Provisions also exist for the addition of chlorine and ammonia to filtered water, should the combined chlorine residual require adjustment.

Table 2.16 Membrane feed water quality at MWW Columbia Heights WTP

* ultraviolet absorption at a wavelength of 254 nanometers (UV254)

Parameter Average Maximum Minimum Temperature (oC) 11.5 29.9 0.1 pH 8.6 9.2 7.7 Total hardness, mg/L as CaCO3 19 92 12 Turbidity, NTU 1.8 8.0 0.4 Alkalinity, mg/L as CaCO3 32.1 41 22 TOC, mg/L 5.0 8.1 2.7 DOC, mg/L 4.4 7.7 2.4 UV254 * 0.07 0.20 0.03 Color (CU) 5 20 2 TDS, mg/L 134 213 96 Manganese, mg/L 0.013 0.020 <0.010 Aluminum, mg/L 0.09 0.22 <0.01 Silica, mg/L 8.3 16.0 4.8 Total iron, mg/L 0.64 1.10 0.08

Figure 2.4 Process flow diagram for the MWW Columbia Heights WTP, Minnesota, USA

Recarbonation

CO2

StorageMississippi River

Storage

FeCl3

Cl2NH3

FeCl3

Cl2NH3

Softened Water Storage

Coagulation& Clarification Filtration

UF Units

Supply

Supply

LimeAlum

PAC

Sludge

Recarbonation

Sludge

PAC orKMnO4

Figure 2.4 Process flow diagram for the MWW Columbia Heights WTP, Minnesota, USA

Recarbonation

CO2

StorageMississippi River

Storage

FeCl3

Cl2NH3FeCl3

Cl2NH3

FeCl3

Cl2NH3

Softened Water Storage

Coagulation& Clarification Filtration

UF Units

Supply

Supply

LimeAlum

PAC

Sludge

Recarbonation

Sludge

PAC orKMnO4


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Table 2.17

Characteristics of the X-Flow membranes installed in Columbia Heights WTP Module model number Xiga No. of cartridges 4,032 Dimensions of cartridge 8 inch (200 mm) diameter x 60 inches

(1,500 mm) long Active membrane area (feed side) 377 ft2/cartridge (35 m2) Nominal pore size (µm) 0.02 Membrane material PES and poly vinyl pyrrolidone blend Fiber flow configuration Inside-to-outside Membrane hydrophobicity/hydrophilicity Hydrophilic Maximum allowable operating pressure 45 psi (300 kPa) Allowable operating pH range 2 to 12 Allowable cleaning pH range 1 to 12 Maximum allowable feed turbidity 5 to 7.5 NTU, but with unique conditions

and protocols, 15 NTU Oxidant tolerance 500 mg/L as chlorine up to 40oC, and up

to 200 mg/L hydrogen peroxide at 40oC

Post-treatment. Filtrate is dosed with fluoride, polyphosphate, ammonia, and chlorine. Treated water flows via an effluent wet well that provides back pressure on the membrane process to provide surge protection. From the effluent wet well, treated water enters a system of reservoirs that provide the required disinfection and treated water storage for the distribution system.

Backwashing and Cleaning. Backwashing is performed every 25 minutes. A complete row of membrane units can be backwashed in cascade fashion, which means that all nine units are backwashed in sequence without restarting the common BW pump between backwashes. This approach minimizes pump start and stop sequences and enables good coordination of the backwashing process, which is an important consideration when as many as 36 individual units are in operation at any one time. For the MWW Columbia Heights WTP, CIPs that require hours of chemical contact and system downtime are not being used routinely. Instead, chemical cleans are performed with a modified BW sequence which includes chemical addition. This is technically a CEBW, and any number of CEBWs can be performed per day, depending on influent water quality and the ability of CEBWs to restore permeability. The following chemical cleaning constituents are being used in MWW’s CEBWs:

• 200 mg/L NaOCl, as a 12.5 percent solution. • 300 mg/L sodium bisulfite (NaHSO3), as a 38 percent bisulfite solution, with 600 mg/L

hydrochloric acid as a 30 percent solution. • 800 mg/L hydrochloric acid as a 30 percent solution.

The CEBW sequence comprises an initial wash phase, a soaking period of 10 minutes

and a wash, or rinse phase. CEBW solutions are fed by segregated piping systems to prevent


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cross connections with filtered water. CEBWs were developed during extensive pilot plant trials that continued during the design phase of the project. The design of the chemical storage and dosing systems allows for a variety of cleaning regimes, should they require adjustments due to water quality changes.

A chemical CIP system is also provided at the facility in case of a severe fouling event. This system includes a 6,000-gallon (1,580 L) tank that is equipped with a heater and fed with dry chemical by an eductor or by liquid chemicals via a drum pump. Softened water is available to dilute the chemicals to appropriate concentrations for CIPs and it is used to avoid scale formation in the cleaning solutions. A CIP supply pump mixes the solution in the tank in addition to feeding the CIP solution to the membrane unit. This procedure is performed manually, and is intended to be used only if routine CEBWs are unable to restore permeability to acceptable values. Pilot plant evaluations have shown that this CIP system will not be used on a regular basis, but is available as an alternative means of cleaning the membranes.

Staff

It is anticipated that the facility will require six full-time staff to perform O&M activities, including instrument calibration and membrane fiber repair. Shifts are in three eight-hour rotations for operations and from 7:30 am to 4:00 pm for maintenance supervisors and instrument technicians. Operations staff will be present at the facility for continuous monitoring, at least in the early operational stages of the facility.

Pilot Plant

Extensive pilot testing has been conducted throughout the procurement, design, and construction phase of this project. Initial pilot testing was performed as part of the procurement process to identify the most economical membrane system that met strict performance goals.

The initial pilot testing program was structured into phases. Membrane manufacturers were first allowed to optimize operating parameters. Following this phase, the membrane suppliers had to identify their operating parameters and then began extended pilot testing, without any further adjustments. For the Columbia Heights WTP project, two membrane systems (i.e., Koch and Ionics, using the X-Flow membrane) were included in the pilot study. The Ionics system successfully met the performance criteria and was ultimately selected for installation. Additional piloting was then performed to further optimize system parameters.

During the extended piloting phase, fouling events associated with spring run-off occurred. It is believed that the fouling events coincided with a change in water quality due to snow thawing in the watershed. Snow thawing has been known to decrease the hardness concentration of the Mississippi River water, as well as a increase in raw water TOC and an increase in the humic fraction of organic matter in the membrane feed water.

An alternative chemical cleaning procedure was developed to address this change in performance. The procedure includes cleaning the membrane with a NaHSO3 and hydrochloric acid solution as opposed to a NaOCl solution. After successful pilot-scale trials, the necessary design adjustments were made to the chemical feed and neutralization systems. This fouling event, and the modified cleaning procedure, was only identified during the final pilot testing phase, which was in parallel with the design. These design adjustments would not have been made had pilot testing ceased following procurement.


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It is the MWW’s intention to continue pilot testing throughout the life of the WTP. A demonstration-scale unit will be installed to enable utility staff to conduct off-line testing. Such testing may include alternative chemical cleaning regimes, additional virus testing and alternative membrane formulations as they become available.

Instrumentation and Control

On-line instrumentation is provided for measuring particle counts, turbidity, temperature, pH, conductivity, and chlorine residual at the Columbia Heights facility sampling the membrane feed water quality. Temperature values are used to automatically calculate flux set-points, according to an algorithm that was calibrated during pilot testing. Particle counts are used to document particle removal for each membrane unit. Conductivity is used to verify that membrane units are rinsed thoroughly after a chemical clean.

Filtrate is sampled for conductivity, particle counts, pH, turbidity, and chlorine residual. Individual membrane units have turbidimeters and particle counters for filtrate monitoring.

The CEBW and CIP neutralization processes have instrumentation for monitoring redox potential, conductivity, and pH. Redox potential is used to ensure residual oxidant and reducing agents are properly neutralized before discharge to a lagoon. Conductivity is used to check the neutralization of acidic and alkaline wastes and pH is used as the final measurement before discharging the solutions to the lagoons.

Flow meters are provided for influent water supply to the membrane units, but control is achieved by utilizing pressure in the feed water manifold. A desired flow set point is determined by the SCADA system based on operating levels of the upstream coagulation basins, and the correct number of units is selected automatically to achieve the desired filtrate flow. The number of units will vary for a given flow according to water temperature, with more units being necessary to achieve the same water production at lower water temperatures.

Feed pressure set points are calculated based on TMP measurements from each unit. The highest values are used to ensure sufficient pressure is maintained in the feed piping to overcome headloss, friction losses in piping, and hydrostatic head of the filtrate wet well. Membrane feed pumps are brought on line and the pumping speed is adjusted automatically to meet the desired pressure set point. Pressure readings are a critical measurement and are triple validated to ensure that correct values are being achieved.

The SCADA system utilizes GE Cimplicity software, which is used throughout the MWW WTPs. Allen Bradley Control Logix PLCs have been installed for control of the process.

Integrity Testing

Integrity testing is performed daily using a water displacement tests, and 4-log rejection capability is maintained. Log removal values are calculated based on displaced water flow during the integrity test and the previous operating filtrate flow rate and TMP. The applied integrity tests pressure ensures a 3-µm test resolution.

Operation to Date

At the time of preparation of this report, the Columbia Heights UF WTP was not fully operational.


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Cost

The membrane equipment bid cost was $17 million for 70 mgd (265 ML/d) system in 2001. This scope comprises the following principal components:

• 40 UF membrane units (36 installed). • Five automatic BW feed strainers. • Four BW pumps with variable speed drives. • All CEBW and neutralization chemical feed pumps. • Neutralization recirculation and discharge pumps. • Master and bank-level PLC cabinets and associated programming.

A separate contract for $34 million was issued for building construction and installation

of the membrane filtration equipment in 2003. The building includes an administrative area, small visitor center, training room, new chlorine and post treatment chemical storage, and a pilot plant room for future experimentation. The building is constructed with a full basement that houses membrane cleaning chemicals, all interconnecting piping, and pumps. Traditional brick and natural stone accents have been used to create a building that blends in to its environment, matching similar buildings located at the WTP that were constructed in the early twentieth century.

Engineering fees were as follows: • Membrane procurement, including supervision of pilot testing and design

coordination was $2.5 million. • Membrane system facility detailed design, design coordination, training, construction

supervision, and start-up assistance was $4.5 million.

The total construction cost, including total engineering fees is $58 million (in 2003 dollars). Operating costs are estimated to be about $3.1 million per annum. Extensive cost estimates have been prepared and a summary is presented in Chapter 3 of this report.


The Minnesota Department of Health (MDH) is the regulatory primacy agent for MWW. The MDH were involved throughout the planning, detailed design, and construction phases of the project. The Columbia Heights WTP was the first major membrane filtration project in the Minnesota, and the MDH has been following closely the developments of this project. It will serve as a template for future membrane treatment plants in Minnesota.

Of particular interest to MDH were the pilot test results, especially those for virus rejection. MDH had the opportunity to comment on pilot testing protocols and to review the test results, and the successful demonstration of the virus rejection during the pilot gave the MDH confidence to grant a 4-log virus removal credit for the UF process.

Regulatory involvement during the design phase ensured compliance with other State requirements and a smooth progression to the construction phase. The MWW will continue close liaison with MDH through start-up phases and into operation.


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Planning Issues

The MWW has planned extensively for the asset renewal and improved treatment at both of its WTPs. Much of the planning occurred in the mid-1990s, and key components of the planning effort are highlighted herein.

An exhaustive study and pilot testing project first identified suitable treatment technologies that were capable of achieving MWW’s goals in 1997. The recommendations of the study were reviewed in depth as part of a value engineering study, which was published in 1999. This gave the MWW the confidence to secure funding for the desired developments at both their Columbia Heights and Fridley facilities.

The study concluded that UF was the most appropriate technology for the MWW based on the following factors:

• Compliance with current and anticipated future regulations. • Reliable treatment to produce high quality water. • Compatibility with future regulatory requirements and technological developments. • Increased utility effectiveness (i.e., reduced staffing levels). • Costs associated with levels of reliability.

The two most feasible treatment technologies were (1) existing treatment with ozone and

GAC, and (2) membrane filtration. Although they concluded that ozone and GAC addition would be less expensive than membrane filtration, membrane filtration afforded better protection against contamination threats that are present in the watershed. It was recognized that optimization of pretreatment would be necessary to successfully integrate membrane filtration into the existing WTPs. Such improvements included optimization of PAC dosing and use of potassium permanganate to control taste and odor. Once the decision was made to implement membrane filtration, the MWW prepared procurement documentation for the testing and purchase of filtration equipment. Bidders were required to submit costs for membrane filtration equipment in conjunction with their technical submittal. Technical evaluations were kept separate from financial evaluations to ensure the best performing membrane system was not unduly influenced by financial considerations. The financial information was revealed only after a membrane filtration system provider had:

• Complied with the technical requirements. • Successfully completed the pilot testing. • Demonstrated the requisite 4-log virus rejection criteria.

Only two membrane systems pre-qualified for the testing phase of the project (1) Koch

Membrane Systems, and (2) Ionics, using Norit Membrane Technology. Only the Ionics system completed the pilot testing phase satisfactorily and the financial information was revealed for this system. Following successful negotiation, Ionics was awarded a contract to supply membrane filtration equipment.

A panel of membrane filtration experts was formed to review the initial value engineering study, provide input to the procurement documents, and review the pilot testing results that accompanied the bidding process.


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MWW also met with local citizen groups to prepare the community for these necessary improvements. A Citizens Advisory Committee (CAC) was formed with community representatives so that the treatment upgrades could be effectively communicated and discussed with the citizens. The CAC was a well-informed group and understood the importance of good quality drinking water. The CAC has been involved throughout the planning and design stages of the project. Additionally, a representative from the largest wholesale purchaser of MWW’s treated water also attended key meetings for the selection of the membrane filtration equipment and design engineer. A local anomaly is that the Columbia Heights membrane filtration plant is actually installed outside of the City of Minneapolis in a neighboring city, the City of Columbia Heights. Close cooperation with the City of Columbia Heights’ staff was necessary to ensure that codes were met and that resident’s concerns were taken into account. These concerns were addressed in the specifications for the construction of the membrane filtration plant. One example in the specification clearly states the allowable construction working hours, traffic routes, and street maintenance requirements.


The MWW staff has found that careful planning has led to a smooth sequence of events in the membrane integration projects for two WTPs. By clearly identifying the best treatment solution and communicating effectively with citizens and council members, the necessary funds were raised and the necessary rate increases were clearly communicated to customers.

Other recommendations are to: • Continue piloting after bid award, especially if the water source has variable water

quality. • Allow for flexible chemical cleaning regimes to deal with unexpected fouling events. • Conduct autopsies to identify nature of fouling materials. • Maintain and enforce rigid protocols for membrane pilot testing to gather high quality

data to accurately determine the best performing membrane filtration unit.

Chaparral WTP, Scottsdale, Arizona, USA

The Chaparral WTP is currently under construction and is expected to be operational in late 2005. The plant uses submerged membranes to treat a surface water (see summary in Table 2.18). Results of the pilot study are highlighted in this section.

Background

The City of Scottsdale began planning for a new 30-mgd (114 ML/d) WTP, (the Chaparral WTP), in 1999. This facility will use iron-salt coagulation, Zenon UF membrane filtration, and GAC to treat water from the Salt River Project (SRP) canal system, and is scheduled for start-up in 2005. This utility case study summarizes the history of this project, including the pilot program, procurement strategy, and full-scale design.


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Table 2.18 Summary of the Chaparral WTP, Scottsdale, Arizona, USA

Status of project Start-up in 2005 Capacity 30 mgd: 114 ML/d Source water Surface; canal Pretreatment Coagulation with ferric sulfate Type of membrane Zenon UF (500D) Design flux 30 gfd; 51 lmh Pilot testing Four membrane systems piloted for six months Integrity testing Daily PDTs Main driver for integration Limited land available for WTP

Summary of the Project

The water quality objectives for the City of Scottsdale included: • Robust turbidity and particle removal. • TOC removal to lower trihalomethane (THM) formation. • 2-methylisoborneol (MIB) removal. • Arsenic removal.

There were several viable process alternatives for the new WTP. However, the City of

Scottsdale preferred membranes as a filtration barrier because of the ruggedness of the process; the small footprint; and the ability to produce a consistent, high–quality, finished water. Pretreatment with coagulation was deemed necessary for arsenic removal. GAC, possibly with ozone, was identified for MIB and TOC removal.

There were several unknowns associated with these process alternatives. For example:

• Would the membranes perform well without upstream clarification? • How much coagulant would be needed for arsenic removal? • Which membrane systems could perform well with these pretreatment conditions?

To answer these and other process questions, the City of Scottsdale decided to use a pilot

program to assist with qualification and procurement of membrane systems, as well as to define the design of pre- and post-treatment facilities. The treatment process train for the pilot study included coagulation, membrane filtration (MF or UF), ozone oxidation, and GAC contacting. The pilot study achieved several objectives. Two membrane systems successfully completed the pilot trial, and were pre-qualified for the full-scale project. Operating conditions established during the pilot study were used to establish bid criteria for life cycle cost analyses. Among these were power and air consumption, flux, recovery, and chemical cleaning requirements. Pre- and post-treatment requirements were also defined. These requirements included the coagulant dosage that was needed for arsenic removal (e.g., up to 15 mg/L ferric


40

sulfate), the selection of bituminous GAC over lignite GAC, and the elimination of ozone from final process selection. The plant is under construction and due for start up in the autumn 2005. Zenon was the successful bidder for the membrane system.

Schedule

Planning for the City of Scottsdale’s SRP Pilot Program and full-scale Chaparral WTP began in December 1999. The City’s approach to this project included a pilot program, which would pre-qualify the membrane systems, followed by procurement, design, and construction. The major elements of the program included the following: Pilot Program (1999 – 2001)

• Select participating membrane systems for pilot testing (March 2000 to May 2000). • Develop testing protocols for membrane and water quality pilot-scale testing

(March 2000 to May 2000). • Design the pilot plant (May 2000). • Conduct pilot study (August 2000 to January 2001). • Recommend full-scale process design parameters, process train, and membrane

procurement approach (April 2001). Full-Scale Program (2001 – 2005)

• Select design engineer (April 2001). • Pre-select membrane system (June 2002). • Design WTP (November 2001 to April 2003). • Construct WTP (January 2004 to May 2006).

Selection of Membrane Systems for Pilot Testing

In March 2000, a request for Statements of Interest (Request) was delivered to nine interested membrane suppliers. The Request included specific requirements for participation in the pilot program and a detailed questionnaire to be completed by each interested supplier. The requirements for participation were as follows:

1. MF or UF membranes with a nominal pore size ≤0.2 µm were to be tested. 2. The supplier must have supplied at least two MF or UF treatment plants, having a

capacity of 1 mgd or more. The referenced facilities must operate the same membrane material as proposed and have been in operation for at least one year, demonstrating reliable continuous operation, while maintaining its design capacity.

3. The supplier had to propose a membrane system which: - has previously received Surface Water Treatment Rule (SWTR) pathogen removal

credits in any state, - the supplier can satisfy the City of Scottsdale that the proposed process is likely

capable of receiving an “Approval to Construct” from Maricopa County Environmental Services Department (MCESD), following the pilot study.


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4. The proposed membrane system had to be compatible with the use of 10 to 20 mg/L iron-salt coagulant in the feed water to the membrane system.

5. The use of PAC would not be allowed during the pilot testing. 6. All components of the proposed membrane system, which contact drinking water, had to

comply with NSF International (NSF) 61. 7. The supplier must be capable of providing timely (i.e., 24-hour response by phone, and if

necessary 48-hour on-site representation) on-site technical support to the pilot test program.

8. The supplier must be capable of manufacturing and installing a full-scale system in a timely manner.

9. A maximum of four qualified membrane systems were to be accepted for pilot testing. Should statements of interest be received for more than four qualified systems, the four most qualified systems with the greatest installed capacity would be accepted.

Eight membrane suppliers responded, of which four qualified for pilot testing: Koch, USFilter, Pall, and Zenon.

Pilot Plant

Two testing protocols were developed: membrane testing, and water quality. These protocols were separated into three phases. Phase 1 allowed for the determination of optimum coagulant dosages and membrane operation setpoints. Phase 2 was performed at the optimum conditions identified in Phase 1 for a total of 11 weeks. Phase 3 allowed for additional arsenic removal trials or membrane setpoint evaluations, if necessary. The membrane testing protocol outlined the minimum requirements for acceptable performance. These requirements included system recovery, integrity tests, and regulatory compliance. The water quality protocol outlined testing procedures for determining conditions for arsenic, TOC, and MIB removal. Pilot Plant Design. The process schematic is shown on Figure 2.5. The following text summarizes different components of the pilot plant. Pilot Plant Influent. Initially, the intake was equipped with a ball-type screen with quarter-inch holes; however, this screen became plugged with algae, and the screen was eventually replaced with a PVC box with 1/2-inch diameter holes. Pretreatment. Pretreatment consisted of an influent pump, strainer (which was added after the algae plugging episode), static mixers, and a contact basin with rapid mixing. An automatic backwashing strainer with slotted cones was installed upstream of the chemical spike injection point. The slotted cones were still allowing significant algal mass to pass through the strainer, so the slotted cones were later replaced with 400 µm Delrin discs. The baffled chamber provided about two minutes of contact time before the water was routed to each of the four membrane systems. The influent flow to the contact basin remained constant to allow for simple control of coagulant dosing at the pilot plant. Ferric sulfate was dosed at 0 to 15 mg/L for arsenic removal. Excess water not treated by the membranes was discharged to the sewer.


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Zenon Membrane System. Zenon’s system utilized the ZW-500b membrane, which has an outer diameter surface area of 650 sq ft (60 m²). The membrane material is a Zenon proprietary hydrophilic polymer, similar to polyvinylidenefluoride (PVdF), which is resistant to free chlorine. The nominal molecular weight cutoff is 0.04 µm, with an absolute cut off of 0.1 µm. The flow configuration is outside-to-inside for this hollow-fiber system. The Zenon pilot skid included a 200-gallon (760 L) process tank, a 20-gallon (76 L) permeate holding tank, a small chemical tank, a raw water feed pump, a permeate pump, a reject pump, and a chemical feed pump. A coarse, 1/4-inch pre-strainer was used for the feed water for the entire pilot study. The Zenon membrane was submerged in the process tank, and the tank water level fluctuated between programmed setpoints during operation. Throughout the pilot, Zenon’s production mode operation included a constant reject flow from the process tank and a constant airflow into the process tank across the membrane fibers. The Zenon run cycle included 15 minutes between backwashes and a BW duration of 15 seconds. Zenon maintained this cycle throughout the pilot study. Zenon’s BW consisted of a reverse flow (i.e., inside-to-outside) through the membrane fibers of approximately 5 gallons of permeate pumped from the permeate holding tank and injected with a NaOCl solution at a dose of approximately 6.8 mg/L free chlorine. At the end of a BW, the Zenon unit returned directly into production mode without wasting concentrate from the process tank. Pall Membrane System. The Pall system utilized a PVdF membrane (Model USV-6203-6 inch) having a 0.1 µm cut off. It is tolerant to chlorine and has 538 sq ft (50 m²) of surface area (based on the outside diameter of the fiber). The Pall pilot skid included a feed tank, a permeate tank, a cartridge membrane, a feed pump, a permeate pump, and a recirculation pump. A 400-µm bag-type prestrainer was used throughout Phase 1, but was removed during Phase 2 after the strainer was installed in the pilot plant. Pall’s production cycle included 20 minutes between backwashes, and a two-step BW procedure consisting of a 60-second air scour plus reverse flow step followed by 30 seconds of reverse flow only. Permeate was used for reverse flow, and no chemicals were used in the BW procedure. At the end of the BW, the contents of the membrane cartridge and system piping were drained to waste then refilled with feed water to restart production mode.

Figure 2.5 Process flow diagram for the pilot plant for the Chaparral WTP, Arizona, USA

Zenon UF

Pall MF

US Filter MF

Koch UF

Ozone Contactor

Salt River Project Canal

Arsenic Spike

Fe2 (SO4)3

Strainer

Backwash to Sewer

InlineMixer Contact

BasinPermeate

Tank

Cl2

NH3

GAC

Sewer

O3

InlineMixer

Sewer

Figure 2.5 Process flow diagram for the pilot plant for the Chaparral WTP, Arizona, USA

Zenon UF

Pall MF

US Filter MF

Koch UF

Ozone Contactor


Arsenic Spike

Fe2 (SO4)3

Strainer

Backwash to Sewer

InlineMixer Contact

BasinPermeate

Tank

Cl2

NH3

GAC

Sewer

O3

InlineMixer

Sewer


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USFilter Membrane System. The USFilter unit was a 4S10T CMF-S system with a PVdF, chlorine tolerant membrane. The membrane modules have a surface area of 320 ft2 (30 m²) based on the outside diameter of the fiber. The molecular weight cut-off for the membrane was 0.2 µm. The USFilter pilot skid included a membrane submerged in a process tank, feed and permeate pumps, a chemical storage tank, and a chemical feed pump. A Y-strainer (500 µm) was used throughout Phase 1, but was not used during Phase 2 after the strainer was installed in the pilot plant. The USFilter production cycle consisted of 20 minutes between backwashes and a 45-second BW that included air scour and used approximately 10 gallons (38 L) of permeate. At the end of a BW, the contents of the process tank were wasted, and the tank was refilled with feed water to begin another production cycle. In addition, USFilter employed a chemically enhanced BW consisting of a normal BW followed by a 30-minute relaxation period while soaking in a NaOCl solution. Initially the enhanced BW occurred once a day and was eventually increased to twice a day. Koch Membrane System. The Koch system was an HF2 UF Pilot Unit with an 8-inch diameter, by 48-inch length (0.2 by 1.2 m) membrane module. The membrane is a chlorine tolerant, polysulfone (PS) material with a surface area of 319 ft2 (30 m²). The nominal molecular weight cut-off (MWCO) was 100,000 Daltons (Da). This system operated in an inside-to-outside mode. The Koch pilot skid included a feed tank, a permeate tank, a cartridge membrane, a feed pump, a permeate pump, a recirculation pump, chemical storage tanks, and chemical feed pumps. This system was installed with a 500 µm self-backwashing prestrainer. Various prestrainers were evaluated during the pilot, including a Y-strainer upstream of the self-backwashing prestrainer. Koch membrane operation included both recirculation and reject flows. The Koch BW used 27.5 gallons (104 L) of filtrate in a reverse flow (i.e., outside-to-inside) through the membrane and was chemically enhanced with NaOCl solution. After a few weeks of testing, every fourth BW was performed with a citric acid. The Koch membrane was also given a 30-minute relaxation period each day (i.e., the unit was turned off for 30 minutes). Post-treatment. The ozone system consisted of a 1.1 pounds per day (lb/day) [0.5 killograms per day (kg/d)] Osmonics ozone generator, an oxygen separator to supply oxygen to the ozone generator, a venturi injector (Model 484V, Kynar), and a degas separator for the ozone off-gas flow. The ozone contactor piping allowed for almost 10 minutes of contact time at a design flow of 3.2 gpm (0.2 l/s). The contactor was constructed of 6-inch diameter (15 mm) Schedule 80 PVC with 22 sample taps evenly spaced throughout the length of the contactor. Flow from the membranes and ozone contactors was pumped to the top of four GAC contactors. The empty bed contact time used for testing was designed to be approximately 15 minutes. Calgon F400 (bituminous) and Norit HD4000 (lignite) carbons were selected for pilot testing. The performance of each carbon, in the presence or absence of preozonation was evaluated. Data Management. A data network was installed at the pilot plant to collect, record, and store membrane performance data, as well as the turbidities and particle counts for raw water and contact basin effluent. Data were collected and stored on a central computer located in a locked trailer at the pilot plant. Data were logged at one-minute intervals, and a data analysis software program was used to develop real-time trend graphs for each set of data then write the data to database files each week. Each membrane vendor also collected data from their respective units


44

through a dedicated phone line to provide data collection redundancy and to allow their staff to monitor their membrane’s performance. Instrumentation. Turbidity and particle counts of raw and permeate water were measured continuously to determine log removals for compliance assessments by MCESD. Other on-line instruments (i.e., pressure gauges, flow meters, etc.) were provided by the membrane suppliers with their membrane skids. The turbidity of the GAC effluents was also monitored with on-line turbidity monitors.

Integrity Testing. Weekly PDTs were performed throughout Phase 2 to check the integrity of membrane fibers. Pilot Plant Results. The results of the pilot study are presented in the following text. A summary of some of the pertinent pilot results can also be found in Shorney et al., 2001. Source Water Quality. Source water for both the pilot and full-scale plant is the Arizona Canal of the SRP system. The canal is operated approximately 11 months per year. Flow to the canal is usually terminated in January or February to allow for canal maintenance. Water delivered through the SRP system is a blend of four different sources:

1. Salt River. 2. Verde River. 3. Colorado River water delivered via the Central Arizona Project (CAP) Canal. 4. SRP Wells, which are the smallest contributor to the SRP system.

The quality of raw water during the pilot tests is summarized in Table 2.19. These parameters were affected by the blend in the canal, but the summary shows the general water quality observed during testing. TOC averaged 2.9 mg/L during the study. Geosmin and MIB concentrations averaged 2.8 and 13.2 nanograms per liter (ng/L), respectively. Raw water iron and manganese concentrations averaged 0.56 mg/L and 0.07 mg/L, respectively. The turbidity was typically between 5 and 25 NTU, but on several occasions it exceeded the range of the instruments (i.e., 35 NTU for the raw water turbidity monitor, and 90 NTU for the membrane influent turbidity monitor). These higher turbidities were typically associated with rainfall events. The maximum recorded turbidity of 800 NTU occurred in October, based on a grab sample. Membrane System Performance. Pall and Zenon successfully completed the pilot study by meeting the requirements of the membrane testing protocol. The Zenon system operated with a net flux of 30 gfd (51 lmh), 90-percent recovery, a 15-minute BW interval, and an average cleaning interval of 29.5 days. The Pall system operated with a net flux of 30 gfd (51 lmh), 91-percent recovery, a 20-minute BW interval, and an average cleaning interval of 14 days. The cleaning chemicals used for Zenon were chlorine followed by citric acid, and for Pall, caustic chlorine followed by citric acid. Pre- and P-treatment Performance. The pilot trials proved that effective arsenic removal could be achieved with 15 mg/L as ferric sulfate coagulation upstream of the membranes. Downstream bituminous GAC was needed to improve TOC removal and remove MIB to less than 5 ng/L.


45

Table 2.19 Summary of SRP canal raw water quality during pilot trials

* Geosmin and MIB are taste-and-odor-causing compounds.

Intentional fiber breakage. Fiber breakage tests were performed on the Pall and Zenon systems to test the sensitivity of PDTs, particle counts, and heterotrophic plate counts (HPCs) to a broken fiber. In each system, one fiber was cut and the membrane module was placed back into service. PDTs were reliable indicators of fiber breakage for both membranes. Particle counting did not prove to be reliable for either system in detecting the presence of a broken fiber or in confirming the integrity of the membrane after fiber repair. HPCs did not increase in the filtrate of the Pall skid with a broken fiber, but were dramatically higher in the filtrate of the compromised Zenon skid.

Full-Scale Design

The full-scale plant will be operated to produce from 4.5 and 27 mgd (17 to 102 ML/d), with an annual average production of 11.2 mgd (42 ML/d). Zenon’s ZeeWeed 500d modules will be used in a 10-train arrangement, and the individual trains will have six cassettes, each with 52 modules. The cassettes are capable of housing up to 64 modules, so additional membrane area can be installed if needed in the future. Two extra basins will also be constructed, but not equipped with membranes.

Ten gravity-fed GAC contactors are immediately downstream of the membranes. The adsorptive capacity of the GAC media is expected to be approximately 12 months. As with the membrane basins, two extra contactors will be constructed but not outfitted.

There is a 5.5-MG (21 ML) reservoir on the site. The WTP must achieve 3-log Giardia and 4-log virus inactivation. Disinfection will be provided by on-site chlorine generators. Solids handling will be included due to the high arsenic concentrations expected in ferric solids.

The process flow diagram for the full-scale plant is shown in Figure 2.6.

Minimum Value

Average Maximum Value

Median Number of Samples

As (µg/L) 3.0 6.6 20.0 5.0 36 TOC (mg/L) 2.0 2.9 3.6 3.0 25 DOC (mg/L) 1.9 2.8 3.4 2.8 22 Geosmin (ng/L)* 2.0 2.8 5.0 2.5 20 MIB (ng/L)* 4 13.2 33 11 21 Bench Turbidity (NTU) 1.5 8.0 29.7 4.9 48 pH 7.7 8.1 8.5 8.1 59 Total suspended solids (TSS) (mg/L)

18 38 59 36 7

Alkalinity (mg/L as CaCO3)

126 151 220 136 21


46


The MCESD has primacy of drinking water regulations in Maricopa County, Ariz. MCESD was included in the planning of the pilot program, integrity testing, and performance evaluations of the pilot plant. They were responsible for approving the final design of the full-scale plant. One key issue that required MCESD input was the removal credit granted to the membranes and overall treatment train. A representative of MCESD has been attending design meetings, beginning just prior to 30 percent design.


The City of Scottsdale, Ariz., offers the following recommendations to utilities considering membranes for water treatment. First, select engineering teams experienced with membrane systems. Review the approach herein for pre-qualifying membranes, pilot testing of process alternatives, and establishing design criteria for bidding and procurement. This approach fosters fair competition among the suppliers as well as reduces the risks of both parties for meeting performance and operations targets. Allow time and funding for a thorough pilot testing program. In this project, six months of pilot testing were used to verify the process train; additional testing would be recommended for plants that have source waters that experience a seasonal variation in water quality. The pilot testing effort successfully achieved the goals for establishing design criteria for membranes as well as for pre- and post-treatment. In addition, it allowed the City to validate vendor claims and to assess the level of vendor support for the project. It also identified two challenges that could


Traveling ScreenStrainer

Raw Water Pumps

Strainers

Zenon UF

Filtrate

GAC Filtrate

GAC Bypass

GACDirty BackwashWash Water

Recovery Basin

Sludge Storage

Reservoir

Distribution

NaOCl

NaHSO3

CIP Receiving Basin

Sewer

Fe2(SO4)3WashwaterReturn

GAC Contactor

Figure 2.6 Process flow diagram for the full-scale Chaparral WTP, Arizona, USA

Bac

kwas

h

Centrifuges



Traveling ScreenStrainer

Raw Water Pumps

Strainers

Zenon UF

Filtrate

GAC Filtrate

GAC Bypass

GACDirty BackwashWash Water

Recovery Basin

Sludge Storage

Reservoir

Distribution

NaOCl

NaHSO3

CIP Receiving Basin

Sewer

Fe2(SO4)3WashwaterReturn

GAC Contactor

Figure 2.6 Process flow diagram for the full-scale Chaparral WTP, Arizona, USA

Bac

kwas

h

Centrifuges



47

have severely impacted production on a full-scale. These included an algae bloom and a high TMP event, and are explained in more detail. During the first month of pilot testing, algae filaments were so prevalent that the individual pre-strainers to the membrane units were clogged after only four hours of operation. A sample of the algal mass was analyzed by the staff microbiologist at the City of Scottsdale’s laboratory and Cladophora was identified as the algae species. It is described as having dichotomously-branched filaments that can grow to nuisance levels in nutrient-rich, hard water. This algae-clogging episode prompted the installation of an automatic backwashing pre-strainer in the pilot plant. Similar equipment will also be installed in the full-scale plant.

There was a notable change in the fouling rate of both the Pall and Zenon membranes when the SRP authority began reducing flow for canal maintenance in December. The time between cleaning for each membrane system was reduced by more than 50 percent. The flow in the canal was very low, and SRP personnel reported that a dam at a pond that is used to collect cotton field irrigation runoff breached sometime around December 25, 2000. These factors are believed to have contributed to the poor water quality and poor performance of the membrane systems. A well water supply was put into service, and the fouling was found to be reversible. The membranes operated using well water for the next two weeks, with normal flux rates. This was a particularly interesting event in that all water quality parameters known to impact membrane performance were being monitored and were showing improvement during this fouling event.

Cost

The cost of the pilot plant was approximately $850,000. This cost estimate includes site preparation, pilot equipment, staffing, sampling, and data collection. The City’s water quality laboratory performed all of the water quality samples for the pilot trial and estimates the value of analyses for the pilot was $220,000. The full-scale plant is expected to cost $55 million.

Clay Lane WTP, England, UK

The Clay Lane WTP uses UF filtration of a groundwater source. This facility has been in operation since 2001 and is summarized in Table 2.20.

Background

The Clay Lane WTP, which is owned and operated by Three Valleys Water, part of Veolia, supplies up to 42.3 mgd (160 ML/d) of drinking water to a suburban region of northwest London. In 2001, UF membranes were integrated into the WTP after Cryptosporidium was detected in the finished water in the mid 1990s. At the time of installation, the Clay Lane WTP became the largest UF treatment plant in the world, and now has the most operating experience with large-scale UF systems in the UK.

The existing treatment consisted of ozone followed by GAC filtration for pesticide removal, followed by chlorination for primary disinfection. Without coagulation, this treatment was not effective for the removal of Cryptosporidium, which has the potential to enter the source of supply as a result of rainfall events.


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Table 2.20 Summary of the Clay Lane WTP, England, UK

Status of project Start-up in 2001 Capacity 42 mgd: 160 ML/d Source water Groundwater under the

influence of a surface water Pretreatment Ozone, GAC, chlorine Type of membrane Norit X-Flow UF Design flux 73 gfd; 124 lmh Pilot testing Four membrane systems Integrity testing Daily air integrity test (AIT) Main driver for integration

Cryptosporidium removal

Three Valleys Water embarked on an investigation of suitable, long-term treatment of the

groundwater supply. As an interim measure, the applied ozone dosage was increased to provide inactivation of Cryptosporidium at the plant. Some of the groundwater sources were also equipped with temporary filters for extra protection against Cryptosporidium.

These events preceded the passage of the Cryptosporidium Regulations (see Appendix A) by the DWI; thus, there was no regulatory requirement to serve as a guide for design. Three Valleys Water, with guidance from their parent company Veolia, carefully evaluated the performance, reliability, feasibility, and cost of several treatment alternatives, and ultimately chose UF to reduce the risk of Cryptosporidium in the finished water.

Several alternative process trains were evaluated. Ozone was not deemed a long-term solution, because the DWI of the UK required removal of Cryptosporidium rather than inactivation. Conventional treatment followed by filtration was likely to be suitable for Cryptosporidium removal. However, because of various issues including the low turbidity source was not ideal for conventional coagulation, sludge removal would be challenging in the urban location, and the excessive use of chemical for coagulation was not desirable, convention treatment was not considered. Membrane filtration, downstream of the existing chlorine contact basin was the best alternative, and in the summer of 2001, the plant was delivering UF filtered water to distribution.

The design-build project was executed by OTVB Ltd. (also a subsidiary of Veolia) based in Birmingham, UK.

Source Water

Water is pumped from eight wells, or boreholes, from aquifers at a depth of about 328 ft (100 m). The combined flow to the plant is 42.3 mgd (160 ML/d). The source water typically has a turbidity of less than 0.5 NTU; however, rainfall events can cause elevated turbidities of up to 2 NTU. The temperature of the water remains constant at 52°F (11°C).

Description of Treatment

A process flow diagram is shown in Figure 2.7.


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Pretreatment. Ozone is dosed to the raw water to oxidize pesticides (e.g., atrazine, diruon) and organics, as well as providing a disinfection barrier. On average, seven minutes of contact time are provided before the ozone residual is quenched with NaHSO3. Ozonated water then flows by gravity to twelve GAC filter/adsorbers, each with 4,200 ft3 (120 m3) of GAC, which are backwashed every 22 days and replaced/regenerated every eight years.

Chlorine disinfection is provided just upstream of the UF membranes in a clearwell that is located below the GAC filters. Due to the close proximity of residential housing and the associated health and safety concerns with gaseous chlorine, NaOCl is used as the chlorinating agent. In the original plant, 20 minutes of super-chlorination (i.e., chlorination at a high dosage) was provided before de-chlorination with NaHSO3. Since the UF membrane plant was installed, the chlorination time and concentration have remained the same, and a 0.2 to 0.4 mg/L chlorine residual is carried through to the UF membranes. The chlorine dosage may be reduced in the future. No further chlorination takes place after membrane filtration, as it was deemed that the existing chlorination at the facility was sufficient disinfection when integrated with the membrane system.

The plant currently operates with 200-μm basket strainers which are installed in line on each of the two pipes that feed the UF plant. Every four to six weeks, these strainers are removed from service with a permanently installed davit and hoist so that they can be cleaned. Removal, cleaning with a high-pressure hose, and re-installation require one or two manhours per basket. The basket strainers are wedgewire construction (i.e., continuous ‘v’ shaped wire wrapped around support rods and welded at each junction for increased durability and strength) rather than a gauze wire mesh. This is because the original 80-μm and subsequently the 150-μm wire mesh baskets were tested during commissioning, and could not withstand the hydraulic conditions in the pipe. These were replaced with the wedgewire strainers. Primary Membranes. The plant uses Norit’s horizontal cross flow UF membranes (polyethersulfone (PES), hollow fiber, UFC M, 8-inch or 200-mm diameter) which are operated in a dead-end configuration. There are 32 units which are arranged in four trains. Each unit has 12 vessels, and there are four membrane modules per vessel. There are 1,536 membrane modules in the entire primary system.

The maximum feed flow is 44 mgd (165 ML/d) and the design net flux is 73 gfd (124 lmh). The maximum instantaneous flux is (132 lmh) at 52°F (11°C). The recovery in the

O3

Wells

To WWTP

Supply

Figure 2.7 Process flow diagram for the Clay Lane WTP, England, UK

GAC

Ozone Contact Chamber

BasinStrainers

Cl2

Storage

Primary UF

Secondary UF

ChemicalWasteBackwash

Corrosion Inhibitor

Filtrate Recycle

Backwash

Backwash and CIP Waste

O3

Wells

To WWTP

Supply

Figure 2.7 Process flow diagram for the Clay Lane WTP, England, UK

GAC GAC



BasinBasinStrainers

Cl2

StorageStorage

Primary UF

Secondary UF

ChemicalWasteBackwash

Corrosion Inhibitor

Filtrate Recycle

Backwash

Backwash and CIP Waste


50

primary system is greater than 99 percent. In practice, the operating TMP is between 5.8 and 11.6 psi (0.4 and 0.8 bar). Post-treatment. Phosphoric acid is added for corrosion control just downstream of the UF system. Additional chlorine feed points are available to increase the chlorine residual, if necessary. Water enters one of four reservoirs, prior to distribution. Much of the distribution system is fed by gravity, but some local customers receive a pumped supply. Secondary Membranes. The BW from the primary units is delivered to two BW tanks that supply the secondary, or recovery, membrane units. There are four secondary membrane units, each with 12 PVs. These vessels house two membranes each, thus there are 96 membrane modules in the secondary system. Neutralized CEBW waste is also treated by the secondary units. The concentrated waste from this system is discharged to the sewer, and permeate is recycled to the head of the WTP. The design capacity for this system is 1.32 mgd (5 ML/d). During periods of high-turbidity feed water to the primary UF units, the BW interval is shortened, thus increasing the volume of BW water that is delivered to the secondary membrane units. Under these conditions, the capacity of the secondary systems is sometimes exceeded, and it is necessary to divert excess flow to a surface lagoon on the premises, so that the primary units can continue production. Overall, the waste flow from the plant has been reduced since the membrane systems have been installed. Originally, waste flow consisted of GAC BW and filter-to-waste; however, these flows are consolidated and treated in a separate, traditional settling system and along with the UF secondary system, to achieve greater than 99-percent recovery for the entire WTP. Backwashing and Cleaning. Under typical operations, the UF units are backwashed every 40-150 minutes, and the BW duration is about 50 seconds. The interval and duration changes based on the feed water quality. Originally, selection of these parameters was automated, but now the operator chooses the interval and duration.

Both CEBWs and CIPs are performed. The original design specified a caustic CEBW at pH 12 after 36 BWs, and a hydrochloric acid CEBW at pH 2 after 144 BWs. Now the CEBW frequency is controlled by the operator and performed as needed. This regime continues to be adjusted to best suit the system performance. A typical CEBW duration is from 10 to 40 minutes, depending on the soaking chemical, and this is adjustable to suit the cleaning needs at the plant. Three Valleys Water has investigated a third type of CEBW with NaOCl. This third CEBW did not improve UF performance. The caustic and acid CEBW waste is typically self-neutralized in the neutralization tanks; however, either chemical can be added if necessary to ensure complete neutralization. CIPs are currently performed with citric acid to improve the removal of lime scale and organic foulants from the membranes. CIPs are a manual operation, as it was expected to occur every six months. The frequency of CIPs has increased due to higher-than-expected turbidity in the feed water, and the manual operation is being converted to an automatic operation to minimize the amount of staff time associated with CIPs. The current practice is to clean one entire filtration unit (i.e., 12 PVs with 96 membranes) at once. During the CIP, the membranes are allowed to soak overnight at about pH 2, and the cleaning solution is recycled back to a storage area. The citric acid solution is reused until the pH is greater than four. At this time, fresh citric acid is added to the used solution to lower the pH. Each unit is cleaned at least once every six months. Citric acid CIP waste solution can also be neutralized with caustic chemical, if necessary and also discharged to sewer under a regulatory permit.


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Integrity Testing

The integrity testing method used for the primary membranes at the Clay Lane WTP has been developed and modified since start-up in 2001. Each day, the AIT (i.e., water displacement test) is automatically performed on each of the 32 units. The following steps are taken during the AITs and subsequent fiber repairs:

1. An entire unit is removed from production by automatic inlet valve closure. 2. The AIT is then initiated on half of the unit (i.e., six PVs in vertical alignment) by

allowing the six PVs to drain under 1-bar pressure while monitoring the flow rate. If the first six PVs pass the AIT, the second six PVs are tested. The AIT test is about 12 minutes in duration for two racks.

The draining, or leakage, rate is measured by a flow meter on the permeate pipe. The baseline drainage rate for comparison is established at the factory when the membrane modules are produced. The factory rate (which could be termed diffusion rate) is near 60 liters per hour (l/h) for this type of membrane. If the integrity of the system is breached, the drainage rate, or leakage rate, is greater than 60 l/h. Experience at the Clay Lane WTP has shown that the majority of integrity breaches are from multiple minor defects rather than entire fiber breakage. An extensive evaluation of allowable leakage has resulted in a complex algorithm-based SCADA system which identified 150 l/h as the maximum leakage rate per all units in service to maintain >5-log Cryptosporidium removal. This level of Cryptosporidium removal, coupled with a 4-log virus removal requirement, was selected by Three Valleys Water as a target to provide the best quality of water to their customers. While a lower log removal target would allow a higher tolerance of compromised membranes in the system, it is recognized that compromised membranes will eventually have to be repaired or replaced, and it was decided to operate under the more stringent criterion to provide improved protection against pathogens.

The SCADA system monitors the leakage rate of the AIT, and if it exceeds 100 l/h, a warning is issued, and the six PVs are returned to production and monitored closely. If the leakage rate exceeds 150 l/h, a failure is issued, and the unit is isolated and removed from service.

The following steps are followed after an AIT failure:

1. After an AIT failure, the AIT is manually repeated and individual PVs are isolated until the leakage rate is reduced. This procedure identifies the breached PV. This breached PV is isolated until staff performs the next set of diagnostics on the membranes. If more than 2 PVs are isolated, the unit is taken offline by the operator.

2. With the unit offline and drained, the membrane elements in the identified PV are removed and tested by a vacuum test device (VTD). The VTD is similar to one used at the Norit production factory, and provides an indication of which membrane has a breach of integrity. Six membrane elements can be evaluated at once. A vacuum is applied to the permeate central pipe of the membrane element and the vacuum stability is measured over time. Membranes that pass the VTD at this stage are re-installed into an available PV.

3. After the breached membrane has been identified by the VTD, the broken or breached fiber is identified by the immersion test. Each membrane module is connected to an


52

air supply and air leaks are visually detected. The compromised fiber is pinned with a plastic pin that is glued into place.

4. After the membrane module is pinned, it is vacuum tested again. If it passes the test, it is re-installed into an available PV. If it fails, another immersion test is performed.

The staff has modified the procedure to minimize the operator’s time during the repair of the membrane modules. Their staff has also designed a hoisting device which aids in the removal and transport of the membranes when they are taken to the VTD.

The VTD and immersion bath testing are time consuming and are performed by a subcontractor. The testing procedures have been modified to lessen the time per vacuum test to about 10 minutes per six vessels. The actual vacuum is three minutes in duration. The immersion test duration varies depending on the nature of the integrity breach.

The permeability of the unit decreases after an AIT test. To reduce this effect, the units are backwashed after an AIT. A CEBW is performed if the units/modules have been exposed to atmosphere or manual handling. The secondary units undergo monthly AIT. This is because they are deemed to pose a low risk if the integrity is breached. All filtrate from the secondary units is recycled to the head of the WTP. The same AIT and repair procedures are used for the primary and secondary units.

Pilot Plant

Pilot trials were conducted to establish design criteria for the bidding and tendering process. Four membrane systems were evaluated, and the program allowed vendors to test water from the existing plant, as well as raw water. Vendors were allowed to test their systems to establish their own design criteria for bidding. Pilot testing was not conducted as part of a performance requirement or verification at this facility. Three Valleys Water has recently purchased a pilot facility to conduct ongoing optimization tests to improve operation of its membrane filtration facilities. This has proved most beneficial for conducting experiments off line without impacting the full-scale plant.

Cost

The cost for installing the membrane equipment in 1999 and 2000 was $18 million (£10 million).

Staff

The plant is operated with a three-person crew: process technician, production technician, and production operator, and supported by 16 staff (i.e., 14 technical and 2 administrative) as and when required. The staff operates the entire treatment facility, including the existing ozone and GAC plant, as well as the new UF plant. A contractor assists with the vacuum and immersion tests at the plant. Day shifts are from 8:00 am until 4:00 pm, and the system operates unmanned during the evening and night. SCADA for the entire system can be accessed remotely. The Three Valleys Water telemetry system can also monitor plant performance, and staff are able to come to the WTP anytime of the day on an emergency basis. The level of staffing increased after membrane integration. This is because membranes were added to an existing WTP, which also requires operator attention and maintenance.


53

Recommendation to Other Utilities

One recommendation from Clay Lane staff is to provide essential services around the perimeter of the membrane building. This design feature allows for convenient access to services such as potable water, air, and network cabling. Docking stations for portable computers have also been installed at various locations within the plant. This has proven beneficial when collecting and analyzing data during commissioning. The compact nature of membrane facilities sometimes leads to close proximity of chemicals to the membrane equipment. It is recommended that chemical storage and feed systems be completely segregated from the membrane equipment to minimize corrosion from any chemical release in the storage area. During commissioning, a leak of hydrochloric acid resulted in an increased rate of corrosion on the membrane racks, piping, and valves. The PVs were passivated; however, some corrosion still occurred. Another recommendation would be to use a more diluted sulfuric acid (e.g., 30 percent) for the CEBW system. A greater storage area would be required; however, the effect of an accidental leak would be less harmful. Cleaning of the racks and equipment after the corrosive incident has been quoted to be about $14,400 (£8,000). It is recommended that careful consideration be given to the choice of a grated floor versus a solid, concrete floor with drains. The Clay Lane facility uses a grated floor, and much of the influent, effluent, and chemical feed pipe-work is located beneath the grated floor. This allows for a safe working environment with excellent access to the membrane units; however, when PVs are removed from service, they can only be drained to half full. When physically removed from the rack, a significant amount of water falls below. Any equipment (actuators, valves, pumps, etc.) beneath the grated floor will get wet and needs to be water resistant or adequately covered. Pilot testing of adequate duration and with the most challenging feed water is recommended for those systems considering membrane integration. At Clay Lane, some of the pilot-scale evaluations were performed with finished water from the full-scale plant. Although this is ultimately the water being treated by the UF plant, the pilot-scale feed water was only feed water that was potable, finished water. During the pilot trials, high turbidity water from the GAC beds was not evaluated; thus, when turbidities are higher than normal at the full-scale plant, operational modifications (e.g., decreased backwashing interval, excess BW flow to surface lagoon, etc.) are necessary to maintain adequate production levels. Checking the durability of the strainers upstream of the membrane system is also recommended. Even with GAC filtration upstream of the membranes at the Clay Lane facility, operators report that debris, the source of which is unknown, is often collected from the prestrainer baskets when they are cleaned.

Instrumentation

The filtrate of each stream is monitored for turbidity, pH, and conductivity. Conductivity is used as a surrogate safety measure to identify any poor quality (e.g., excess chemical from CIPs or CEBWs) in the permeate line. The finished water is monitored for pH, turbidity, conductivity, and free chlorine residual. This facility also maintains on-line Cryptosporidium operational monitoring. This is now a voluntary monitoring program, because Three Valleys Water, with the new UF treatment


54

facility, has successfully applied for a waiver from the mandatory Cryptosporidium monitoring requirement of DWI.

The pH and conductivity of the filtrate from the secondary units is measured on the recycle stream. Particle counts are not measured continuously at this facility, but are periodically measured with a portable, on-line particle counter. On-line turbidity meters will be added to the feed streams to the secondary UF units as well as the BW from these units. These are being added to accurately assess the solids loading to the secondary units and the discharge to the sewer.


The feed pumps are automatically controlled to maintain the level in the feed sump. The well pumps, however, are manually controlled. At this time, the automated integration of the existing plant to the membrane plant has not occurred due to the desire to maintain independent control of the existing plant and the membrane plant. The plant is currently operated with all units in production if the integrity limits of the AIT are met; thus, when demand is low, the operating flux is less than the design flux. The plant was designed to operate with less than 0.1 percent discharge. This high level of recovery is established when the system is operating under normal conditions. However, when the plant is challenged by high turbidity feed water, the recovery is decreased as the rate of backwashing increases. The software used for the control and data storage was developed by a subcontractor to suit the needs of Three Valleys Water. The SCADA system performs standard functions, but also includes some special features. For example, a hierarchy of control and access exists for any individual with access to the system. Only staff with approved authority can change operational settings. This minimizes the risk of accidental, unintentional, or unknown operational changes. The SCADA system also tags and time stamps certain operational changes so that actions can be monitored at a later date when troubleshooting or tracking historical events.

The SCADA information is available at several ethernet-connected computer stations located in the WTP. There are two main control rooms, and several offices and docking stations within the premises. The system can be accessed remotely, and many of the controls and functions require privileges and passwords. Data are automatically saved to one computer station on a daily basis. The Clay Lane WTP is a critical source of supply for its service area. As a result, all systems and pieces of equipment have dual redundancy to minimize the risk of a system shut down. The PLC, chemical feed pumps, tanks, strainers, and piping were designed to allow flexibility and redundancy, where necessary.

Bexar Metropolitan Water System (Bexar Met) WTP, Texas

The Bexar Met WTP uses UF to treat a surface water. This plant has been operational since 2000. A summary of the WTP is shown in Table 2.21.


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Table 2.21

Summary of the Bexar Met WTP, Texas, USA Status of project Start-up in 2000 Capacity 9 mgd: 34 ML/d Source water Surface; Medina River Pretreatment Coagulation with ferric sulfate solids blanket clarifier Type of membrane Aquasource UF Design flux 68 gfd; 115 lmh Pilot testing Required by regulatory agency, three membrane

systems tested Integrity testing Weekly PDT Main driver for integration Cryptosporidium removal

Background

The Bexar Met is one of the two largest water suppliers in the San Antonio/Bexar County area. Historically, the primary source of water was the Edwards Aquifer, one of the largest aquifers in the USA. The quality of the water obtained from the aquifer typically exceeds federal drinking water standards, requiring minimal treatment before distribution. Due to declining aquifer water levels caused by increasing demand Bexar Met investigated other sources of drinking water, and purchased land that held rights to about 7,000 acre-feet (ac-ft) of water from the Medina River. The District constructed a WTP and is the first plant in the San Antonio area that produces potable water from a surface water source.

Source Water

The source water to the membrane plant is the Medina River. The river originates in the northwest Bandera County and flows southeast through Medina and Bexar Counties, where it joins the San Antonio River. The river forms a major reservoir, Lake Medina, in the Bandera and Medina Counties. The water from the plant is drawn from the Medina River at a point near IH35, a few miles southwest of Loop 410. The source water quality is listed in Table 2.22.

Water in the Medina River can have high turbidity (i.e., > 2,000 NTU), but overall has a low TOC and DOC concentration (i.e., average < 3 mg/L). The water is relatively hard and has a pH near eight.


A process flow diagram is presented in Figure 2.8.


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Table 2.22 Raw water quality for the Bexar Met MF facility

Parameter Number of Samples

Minimum Average Maximum

pH 1153 6.60 8.05 8.93 Hardness, mg/L as CaCO3 1141 140 254 316 Temperature, oF 1433 45 71 85 Turbidity, NTU 1176 1.1 40 2,460 TOC, mg/L 37 0.8 2.4 6.0 DOC, mg/L 8 0.6 1.5 3.3 Color 965 0.03 7.48 48 UV 254, cm-1 910 0.01 0.08 7.00 Ammonia, mg/L 235 -- 0.04 0.91 Nitrate, mg/L 29 -- 0.00 0.04 Chloride, mg/L 228 0.25 25 50 TDS, mg/L 966 -- 277 635 Manganese, mg/L 234 0 0.02 0.05 HPCs 3 3,110 12,503 15,900

Figure 2.8 Process flow diagram for the Bexar Met WTP, Texas, USA

MedinaRiver

Cleaning Waste

SupplyPresedimentation

Ferric SulfateSuperpulsatorCoagulation &

Clarification

Disposal

AcidPAC

Static Mixer

UFStrainers

BackwashRecycle

Lagoon

WetWell

Cl2 F NH3

LagoonsBasin

Decant Recycle

Storage

Figure 2.8 Process flow diagram for the Bexar Met WTP, Texas, USA

MedinaRiver

Cleaning Waste

SupplyPresedimentation

Ferric SulfateSuperpulsatorCoagulation &

Clarification

Disposal

AcidPAC

Static Mixer

UFUFStrainers

BackwashRecycle

Lagoon

WetWell

Cl2 F NH3

LagoonsBasin

Decant Recycle

StorageStorage


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Pretreatment. Water from the Medina River is drawn from a small pool created through construction of a variable height weir in the river. The weir can be adjusted from zero to 5.5 ft depending on the water level in the river. Three submerged, ¼-inch screens are provided at the intake. These are air backwashed, and the BW is initiated at regular intervals or based on headloss across the screen. Three submersible pumps, each with a nominal capacity of 5 mgd (18.9 ML/d) pump the water via a 30-inch (0.76 m) diameter pipeline over a distance of 2,000 ft (610 m) to the WTP. The actual combined pumping capacity of the raw water pumps is 18 mgd (68 ML/d). Two of the pumps incorporate a variable frequency speed drive to allow withdrawal in the range of 2.5 to 9 mgd (9.5 to 34 ML/d) to match the raw water demand by the plant. Since the intake facility is built in the flood zone, all mechanical equipment including pumps is designed to tolerate moisture.

Facilities for addition of PAC, ferric sulfate, sulfuric acid, and a spare chemical to the influent line are provide at the plant site. An inline static mixer is used to mix the chemicals. Currently, only ferric sulfate is being added to the water and the dose varies from 10 to 120 mg/L depending on the water quality. The PAC feed equipment is designed for a dosing rate of 2 to 30 mg/L.

The water then travels through a mixing chamber, and the coagulated water then enters the main clarification chamber of the superpulsator through distribution laterals that span the basin. A vacuum pump and a vacuum chamber are used to create a pulsing effect within the flocculation zone at the bottom of the basin. The pulsing expands and contracts the solids blanket, increasing the efficiency of the flocculation and maintaining the uniformity of the blanket. Clarification occurs with the use of inclined plates above the sludge blanket that settle the remaining floc. The sludge blanket surface elevation is maintained through the use of a solids overflow weir. The clarified effluent is discharged at the top of the unit. The superpulsator is operated at a loading rate of 1.6 gpm/ft2 (3.9 lmh) at a plant capacity of 9 mgd (34 ML/d). It is designed for a loading rate of 2.5 gpm/ft2 (6.1 lmh). The clarified water quality is listed in Table 2.23. Approximately 0.4 mg/L of iron passes through the superpulsator.

The sludge is transferred to a solids transfer basin and pumped to two sludge lagoons for decanting. The supernatant is pumped to an equalization basin from which it is pumped to the head of the plant. The sludge from the lagoons is removed twice a year (i.e., once a year per lagoon) and is hauled offsite.

Table 2.23

Settled water quality at the Bexar Met facility Parameter Minimum Average Maximum pH 7 7.58 8.60 Hardness, mg/L as CaCO3 142 256 310 Turbidity, NTU 0.09 2.05 92 Alkalinity, mg/L as CaCO3 122 180 234 Color, CU - 3 21 Dissolved iron, mg/L 0 0.02 0.09 Total iron, mg/L - 0.42 3.30


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Primary Membranes. Water from the superpulsator flows into a small wet well (approximately 10 by 10 by 20 feet; 3 by 3 by 6 m). Three membrane feed pumps, including one standby, which are equipped with variable frequency drives supply water through three strainers that have 200 µm pore size openings to the membrane system. All three strainers are operating at any given time. The strainers are backwashed every 90 minutes or whenever pressure difference across the strainers is greater than 3 psi.

The membrane system consists of seven Aquasource UF trains. Each train is equipped with 48 modules and can be operated in either a dead-end or recirculation mode. A description of the membrane module is given in Table 2.24.

The design net flux is 68 gfd (115 lmh) at 68°F (20ºC). The membranes are typically operated in a dead-end mode; however, the plant operators have initiated recirculation during high turbidity events. The recirculation flow is typically less than 8 percent of the feed flow. The membrane system is operated at a recovery of 89 to 95 percent.

The membranes are housed in a building of size 153 ft by 125 ft. The membranes occupy 100 ft2 of the building. There is no area in the existing building for future expansion. Post-treatment. The filtrate from the membrane system flows to a 1 MG (3.8 ML) storage reservoir. NaOCl is added upstream to achieve a residual of 3.5 mg/L. The required virus log removal is achieved in the storage reservoir.

Three high service pumps, including one standby pump, deliver the water to a 12.5 MG (47 ML) storage tank that is located 5 miles away. Fluoride and ammonia are added after the high service pumps. The chloramine residual is typically 3.5 mg/L and fluoride concentration in treated water is in the range of 0.8 to 1 mg/L. Finished water from the 12.5 MG (47 ML) offsite storage tank is pumped into the distribution system. Backwashing and cleaning. The system was originally designed to perform backwashes at fixed time intervals in the range of 30 minutes to 45 minutes. However, the operators have reprogrammed the controls such that initiation of BW is based on several parameters.

Table 2.24 Characteristics of the Aquasource membrane modules at Bexar Met

Module model number LB35 No. of modules 336 (total) Dimensions of module 12 inch diameter by 4 feet long Active membrane area (feed side) 55 m2/module Pore size (µm) 0.01 Membrane material Cellulose acetate (CA) Fiber flow configuration Inside-to-outside Membrane hydrophobicity/hydrophilicity Hydrophilic Maximum allowable operating pressure 50 psi (3.4 bar) Allowable operating pH range 1.6 to 9 Allowable cleaning pH range 1.6 to 9.5 Maximum allowable feed turbidity Original design 5 to 7.5 NTU. With

unique conditions and protocols, 15 NTU Chlorine/oxidant tolerance Yes, 200 mg/day


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During cold weather, the BW frequency is once every 45 minutes or after 45,000 gallons (170,000 L) of filtrate production per module. During warm weather, the BW is performed every 90 minutes or after 90,000 gallons (340,000 L) of filtrate production per module. In addition to these set time limits, a BW is also initiated whenever the net TMP exceeds 22 psi (1.52 bar). This TMP is derived from a filtrate backpressure of 8 psi (0.55 bar). The BW is also initiated if the permeability falls below 2.8 gfd/psi (68 lmh/bar).

BW is performed on one half of the train at a time with a 120 horsepower (hp) pump. The BW water is drawn from a 1 MG (3.8 ML) finished water storage tank, using two pumps, of which one is on standby. The staff indicated that backwashing one whole train would require a 300 hp [225 kilowatt (kW)] pump and that is not cost effective. The amount of water used for BW is 6,000 gallons (22,700 L) per train. During warmer weather, a typical BW is approximately 90 seconds for one train; however, during colder weather, the staff indicated that a BW could take up to 300 seconds, due to the low flow rate of water with higher viscosity when the BW pressure is typically limited to below 40 psi (2.7 bar). During every fifth BW, recirculation pumps are used to maintain the pressure at 40 psi (2.7 bar). No chemicals are added to the BW water. No air scouring is currently used during BW, though the utility is considering implementation of air scour in future. The BW water is sent to an equalization basin, from which it is pumped to the head of the plant.

A CIP is performed once every ten days. A 1-percent citric acid solution is made in an 800 gallon (3,028 L) tank. The acid solution is then re-circulated through the system for 45 minutes. During re-circulation, the solution temperature increases to approximately 30 to 40ºF (16.7 to 22.2ºC). After the CIP, the system is rinsed and an integrity test is performed. Unless any defective modules are detected, the system is returned to service. Typically, CIPs are performed on four trains during the first day and the remaining three trains are cleaned the following day. The CIP waste is mixed with the rinse solution, which is typically 10,000 gallons; 37,850 L, and the resulting pH is approximately 7.5. The solution is then pumped to a lagoon, which is dedicated to holding CIP solution.

Staff

The plant is staffed by four certified (i.e., one Class B and three Class C) operators on Monday through Friday, 7:00 am to 3:30 pm. The plant is unmanned from 4:00 pm onwards during weekdays. One person is present for two hours each day during weekends; however, the operators are on call when the plant is unmanned. The PLC calls an operator whenever an alarm is triggered. The first call is to the operator on call and if unanswered, the second call is to the operator for the following shift.

Pilot Plant

Because there were no surface WTPs treating water from Medina River, the state regulatory agency required pilot testing for any treatment process, membrane or conventional. A pilot study was conducted to gain a better understanding of the pretreatment needs and membrane performance for treating the Medina River supply. A membrane pilot study was conducted with three membrane systems (1) Memcor, (2) Koch, and (3) Aquasource. The pilot testing was conducted during the spring of 1997 when the water quality was expected to be poor (i.e., highest turbidity). A detailed description of pilot studies can be found in Moreno, Shields,


60

Kolkhorts et al. 2001, Durand-Bourlier, Levasseur, and Thaxton 2001, and Braghetta, Price, and Kolkhorst 2001.

The pilot study was conducted in San Antonio in the proximity of full-scale plant. During the pilot study, the raw water turbidity ranged from 10 to 1,000 NTU and the TOC ranged from 1 to 6 mg/L. The TOC was as high as 11 mg/L for short duration during a storm event. The water temperature ranged from 50 to 86ºF (10 to 30ºC). A superpulsator was used as pretreatment.

Based on the pilot testing results, Aquasource membranes were found to be better suited for their plant. Because the objective of the initial pilot study was to select the best performing membrane in a 90-day trial, a second pilot study was conducted with Aquasource system to optimize the operating parameters. The effect of membrane BW water recycle to the superpulsator feed line was also evaluated. The full-scale plant was designed based on the results from the second pilot study.

Instrumentation

The flow, pH, turbidity, conductivity and temperature are monitored at the head of the plant. The raw water streaming current measure is also performed at the head of the plant. The turbidity and temperature of the clarifier effluent is monitored. The feed water flow and filtrate turbidity is monitored for each of the trains. Laser turbidity monitors are used for filtrate turbidity measurements. One particle counter measures the particle concentration of combined filtrate effluent. Chlorine concentration is measured downstream of UF (after chlorine addition) and down stream of on site storage reservoir.

Integrity Testing

A standard PDT is performed to detect any broken fibers. The test is performed on half a train at a time. The system is capable of detecting one broken fiber in 24 modules. The defective module is detected by looking for bubbles through a transparent tube at the top of the module. The broken fibers are sealed with a “dental epoxy” and UV light is used to cure it. During the repair of any module, the entire train is off line. The frequency of integrity test is once every seven days or after a CIP. It is conducted manually.

Since the plant went online three years ago, 100 to 120 fiber breaks have occurred. They found four compromised fibers that split longitudinally. The staff refers to them as “rollers” compared to a clean lateral beak of the fiber. The bid documents specified one percent fiber breaks as the limit, and up to 150 fiber breaks per module would still be within the specified limits. The plant staff has not been able to correlate the fiber breaks with either the water quality or operating conditions.

Operation to Date

The staff expressed complete satisfaction with the operation of the plant so far. The chief operator, Joe Thaxton has extensive background in controls. He has modified the initial main control logic significantly. For instance, as discussed above, the BW interval was reprogrammed such that it is triggered based on several operating parameters instead of original programming, which was set a fixed time interval.


61

The iron carryover from the superpulsator periodically clogs the cartridge filters that are upstream of the membranes. The operators felt that a different type of cartridge filter housing with easier access (e.g., with fewer bolts) and an opening to allow cleaning of the cartridge with a hose would simplify maintenance procedures.

The full-scale plant has several ongoing research studies on site. For example, the plant has some representative fibers potted in smaller, transparent tubes that treat the same water as the full-scale plant. Because this research is for development of new products through their parent company, Ondeo Degremount and AquaSource, the plant personnel could not discuss the details of their findings.

There was also an Aquasource pilot skid on site for testing of new products. For example, Aquasource is in the process of developing newer membranes with better productivity that may be considered for implementation during expansion of the existing facility. Due to confidentiality agreements, the utility personnel could not discuss the details. The plant also has a small-scale bottled water facility. The water from the UF plant goes through a RO system and the RO permeate is bottled.

Cost

The membrane equipment bid cost was $3.8 million for a 9 mgd (34 ML/d) system in 1998. The entire facility cost was $15.6 million. The cost estimate for operation for 10 years was $10 million. The monthly costs for operating the plant are shown in Table 2.25.

Bexar Met pays for all maintenance over $5,000 for each occurrence; however, the design-build-operate (DBO) contractor, United Water, is responsible for all repairs.

The total cost of delivered water is $1.29/1,000 gallons. Of this, $0.69 is debt service, $0.20 is capital replacement cost, and $0.40 is operating expenses.


Because this was one of the first membrane facilities treating surface water in Texas, the utility worked closely with regulators. As per the applicable regulations, a 90-day pilot test was conducted.

Table 2.25 Monthly operating costs for Bexar Met AquaSource WTP

Parameter Cost ($/month)

Power @ $0.07/kWhr $39,000 Sludge $850 Chemicals $20,000 Maintenance $20,000 Labor $20,000 Membrane replacement $50,000


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Planning Issues

As Bexar Met was required to decrease the usage of water from the Edwards Aquifer, it considered development of a surface WTP to reduce its dependency on groundwater. In 1999, the Bexar-Medina-Atascosa (BMA) Counties Water Control and Improvement District 1, which owns the Medina Lake, approved a long term contract with Bexar Met to supply 10,000 ac-ft (12,334 ML) annually, increasing to 20,000 ac-ft (24,667 ML) by 2012. In return, Bexar Met would spend at least $500,000 per year for eleven years for infrastructure maintenance along the Medina River system. In addition, Bexar Met purchased land adjacent to the river that brought rights to withdraw 7,000 ac-ft (8,631 ML) per year.

With the surface water supply secured, Bexar Met began planning for the development of a surface WTP. In response to Bexar Met’s request for proposal, United Water submitted a proposal for a surface WTP using a superpulsator for clarification followed by low-pressure membrane filtration. Membranes were chosen primarily due to the widely varying quality of surface water, pathogens and the Cryptosporidium incident at Milwaukee. Note that this is the first surface WTP in that area and due to the superior performance of membranes in terms of water quality, Bexar Met was willing to pay a premium over conventional treatment. In addition, the combination of superpulsator and membranes required a small footprint.

Bexar Met is currently considering expansion to 14.5 mgd (54.9 ML/d). After expansion, the superpulsator will operate at its maximum loading rate of 2.5 gpm/ft2 (6.1 m/h). The plant would need to procure and install additional raw water pumps, UF trains, and high service pumps. The plant would ultimately expand to 20 mgd (76 ML/d) by year 2006.


The utility personnel emphasized the importance of operator involvement from conception to startup. This helps educate the operators on various process parameters and their effect on successful operation of the plant.

The utility personnel also suggested that prior to selection of the engineer, the last design by the engineer should be evaluated and references be obtained from the operators. This would verify that the previous design by the engineer was satisfactory to the owner and operating as designed. This investigation may also highlight design problems that should be corrected in future designs.

As for the facilities and equipment, Bexar Met staff had few comments. One was the maintenance issues associated with pre-filters that are upstream of the membranes. The other was that the chemical containment needs to be adequately designed with proper access and catch basins.

Inverness WTP, Scotland, UK

The Inverness WTP uses UF to treat surface water. The plant has been in operation since 2002. A summary of the WTP is shown in Table 2.26.


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Table 2.26 Summary of the Inverness WTP, Scotland, UK

Status of project Start-up in 2002 Capacity 9 mgd: 34 ML/d Source water Surface, lochs Pretreatment PACl coagulation (pH 6.7), flocculation Type of membrane Norit X-Flow UF Design flux 41 gfd; 69 lmh Pilot testing 2001-2002; four membrane system

evaluated Integrity testing Particle counters and SIM every three

days Main driver for integration

Cryptosporidium removal

Background

The Inverness WTP is part of Scottish Water, and is located to the southwest of Inverness, Scotland. The design capacity is 9.1 mgd (34.5 ML/d), and the average demand is currently 6.8 mgd (26 ML/d). The WTP began distributing water in February 2002, and currently serves about 70,000 customers.

The previous WTP used only micro-strainers and chlorine disinfection for treatment. The new WTP uses Norit X-Flow UF membranes as a barrier for Cryptosporidium.

Source Water

The source water for the Inverness WTP is surface water from two lochs: Loch Duntelchaig and Loch Ashie. Loch Duntelchaig comprises 80 percent of the supply, whereas Loch Ashie, comprises 20 percent. Loch Ashie is relatively shallow and is prone to water quality deterioration due to seasonal turn-over events and algal blooms. Scottish Water owns perimeter land around Loch Duntelchaig and Loch Ashie. Most of the watershed is forest or open pasture. Some sheep and deer graze in the pastures and are deemed to elevate the risk of Cryptosporidium contamination. The watershed experiences a high amount of annual rainfall (> 28 inches; 710 mm). This flushes the watershed, yet the runoff is generally of high quality (i.e., low color and low turbidity). Staff believes the subterranean infiltration in the watershed contributes the most color to the lochs. Water quality threats to the loch were identified to be algal blooms to Loch Ashie, and Cryptosporidium in both lochs. Overall water quality characteristics are shown in Table 2.27.


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Table 2.27 Feed water quality to the Inverness WTP (January 1, 2000 to December 31, 2000)


The WTP is housed in a steel-framed, pre-engineered building having dimensions of about 148 by 148 ft (45 by 45 m), or 21,900 ft2 (2,025 m2). The treatment works is located in a rural area, and the treated water is gravity fed to the distribution systems of Inverness and the surrounding areas, which extend as far east as Nairn. The process flow diagram is shown in Figure 2.9. Pretreatment. Water is pumped from the lochs through three, 80-µm rotating drum strainers. Waste from these strainers is returned to Loch Ashie. The strainers are backwashed automatically using pressurized water. Backwashes are initiated on headloss. Typically 1 to 2 mg/L of hydrochloric acid is used to adjust the pH, and PACl is used for coagulation. Coagulant is added to remove color. The UK limit for color is 20 Hazen Units, and Scottish Water strives for less than 5 Hazen Units. The target pH for coagulation is 6.7. The acid and coagulant are fed as fixed dosages, adjusted to flow, and are only changed when there has been a change of feed water quality.

A micro-flocculation basin provides baffled mixing for floc development. Primary Membranes. There are seven primary treatment membrane units and two secondary units for treating BW water. Each primary unit as 21 stainless steel PVs, with four membrane elements per PV. There are 376.7 ft2 (35 m2) per membrane element, so each primary unit has 31,643 ft2 (2,940 m2). At a peak flow of 9.1 mgd (34.5 ML/d), the design flux would be 41.1 gfd (69.9 lmh) if all seven units are operating. The maximum instantaneous flux is about 52 gfd (88 lmh) and the maximum net operating flux is about 47 gfd (80 lmh).

Parameter Number of Samples

Minimum Average Maximum

pH 10 7.1 7.6 8.9 Alkalinity, mg/L as CaCO3 1 -- 17.1 -- Hardness, mg/L as CaCO3 1 -- 7.8 -- Temperature, oC 8 3 10.1 17.2 Turbidity, NTU 10 <0.06 0.36 0.73 TOC, mg/L 1 -- 2.4 -- Color (Hazen) 10 3 5.8 9 Ammonia, mg/L 10 <0.02 <0.021 0.03 Nitrate, mg/L 10 <0.3 <0.65 1.0 Chloride, mg/L 1 -- 7.6 -- Sulfate, mg/L 1 -- 3.5 -- Iron, mg/L 48 0.011 0.041 0.148 Manganese, mg/L 10 0.001 0.005 0.013 E. Coli, No./L 94 0 -- 0 Total coliforms, No./L 94 0 -- 1 Plate counts, 22oC 93 0 -- >10,000 Plate counts, 37oC 94 0 -- 350


65

The primary units can each hold 24 PVs and the skid arrangement is four PVs across and six deep. There are currently three empty PV positions on each unit. The membrane warranty for both primary and secondary units is seven years.

The process pipes immediately upstream, inside, and downstream of the membrane equipment are stainless steel. The PVs are also stainless steel which is rated at 145 psi (10 bar). Ductile iron pipes with epoxy coating were used for the raw water mains from the lochs, and for much of the mains to the distribution system.

The plant is equipped with an emergency bypass of the membrane units. This bypass was installed with blank flanges to minimize the risk of bypassing the plant unintentionally. Post-treatment. Filtrate from the secondary units is combined with filtrate from the primary units and sent to production. Lime, phosphoric acid, chlorine, and sometimes ammonia are added to the filtrate water. The final pH is maintained near 8.8, and the chlorine residual leaving the clearwell is about 0.4 to 0.5 mg/L. Backwashing and Cleaning. The backwashing interval for the primary and secondary units is 40 minutes, and the duration is 45 seconds. The BW flow is 147 gfd (250 lmh). The Norit system does not have extended chemical cleans, but has CEBWs. They consist of a 10-minute caustic/hypochlorite CEBW with about 200 mg/L Cl2 and 400 mg/L NaOH followed by a 10-minute hydrochloric acid CEBW at 800 mg/L. The primary unit’s CEBWs are initiated after 109 backwashes, which equates to about every three days. The secondary units have CEBWs about every other day, based on a 109 BW schedule.

CEBW waste is neutralized and sent to the sewer. BW from the secondary units is also sent to the sewer. The only waste that is not sent to the sewer is the BW from the micro-strainers, which is delivered to Loch Ashie. Secondary Membranes. BW water from the primary UF units is collected in a receiving tank. This is kept stirred and then pumped through a secondary UF membrane process to recover

Loch Ashie

Loch Duntelchaig

HCI

Baffled Flocculator

Micro Strainers(80 μm)

Emergency Bypass

Strainer Waste

Feed Pumps

PaCl

Dirty Backwash

Primary UF’s

To Distribution

Ca(OH)2

PO4

Cl2NH3 (future)

Treated Water Storage

Mixing BasinsMicro

Strainer

Secondary UF

NaHSO3NaOH

CEB Neutralization Tank

Secondary Dirty Backwash

To Sewer

CEBW Waste

CEBW Waste

Figure 2.9 Process flow diagram for the Inverness WTP, Scotland, UK

Backwash

Loch Ashie

Loch Duntelchaig

HCI

Baffled Flocculator

Micro Strainers(80 μm)

Emergency Bypass

Strainer Waste

Feed Pumps

PaCl

Dirty Backwash

Primary UF’s

To Distribution

Ca(OH)2

PO4

Cl2NH3 (future)

Treated Water Storage

Mixing BasinsMicro

Strainer

Secondary UF

NaHSO3NaOH


NaHSO3NaOH


NaOHCEB Neutralization Tank

Secondary Dirty Backwash

To SewerTo Sewer

CEBW Waste

CEBW Waste

Figure 2.9 Process flow diagram for the Inverness WTP, Scotland, UK

Backwash


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the BW water. Secondary membrane filtrate is supplied to the common primary filtrate pipework. It is also possible to return the secondary filtrate back to the head of the works, but this is not the normal mode of operation.

The secondary treatment train consists of two UF units, each with 12 PVs and four membrane elements per vessel. Each secondary unit has 18,083.5 ft2 (1,680 m2) of membrane area. The design flux for the secondary units would be 25.1 gfd (42.8 lmh) if both units were operating at 90-percent recovery.


The UF membrane facility is operated using feed back control which is based on a level measurement in the final water storage reservoir. Membrane units are brought on and off-line as required to maintain a set operating level. Each membrane unit is operated within fixed flow set points. Flow is adjusted between each flow set point to avoid undue cycling of units in and out of service and to minimize disruption to the downstream chemical dosing systems for lime, phosphoric acid, and chlorine.

The flow rate of raw water that enters the treatment facility is manually adjusted following an evaluation of raw water quality. For example, if the water quality deteriorates in one of the lochs due to algal blooms, then the abstraction rate will be decreased from the affected loch, and abstraction will increase from the other loch. Raw water is pumped from each loch to the membrane facility. Following straining, the feed water is re-pumped to the membrane filtration units using variable speed drive units adjusted to achieve a set pressure in the feed manifold to the membrane system. The plant is operated to maintain a constant level in the clearwell (i.e., 83 to 85 percent capacity of a 1.3 MG, or 5 ML, tank). Final treated water gravitates through two clearwells and then is delivered to distribution.

Waste resulting from the CEBW procedures is collected in a tank, stirred, and dosed with neutralization chemicals (i.e., NaHSO3 for NaOCl washes and caustic soda for hydrochloric acid washes) before mixing with the BW water from the secondary membranes. This combined flow is discharged to sewer.

Staff

The treatment plant is not manned 24 hours per day. A team of three operators is responsible for several Scottish Water WTPs, and Inverness is one of the plants they monitor. The entire system can be controlled remotely because all functions are fully automated. One additional operator is on call in case of emergency.

Pilot Plant

An extensive pilot plant was operated by a process contractor for 12 months from September 2001 to September 2002. Due to the timing of the pilot plant in relation to the full-scale design, only two months of pilot-scale data were available to aid full-scale design. Scottish Water, however, wanted to operate the pilot over all seasons to identify the impact of water quality changes on performance. The extended pilot program proved valuable, because pilot testing over an extended period gave confidence that the frequency of CEBWs would be


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lower than originally planned. After commissioning the plant at the specified CEBW frequency and an overall plant recovery of 98 percent, the CEBW frequency was reduced to every 109 backwashes, and the plant recovery increased to 99 percent. Four membrane units were evaluated during the pilot trial (1) Norit, (2) Koch, (3) USFilter’s CMF, and (4) USFilter’s CMF-S. The Norit and CMF-S systems provided the highest recovery, and bids were accepted for both systems. A decision making matrix was used to rank these two systems, and both systems ranked almost equally. Norit’s system was ultimately selected by Scottish Water for installation.

The pilot cost was estimated to be about $270,000 to $360,000 (£150,000 to £200,000).

Instrumentation

The level of water quality instrumentation at Inverness WTP is a function of general monitoring requirements, integrity monitoring requirements, coagulation control, and post-treatment requirements. Turbidity and color monitoring of the raw water helps set the coagulant dosage. There is a pH monitor after the flocculation tank to assist with acid dosing.

There are five particle counters in the WTP. One instrument measures particle counts on the combined filtrate of three primary units, and another on the combined filtrate of the remaining four primary units. One instrument is located along the total combined filtrate. The filtrate from each of the secondary units is also monitored by particle counting. Raw water particle counting is not performed. A residual aluminum monitor is installed on the combined filtrate flow. The UK standard for aluminum is 200 µg/L, which is also the EU limit. Color and conductivity are also monitored on the combined filtrate flow. A Cryptosporidium monitoring system is used to collect samples for analysis of the filtrate water prior to chlorine addition.

Integrity Testing

The Inverness WTP uses filtrate particle counters for monitoring integrity during normal operations. The particle count is typically less than 5 per mL. If any of the particle counts increases to greater than 10 per mL, the units are isolated to identify the location of the problem. Because the permeate particle counters on the primary units are common to three or four units, all units in that group would be removed from service until the breached unit is identified. Each of the secondary units has a dedicated filtrate particle counter. This arrangement simplifies the identification of any integrity problem in the secondary units.

Filtrate particle counting during normal operations, however, is not always effective. This is because the ability of filtrate particle counting to detect a breach depends on the concentration of particles in the feed stream, and the resulting concentration of particles that would appear in the diluted filtrate flow. For this reason, membrane systems undergo rigorous integrity tests to demonstrate the integrity of the system.

On every third day, the Inverness WTP uses Norit’s SIM method of integrity testing on both the primary and secondary units. A particle suspension (i.e., PAC slurry; Norit’s SA Super peat-based carbon) is introduced to the feed water, and the particle counts are monitored in the


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filtrate flow. Only one unit is challenged with the SIM at any time. If more than 10 particles per mL are detected, the unit is isolated and the PV that has a breach is identified by PDTs. When the breached PV has been identified, the four membrane elements are removed and submerged in a water bath. A PDT is performed in that water bath to identify which fiber is defective. The element can be repaired and then re-tested in the water bath to verify that a successful repair has been made before installing it into the system. If no defects are found in the four membrane elements, further investigations to identify the source of the breach (e.g., possible leaks in the O-rings or seals, air bubbles, etc.) are made.

Operation to Date

At the time of the interview, the Inverness WTP had been in operation for about eight months. During that time, no fiber breaks or breaches in integrity, in either the primary or secondary units, had occurred. During commissioning, one O-ring was found to be aligned improperly, but it was replaced.

Cost

The cost of the Inverness WTP, which included a 1.3 MG (5 ML) storage reservoir and new treated water mains, was $26.1 million (£14.5 million). Of the $26.1 million, about 40 percent was mechanical and electrical, and the remaining 60 percent was civil cost.

The scheme was bid as a design and build project by competitive tender in compliance with EU procurement rules. The successful contractor was Earthtech Ltd.


The Inverness WTP falls under the authority of the Scottish Executive. The Executive adopts EU legislation and also follows the more stringent guidelines set by the DWI, which is responsible for upholding drinking water standards in England and Wales.

Planning Issues

This project did not have significant planning issues, other than landscaping requirements, noise reduction during construction and operation because the area is a bird nesting site, and permitting for the micro-strainer waste to be returned to Loch Ashie.


Pilot testing was recommended to observe performance over all seasons, and gather data to optimize operations.

Choa Chu Kang WTP, Singapore

The Choa Chu Kang (CCK) WTP is a surface water treatment plant using Zenon 1000 UF membranes. The existing rapid sand filter beds will be modified to house the submerged membranes. A summary of this WTP is shown in Table 2.28.


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Table 2.28 Summary of the Choa Chu Kang WTP, Singapore

Status of project Construction in 2006-2007 Capacity 48 mgd: 182 ML/d (for Phase 1) Source water Surface, reservoirs Pretreatment Alum coagulation, clarification Type of membrane Zenon 1000 Design flux 40 gfd; 68 lmh Pilot testing In 2000, USFilter and Zenon submerged

pilots; In 2006, 8-month demonstration of Zenon 1000

Integrity testing Daily PDT; turbidity and particle counting

Main driver for integration Pathogen and algae removal

Background

The Public Utilities Board (PUB) operates the CCK WTP in Singapore. With the aim of improving treated water quality, PUB is integrating UF into the treatment process. The existing CCK facility has a total treatment capacity of 96 mgd (364 ML/d), and this project involves the integration of 48 mgd (182 ML/d) of UF for Phase 1, which comprises half of the CCK facility.

The existing treatment process includes aeration followed by pre-chlorination. Flow is split between the existing Phase 1 and 2 facilities, which provide similar treatment. Lime is used to adjust the pH and then alum is added for coagulation. A coagulant aid polymer is also used. Flat-bottom sludge blanket clarifiers are used upstream of rapid sand filters. The filtered water is oxidized with ozone and then fluoride is added. Lime is used for a final pH adjustment, and chlorine is added for maintaining a distribution system residual.

The PUB’s treatment goals for the upgrade to the CCK facility require that the finished water comply with the following:

World Health Organization (WHO) Guideline Values for Drinking Water Quality. Be free of live or dead animals, which is a PUB-specific term for any waterborne

organisms that do not fall into the traditional micro-organism categories. Be free of algae. Have a minimal DOC concentration. Have prolonged disinfection by using chloramines.

A number of treatment process options were evaluated for upgrading CCK treatment.

Based on an economic analysis and feasibility assessment, submerged MF/UF to replace the rapid sand filters was selected for the CCK WTP. This arrangement also takes advantage of the local topography, which allows for a siphon-driven filtration through the membranes. After the Phase 1 upgrade, post-filtration ozone will be converted to post-filtration chlorine disinfection.


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Source Water

CCK draws raw water from three reservoirs: Kranji, Pandan, and Tengeh. The Pandan source has the best water quality, and the Kranji reservoir has the highest organic content. The Tengeh reservoir can experience peaks of suspended solids and TOC after rainfall events. The average raw water blending for 2003 was 51 percent Kranji, 24 percent Pandan, and 25 percent Tengeh.

A review of historical water quality data shows that the raw water contains high concentrations of TOC (i.e., 8 to 15 mg/L), high apparent color, and high turbidity (up to 200 NTU). The alkalinity is about 40 mg/L as CaCO3. The raw water also contains high algal counts (up to about 45 x 108 cells per m3).

Pilot Plant

In order to establish whether or not treatment using immersed membranes was feasible at CCK, pilot plant trials were conducted in 2000. The principal objectives of the pilot plant trials were:

To verify the effectiveness of immersed membrane systems (i.e., Zenon and USFilter) operating together with enhanced coagulation, to effectively remove THM precursors so that THM levels in the product water are within the guidelines set by the WHO, the EU, and the USEPA.

To determine whether the product water from the membranes is biologically stable. To verify that immersed membranes are able to achieve 100 percent removal of

micro-organisms and algae. To establish the appropriate hydraulic and engineering design parameters for a full-

scale immersed membrane plant.

The pilot plant included coagulation and flocculation, with alum and PAC addition. The USFilter pilot plant train included a clarifier upstream of the membranes, and the clarifier could be bypassed during the pilot trials. Table 2.29 shows the main operating parameters for the two immersed membrane pilot plants. During the first two-week period, the feed water to each pilot plant was drawn from the Kranji Reservoir, which has the poorest quality of the three reservoir sources in terms of the DOC concentration. Over the second two-week period, the feed water to each pilot plant was a blend of the three reservoirs.

Table 2.29 Membrane pilot plant characteristics CCK WTP, Singapore

Parameter Zenon USFilter Flow rate, m3/hr 3 1.7 Pore size 0.04 microns 0.2 microns BW Frequency 20 minutes 30 minutes TMP 5 to 18 inches Hg 5 to 18 inches Hg BW duration 30 s 30 s


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The evaluation of the membrane performance focused on DOC removal and the THM formation potential of the product water. The pilot plant trials demonstrated the following:

1. DOC concentrations were reduced to about 2 mg/L. 2. PAC addition slightly improved DOC removal and subsequent THM formation. 3. The ability of immersed membranes, operating with upstream enhanced coagulation, to

reduce the DOC concentration and THM formation potential to acceptable levels was demonstrated.

4. The ability of the immersed membranes to completely remove animals and algae from the raw water was demonstrated.


The process flow diagram is shown in Figure 2.10. Pretreatment. The existing pretreatment as described previously will be utilized. This includes pre-chlorination for disinfection and algae control, and coagulation with alum and a coagulant aid polymer. The existing clarifiers will remove flocculated particulate matter. Primary Membranes. The submerged UF membranes will be mounted into existing rapid sand filter beds. The contractor has proposed five cassettes (each with 30,000 ft2 (2,790 m2) of membrane area) in each train and two trains in each existing sand filter bed. A total of eight trains are required to treat the full flow. The remaining un-used filter beds will be converted to backwash storage tanks, CIP neutralization tanks, and areas for housing backwash pumps. All of the membrane tanks will be covered to minimize algal growth in the process basins.

It is estimated that the membranes will be operated in a siphon mode about 30 percent of the time at average flow. As the TMP rises, filtrate pumps will be used. The design flux is 40 gfd (68 lmh), and the anticipated recovery is >95 percent.

Aeration Rapid Mix Submerged UF Chlorine Contact

Chamber

Storage

NH3

F

Lime

Cl2

CO2

Distribution

Residuals Handling

PulsatingClarifier

KranjiPandanTengeh

Reservoirs

AlumPolymerCl2

Disposal

Figure 2.10 Process flow diagram for the CCK WTP, Singapore

Aeration Rapid Mix Submerged UF Chlorine Contact

Chamber

Storage

NH3

F

Lime

Cl2

CO2

Distribution

Residuals Handling

PulsatingClarifier

KranjiPandanTengeh

Reservoirs

AlumPolymerCl2

Disposal

Figure 2.10 Process flow diagram for the CCK WTP, Singapore


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Post-treatment. Downstream of the membranes, the water will receive break-point chlorination. The existing ozone contactors are to be converted to a chlorine contact tank. Backwashing and Cleaning. The target CIP interval is 30 days for recovery cleans using citric acid and NaOCl. Daily NaOCl CEBWs are also planned. The BW interval is 38 minutes and it is accompanied by air scour and a tank drain to waste.

Construction Scheduling

The construction schedule is 24 months to substantial completion, followed by three months operation by the contractor. The contract was awarded in December 2005.

Because CCK is an operating plant, it is a requirement of PUB that half of the plant must be operating at all times during the construction. The construction schedule is therefore split in two principal parts. The first half of the contract will involve demonstration pilot testing with the proposed membrane system and upgrading the existing control systems and chemical feed systems. Once these are completed, and the mechanical equipment procured, the existing Phase 1 facilities will be decommissioned to allow for construction. The contractor is restricted to an 11 month period to decommission Phase 1 facilities, modify the existing filter beds, install equipment, perform testing, and finish commissioning.

Cost

The procurement of the membrane system for CCK encouraged competitive bidding, but was restricted to those systems with NSF 61 approval and 4-log Cryptosporidium and 4-log Giardia approval from the State of California, or equivalent. Preliminary designs for both cartridge and submerged technologies were developed and included in the bid documents. The flux was limited to 53 gfd (90 lmh), and performance guarantees were established for all waste volumes, chemical consumption, and energy use.

Bids, or tenders, were invited in June 2005, for the construction contract and membrane plant detailed design. The successful bidder was United Engineers, with a tender of $19.5 million (S$32.5 million; conversion factor of 0.6 for $US to Singapore dollar, S$). This cost is lower than the pre-bid estimate by almost 20 percent and represents the competitive nature of membrane systems and the water construction business in Singapore. CASE STUDIES OF NF/RO INTEGRATION Three case studies of NF/RO integration are presented herein. The Méry-sur-Oise and Heemskerk facilities use NF and RO, respectively, as a final barrier in treating surface waters. The Torreele facility in Belgium treats wastewater effluent for recharge, or infiltration.

Méry-sur-Oise WTP, France

The Méry-sur-Oise WTP is a NF facility that has been in operation since 1999. A summary of this WTP is shown in Table 2.30.


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Table 2.30

Summary of the Méry-sur-Oise WTP, France Status of project Start-up in 1999 Capacity 37 mgd: 140 ML/d Source water Oise River Pretreatment Ballasted flocculation, ozone filtration Type of membrane Dow /Filmtech NF (NF200B-400) Design flux 10 gfd; 17 lmh Pilot testing 1993, NF/RO, and on-going NF pilot trails Integrity testing Not applicable Main driver for integration To remove TOC to lower applied chlorine

dose and as a final barrier for treatment.

Background

The recent expansion of the Méry-sur-Oise WTP was designed, built, and operated by Compagnie Générale des Eaux (CGE) for the Syndicat des Eaux d’Ile de France (SEDIF), which is the water authority of the Ile de France region of Paris. The Méry-sur-Oise plant has a total capacity of 90 mgd (340 ML/d) and includes an existing conventional WTP and a new NF plant, which began operation in the autumn of 1999. The plant supplies over one million customers in the northern suburbs of Paris.

Source Water

The Oise River is the source water and it is subject to a wide range of water quality conditions. The temperature ranges from 34 to 77°F (1 to 25°C). There are also fluctuations in the organic content, suspended solids concentration, and pollutant (e.g., hydrocarbon and pesticide) concentrations. The SEDIF monitors water quality at river stations that are positioned at least one hour upstream of the plant intake. Samples are collected at regular intervals for temperature, pH, TOC, nitrate, metals, cyanide, hardness, conductivity, oxygen, ammonia, and global toxicity. The source water turbidity is typically between 8 and 60 NTU. The TOC concentration can be as high as 3.5 mg/L and the atrazine concentration as high as 620 μg/L (Ventresque et al. 2001).


There are two parallel treatment trains at the Méry-sur-Oise facility (1) the older conventional facility (53 mgd; 200 ML/d), and (2) the new NF extension (37 mgd, 140 ML/d). The original conventional treatment train was built in the 1960’s and in the 1980’s, GAC was added. The process train includes: pre-ozonation, flocculation and sedimentation, rapid sand filtration, ozonation, biological GAC filtration, chlorination, and pH adjustment for corrosion control. The process flow diagram for the NF facility is shown in Figure 2.11.


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Pretreatment. The pretreatment to the NF plant includes coagulation and sedimentation with ballasted flocculation using 30 mg/L PACl, 5 g/L microsand, and 0.17 mg/L polymer, followed by ozonation, and dual-media rapid gravity filtration. Optimized TOC and aluminum removal during coagulation occurs at pH values between 6.8 and 7.0. Operating under these conditions is very important as both residual aluminum and TOC affect the downstream NF process. There are eight 6 μm Pall pre-filters that automatically BW every 24 to 36 hours, depending on differential pressure. These pre-filters require cleaning with heated water (i.e., 86 to 104 °F; 30 to 40 °C) which contains acidic detergent to remove fats and organic compounds or citric acid to remove inorganic scaling. These pre-filters are washed every two weeks. Membranes. The NF membranes are 6-inch (15 mm) diameter, 40-inch (100 mm) length, DOW/Filmtech membranes (NF200 B-400). These membranes were designed for treating the type and concentration of organics in the Oise River, while still allowing the passage of some hardness. Each membrane element has an area of about 400 ft2 (37 m2). There are eight trains that have three NF stages in a 4:2:1 array design. The first stage has 104 PVs, the second 54, and the third, 28. Each PV houses six membrane elements, thus each train has 1,140 membrane elements. There are a total of 9,120 membrane elements in the plant.

The Méry-sur-Oise NF equipment achieves 85 percent recovery. The maximum flow to each unit is 3,700 gpm (860 m3/h). Based on this flow, the design flux is 11.8 gfd (20 lmh). In practice, the plant is operated to achieve a constant permeate output, with variable feed pressure to overcome changes in temperature and in the degree of fouling. The target output has been set to 10 gfd (17 lmh) during the first three years of operation (Ventresque et al. 2001). A 2 mg/L dose of anti-scalant (Hypersperse AF200) is also used (Ventresque et al. 2001) at the facility. Cleaning. The cleaning interval is about every seven weeks, and the cleaning period ranges from 24 to 48 hours per unit. The CIPs are automated. The system consists of a hydraulic loop, 10,500 gallon (40 m3) tank, pre-filter, and a variable speed pump. A high and

Microsand

Figure 2.11 Process flow diagram for the Méry-sur-Oise WTP, France

River Oise

StorageBallastedFlocculation

Ozone

PACl Polymer

O3

Dual Media Gravity Filters

PAC

Balance Tank

8 Pre-Filters(6 μm)

8 NF Trains

UV

Supply

Waste

NaOH

Flow from Conventional WTP

CO2 Anti Scalant

Microsand

Figure 2.11 Process flow diagram for the Méry-sur-Oise WTP, France

River Oise

StorageBallastedFlocculation

Ozone

PACl Polymer

O3

Dual Media Gravity Filters

PAC

Balance Tank

8 Pre-Filters(6 μm)

8 NF Trains

UV

Supply

Waste

NaOH

Flow from Conventional WTP

CO2 Anti Scalant


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low rate for pumping the cleaning solutions is used, because the stages of treatment contain different numbers of PVs. The filtrate used for preparing the cleaning solutions is heated to 140°F (58°C) to improve the efficiency during the clean (Ventresque et al. 2001). There are four different cleaning solutions that can be selected by the operator for cleaning (1) detergent, (2) sodium hydroxide, (3) citric acid, and (4) a disinfectant solution made from a combination of acetic acid, peracetic acid, and hydrogen peroxide (Ventresque et al. 2001). Generally, a cleaning period consists of a 30-minute soak with a basic solution followed by a 30-minute soak with an acidic solution. A rinse cycle is used between each soak and before the system is brought into production. Rinse water must also be heated to prevent precipitation from cleaning chemicals during a clean. After the clean, the solutions are neutralized if the pH is less than 6.5 or greater than 8.5 and discharged to the sewer. Post-treatment. Post-treatment includes degassing of CO2, medium pressure UV disinfection, blending with treated water from the conventional plant, and pH adjustment with sodium hydroxide for corrosion control. No additional minerals are added to the finished water. The waste streams from the NF plant include BW and cleaning waste from the pre-filters and concentrate and cleaning waste from the NF. Sludge is also generated from the ballasted flocculation process, as well as from the BW from the filters. About 20 percent of the raw water flow is converted to a waste stream in the new facility. Fifteen percent is membrane concentrate, and about five percent is from the pretreatment.

Instrumentation

Samples are collected and analyzed every 30 minutes for SDI and TOC upstream of the NF using on-line analyzers. Additional water quality analyses are performed, but details were not provided during the interview.

Staff

There is a high level of automation at this facility and it is monitored remotely in the evenings and on weekends.

Pilot Plant

The French Ministry of Health investigated NF using a pilot plant in 1993. NF and RO were considered for the primary purpose of improving the taste of the finished water. NF was selected for the expansion because it required less energy than RO, and it removed some of the hardness and organics, thus reducing the chlorine demand and objectionable taste in the water. There are several on-going pilot trials at this plant. One trial involved the evaluation of different anti-scalants to lengthen the cleaning interval (Plottu-Pecheux et al. 2002). This pilot trial was conducted with three parallel NF trains that treated secondary concentrate from the main plant. Each train housed two NF membrane elements that had a 2.5-inch diameter and 40-inch length (6.3 mm by 100 mm) which were operated in series. The use of anti-scalant was found to significantly increase the cleaning interval of the NF membranes.


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Some pilot trials were conducted on fouled membrane elements to determine the best practice for cleaning (Ventresque et al. 2001). Using hot water for the rinse between chemical soaks reduced the effects on permeability due to cleans.

Cost

The NF plant expansion, including some improvements to the existing conventional plant, was $135 million in 1994. The cost associated with NF treatment alone is approximately $0.45 per 1,000 gallons ($0.12/m3). The cost for staffing is less at the NF plant than at the conventional plant, and the footprint of the NF plant is about half of the conventional processes.

Reasons for Membrane Integration

Taste was one of the key drivers for installing NF at Méry-sur-Oise. The NF plant has reduced the amount of TOC that enters the distribution system from about 1.8 mg/L to 0.7 mg/L. The chlorine demand has decreased by as much as 30 percent, and the free chlorine residual leaving the plant was reduced from 0.4 to 0.2 mg/L. The average TTHM formation has been reduced by 50 percent (Cyna et al. 2002).

Heemskerk WTP, The Netherlands

The Heemskerk WTP includes both UF and RO, and has been in operation since 1999. A summary of this WTP is shown in Table 2.31.

Background

In the 1980s, the Provinciaal Waterleidingbedrijf van Noord-Holland (PWN) Water Supply Company of North Holland identified increasing salt concentrations in the Rhine River as a potential water quality problem. PWN uses about 88 percent surface water (i.e., from Lake IJssel which is fed by the Rhine River) and 12 percent groundwater, so PWN staff began investigating methods of lowering the salt concentration in finished water. They first contacted industries along the Rhine River, but soon realized that the salt concentration was not going to decrease, so treatment alternatives for salt removal were investigated.

Table 2.31 Summary of the Heemskerk WTP, The Netherlands

Status of project Operating since 1999 Capacity 13 mgd: 49 ML/d Source water Surface, Lake IJssel Pretreatment Ferric coagulation, sedimentation, and filtration Type of membrane UF: Norit X-Flow

RO: Hydranautics ESPA Design flux UF: 66.5 gfd; 113 lmh

RO: 17.6 gfd; 30 lmh Pilot testing Since 1993, various systems and pretreatment Integrity testing UF: Particle counts

RO: Sulfate monitoring Main driver for integration Pesticides, Cryptosporidium barrier, disinfection.


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In 1988, bentazone, a pesticide, was discovered in the Rhine water. With improved analytical capabilities and further investigations, an additional 150 pesticides were discovered in the Rhine River, and improved treatment was required. PWN also required additional production capacity. The existing WTP consists of screens, coagulation with an iron-salt coagulant, flocculation, sedimentation, rapid sand filtration with GAC, infiltration, pellet softening, aeration, rapid sand filtration, and chlorine dioxide disinfection. No residual disinfectant is used in the distribution system. PWN had some pilot testing experience from the 1970s with CA RO membranes. They experienced some fouling problems and could not maintain a CIP frequency of more than once per month. They realized that better pretreatment would be needed. Two treatment schemes were identified, and funded for pilot testing. One included RO, ozone, and GAC, downstream of the infiltration of the existing treatment train. Rapid sand filtration upstream of the RO was deemed necessary. This train was compared to an ozone and GAC train.

In 1990, PWN learned that bromate would be regulated by the EU to 5 µg/L. This created a treatment challenge for ozone in both of the pilot treatment trains. The on-going pilot trials provided data showing that these trains were not meeting the treatment goal of a CIP once per month or the water quality goal for bromate, so the proposed treatment trains were considered unsuitable for PWN. PWN staff had learned about MF and UF during trip to the USA, and in 1993 began pilot testing two units (i.e., Aquasource and Memcor) upstream of RO. The use of MF/UF upstream of RO was compared to ozone and GAC upstream of infiltration in the existing treatment train. The UF pretreatment to RO was selected, because it achieved more virus removal, and the RO treatment targets were achieved. In late 1993, an engineering design team was selected, but with the Cryptosporidium problems in Milwaukee, the Dutch Health Minister, which is a regulatory agency in The Netherlands, had reservations about using membranes as a drinking water barrier. Pilot testing of MS2 phage spiking was performed to establish the log removal values (LRVs) of the membranes. MF achieved from 1- to 2.3-log removal, UF from 5.4- to 5.8-log removal, and RO from 3.8- to 4.8-log removal. With these data, PWN was allowed to proceed with design of UF followed by RO. Initial designs were unfortunately not efficient and too costly, but with perseverance and further innovations and investigations, the final design was approved. During this time, additional UF suppliers were in the market, and this allowed for a competitive bid. Ultimately, Norit X-Flow membranes were selected. These are the same membranes as used for the MWW Treatment Plant described earlier in this chapter.

Source Water

The source water to the UF and RO facility is pretreated water from Lake IJssel. The temperature ranges from 32 to 77ºF (0 to 25ºC). The TOC concentration is about 3 mg/L and the TDS is 640 mg/L (Schippers et al. 2004). The water can contain pesticides. Schippers et al. (2004) reported maximum concentrations for atrazine and simazine to be 0.09 µg/L and 0.02 µg/L in the IJssel lake water during pilot trials.


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Description of the Treatment Plant

Figure 2.12 illustrates the process flow diagram for PWN. The WTP has the capacity to treat 13 mgd (49 ML/d).

Pretreatment. Water from Lake IJssel is pretreated by rapid mix, coagulation, and sedimentation at the Prinses Juliana facility. An iron-salt coagulant is used for coagulation, and a coagulant aid is sometimes employed. The filtration step at this facility is an up-flow filtration system. Primary Membranes. There are eight UF units. The flux is 66.5 gfd (113 lmh). There are some unique design features at PWN. Each skid for UF and RO has a dedicated pump to eliminate any hydraulic influence from valve changes on production. The pumps are also in sound-proof enclosures to improve the working environment. There are no pipe trenches in the floor. Instead, the plant is built on two floors, with all pipes being directed to the lower floor, where all valves, connections, and meters are installed. This lower floor was designed ergonomically.

Two membrane types are now installed in the UF plant at Heemskerk. Seven of the eight units contain the original membrane modules, whereas an eighth module contains a new module that has different characteristics. PWN staff has noted different modes of fiber breakage between the two membrane types. The original membrane appeared to have a flattened appearance from autopsy results. This was not believed to be a pressure related issue, but a manufacturing problem where fibers may have been trapped or compressed against one another. Spacers installed within the modules were also found to be loose, where they should have been glued in place. This is believed to have caused cut fibers. Initial problems were also found from lined steel, foreign particles released during start up. As the plant was initially operated at a constant flux (i.e., the flux was not adjusted with water temperature to account for increased viscosity), the higher pressures experienced during cold water operation may have contributed to fiber damage. At lower operating temperatures, flux is now reduced to 50oF (10oC) and 41oF (5oC). The RO flux is adjusted when water temperature drops below 50oF (10oC). The new membrane modules experienced the same mode of failure. However, these membranes operated at higher TMP than the old membranes. Their permeability has also been lower. This has been confirmed through pilot plant studies.

Figure 2.12 Process flow diagram for the Heemskerk WTP, The Netherlands

Iron Coagulant

Lake IJssel Flocculation SedimentationBasin

UpflowSand

Filtration

Distribution

Sludge

Concentrate

Secondary UF

Recycle

Primary UF

ROUV

To Sea

Anti-Scalant

Backwash

Figure 2.12 Process flow diagram for the Heemskerk WTP, The Netherlands

Iron Coagulant

Lake IJssel Flocculation SedimentationBasin

UpflowSand

Filtration

Distribution

Sludge

Concentrate

Secondary UF

Recycle

Primary UF

ROUV

To Sea

Anti-Scalant

Backwash


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PWN staff also report that O-rings need to be replaced each year to account for movement within the PVs. They attribute this to water temperature effects causing expansion and contraction. There are also eight RO units. These operate at 17.6 gfd (30 lmh) and achieve 80 to 82 percent recovery. In the summer of 1995, the design team faced delays because the building site had to be changed. During this delay, PWN staff was able to simplify the RO design by reducing the stages from three to two. Backwashing and Cleaning. The extensive pretreatment at this facility minimizes the quantity of foulants in the membrane feed water. Typical CIPs are not performed for the UF units. Instead, a CEBW is performed three times per day using 100 mg/L, and sometimes up to 500 mg/L, free chlorine. A warm water chlorinated CEBW is performed in the winter. The RO units were not cleaned for the first three years of operation. The concentrate is discharged to the sea using a discharge pipeline shared with the neighboring steel mill. Secondary Membranes. There are no secondary membrane skids at the Heemskerk facility. Spent hypochlorite CEBWs are neutralized with activated carbon and then combined with UF BW water. This residual stream is returned to the head of the process.

Integrity Testing

PWN was one of the first large installations of the Norit X-Flow membranes, and has worked with Norit to improve integrity testing (via vacuum testing). PWN staff is also included in some patents for Norit, as they have helped re-design the hydraulics in the modules.

PWN staff has experienced an increasing rate of fiber breakage since start up of the facility. In the first year a total of 389 broken fibers, or 0.05 percent of the total number of fibers, were found to have defects. After three years, the rate of fiber breakage increased to a total of 2,641, or 0.35 percent. The reason behind this increased rate of breakage is not known. However, PWN staff has worked closely with the membrane manufacturer to establish potential causes.

Particle counters are used to monitor the integrity of the UF units, and sulfate monitoring is used to track the integrity of the RO units. PWN uses monitor particles of size >0.05 µm. During pilot trials, the feed water to the UF contained up to 10 x 106 particles per mL, and the UF units achieved 2- to 3.5-log removal of particles. PWN have found that on-line sulfate monitoring verifies up to 3-log removal, as the influent sulfate concentration is about 140 mg/L and the concentration in the RO filtrate is about 0.1 mg/L.

Pilot Plant

A thorough account of pilot tests that led to the design and installation of UF and RO at the Heemskerk WTP is in Schippers et al. 2004. The pretreatment trains for the RO pilot skid were (1) conventional coagulation sedimentation and rapid sand filtration, (2) UF, and (3) coagulation, sedimentation, rapid sand filtration, and UF.


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Staff

Heemskerk operates as a base loaded plant. They have eight operations staff and one process engineer to monitor plant performance. The plant is manned for 16 hours per day via two shifts, and the plant is unmanned overnight.

Torreele Facility, Belgium

The Torreele facility treats wastewater effluent by UF and RO, and the plant has been in operation since 2002. This system is summarized in Table 2.32.

Background

The Intermunicipal Water Company of the Furnes Region (IWVA) uses membrane integration for an aquifer recharge project in northern Belgium. The drinking-water supply in this region (Figure 2.13) has historically been based on groundwater. As the production capacity in the region reached a maximum, a project for artificial recharge of this unconfined aquifer was developed to help maintain a sustainable groundwater supply. IWVA chose to treat wastewater effluent from the Wulpen WWTP with membranes to provide recharge water for this aquifer. Due to the sensitive environmental nature of the dune area for recharge, the quality of the infiltration water is subject to stringent standards. As the wastewater effluent is high in both salt and nutrient content, RO was chosen as the final treatment step for the production of infiltration water, because there are no conventional processes capable of removing both salts and nutrients. As RO requires a high-quality influent, the wastewater effluent needed to be pre-treated, and UF was chosen, because it removes bacteria and suspended solids from the feed water. This project has been a success and has resulted in a reduction of the extraction of natural groundwater in the region (i.e., from 2.7 to 2.0 mgd; or 10,200 to 7,400 m3/d). The existing infrastructure has been used as much as possible to minimize the impact on the environment. Overall, level of groundwater has risen since initiation of the recharge project.

Table 2.32 Summary of the Torreele facility, Belgium

Status of project Operating since 2002 Capacity 1.8 mgd; 3.8 ML/d Source water WWTP secondary effluent Pretreatment Chlorine/Chloramines Type of membrane UF: Zenon (ZW500C)

RO: Dow (30LE-440) Design flux UF: 17.8 gfd; 7.3 lmh

RO: 13.8 gfd; 5.7 lmh Pilot testing 1996, different source water, different MF/UF

and RO systems Integrity testing --- Main driver for integration

Stringent water quality standards for recharge water and limited land space available.


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Figure 2.13 Location of the Torreele Plant and surrounding geology Source: Van Houtte and Verbauwhede (2005) The Torreele facility was designed to produce 1.8 mgd (6.8 Ml/d) of infiltration water. This water is then recharged in the dune area of the Doornpanne at a rate of 1.8 mgd (6.8 ML/d). IWVA began pilot tests in November 1996, and in July 2002, the production of recharge water began at the Torreele facility, which was built on the site of the Wulpen WWTP.

Source Water

The source water is secondary effluent from the Wulpen WWTP. The quality of the source water is shown in Table 2.33.


The process flow diagram for the Torreele treatment plant is shown in Figure 2.14. Pretreatment. WWTP effluent passes, by gravity, a mechanical screen with 0.04 in (1 mm) openings. Before entering the effluent holding reservoir chlorine is added, with the intent of controlling biological growth.


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Table 2.33 Water quality at IWVA’s Torreele facility*

Parameter Effluent MF filtrate RO filtrate Infiltration water Conductivity (µS/cm) Chloride (mg /L) Sulfate (mg/L) Total hardness (mg/L as CaCO3) Total nitrogen (mg N/L) Nitrate (mg NO3/L) Nitrate (mg NO2/L) Ammonia (mg NH4/L) Total phosphorous (mg P/L) TOC (mg/L)

1,177 (455 – 1,618)

196 (49 – 469) 96 (40 – 130)

31.2 (12.8 – 40.8)

12.7 (5 – 37)

-- -- --

1.27 (0.5 – 2.5)

8.95 (4.8 – 12.5)

1,209 (473 – 1,591)

203 (63 – 357) 98 (42 – 130)

31.7 (12.8 – 41)

12.2 (5 – 36)

-- -- --

1.21 (0.6 – 3.2)

8.0 (4.25 – 10.9)

<20 (<20 – 30)

<2 (<1 – 3.6) < 1 < 1

< 2

-- -- --

< 0.1

< 0.2

143 (35 – 262)

21.7 (14 – 35.7) 10.1 (8 – 17) 3.8 (2.8 – 5.8)

2 (<2 – 3)

5.9 (1.2 -11.8)

0.02 (<0.02 – 0.16) 0.28 (0.15 – 0.7) 0.1 (< 0.1 – 0.3)

0.9 (0.6 – 1.3)

* Mean values are presented with minimum and maximum values provided in parentheses. Primary Membranes. From the effluent reservoir, the water flows to five, parallel UF trains. Each train contains five membrane cassettes (i.e., ZeeWeed® 500c, 26 elements per cassette). The total surface area of membranes in this process is 162,900 ft2 (13,000 m2). The UF process can treat a maximum of 2.9 mgd (11 ML/d), and the minimal recovery is 85 percent. Air is used about fifty percent of the time to induce turbulence to help minimize fouling. The five basins are built of concrete, and normally fed by gravity. If the flow is low, however, pumps can be used to deliver water to the membrane tanks.

WWTPEffluent

Prescreen

Chlorine

ChlorineNH4

UFConcentrate

CartridgeFilter

RO

UV

Figure 2.14 Process flow diagram for the Torreele facility, Belgium

pH AdjustmentAntiscalant

BackwashTo Sea

WWTPEffluent

Prescreen

Chlorine

ChlorineNH4

UFConcentrate

CartridgeFilter

RO

UV

Figure 2.14 Process flow diagram for the Torreele facility, Belgium

pH AdjustmentAntiscalant

BackwashTo Sea


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All the mechanical and electrical equipment for the UF is placed on five identical skids in

the basement of the building. Each skid contains a pump that is used both for permeate extraction and to BW the system. The BW supply is filtrate. An online turbidity monitor analyses the quality of the filtrate. The filtrate from all of the UF skids is piped to a UF filtrate reservoir with a capacity of 0.042 MG (0.16 ML). Before entering this reservoir, the filtrate is chloraminated. From the UF filtrate reservoir, the water is pumped to the RO system. Both anti-scalant and the acid are injected to control the scaling on the RO membranes. A third pump can dose NaHSO3 to neutralize free chlorine and the dosing rate is controlled by a redox measurement. The RO system is designed in two trains. The water first passes through a cartridge filter, after which high pressure pumps (at 1.1 mgd, or 4.2 ML/d) feed the two RO skids. The cartridge filters can treat up to 1.3 mgd (4.9 ML/d) and are comprised of eight cartridges with a pore size of 15 µm. Both the low- and high-pressure pumps are flow controlled. The pumps, cartridge filters, and chemical dosing equipment are located in the basement; but the RO skids are located on the ground floor. The two RO skids are identical, and were designed based on the experiences of the pilot testing. Each skid has two stages of 36, eight-inch diameter PVs, which are 20 ft (6 m) in length. Thirty of the 36 PVs contain six, high-surface-area, low-energy, brackish water RO membrane elements (i.e., 8-inch BW 30LE-440 DOW), in a two-stage configuration. This means that the capacity of every skid can be increased by filling and using the other six PVs. Each skid currently contains 79,300 ft2 (7,380 m2) of membrane area. The recovery of the RO system is set at 75 percent. The filtrate produced with RO is stored in a RO filtrate reservoir, which has a capacity of 0.02 MG (70 m3). Post-treatment. Originally, the infiltration water was composed of 90 percent RO filtrate and 10 percent MF filtrate, but now the infiltration water is 100 percent RO filtrate. The original blending was used to re-mineralize the RO filtrate to match the salt content of natural dune water, and as an additional treatment barrier, all infiltration water was treated with UV irradiation at a dose of 40 milli-joules per square centimeter (mJ/cm2). UV is no longer used now that the infiltration water is 100 percent RO filtrate. Backwashing and Cleaning. Both the MF and RO membranes need to be cleaned periodically with chemicals that are stored in the basement of the WTP. For the MF plant, the feed pumps are used for cleaning. Additional dosing pumps add NaOCl or acid to the filtrate which is used for cleaning. For the RO plant, a special CIP system was constructed. Two tanks are available: one for alkaline and one for acid cleaning agents. The chemicals can be heated and both tanks have a pump to circulate the chemicals through the RO membranes. The RO concentrate is drained continuously and, together with the MF BW, is collected in a tank which is emptied to the existing discharge of Wulpen WWTP. This water goes to a nearby brackish canal that flows to the sea. The CIP chemicals are discharged at a low flow rate of 3.4 gpm (0.2 l/s) to the RO concentrate stream, which is measured continuously.

Staff

IWVA provided the design concept for the Torreele facility and performs the daily operation of the plant. A ten-year contract was awarded for plant maintenance to an outside contractor.


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For the transition from pilot-scale to full-scale, IWVA’s experience is that it was valuable to have the same staff involved in both pilot operations and full-scale design decisions. The staff has the most knowledge about the membranes, the processes, and the potential operational problems.

Pilot Plant

Pilot testing was initiated in 1996. A consultant was used to help set up the pilot testing protocol, and as IWVA staff gained experience, the role of the consultant became less and less, and eventually IWVA staff was conducting all of the pilot evaluations.

The pilot testing effort was extensive – over five years of testing was conducted on several different types of feed water, as highlighted below:

• Local drainage water was treated using different MF membranes (from November 1996 to February 1997).

• Canal water was treated using MF (from March 1997 to May 1997). • WWTP effluent was treated using MF/UF and RO (from May 1997 to

December 1997). • MF/UF and RO were tested on water that was artificially recharged by passage

through local soil/aquifers (from December 1997 to April 1998). • WWTP effluent was treated using MF/UF and RO, and different MF systems were

compared (from July 1998 until December 1999). • MF/UF and RO were tested again with water that was treated by artificial recharge,

but sand filtration was added to remove the iron (from December 1999 until April 2000).

• WWTP effluent was treated with MF/UF and RO (from May 2000 until February 2001).

The detailed results will not be discussed in this report, but are presented in Van Houtte et al. 1998a; Van Houtte and Vanlerberghe 1998b; Van Houtte et al. 1998c; Van Houtte et al. 2000; and Van Houtte and Vanlerberghe 2001. MF/UF Pilot Testing - Lessons Learned. IWVA found that the key factors for successful MF/UF integration for treating WWTP effluent or other source waters with highly variable quality are:

• Outside-to-inside filtration mode on the hollow fibers. • Vertical position of the membranes as opposed to horizontal. • Use of air during operation and BW modes of operation.

In terms of UF versus MF, IWVA reported that the smaller pore size of UF results in a slightly better quality than MF for downstream RO. During the pilot testing, IWVA observed that every MF/UF membrane needs a pre-screen to remove larger-sized debris. As evidenced during pilot testing, pre-screens could cause more shutdowns than the membranes, so they must be selected carefully. Some MF/UF manufacturers


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use pre-screens with fine openings (i.e., ≤ 200 µm); however, it is possible to use pore sizes of 500 to 1000 µm, which results in negligible energy consumption and less maintenance. Another benefit of pilot testing is that methods to optimize treatment can be developed. Membrane manufacturers may know their system well, but they can not always predict its performance based on anticipated feed water quality data. During the pilot tests, the interaction between the IWVA and the membrane manufacturers helped to improve the performance of the membrane systems. Examples are the acid wash that was introduced on the Memcor system (Van Houtte and Vanlerberghe 1998b) to control oxidation of iron and the introduction of an extended back pulse with chlorinated filtrate on the Zenon system (Van Houtte et al. 2000). Ultimately, the extended back pulse procedure was implemented at the Torreele facility.

Determining the maximum instantaneous flux for routine operations is always a goal of pilot testing. IWVA staff felt that the operating fluxes of the different membranes were not the only consideration when comparing the different MF/UF systems. The critical issues are the initial capital investment and maintenance costs that are necessary to achieve water production targets at the facility. IWVA recommended that pilot studies should first operate at a conservative flux, and then optimize to a higher or lower flux, depending on performance. IWVA staff also reported that each membrane has a critical flux when treating a specific water; exceeding this critical flux leads to unstable and unsustainable operation. The consequences are more backwashes and chemical cleanings, which result in lower system recovery and higher operating cost. RO Pilot Testing – Lessons Learned. Despite pretreatment with MF/UF, treatment of secondary effluent using RO was affected by bio-fouling. Bio-fouling could not be controlled by MF/UF alone, and experiments were conducted to develop a mitigation procedure to minimize bio-fouling of the RO membranes Continuous chloramination of the effluent was performed, and this choice was based on successful experiments in the USA (e.g., Freeman and Crook 1995 and Leslie et al. 1996). Monochloramine (NH2Cl) is a non-oxidative biocide that forms when the chlorine-to-ammonia weight ratio is less than 5:1. It can be tolerated by both polypropylene (PP) and thin film composite materials. Chloramination proved to be a robust method for preventing biofouling. Further pilot tests indicated that continuous chloramination could be reduced to intermittent dosing, which resulted in less operating cost and fewer impacts on the environment. Scaling is another issue associated with the use of RO; however, IWVA’s experience is that bio-fouling is more difficult to control and detect than scaling. The use of scale inhibitors and pH adjustment is common, and performance was verified on the pilot-scale. Re-growth in reservoirs and pipes is an important aspect of integrated MF/UF with RO systems. Chloramination immediately before or after MF/UF is the method used by IWVA for controlling re-growth upstream of RO. IWVA staff also report that the use of a cartridge filter just before the RO not only protects the RO membranes, but also provides a good indicator of bio-fouling.

RO systems are standardized to a common configuration, and thus, fluxes can be compared directly. High fluxes translate to less initial capital cost, but the operational costs will be higher. IWVA used a flux of 10 to 10.6 gfd (17 to 18 lmh) and a recovery of 75 percent for treating WWTP effluent. The same fluxes are currently used in the Torreele facility.


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Although bio-fouling and scaling are controlled, RO membranes needed periodic cleaning. IWVA found that different chemicals and cleaning regimes gave variable results, and ultimately, the best cleaning procedure for the RO system consisted of:

• Alkaline cleaning; pH 12, 86 to 95 (30 to 35°C); approximately four hours

re-circulation and soaking; the first and second stage were sometimes flushed separately.

• Cleaning with a biocide chemical; 77°F (25°C) and 30 minutes of re-circulation. • Alkaline cleaning.

The next cleaning cycle was similar, except that the biocide was replaced by an acid

solution. The process targets for the acid clean were pH 4, 77°F (25°C), and four hours of re-circulation and contact time.

IWVA staff also learned that biofouling and scaling could be detected by monitoring system pressures, fluxes and conductivity. Biofouling generally occurred in the first RO elements, and scaling generally occurred in the last elements. Calculating the differential pressures, salt removals, and specific fluxes proved to be good tools for early detection of biofouling and scaling problems.

Instrumentation

Free chlorine and the redox potential of the UF filtrate are measured to protect the RO membranes from oxidation. In addition, the following parameters are monitored at the facility:

• Flow and pressure of each UF skid. • Turbidity of UF filtrate for each skid. • pH, conductivity, temperature of RO feed and RO filtrate. • Flow and pressure of every RO stage.

Manual grab samples are routinely collected by the operator and analyzed for:

• SDI of total UF filtrate on a daily basis and of UF filtrate from individual skids approximately twice per week.

• Conductivity and pH of RO feed, filtrate, and concentrates, as well as the finished water that is used for infiltration.

The pH, conductivity and temperature of the infiltration water are also monitored continuously, as well as the UV irradiation intensity, which enables control of the UV disinfection stage. Weekly laboratory analyses are made for:

• Total and fecal coliform bacteria, fecal Streptococci, Escherichia coli (E. coli), and HPCs.

• Nutrients (i.e., phosphorus, ammonia, etc.).


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The infiltration water is also sampled monthly for an extensive suite of analyses, including common ions, pesticides, THMs, heavy metals, polyaromatic hydrocarbons, and mineral oils. The same set of parameters is also analyzed for any extracted groundwater.

Operation to Date

In the first nine months of operation 325 MG of infiltration water was produced. The cumulative recovery over this period was 74.6 percent for the RO system and 86.7 percent for the MF system. For the first two months of operation the plant functioned normally, but then, some operational problems occurred. The pressure through the cartridge filters increased very rapidly and the cartridges needed replaced. Unfortunately, the problem could not be solved rapidly, because one of the contractors was in having financial problems. The solution was to operate only one RO skid, using all three cartridge filters. Six months after startup, all of the cartridges were replaced, and since then the pressure over the cartridge filters has remained stable. The plant has functioned normally except for some alarms caused by valve and solenoid problems on the UF system. Those valves and solenoids open and close all the time due to the change in direction of flow, and it is an on-going O&M issue. The RO has performed well since the start-up. There has been a gradual decrease of performance, which was expected due to fouling. After ten months of operation, the RO skids were cleaned for the first time using a biocide/alkaline solution. The plant now has over 40 months of operation.


The quality of the infiltration water and of the various process flows within the facility is shown in Table 2.34. The quality of the process flows has been acceptable, and as a result, the infiltration water meets the water quality targets (Table 2.34), as set by the local regulatory authorities. The regulatory agent did not require membranes for this treatment process; however, membranes were needed to meet the stringent water quality targets for the infiltration water.

Table 2.34

Infiltration water quality standards for the Torreele facility Parameter Infiltration

water Conductivity (µS/cm) Chloride (mg Cl/L) Sulfate (mg SO4/L) Total hardness (mg/L as CaCO3) Nitrate (mg NO3/L) Nitrate (mg NO2/L) Ammonia (mg NH4/L) Total phosphorous (mg P/L)

1,000 250 250 400 15 0.1 1.5 0.4


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Planning Issues

Another important issue in the choice of filtration techniques was that the IWVA is in a coastal area where space is scarce. Membrane filtration requires less space compared to conventional plants, and this was a key consideration during process selection. In addition, they are modular processes, which can be expanded easily. When using RO, after MF/UF or any other treatment, care should be taken to avoid re-growth. Chloramination could be used to treat water that is in a storage reservoir upstream of the RO system. With this configuration, not only is bio-fouling on the RO membranes prevented, but also re-growth can be controlled. A cartridge filter just in front of the RO protects the membranes and can provide an indication of biofouling, especially if slime has developed in the cartridge filter.

Main Drivers for Membrane Integration

There were two main drivers for using membranes at the Torreele facility. First, the strict water quality targets for the infiltration water required RO treatment. Second, land availability in the coastal area of northern Belgium is low, thus requiring treatment processes that have a relatively small footprint. PILOT EVALUATIONS OF MEMBRANE INTEGRATION This section highlights two pilot studies that had different outcomes in terms of membrane integration. The Monroe WTP study yielded satisfactory results for MF/UF integration, although a decision is still pending. The Fort Thomas WTP pilot evaluation of NF and RO highlighted the treatment challenges that overshadowed the potential benefits of membrane integration for DBP precursor removal.

Monroe WTP, Bloomington, Indiana

This case study summarizes the results from a pilot study conducted to investigate the feasibility of MF/UF membrane integration into an existing facility to increase the capacity of the plant and also to improve finished water quality. It also evaluates the performance of MF/UF membranes when treating raw water and pretreated water.

Background

City of Bloomington Utilities (CBU) owns and operates the 24 mgd (91 ML/d) Monroe WTP that treats water from a reservoir. To meet increased water demands in its service area, CBU has considered several options, including expanding the existing WTP by integrating membranes into existing facilities or constructing a new membrane WTP for direct treatment of raw water from the lake. A membrane pilot study was conducted to determine the performance and cost of the membrane treatment and the effect of pretreatment on the performance of the membranes. The results from this pilot study were incorporated into a master plan to meet the


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future needs of CBU, both in terms of water quality and quantity. Described herein are the membrane pilot study that was performed and its impacts on future planning.

Source water

The Monroe WTP obtains water from Lake Monroe that is located approximately seven miles southeast of Bloomington, Indiana. Lake Monroe is owned by the Indiana Department of Natural Resources (IDNR), managed by the U.S. Army Corps of Engineers (ACOE), and is used for water supply, flood control, and recreation. The lake has a total surface area of 18,450 acres and a drainage area of 432 square miles. CBU purchases raw lake water, under an existing purchase agreement with IDNR for the Monroe WTP, which is located about a half mile west of the lake. Typically, Lake Monroe water is characterized by low alkalinity and low hardness. The turbidity is also relatively low, while wide fluctuations in temperature and TOC are common. Representative raw water quality data are shown in Table 2.35.

Existing Facilities

The existing Monroe WTP has a rated treatment capacity of 24 mgd (91 ML/d). Existing facilities are listed in Table 2.36. The facility is a conventional WTP with two flocculation and sedimentation basins followed by four mixed-media filters. Typical finished water quality is shown in Table 2.35.

Pilot Plant

The objectives of the pilot study were to investigate the feasibility of using membrane filtration to treat (1) the raw water from Lake Monroe directly without any pretreatment and (2) settled water from the existing WTP. Another objective of the pilot program was to evaluate the filtered water quality when treating both raw and settled water and to obtain regulatory agency approval for membrane implementation at the existing plant. The pilot study was conducted from August 2001 to April 2002.

A process flow diagram illustrating the existing plant and piloting locations is shown in Figure 2.15.

Table 2.35

Raw and finished water quality at the Monroe WTP, Bloomington, Indiana, USA Raw Finished Parameter Average Range Average Range

Turbidity (NTU) 5.8 0.7 – 13 0.15 0.08 – 1.0 pH 7.4 6.9 – 8.0 8.8 7.9 – 9.7 Alkalinity (mg/L as CaCO3) 29 20 – 40 34 22 - 41 Total hardness (mg/L as CaCO3)

48 30 – 62 62 36 – 73

Finished water chloramine residual (mg/L)

-- -- 2.0 1.8 – 2.2

Temperature (ºF) 59 37 - 84 -- --


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Table 2.36 Treatment components of the existing conventional

Monroe WTP, Bloomington, Indiana, USA Equipment Number or Value

Primary Rapid Mix Number 1 Detention time, sec 23 Flocculation Basins Number 2 Detention time, min 23 Flocculators per basin 2 Sedimentation Basins Number 2 Tube settlers depth, ft 2.5 Tube settlers surface area per basin, ft2 3,580 Loading rate over tube settlers per basin, gpm/ft2 2.3 Secondary Rapid Mix Number 1 Detention time, sec 20 Filters Number 4 Media Anthracite 26 inches deep and 1 mm

effective size Sand 12 inches deep and 0.5 mm

effective size Filter Rate, gpm/ft2 4 Finished Water Reservoir Number 1 Capacity, gallons 5,000,000

Feed Water

The pilot study was conducted with two different feed waters (1) raw water from Lake Monroe and (2) settled water from the Monroe WTP that has undergone coagulation, flocculation and sedimentation. In addition, because the utility uses PAC occasionally to control taste and odor, raw water with PAC concentrations ranging from 10 to 40 mg/L was fed to the membranes over a two-week period.

The raw water was pumped from the mixing flume to the pilot units using a submersible pump. The water was drawn downstream of PAC addition but upstream of the primary rapid mix chamber where chlorine, alum, and coagulant aid polymer are added. During the period of pilot testing, PAC was not used in the full-scale facility. Settled water was drawn using a submersible pump from the north settling basin effluent.

Raw water quality is summarized in Table 2.35, and settled water quality during the pilot is summarized in Table 2.37.


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Table 2.37 Settled water quality at the Monroe WTP (May 2000 to April 2001)

Settled Water Quality Parameter Average Range Total Alkalinity, mg/L (as CaCO3)

45 N/A

Total Hardness, mg/L (as CaCO3) 60 N/A Turbidity* (NTU) 0.99 0.07 – 8.4 TOC†, mg/L 2.3 2.3 – 5.6

pH (Units) 9.0 6.7 - 6.9 with alum 7.3 - 7.4 with PACl

8.7 – 9.3 applied to filters Temperature, oF 59 37 – 84 * Varies widely due to the addition of lime. † TOC samples taken from June 1999 through June 2001.

Pilot Units

Three membrane systems were tested in parallel throughout the pilot study. These included a cartridge type MF unit, a submerged MF unit, and a submerged UF unit. The membrane units were located in a storage room adjacent to the main building of the plant. This location was close to the power supply, the plant influent, and the sedimentation basins. The filtrate and reject streams from the pilot units drained by gravity to a holding tank. To meet

Figure 2.15 Process flow diagram for the pilot plant at the Monroe WTP, Indiana, USA

LakeMonroe Parshall

Flume

Flocculation Basins

Sedimentation Basins

DryingBeds

ResidualsHoldingStation

ResidualsDistribution

Chamber

ClarifierEffluent

Chamber

To Upper Lagoon

To Outfall No. 11/Lake Monroe

To Head of Plant

BackwashHoldingBasin

BackwashClarifier

GravityThickener

PressureFilter Press

To Landfill

Filters

MF

MF

UF

MF

MF

UF

Transfer PumpStation

FinishedWater

ReservoirRapidMix

SecondaryRapid Mix

ChlorineAlumPolymer Lime Chlorine

PAC (Occasionally)

Pilot Skids Pilot Skids

To Distribution

Figure 2.15 Process flow diagram for the pilot plant at the Monroe WTP, Indiana, USA

LakeMonroe Parshall

Flume

Flocculation Basins

Sedimentation Basins

DryingBeds

ResidualsHoldingStation

ResidualsDistribution

Chamber

ClarifierEffluent

Chamber

To Upper Lagoon

To Outfall No. 11/Lake Monroe

To Head of Plant

BackwashHoldingBasin

BackwashClarifier

GravityThickener

PressureFilter Press

To Landfill

Filters

MF

MF

UF

MF

MF

UF

Transfer PumpStation

FinishedWater

ReservoirRapidMix

SecondaryRapid Mix

ChlorineAlumPolymer Lime Chlorine

PAC (Occasionally)

Pilot Skids Pilot Skids

To Distribution


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regulatory requirements, a submersible pump was used to convey the combined filtrate and reject streams to the head of the existing WTP. The chemical cleaning solutions drained by gravity to a neutralization tank where sulfuric acid, sodium hydroxide, and NaHSO3 were added, as needed, prior to draining the neutralized solution to the treatment plant’s septic system.

Sampling

Operating data from the pilot units were collected online as well as manually throughout the study. Pressure, flow, turbidity, and particle counts for the feed water were recorded twice per day. Feed water temperature and pH were recorded daily. Pressure and flow for the filtrate water also were recorded twice per day; while turbidity and particle counts were recorded every 15 minutes. Grab samples of feed, filtrate, raw and BW waters were collected at regular intervals for bench-top analyses of various parameters. Turbidity, pH, temperature, and chlorine residual were measured twice daily. Total alkalinity, total hardness, and calcium hardness were measured twice per week. TDS, TSS, HPCs, iron, manganese, and particle counts were measured once every week. TOC, DOC, and UV254 absorbance were measured every two weeks.

Results

The pilot program was structured with four phases to test the membranes under varying feed water conditions. The four phases were as follows:

1. Phase 1: Start-up period of two weeks. 2. Phase 2:

- Raw reservoir water as feed water to the membranes without any chemical addition for approximately 3.5 months.

- Raw reservoir water with PAC addition as feed to the membranes for approximately two weeks.

3. Phase 3: Settled water from the full-scale Monroe WTP as feed to the membranes. The feed water was pretreated by coagulation and sedimentation, and this testing was conducted over a period of approximately two months.

4. Phase 4: Raw reservoir water as feed water to the membranes without any chemical addition for approximately one month.

The results discussed herein are presented in a generic manner, to avoid any direct

reference to the performance of each of the membranes, at the request of the CBU. Phase 1. During phase 1, the vendors were allowed to install their pilot units and prepare

them for continuous operation. During this phase, the membrane manufacturers optimized the operating parameters, including flux, BW sequence and frequency, chemical usage, and recovery. Manufacturers’ representatives also trained the pilot plant’s operators on the operation, maintenance, and data collection required for each shift.

Phase 2a. During this phase, the membranes treated raw water without any pretreatment or chemical addition. The turbidity of the raw water varied from 8 to 26 NTU with an average value of 13 NTU, while the temperature gradually declined from 68 to 50ºF (20 to 10ºC). Other


93

parameters such as alkalinity, TOC, DOC, hardness, UV254 absorbance, and TDS did not vary significantly.

The performance of all the membranes, in terms of water quality, was comparable, providing filtered water with consistently low turbidity (i.e., <0.1 NTU, more than 95 percent of the time), particle counts, and suspended solids. Removal of particles in the size range of 2 to 5 µm ranged from 2.5- to 3.8-log, depending on the membrane and feed water particle concentrations. Note that the estimation of log removals of particles by membranes is highly dependent on the feed water particle concentrations: with higher particle concentrations, membranes are capable of demonstrating higher log removals. As expected, no removal of any of the dissolved constituents such as TOC, DOC, TDS, and hardness was observed. Good removal of iron and manganese was observed, indicating that these constituents were present in their insoluble, particulate form.

The recovery of the membrane systems varied from 86 to 94 percent. The operating flux also varied and the results clearly showed that operating at a higher flux increased system recovery, but reduced the operating time between CIPs. Overall, the results were favorable, and indicated that the membranes are capable of treating raw water from Lake Monroe without any pretreatment and that certain water quality objectives such as turbidity can be achieved.

Phase 2b. During this phase, PAC was added to the raw water over a two-week period. The concentration of PAC was gradually increased from 10 to 40 mg/L. All membranes exhibited stable performance, although the average flux during this phase was 10 percent less than that of the previous phase for some of the membrane systems. This was expected because the addition of PAC increased the solids loading to the membranes.

Phase 3. During this phase, settled water from the full-scale facility served as the feed water to the membrane units. The water was treated with prechlorination, coagulation, flocculation, and sedimentation. The settled feed water quality was characterized by relatively low turbidity (i.e., from 2 to 4.5 NTU), high pH (i.e., 7.8 to 9.9) and a TOC concentration less than 1.9 to 2.4 mg/L. The highest turbidity and pH resulted from the addition of lime downstream of sedimentation for pH adjustment. The temperature throughout this phase was relatively stable at 46ºF (8ºC).

As observed in previous phases, the filtered water was consistently of high quality with a turbidity <0.1 NTU most of the time. The performance of the membranes treating settled water was better than when treating raw water. While the membrane recovery was similar to that during the previous phase, operating flux of the membranes was 15 to 30 percent higher. This indicated substantial savings in membrane capital costs when feeding settled water to the membranes.

Phase 4. During this phase, the raw water was again supplied to the membranes as feed water. The main objective of this phase was to investigate the DBP formation potential of the filtered water, and to determine the effectiveness of the CIP in restoring the permeability of the membranes after treating the raw water. The turbidity during this phase varied from 6 to 17 NTU, while the temperature gradually increased from 46 to 65ºF (8 to 18ºC). The TOC concentration was near 2.7 mg/L. The membranes exhibited stable performance. The CIP conducted at the end of this phase indicated that the membrane permeability was effectively restored to its original permeability.

The simulated distribution system (SDS) formation potential tests for THMs and haloacetic acids (HAAs) conducted during this phase indicated that when chlorination was


94

practiced to achieve 0.5-log Giardia inactivation downstream of the membranes, the concentrations of THMs and HAAs were below the current maximum contaminant levels (MCLs). Additional SDS tests were recommended to account for formation potential during different seasons of the year.

Staff

The pilot plant operating staff included a consulting engineer visiting the site at least once a week, a process engineer monitoring the data regularly, and the full-scale plant operators taking the necessary readings twice a day. At times, the plant operators performed membrane cleaning by following directions from the manufacturer by telephone communication.


Prior to the initiation of the pilot study, the Indiana Department of Environmental Management (IDEM) was provided a copy of the proposal for their review to verify that the protocol included all testing necessary for validating membrane filtration as an alternate filtration technology in Indiana. During the pilot study, IDEM was invited to observe the membrane units in operation. When IDEM was present, an intentional fiber cut test was performed on each of the units to show how the integrity test detects a broken fiber.

Conclusions

Subsequent to the pilot study, the results were used to estimate capital costs of a full-scale membrane filtration facility. These costs were used in the development of a master plan for the CBU’s water needs through the year 2030. To meet future water demand, the CBU will need to either expand its existing conventional WTP or construct a new WTP. The new WTP can draw water either from several surface water sources, including Lake Monroe, or groundwater. Several alternatives were developed: (a) expand existing Monroe WTP (24 to 36 mgd); (b) install new WTP (12 mgd) using Lake Monroe as source; (c) install new 12 mgd ground water plant using MF/UF and RO and retrofitting Monroe WTP with MF/UF; (d) install new 12 mgd WTP treating surface water from other lakes and retrofitting Monroe WTP with membranes. Of all these alternatives, (a) and (d) were lowest in cost, resulting in the lowest rate increases. A final decision is still pending.

Fort Thomas WTP, Kentucky, USA

The results of this pilot study highlighted the challenges of biofouling that are faced when treating surface waters with NF and RO membranes.

Background

The Northern Kentucky Water District (NKWD) is the third largest water district along the Ohio River. It owns and operates three conventional surface WTPs. The Fort Thomas WTP, the largest of the three plants, serves as the primary source of water supply to the system. Taylor Mill, the second largest plant, is used to supplement flow from Fort Thomas. The water from both plants is blended in a clearwell prior to being pumped into the distribution system.


95

Pilot testing was conducted at the Fort Thomas WTP to investigate the applicability of NF or RO membranes to lower the DBP formation potential at the 44 mgd (167 ML/d) conventional settling/filtration plant. The results of this pilot study indicated that biofouling could be a potential hindrance to the implementation of the NF/RO process.

Source Water

The source water for Fort Thomas WTP is the Ohio River. The river is used for numerous recreational activities along its length. It is also a major transportation route and provides water for drinking supplies, as well as manufacturing and power generation purposes.

A summary of the raw water quality is shown in Table 2.38. The raw water quality varies significantly throughout the year. In particular, there are large variations in turbidity, temperature, TOC, and microbial content, such as HPCs and coliforms.

As listed in Table 2.38, the raw water is characterized by relatively high concentrations of TOC, a precursor to DBP formation when chlorine is used for disinfection. The Stage 2 DBP Rule requires the locational running annual average of concentrations of TTHMs and HAA5 to be below 0.080 mg/L and 0.060 mg/L, respectively, by the year 2008. The NKWD is in compliance with these MCLs; however, to provide the highest water quality to its customers, the NKWD strives to limit the concentrations of DBPs to 80 percent of the MCLs. To achieve this goal, the NKWD has investigated several options, including implementation of NF or RO membranes to remove DBP precursors as well as any pre-formed DBPs, which are present due to the practice of pre-chlorination at the head of the plant.

Table 2.38

Ohio River raw water quality (1999 to 2000) Parameter Raw water quality Avg. Range Alkalinity (mg/L as CaCO3) 53.4 10.6 – 113 Total hardness (mg/L as CaCO3) 137 100 – 186 pH 7.32 6.3 – 8.07 Temperature (°C) 19 5.1 – 31 Turbidity (NTU) 14.8 2.20 – 68.6 Chloride (mg/L) 30.2 17.5 – 55.5 Conductivity (ohms) 394 270 – 582 Sulfates (mg/L) 84.6 55.8 – 116 Aluminum (mg/L) 0.99 0.11– 2.9 Copper (mg/L) 0.01 0.00 – 0.02 Iron (mg/L) 0.70 0.00 – 3.3 Manganese (mg/L) 0.15 0.02 – 0.59 Nitrate (mg/L) 1.9 1.2 – 2.8 Nitrite (mg/L) 0.01 <0.01 – 0.02 Total coliform (#/100ml) 220 4 – 1250 Fecal coliform (#/100ml) 36 0 – 250 HPC (#/100ml) 1588 0 – 7000 TOC (1999 , only) 3.3 1.2 – 12


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Existing Facilities

The existing facility design and process characteristics are listed in Table 2.39. The facility is a conventional WTP with sedimentation and filtration. One of the unique features of this plant is raw water storage in two large intake reservoirs at the head of the facility. These provide some buffer against rapid changes in raw water quality that can occur in the Ohio River.

Table 2.39

Summary of the existing facilities at the Fort Thomas WTP Component Design Characteristics Process Chemical Intake structure

Pumps Number Capacity, mgd, each

6

12 potassium permanganate

Reservoirs Number Surface area, acres Capacity, MG, total

2 11 72

seasonal copper sulfate PAC

Rapid mix Number Dimensions, ft Mixing time, seconds

2 10 x 11.3

60

ferric sulfate cationic polymer NaOCl

Flocculation/ sedimentation basins

Number Dimensions, ft Detention time, hrs

4 90 x 132.6

7.9

Filters

Number Area, sq ft, each Avg. filtration rate, gpm/sq ft (with 2 filters out) Media Anthracite Depth, inches Effective size, mm Uniformity coefficient Sand Depth, inches Effective size, mm Uniformity coefficient Garnet Depth, inches Effective size, mm Gravel Depth, inches

12 560 3.41

16 0.95 – 1.05

1.40

13 0.45 – 0.55

1.60

4 0.18 – 0.28

10

NaOCl filter aid polymer

Clearwell Number Capacity, MG

2

6.5

corrosion inhibitor sodium hydroxide fluoride NaOCl


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Raw and Finished Water Quality

Representative finished water quality data from 1999 and 2000 are shown in Table 2.40. The finished water quality presented in Table 2.40 indicates that the plant meets all the MCLs for the parameters listed. The water quality in the distribution system is shown in Table 2.41.

Table 2.40

Fort Thomas finished water quality data (1999 to 2000) Finished water quality Parameter

Avg. Range Alkalinity (mg/L as CaCO3) 53.9 0 – 103 Total hardness (mg/L as CaCO3) 143 111 – 184 pH 7.5 7.1 – 7.7 Temperature (°C) 17 5.3 – 30 Turbidity (NTU) 0.33 0.11 – 1.8 Chloride (mg/L) 33.6 20.5 – 57.0 Conductivity (ohms) 310 305 – 316 Sulfates (mg/L) 87 54 – 130 Aluminum (mg/L) 0.04 0.01 – 0.12 Copper (mg/L) 0.03 0.00 – 0.14 Iron (mg/L) 0.01 0.00 – 0.07 Manganese (mg/L) 0.01 0.00 – 0.02 Nitrate (mg/L) 1.22 0.85 – 2.62 Nitrite (mg/L) <0.01 <0.001 - <0.01 Total phosphate (mg/L) 0.76 0.14 – 1.6 Free chlorine (mg/L) 1.9 0.7 – 3.1 Total coliform (#/100ml) <1 <1 HPC (#/100ml) <1 <1 – 2

Table 2.41 Fort Thomas distribution system water quality data (1999)

Distribution system water quality

Parameter

Avg. Range Alkalinity (mg/L as CaCO3 ) 58 55 – 62 Total hardness (mg/L as CaCO3) 132 112 – 144 pH 7.7 7.7 – 8.2 Temperature (°C) 21 20 – 23 Turbidity (NTU) 0.3 0.2 – 0.5


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Pilot Plant

As discussed above, the NKWD considered several alternative treatment technologies including NF and RO to remove DBP precursors as well as any pre-formed DBPs. A pilot study was conducted to investigate the effectiveness of these membranes in removing DBP precursors as well as to develop full-scale design parameters and operating conditions. Depending on the reduction of DBP formation potential using these membranes, a portion of the conventionally treated water would bypass the NF/RO system and then be blended with the filtrate from membranes to meet NKWD’s water quality goals.

A process flow diagram is shown in Figure 2.16. Feed Water. The feed water to the NF/RO pilot was obtained from the filter effluent of

the full-scale plant. Because a chlorine residual is maintained across the filters, the filter effluent was collected in a holding tank and pumped to the dechlorination tank upstream of the pilot. NaHSO3 was used for dechlorination. The water flowed by gravity to the membrane feed tank which was mounted on the pilot skid.

Pilot Skid. The pilot unit consisted of four PVs, each capable of holding two, 2.5-inch diameter by 40-inch long membranes in series. The pilot system allowed recycle of the concentrate stream to the feed to facilitate operation at a higher recovery. The system was equipped with antiscalant and acid addition systems to control scaling. Cartridge filter housings containing 5 µm filters were used upstream of the membranes to prevent clogging of the membrane feed channels by large debris. The membranes were cleaned whenever the normalized flux declined by more than 15 percent or when the pressure drop along the vessel increased by 15 percent. The pilot was located in the chemical feed room of the existing facility.

Figure 2.16 Process flow diagram for the pilot plant at the Fort Thomas WTP, Kentucky, USA

Flocculation Basins

RapidMix

ReservoirSedimentation

Basins Clearwell

Filters

Sodium HypochlorideFilter AidPolymer

Sodium Bisulfate

Corrosion InhibitorSodium HypochlorideFluorideSodium Hydroxide

NF

NF

NF

RO RO

RO

RO

RO

RO

RO

RO

UF

CopperSulfate(Seasonal)

Ferric SulfateCationic PolymerSodium Hypochloride

Phase I & IIPilot Skid

Phase IV & VPilot Skid

Figure 2.16 Process flow diagram for the pilot plant at the Fort Thomas WTP, Kentucky, USA

Flocculation Basins

RapidMix

ReservoirSedimentation

Basins Clearwell

Filters

Sodium HypochlorideFilter AidPolymer

Sodium Bisulfate

Corrosion InhibitorSodium HypochlorideFluorideSodium Hydroxide

NF

NF

NF

RO RO

RO

RO

RO

RO

RO

RO

UF

CopperSulfate(Seasonal)

Ferric SulfateCationic PolymerSodium Hypochloride

Phase I & IIPilot Skid

Phase IV & VPilot Skid


99

Staff. The pilot staff included one operator from the WTP visiting the pilot typically twice a day to record the operating parameters, making adjustments as needed, and collecting samples for laboratory analyses. One engineer from the consulting company visited the site twice a week to verify the operation of the pilot, to gather the data collected by the operator, and to prepare chemical feed solutions (i.e., antiscalant and acid solutions). When a CIP was required, the engineer conducted the cleaning procedure, which typically lasted four to six hours. Sampling. The membrane feed water, filtrate, and concentrate streams were analyzed for conductivity, pH, and various organic and inorganic constituents, including hardness, alkalinity, barium, iron, manganese, fluoride, nitrate, phosphate, aluminum, sodium, potassium, silica, TDS, strontium, TOC, DOC, and UV254 absorbance. Disinfection byproduct formation potential tests were performed on the feed and filtrate water using simulated distribution system (SDS) tests at an initial chlorine concentration in the range of 2.5 to 3 mg/L and at incubation periods of 2, 24, and 72 hours. Pilot Testing Results. The pilot program was structured into five phases, which are summarized herein. Phases I and II. During phases I and II, three NF membranes, four RO membranes, and one UF membrane with a MWCO of 10,000 Da were evaluated over a period of two to four weeks to compare their organic rejection ability. The pilot was operated at approximately 50 percent recovery and the flux varied from 10 to 14 gfd (17 to 24 lmh). SDS tests were performed with a 72-hour contact time with chlorine.

Results from these initial phases indicated that RO membranes were capable of a high rejection of DBP precursors, achieving 72 to 83 percent lower TTHM formation and 90 percent lower HAA5 formation in the SDS tests. This reduction in DBP formation potential correlated well with TOC rejection by RO membranes, which ranged from 92 to 97.5 percent. NF filtrate exhibited significantly lower reductions in DBP formation during SDS tests compared to RO. For instance, the formation of THMs was reduced by only 7 to 36 percent and HAA5, by 30 to 68 percent. The TOC rejection varied from 27 to 80 percent. The variability is attributed to the MWCO of the various NF membranes that were tested. The UF membrane reduced DBP formation potential by only 11 and 6 percent for THMs and HAA5 respectively, due to its rather large MWCO.

Phase III. Based on these results, the four RO membranes that achieved the highest reduction in DBP formation potential were selected for further testing. During Phase III, the pilot study was conducted from April to August 2000. The operating conditions were initially set at 50 percent recovery and at a flux of 14 gfd (24 lmh). Three of the membranes exhibited a rapid decline in flux within the first few days, while the fourth membrane, characterized by highest rejection, did not experience flux decline. This initial flux loss was attributed to plugging of some the larger pores in the membranes by foulants in the feed water. The pilot plant operated for eight weeks before the specific flux declined by 15 percent. The membranes were cleaned with hydrochloric acid solution at pH 4 followed by a rinse with a commercial caustic detergent solution at a pH of 10.5. Cleaning restored the flux to 87 to 100 percent of the initial flux, which indicated that this cleaning regime was not effective for all the membranes.

Subsequent to these Phase III trials, three other runs were performed that resulted in a decrease in run times from 25 days to 17 days. Cleaning with acidic and basic solutions did not restore the flux. To identify the nature of foulants, one of the membrane elements was sent to the manufacturer, as well as an independent laboratory, for an autopsy.


100

The autopsy results indicated that the principal nature of foulant was organic, even though metal oxides were detected in limited amounts. Microbiological analyses indicated that approximately 75 percent of the deposits on the membrane surface consisted of decomposing unicellular and filamentous bacteria and that this biofilm could be effectively removed with a cleaning solution at pH 12. Based on these results, the cleaning regime was modified to include a cleaning at pH 12. Prior to the autopsy, the membranes were cleaned at pH 11.

Throughout Phase III, even though fouling was evident, all the tested membranes achieved a high rejection of TOC, as well as a high rejection of preformed DBPs. The TOC in the filtrate was typically less than 1 mg/L even when feed water TOC concentration increased from 3 to 7 mg/L. The addition of chlorine upstream of conventional filters resulted in THM concentrations in the range of 15 to 40 micrograms per liter (µg/L) in the membrane feed flow. The membranes achieved 40 to 55 percent removal of these preformed THMs.

Phase IV. Phase IV was conducted from October through December 2000, with four membranes: two brackish-water RO membranes, and two low-pressure RO membranes. Because biofilm growth was determined to be the cause of fouling, and due to some concerns regarding potential contribution to biofouling by the polyphosphate antiscalant used during the previous phases, a polyacrylic-based antiscalant was used during this phase on two of the membranes. No antiscalant was used on the other two membranes, and scaling calculations indicated that no significant scaling was expected at 50 percent recovery. No significant difference in the performance of the membranes operated with and without antiscalant was observed.

All membranes performed well for four weeks. During fifth week, the low pressure RO membranes exhibited rapid fouling. Acid cleaning of the membranes did not restore flux; however, cleaning with a caustic detergent solution at a pH of 12 resulted in a flux that was significantly higher than observed at the beginning of the phase. There was also a small temporary increase in the conductivity of the filtrate, indicating potential damage of the membranes. The higher pH could have broken some bonds of the polymeric phase of the membrane, even though the manufacturer indicated that the membranes could tolerate occasional exposure to solutions with a pH of 12. During Phase IV, all of the membranes achieved up to 50 percent removal of the preformed THMs. In addition, the THM formation in SDS tests indicated that the THM formation potential was reduced by 80 to 98 percent. The HAA concentration in the filtrate was below the detection limit.

In summary, biofouling caused significant loss of flux in the RO membranes, especially during the summer months, when the organic matter in the feed water was high.

Phase V. Further testing was conducted during Phase V to observe the effect of recirculation. Two membranes were operated with recirculation to achieve 50 percent recovery, and two membranes were operated at 20 percent recovery without any recirculation. The fouling tendency of all the membranes was similar: 15 percent flux loss over a period of four weeks. Cleaning at a pH of 12 restored the flux, thus indicating that biofouling was occurring. To determine the potential location of biological activity, HPCs were measured at several locations on the RO feed water supply and also on the RO concentrate stream. The HPC monitoring results indicated a general trend of increasing HPCs from media filter effluent to the dechlorination tank.


101

Conclusions

The results of the pilot study indicated that while NF/RO membranes could be used to meet the water quality objectives, persistent biofouling affected the performance of the membranes, requiring frequent cleanings that would not only lead to significant downtime, but also reduced membrane life. Extensive pretreatment would be required to control biofouling; however, past studies on Ohio River water indicated that use of other oxidants upstream of the membranes (e.g., ozone or chloramination) would cause fouling that was attributed to biogrowth. Pretreatment using MF or UF has the potential of controlling biogrowth as these membranes can achieve complete removal of microorganisms that cause biofouling; however, this option was not implemented due to the associated cost of implementing MF or UF and since the existing filters meet or exceed the treatment goals with respect to turbidity. A CASE STUDY OF A UTILITY CONSIDERING MEMBRANE INTEGRATION The following is a case study which illustrates one approach to assessing the feasibility of, and the issues associated with, membrane integration into an existing WTP. The decision tool (see Chapter 4) was used to evaluate membrane integration options.

Richard Miller WTP, Cincinnati, Ohio, USA

The Greater Cincinnati Water Works (CWW) utilizes conventional processes to treat water from the Ohio River. Preliminary investigations of membrane integration are being performed, because there is concern that the source water is potentially at risk of Cryptosporidium contamination. The decision tool of this project was used to generate alternatives for membrane integration at the CWW Richard Miller WTP.

Background

The Richard Miller WTP abstracts water directly from the Ohio River. The utility complies with all regulatory requirements at present, but is concerned that in the future they may encounter high concentrations of Cryptosporidium. The existing treatment plant consists of the following processes:

• Coagulation with alum, with the ability to add PAC and/or polymer. • Primary sedimentation, or clarification, through lamella plate settlers. • Intermediate storage reservoirs, providing between three and five days of storage. • Two basins to provide contact time and chemical mixing if potassium permanganate

or PAC is added. • Filtration through 47 biological sand filters at a constant rate of 3.0 gpm/ft2 (6.1 m/h). • GAC adsorption in 12 biological contactors which provide an EBCT of 12 minutes at

220 mgd. • Fluoridation, pH correction, and chlorine disinfection in clearwells.

Figure 2.17 shows the process flow diagram for the Richard Miller WTP.


102

Source Water The raw water can be characterized as a moderately hard, turbid surface water that contains moderate concentrations of TOC and iron. The quality of the finished water meets all USEPA and Ohio regulatory requirements. A summary of water quality is shown in Table 2.42.

Table 2.42 Summary water quality for the

Richard Miller WTP, Cincinnati, Ohio, USA Parameter

(mg/L unless noted)

Average

Raw water

Maximum

Minimum

Average

Final water

Maximum

Minimum Turbidity (NTU)

42 938 1.2 0.08 0.12 0.04

Total alkalinity (as CaCO3)

65 88 44 71 102 43

Total hardness (as CaCO3)

130 200 78 135 215 78

Calcium (as Ca)

37 70 21 39 71 27

Magnesium (as Mg)

9 20 0 8 16 0

Chloride 31 57 12 32 58 13 Sulfate 84 164 49 86 163 51 Nitrate (as N)

1.17 2.12 0.54 1.19 2.15 0.72

Manganese 0.34 1.11 0.04 <0.01 <0.01 <0.01 Total iron 3.82 11.5 0.4 <0.10 <0.10 <0.05 TDS 255 621 106 247 629 78 TOC 2.7 3.9 1.6 1 2.0 0.2 Chlorine (free)

-- -- -- 1.11 1.50 0.88

Chlorine (total)

-- -- -- 1.17 1.61 0.91

Ohio River Supply

Sand Filtration

PrimarySedimentation

Reservoirs

SecondarySedimentation

GAC

Clearwells

Sludge Discharge

AlumPolymerPAC* PAC*

LimeFe*KMnO4*PAC*

Washwater Recovery

To Distribution System

FluorideNaOHChlorine

Figure 2.17 Process flow diagram for the Richard Miller WTP, Greater Cincinnati Water Works, Ohio, USA

* Denotes use on as-needed basis

Ohio River Supply

Sand Filtration

PrimarySedimentation

Reservoirs

SecondarySedimentation

GAC

Clearwells

Sludge Discharge

AlumPolymerPAC* PAC*

LimeFe*KMnO4*PAC*

Washwater Recovery

To Distribution System

FluorideNaOHChlorine

Figure 2.17 Process flow diagram for the Richard Miller WTP, Greater Cincinnati Water Works, Ohio, USA

* Denotes use on as-needed basis


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Performance of Existing Treatment As expected, the GAC and PAC provide good TOC reduction and the lamella and reservoir coagulation/clarification stages plus sand filtration produce water with very low turbidity. The turbidity values for each major process are summarized in Table 2.43.

Utility staff report that 40 percent of the sand filtrate samples analyzed had a turbidity of less than or equal to 0.1 NTU and 99.7 percent of GAC samples were less than or equal to 0.1 NTU. While this turbidity removal is excellent, the staff is still concerned about Cryptosporidium passing through the WTP. Endospore challenge tests have been performed to better estimate Cryptosporidium removal through the plant. Endospores are smaller in size than Cryptosporidium oocysts: their diameter is approximately 1.2 µm compared to between 3 and 5 µm for Cryptosporidium. The data indicated that in excess of 3-log removal of endospores was achieved by the current treatment train. This demonstrates that the plant is well operated in terms of particulate removal. However, if the Cryptosporidium oocyst concentration in the Ohio River at the abstraction location is high enough to require additional removal due to the requirements of the Long-Term Stage 2 Enhanced SWTR Rule (LT2ESWTR), then alternative technologies, such as chlorine dioxide, membranes, ozone and UV irradiation, would need to be considered. It is conceivable that if high Cryptosporidium concentrations are present in the Ohio River, the CWW may consider membrane filtration as an alternative filtration technology as defined under the LT2ESWTR. Reasons for selecting membrane filtration over other technologies could include:

• Reduced risk of generating by products that may be regulated in the future. • UV licensing fees, due to existing UV patents for Cryptosporidium inactivation. • The need to replace existing infrastructure.

Table 2.43 Turbidity and endospore data throughout the Richard Miller WTP, Cincinnati, Ohio, USA*

Treatment Stage Turbidity (NTU)

Endospore Concentrations

(counts per 100 mL) Raw Water 51 36,700 Primary sedimentation 5.1 3,900 Reservoir effluent 1.5 400 Sand filtrate 0.11 41 GAC effluent 0.08 10 * The challenge study was conducted in 2002.


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Decision Tool Example

The decision tool of this project (see Chapter 4) was used to generate alternatives for integrating a membrane filtration technology at the Richard Miller Treatment Plant. Input and output screens are shown in Figures 2.18 through 2.23. As shown in Figures 2.18 and 2.19, the option of “conventional plant with GAC” was selected. Turbidity and DBPs/DBP precursors were selected as the constituents of concern. The approach to selecting the recommended process trains (Figures 2.20 and 2.21) was to consider many factors that would affect operation. To make efficient use of the existing hydraulic gradient, MF or UF can be installed at the head of the plant. This option is not, however, viable for various reasons. For example, coagulation is required to achieve removal of DBP precursors. Inline coagulation, followed by MF or UF, can be considered as an alternative; however, high turbidity of the raw water would result in low membrane fluxes, thus increasing the capital and operating costs.

Another alternative would be to install membranes in existing filter basins. The turbidity at this stage averages 1.5 NTU and rarely exceeds 5 NTU. Also, DBP precursor removal has already occurred by coagulation and sedimentation. Additional precursors are removed by the GAC, so DBP regulations are not a concern. This may potentially save some of the civil construction costs, providing that the plant can be commissioned in stages to minimize disruption to production. Several modifications will be necessary to the filter basins to provide:

• Adequate clearance for membrane removal. • Protective coatings to withstand chemical cleaning agents. • Improved ventilation to remove any potential gases evolved, either through the use of

air scour techniques or chemical cleaning. • Filter underdrain modifications to accept new piping systems.

However, a detailed cost estimation would need to be performed to compare the cost of

retrofitting existing filters with immersed membranes with the cost of a separate membrane filtration unit. Often, retrofitting an existing structure incurs significantly higher costs than anticipated.

Installing membranes downstream of GAC as a final polishing step will require re-lifting of GAC treated water; however, the lower TOC loading and low solids content of this water will mean less frequent CIPs and backwashing. As a result, less membrane area and a smaller building footprint would be needed. However, such a configuration would result in GAC performing filtration also, which is not desirable.

Pilot testing would be necessary to confirm which option is the most technically feasible and provides the most stable operating performance. One consideration is the water temperature. Winter production targets will influence the membrane design as flux values are much lower during cold water conditions. It is recommended that piloting be performed to:

• Establish a stable operating flux. • Identify the most suitable chemical cleaning regimes. • Determine the design flux at the lowest water temperatures. • Compare pre- and post-GAC membrane performance.


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• Familiarize staff with the technologies MF and UF technologies. • Demonstrate the feasibility of the process and obtain the necessary log removal

credits from the primacy regulatory agency.

The discussion of the decision tool output is shown in Figures 2.22 and 2.23. The simple decision tool provided with this report suggests use of MF or UF technology upstream of the GAC contactors. RO is recommended for DBP reduction, and is shown to be installed downstream of the GAC. It should be noted that the model output indicates that removal of DBPs and DBP precursors is possible with the existing facility. Current and future DBP regulations can be achieved at the existing facility; however, should future DBP regulations be unachievable, the tool suggests potential modifications to the existing plant to improve performance. These include optimizing coagulation and improving GAC contactor operating parameters. If such measures fail to meet the treatment goal, the tool suggests use of NF/RO for removal of DBPs and DBP precursors. Continued operation of GAC, along with NF/RO, should be further evaluated. It may be discontinued if the performance of GAC is not meeting treatment goals. Locating RO after the MF/UF technology may be preferable to better protect the RO membranes from GAC fines and other material that may slough off and block cartridge pre-filters that are upstream of the RO process.

Figure 2.18 Decision tool introduction page


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Figure 2.19 Decision tool retrofitting existing facility options page


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Figure 2.20 Decision tool process flow diagram recommendations


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Figure 2.21 Decision tool process recommendations and discussion


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Figure 2.22 Decision tool discussion of issues of integration recommendations (part 1)


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Figure 2.23 Decision tool discussion of issues of integration recommendations (part 2)


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CHAPTER 3 ISSUES OF MEMBRANE INTEGRATION

Membrane treatment technology is considered for integration into WTPs for a variety of reasons. In this study, examples of integration were gathered from the literature as well as from the participating utilities. For some utilities, the initial driver for installing membranes into a treatment train was to achieve compliance with regulated finished water turbidity targets. As the allowable finished water turbidity in USA surface WTPs decreased from 0.5 NTU in the SWTR, to 0.3 NTU in the Interim Enhanced Surface Water Treatment Rule (IESWTR), more MF/UF systems were installed to meet these limits. With the proposal of the Long Term Stage 2 Enhanced SWTR Rule (LT2ESWTR) and its treatment requirements for Cryptosporidium removal, even more utilities will consider the use of membranes for treatment. This trend is happening around the world. The EU, Australia, and Asian countries are all experiencing an increased interest in membrane technologies to meet drinking water standards, or to treat water that historically would be too expensive or challenging to treat. Membranes are also installed for reuse applications, and NF/RO is typically used as the final treatment process. NF/RO will also continue to be integrated into WTPs for contaminant removal, as well as desalination.

As the industry has gained familiarity with the technology, the size and capacity of membrane installations has increased. Membrane technology is now being implemented at a previously unprecedented scale – the largest facilities interviewed as part of this study were approaching 100 mgd (375 ML/d) and even larger WTPs are being planned. Overall, the integration of membrane systems into drinking WTPs has been a success. Well-operated and designed facilities are meeting their treatment objectives for water quality and production. With the introduction of any leading-edge technology such as membranes, there are lessons to be learned from full-scale installations already in service. These lessons learned are compiled and summarized in the following sections, as well as in Tables 3.1 and 3.2, so that future water systems can benefit from previous experience.

CHOOSING THE RIGHT MEMBRANE SYSTEM

For the utilities interviewed, choosing the type of membrane technology (i.e., MF/UF versus NF/RO) to meet particular treatment goals was relatively straightforward. The differences between MF/UF and NF/RO technologies are discussed in Appendix B, but in general, MF/UF is used for particle and pathogen removal, and NF/RO is used for removing dissolved constituents (e.g., chlorine, calcium, TOC, etc.). The reasons for installing membranes by the participating utilities are shown in Table 3.3. One of the main drivers for membrane integration for the participating utilities is to provide disinfection by pathogen removal. This would be accomplished by installing an MF/UF technology. Several other utilities installed membranes to help meet existing and future regulations for particle removal and Cryptosporidium removal; and for PWN, RO was installed to provide pesticide removal.


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Table 3.1 Summary of lessons learned from the literature review

Category Lesson Learned • Impurities in chemicals (i.e., coagulant, antiscalant, etc.) can contribute

to fouling of MF/UF and NF/RO. • The potential of naturally-organic compounds to foul membranes is site

specific, with both low- and high-molecular weight organics contributing to fouling at different sites.

• Certain polymers (e.g., cationic) will cause fouling of MF/UF membranes if used during pretreatment and their use should be verified with membrane suppliers prior to feeding these polymers upstream of membranes. Residual polymer in the recycled decant from residuals treatment has been less problematic, but the potential exists for polymer-enhanced fouling.

• Prepare cleaning solutions with softened or demineralized water for MF/UF and NF/RO systems.

• On-line monitoring of oxygen uptake has shown potential for predicting biofouling of membranes.

• Computer models and artificial neural networks are, in general, good indicators of membrane performance.

Fouling

• Algae in source water can significantly impact a membrane WTP by clogging pre-strainers, clogging membrane fibers, and secreting polymeric compounds onto the membrane surface. To combat these problems, automatic backwashing pre-strainers are recommended.

Pretreatment • Pretreatment ahead of MF/UF membranes has been shown to lengthen the time between cleanings, reduce feed water quality variability, and allow sustained operation at higher fluxes.

• Certain pretreatment processes ahead of NF/RO can inadvertently contribute to fouling. For example, residual aluminum can react with silicates to create nucleation sites for inorganic scaling.

• MF/UF can provide a lower silt density index (SDI) than conventional treatment upstream of NF/RO; however, fouling of NF/RO can still be problematic.

• Bank filtration can be effective pretreatment to NF/RO. • Allowing oxidants to contact RO membranes can cause increased salt

passage through the affected membrane. The magnitude of this effect depends on the membrane material, the concentration of oxidant, and duration of exposure.

• Oxidation upstream of NF/RO membranes can change the characteristics of any organic compounds present and increase the fouling potential of the feed water.

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Table 3.1 (Continued) Category Lesson Learned

• The extreme water quality characteristics must be considered during MF/UF and NF/RO design. For example, during a drought year, higher-than-usual sulfide concentrations caused premature fouling of NF/RO membranes.

• The flux for secondary MF/UF that treats BW water is typically much lower (e.g., up to 75 percent lower) than the flux of the primary MF/UF units.

• The concentration of contaminants (e.g., heavy metals) in MF/UF BW can be concentrated to higher levels than BW from conventional filters, and this can result in higher costs for disposal.

• Some utilities in the (United States of America) USA are collecting data for regulatory agencies to justify sending filtrate from a secondary MF/UF unit to distribution.

• Some utilities are recycling untreated BW water to the head of the treatment plant where solids are removed in a pretreatment process.

Backwash

• Rigorous integrity testing and fiber repair is not always deemed necessary for secondary membrane systems, but this must be confirmed with the presiding regulatory agency.

Reuse • Using MF/UF and NF/RO membranes for treating wastewater can be challenging due to variable water quality, the potential for biological fouling, inorganic fouling, and algal blooms.

• Retrofitting existing filter beds or process basins requires a thorough investigation of feasible alternatives to identify the most cost-effective system. If membranes are being installed for pathogen removal to achieve a specified level of disinfection, adding other alternatives to the existing facility, such as ozone, may be less costly than adding MF/UF.

• Utilities have installed additional membrane filtration capacity to minimize any risk of lower-than-expected production and allow for flexibility in plant operation. This additional capacity can also help maintain production during periods with unusual water quality, such as higher-than-expected turbidity.

• Multiple barriers of disinfection, by both chemical inactivation as well as physical removal, are required by most regulatory agencies, and MF/UF membranes often serve as a physical barrier that is supplemented with chemical disinfection.

• The flow pattern and hydraulic mixing provided by submerged MF/UF systems can yield a high baffling factor for achieving chemical disinfection within the membrane process, if necessary.

Design

• NF/RO currently do not receive pathogen removal credits by regulatory agencies in the USA, although research has shown that NF/RO membranes can achieve > 5.5-log removal. Other countries, such as The Netherlands, grant removal credits to NF/RO systems for viruses.

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Table 3.1 (Continued)

Category Lesson Learned • The decision to use UF rather than MF is sometimes dictated by the need

for higher virus rejection by UF. However, when using MF/UF for filtration, both can achieve greater than 4-log removal of Cryptosporidium and Giardia, and virus inactivation can usually be achieved with low dosages of commonly used disinfectants, such as chlorine

• Turbidity removal requirements for membrane versus media filter WTPs can be different even though both treatment trains are at the same facility. This has occurred in Canada, but no such facilities have been identified in the USA.

• If there is insufficient time to evaluate MF/UF or NF/RO with pilot testing before design, a conservative flux is typically used to lower the risk of fouling.

• Wetting of a new membrane is usually required at start-up, and this generally requires an extended soak in manufacturer-recommended chemicals during start-up.

• Frequent and sudden flow changes in some of the pressurized, or encased, MF/UF systems can result in enough physical vibration to cause structural fatigue over time

Table 3.2 Summary of lessons learned from the participating utilities

Category Lesson Learned Drivers for Integration

• Most of the participating utilities installed MF/UF to meet more stringent water quality regulations or contractual requirements, particularly for maintaining low-filtered water turbidity, and as a barrier for waters impaired by Cryptosporidium and/or Giardia. Limited land space was identified by Scottsdale as a primary driver for MF/UF at their Chaparral WTP.

• Primary reasons for installing or investigating NF/RO integration by participating utilities were to remove dissolved contaminants or constituents, such as pesticides, organics, DBP (disinfection byproduct) precursors, and trace metals. The European utilities also indicated that improving the taste of the water by NF/RO was a reason for installation.

• Reuse is another key driver for membrane integration. The Torreele facility in Belgium, with UF and RO, has been a membrane integration success and is recharging up to 1.8 mgd.

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Pilot Testing • All of the participating utilities conducted pilot tests, and some continued the pilot evaluations during commissioning and after WTP operation commenced. The extended pilot studies have resulted in improved cleaning regimes for flux recovery and have identified the impact of different operating procedures [i.e., coagulants, backwashing intervals, CEBWs on sustainable operation. Also, other water quality issues have been identified by pilot testing (e.g., the need for taste and odor control at the Bendigo WTP).

• Some regulatory agencies require pilot testing of MF/UF as alternative filtration technologies prior to approval for a full-scale facility. Both San Patricio and Bexar Met conducted pilot trials to meet these requirements in Texas.

• Oxidant-tolerant membranes proved essential for San Patricio, which experiences very warm water conditions in the summer. Chlorine is needed to control microbial growth. Pilot testing had identified the potential for microbial fouling of non-oxidant-tolerant membranes.

• The potential benefits of long-term pilot trials can not be overstated. For example, Columbia Heights and Scottsdale experienced a fouling event during the final phase of pilot testing, and this identified the need for flexible cleaning regimes at these facilities. At the Inverness facility, extended pilot testing allowed for optimization of the CEBWs, which improved the plant recovery from the contractual requirement of 98 percent to over 99 percent.

• Many of the participating utilities are actively involved in the research and development of their membrane systems. For example, the Heemskerk, Méry-sur-Oise, and Bexar Met facilities have test fibers and/or modules to help membrane vendors and operators gain information on long-term operation of new products. Méry-sur-Oise continues to research cleaning regimes, including different temperatures for the chemicals, to improve flux recovery of NF membranes.

Fiber Breakage

• One UK utility reported a high rate of UF filter breakage due to operation at the upper range of acceptable TMP for the membrane. Specialized equipment was developed to streamline the repair procedures to help minimize the required staff time for fiber repair.

• In a large facility, the number of broken fibers is typically a low percentage of the total number of fibers, yet it should be recognized that fiber repair is an off-line activity that is labor intensive. Some utilities contract broken fiber identification and repair to membrane vendors or other contractors.

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• The number of broken fibers experienced at a facility can be a sensitive or confidential topic due to membrane warranty implications; however, several of the participating utilities shared information about their rate of fiber breakage. Some have experienced few fiber breaks since start-up (e.g., San Patricio, Ennerdale), whereas others have experienced a higher rate of fiber breaks (Clay Lane).

Design • The Bendigo facility was designed with a detention basin downstream of the MF cells to account for variations in filtrate flow due to backwashing and tank filling/emptying. This basin helps maintain constant flow to downstream processes.

• During the winter when demands are low, all cells of the Bendigo plant are operated at decreased flux rather than taking them out of service, which would require preservation and/or a maintenance regime.

• Maintaining adequate heating in the building is necessary to prevent freezing of the membranes, especially when some of the racks or cells are removed from service during the winter.

• Extra membrane capacity was included in the initial construction of the San Patricio WTP and this allowed for flexible operation of the facility and helped ensure that production targets could be met.

• Strainers are installed upstream of membranes (MF/UF or NF/RO) to protect the membranes from foreign materials, even when there is extensive pretreatment upstream of the membranes (e.g., Columbia Heights WTP, Clay Lane, Méry-sur-Oise). Also, strainers can capture solids that pass through the pretreatment processes (e.g., excessive iron-salt coagulant solids that occasionally are found in strainers at Bexar Met).

• Allowing for flexible computer programming options of routine functions, such as backwashing intervals, durations, and flow rates, is recommended to optimize treatment over time.

Integrity Testing

• Air bubbles in particle counters are a common problem among the participating utilities.

• Most MF/UF utilities perform daily integrity tests that are typically pressure decay tests (PDTs), and often monitor both turbidity and particle counts in the filtrate of each cell/basin/rack and for the combined filter effluent. Utilities in countries other than the USA tend to perform integrity tests less frequently (e.g., weekly), and often use particle counts as a measure of integrity (Heemskerk and Inverness). Inverness also uses SIMs every three days as a second means of integrity testing.

• Heemskerk staff monitors the integrity of the RO units with on-line sulfate monitoring.

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• Keeping a detailed log of pinned fibers helps maintain accurate calculations of system performance at the Bendigo facility.

• Misaligned O-rings were reported by Bendigo and Inverness as occasional causes for integrity testing failures. At the Bendigo facility, particle counting did not detect the problem.

BW • In an effort to minimize discharges from the plant, the Ennerdale facility recycles as much of the primary and secondary BW flow as possible. The TDS of these recycle streams (including neutralized chemicals) must be carefully monitored because high TDS concentrations can impair the sludge thickening process.

• Because the BW process will concentrate solids, including those that may contain contaminants such as arsenic, disposal options may be more costly than expected. For Scottsdale’s Chaparral WTP, initial plans were to dispose BW to the sewer; however, the high cost for disposal and implications with arsenic in the solids led to on-site treatment of solids by clarification and centrifuge dewatering.

• Ennerdale, Inverness, and Clay Lane use secondary membranes to treat BW water. At the Ennerdale and Inverness facilities, the filtrate from secondary units is delivered into distribution. The flux of the secondary units is generally 40 to 50 percent lower than the flux of the primary units.

Commissioning • When bringing the new MF/UF plant on-line, recognize the impact on pressure within the distribution system. At Ennerdale, the entire MF plant was brought into service at once to minimize disruption to the distribution system.

• Sufficient time needs to be allocated for pinning fibers and wetting of the membrane fibers during commissioning.

Operations • Several of the participating utilities contract maintenance and fiber repair work to the membrane suppliers. Their services are used for tasks ranging from guidance on CIP scheduling, BW interval, broken fiber location, and fiber repair.

• As utilities gain experience with membrane operation, it is likely that some will petition state regulatory agencies to allow operation at a higher flux to increase capacity. The San Patricio District has petitioned its State regulatory agency to increase production from 7.8 mgd to 8.4 mgd, which is an eight percent increase.

• When water demand decreases in the winter, San Patricio and Bendigo both elect to operate all membrane modules at a reduced flux rather than remove racks or cells from service. This eliminates the need to preserve and monitor off-line trains.

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• Some facilities have required an increased level of staffing after membrane integration (e.g., Clay Lane), whereas others have maintained similar staffing levels after installation. Many of the facilities are unmanned during the evening hours.

• At the Torreele reuse facility, biofouling was found to be more difficult to predict and control than inorganic fouling. Chloramination is used to help control biofouling of the RO membranes. Monitoring the pre-filter upstream of the RO membranes is also a good indicator of biofouling.

CIPs • Depending on the chemicals used for CIPs, some facilities (e.g., San Patricio, Clay Lane) are able to re-use chemical batches for multiple CIPs. The acid and caustic CIP wastes are also routinely neutralized without additional chemicals.

• Some facilities rely on full CIPs for flux maintenance (e.g., Chaparral WTP, Ennerdale, Bexar Met) whereas others (e.g., Columbia Heights, Heemskerk) use CEBWs to extend the time between CIPs.


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Table 3.3

Reasons for membrane integration for the participating utilities

WTP Technology installed

or considered

Reasons Bendigo MF Particle removal Clay Lane UF Disinfection Ennerdale MF Disinfection Bexar Met UF Disinfection; particle removal San Patricio MF Disinfection Inverness UF Disinfection Columbia Heights UF Meet regulatory requirements Chaparral UF Meet regulatory requirements;

limited land available CCK MF or UF (undecided) Disinfection and algae

removal requirements Méry-sur-Oise NF To lower TOC concentration Heemskerk UF and RO Disinfection; taste; pesticide

removal Torreele UF and RO Reuse Monroe MF/UF Pilot Meet regulatory requirements Fort Thomas NF/RO Pilot Lower TOC concentration Greater Cincinnati Water

Desk study of MF/UF Disinfection; meet regulatory requirements

Selecting the system, particularly for MF and UF; however, was more challenging. The

reason is that MF/UF systems are largely individual and unique systems, and their performance varies from site to site. Also, the membrane modules and supplemental equipment are not readily interchangeable between vendors, so selection of an MF/UF system means that the utility is dependent on the supplier for the life of the project. The RO/NF industry is different. It has standardized the membrane element diameter and length which allows more flexibility in terms of changing the membrane throughout the life of the project.

Pilot Testing

Because of the unique aspects of available MF and UF systems, pilot testing is commonly used to select an appropriate system and to conduct optimization of the technology for a given source water. For large membrane integration projects, pilot testing is required because investing in membrane technology at a large scale is a multi-million-dollar endeavor; process and treatment risk must be minimized; and the cost for a conservative design is relatively large. All of the utilities in the case studies performed pilot tests prior to design of full scale facility. The participating utilities that had the most success with membrane integration had taken time to carefully evaluate the available membrane systems and conducted pilot tests for extended periods of time. Many utilities like PWN and Vivendi (for the Méry-sur-Oise facility) conducted pilot studies over several years, and continue these tests while the system is in service.

In contrast, when a project is driven by a short timescale, such as in some design-build projects, there is the risk that integration issues are not fully understood prior to start-up. One


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remedy to this challenge is to purchase a pilot skid and conduct pilot tests while the system is operating, which is what Three Valleys Water intends to do to optimize the cleaning regime of their UF plant. Other utilities (e.g., PWN, MWW, and Vivendi, at their Bendigo plant) have either on-going pilot tests or plan to purchase skids for the same reasons.

Many utilities used pilot testing to assist with the bidding process to ensure that the technology provided the desired water quality results under acceptable operating conditions. This approach was used at the Inverness, Clay Lane, and Bendigo facilities. Pilot testing offered the following benefits to the utilities interviewed:

• It enabled utility staff to become familiar with the technology. • It simulated performance of large full-scale facilities. • A stable and sustainable operating flux was identified. • Any required pretreatment processes were identified. • Performance goals, such as energy and chemical consumption, backwash and chemical

cleaning frequency, and removal of target contaminants were verified. • It enabled a performance-based evaluation, in addition to a cost comparison of various

membrane systems.

Pilot testing is not always necessary. Many membrane systems have been designed and built for small groundwater supplies without pilot testing. The design of these installations is relatively straightforward, because the existing processes are usually simple pumping and disinfection systems, and integrating membranes with these processes is not complicated. For groundwaters, the quality is typically high and stable, and the process design for membranes is also straightforward. The design flux and other operating parameters can be designed conservatively, without pilot testing. If pilot testing can not be performed, for example due to schedule, a very conservative flux and recovery may have to be accepted by the utility to lower the risk to the membrane supplier. This was the case for the City of Idaho Springs, Colo. Without pilot testing, the design flux for the MF system was relatively low (i.e., 18 gfd; 30.6 lmh) for a surface water that has had turbidity spikes of 200 NTU during spring run off (Schultz, Miller, and Yang 2003).

If there are any possible foulants or unique water quality issues, pilot testing, even for a short duration, is recommended. In any case, a full characterization of the feed water quality is needed to assess the potential for fouling, and the ability to meet water quality goals for the system. It should be noted that some regulatory agencies require pilot testing. For example the TCEQ requires 90-day pilot study for alternative technologies, and this impacted two of the participating utilities of this project (Bexar Met and San Patricio).

Pilot Plant Requirements

Results from many pilot studies have been reported in the literature. General requirements for pilot testing were reported by Shorney, Hulsey, and Long 1999 and Freeman, Veerapaneni, and Neemann 2001. For the majority of MF/UF systems, pilot skids of membrane systems have been found to be representative of full-scale performance, with design factors being easily scaled up to full-scale, if the pilot testing was conducted on similar water quality.


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Pilot testing is considered essential when the water to be treated, requires significant treatment for either solids removal or contaminant removal. There are several recommended procedures for a successful pilot program:

• Duration: The pilot study duration should account for all seasonal water quality variations. This is especially important with surface waters which can have significant water quality changes throughout a year. An extended pilot study can also show the impact of temperature on treatment with membranes.

• Control: Having control over the pilot plant operational settings helps to establish baseline performance at a steady-state operation. Re-setting operational parameters too frequently during the pilot study gives a sporadic account of performance and yields data that are difficult to interpret. It is best to think ‘with the end in mind’ when considering how to control the pilot tests. For example, if showing that the system can operate for a 30 days without a CIP is a priority, then exerting control over the operating flux for the trial will probably be required. Recognize that there is a lot of competition in the membrane industry, and suppliers may be inclined to operate their pilot skids at a flux that is just able to sustain stable operations. Exerting some control over the flux, recovery, and CIP intervals is recommended.

• Use of Full-Scale Modules: Some membrane suppliers have modules that are smaller than the full-scale modules. Although these modules require less flow than full-scale modules, their use does not fully replicate the hydraulics of a full-scale membrane system. Use of smaller modules could cause problems with scaling up of system design parameters.

• Operating Parameters: Carefully check operational setpoints and sequencing of automated operations, and make sure that they closely match those of full-scale operational membrane units. This is important because all automated operations that involve downtime will impact the quantity of water produced by the full-scale membrane system. One example is the downtime for all valve changes and pump start/stop sequences for a backwash. The downtime on the pilot-scale is often not as long as in a full-scale plant, and should be factored into the evaluation of the membrane system.

• Pretreatment: Monitor pretreatment processes closely, and note changes in water quality and their impact on the membrane’s performance. For example, if coagulation and clarification are used upstream of MF/UF, recognize that deviations from normal performance can occur and that these deviations will impact the MF/UF system’s performance. If the turbidity of the feed water to the MF/UF system is twice as high in the spring due to seasonal run-off events, this will impact the backwashing and CIP intervals of the MF/UF system. If PAC is used seasonally for taste and odor control, it could carry over into the membrane system and help or hinder the performance. All aspects of the pretreatment processes should be carefully monitored and recorded so that changes in the membrane’s performance can be cross checked with changes in pretreatment.

• Integrity Testing: Thoroughly check and understand the integrity test system. Ensure that all air is removed from the system to avoid air locks. Involve regulators as necessary to demonstrate the efficiency of the procedure and agree upon a testing frequency. Recognize that integrity testing procedures on pilot skids are sometimes manual operations, but are fully automated in full-scale systems.


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• Staff Involvement: Involve O&M staff to familiarize them with membrane technology. Allow time in the pilot schedule for operators to take control of the pilot skid. Having an opportunity to test the extremes of operation of the pilot system will give operators and staff a feel for how the system will operate in the full-scale.

• Residuals: Evaluate the quality and quantity of waste streams to develop a residuals management strategy. Recognize that conducting membrane pilot tests with the backwash stream of a primary membrane pilot plant is difficult, due to the low volume of backwash that is typically produced. Bench-scale tests can be performed to give a preliminary evaluation of the performance of some residuals treatment options.

• Representative Feed Water: Test the actual feed water whenever possible, and include any recycle streams, if possible. If chemicals or processes might be used in the full scale, try to include them in the pilot trial. For example, if PAC is used for seasonal taste and odor control, it is wise to include it in the pilot trials because it can impact the membrane’s performance. Likewise, coagulants and oxidant use should also be fully understood and included in the pilot, if possible.

• Equipment Reliability: Recognize that pilot skids are not as reliable as full-scale membrane equipment, and this can impact the pilot testing and project schedule. They are shipped from site-to-site, and are often used in an outdoor setting, which exposes them to a wide range of temperatures and weather conditions. For most membrane pilot skids, there are few redundant systems or pieces of equipment, so the pilot system can shutdown due to a mechanical failure of something simple, such as feed pumps, valves, actuators, and air feed systems. The best way to handle reliability issues is to allow time in the pilot testing schedule for initial pilot skid commissioning and set-up to fix parts that were damaged during shipment, and to factor time into the pilot testing protocol for downtime associated with mechanical failures.

• Pilot Infrastructure: The power supply, shelter or building, applicable building codes, phone lines for remote monitoring, and proper foundation design all need to be considered.

Well planned and executed pilot plant programs have proved their worth in developing a

successfully integrated membrane facility. It is important to determine the need for pilot testing early in the project to minimize delays in the project schedule. The costs associated with conducting a pilot test should also be factored into the overall cost of a membrane facility.

Flux Selection

Selecting the design flux is a critical phase of design. It is often verified with pilot testing prior to design as was done by Scottsdale and Columbia Heights, and many of the participating utilities. The key issues to consider are the maximum sustainable instantaneous flux and related cleaning frequency (either as full CIPs or as CEBWs). For example, the Scottsdale pilot plant confirmed about 32-gfd flux at a 30-day CIP interval without and CEBWs. Other plants like Heemskerk, selected a flux that could be maintained with daily CEBWs. These relationships between sustainable flux and the resulting CIPs or CEBWs are site-specific and depend on the feed water quality.


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The impact of temperature on the flux must also be considered. For example, pilot testing in the summer will provide data for warm water membrane filtration. In the winter, with lower temperature, the sustainable flux can be significantly lower.

MEMBRANE INTEGRITY

The incidence of fiber breaks in MF and UF systems is based on several factors. The quality control during production, storage, shipping, and installation is dependent on the membrane supplier and must be of a high standard (Johnson and MacCormick 2002). Subsequent to the installation, the performance and life of the membrane modules is dependent on the operations and maintenance. Factors such as backwash frequency, backwash and production pressures, chemical cleaning, chemical use, and handling also influence the fiber’s useful life (Johnson and MacCormick 2002).

As more experience is gained with membrane operation, water utilities are identifying factors that affect membrane life at their facilities. Staff at the Clay Lane Facility in the UK reported that a high rate of fiber breaks is related to operating at high TMPs (Lake et al. 2003). The frequency of fiber breaks must be considered in the staffing requirements for a utility. Kruithoff, Kamp, and Folmer 2003 reported that in the first three years of operation, 2,641 fiber breaks occurred. The UF plant has a total of 7,526,400 fibers, so this breakage is less than 0.35 percent of the total plant; however, the labor required for repairs must be included in staffing plans. The utility interviews revealed mixed reports regarding fiber breakage rates with MF and UF technologies, and very few integrity problems were reported for NF/RO facilities. There are several reasons for this difference. First, MF/UF systems for drinking water production use hollow fiber membranes that are operated in a dead-end mode to remove particles, whereas NF/RO membranes are spiral wound, membranes that are operated in cross-flow mode to remove dissolved species. NF/RO membranes are not installed as a particle barrier; however, a breach of MF/UF integrity carries the consequence of disinfectant-resistant organisms passing through the membrane barrier. As a result, there is less impetus for NF/RO systems to be checked for membrane integrity. There are, however, regulated requirements for MF/UF systems to check and maintain integrity. Details of MF/UF fiber breakages, particularly high rates of failure, are rarely discussed in the technical literature due to sensitive, commercial arrangements with the membrane manufacturers. Two utilities with the most operational experience (i.e., four or more years in operation) had greater rates of fiber breakage than other utilities interviewed as part of this research. These two facilities operate as base-load plants, and their production is critical to the water supplies in their region. The following problems were experienced and may have contributed to the high rate of fiber breakage:

• Air entrainment either in pipes that feed the membrane units or in manifolds within the membrane units.

• A flux above the long-term stable operational flux, especially in cold water temperatures. • Surges during normal operation, cleaning procedures, and power outages that creates

either high pressures in supply piping or vacuum conditions in outlet piping. • Incomplete or irregular chemical cleaning regimes. • Inconsistencies with membrane fiber manufacture and packaging.


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• Failure of previous repairs. • Incorrect response to changing feed water quality conditions. • Foreign materials entering the membrane filtration process during start-up and

commissioning.

In turn, each of these problems was quickly addressed by the utilities concerned and this has reduced fiber breakage rates to more acceptable levels. Facilities that are now adopting membrane filtration have the opportunity to learn from these pioneering utilities. Solutions to these integration issues include:

• Automatic air release valves were installed where air pockets can occur. • Flux was decreased in cold water temperature conditions to reduce TMP and the resulting

stress on the membrane fibers. • The operating speed of valves was adjusted to reduce surges. Piping was designed to

maintain sufficient backpressure on the membrane fiber to reduce adverse negative pressures.

• Increased calibration checks were installed on chemical dosing equipment to ensure that cleaning regimes apply the correct quantity of chemicals. In addition, water quality instrumentation has been added to ensure correct pH and oxidant residuals are reached during the cleaning process. Changes to software programming were also reported to better record chemical cleaning progression.

• Close working relationships between the membrane manufacturer and utilities were reported, resulting in improvements to membrane manufacture. Defective cartridges were investigated and replaced under warranty.

• Fiber repair techniques were refined to prevent failure of previously repaired fibers. Modifications to pin type and adhesive were made with a close working relationship between the utility and the membrane manufacturer.

• The addition of process scientists or engineers to the staff has led to appropriate adjustments to operational parameters, and thus to more stable operation. Continuing pilot plant experiments also helps to optimize operations, such as CIPs, to optimize operation.

• The utilities that most recently installed membranes had improved specifications to minimize the possibility of having foreign materials, such as pipe filings, enter into the membrane system during startup. Rigorous cleaning and inspection specifications helped prevent this occurrence.

Without exception, all utilities operated their MF/UF plants to achieve a safe log rejection

value that had been approved by their regulatory authority. In most cases, operation continues with some fibers compromised until either log rejection is close to the alarm set-point, or a scheduled maintenance outage for fiber repairs is performed. Some subtle differences were noted. For example, at the Ennerdale facility, when a broken fiber is detected during routine integrity testing, the affected cartridge is isolated and the unit is returned to service. The available filtration area is reduced slightly; however, as each unit contains ninety cartridges and is operating within design flux, this has a negligible effect on production.

It was noted that utilities with very low fiber breaks were operating well within design capacity, and hence at a stable flux and reasonable TMP for the system. The San Patricio WTP


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has not experienced any fiber breaks since start-up. Similarly, the Ennerdale facility operated by United Utilities has also experienced low rates of fiber breakage. This may be a result of operating at below the design flux.

Membrane Warranty

Membrane warrantees offered by manufacturers vary from five to ten years. The length of warranty period depends on the many factors. Many times, the warranty is factored into the cost evaluation during the procurement process. Membrane warranties are often pro-rated, with a sliding scale of replacement cost over time. If membranes are defective and require replacement within the first few months of operation, the supplier will generally replace them at no cost to the utility. With use, the replacement cost of the membranes increases at a rate that is usually proportional to the usage period. For example, if the membranes are warranted for ten years, and if they are in need of replacement due to some defect after seven years, the replacement cost would be about seventy percent of price for a new membrane module, because the membrane performed as specified for seventy percent of warranted period. It should also be noted that when negotiating with membrane suppliers, a guaranteed replacement cost, with adjustment for inflation, can be included in the initial contract. Utilities are finding, however, that the cost of modules is decreasing at a rate that generally yields the guaranteed replacement cost more expensive than the advertised market price. Module costs for common MF/UF suppliers are currently from $550 to $700. When a significant number of fibers in a membrane module are compromised, the module should be replaced to maintain cost-effective operations of the membrane system. As more experience with membrane integration for water treatment is gained, replacement options for membrane will likely increase. There are discussions within the water industry about standardizing low-pressure MF and UF systems so that membrane modules can be interchangeable between various systems (Crozes et al. 2002). The obvious advantage to standardization is a cost competitive nature for procuring replacement membrane modules; however, more experience must be gained with the various membranes and membrane systems to ensure that standardization will result in efficient operations and cost-effective solutions.

RESIDUALS TREATMENT AND DISPOSAL

Appropriate and cost-effective residuals disposal is also important for the successful integration of membrane treatment technology. The treatment, reuse, and/or disposal of all residual streams (i.e., backwash, CIP, and CEBWs) must be planned thoroughly in advance of design and construction of the membrane plant. The governing regulatory agency will need to fully understand the residuals handling and disposal plans for the facility, and may recommend or dictate certain treatment or disposal requirements. This is particularly true if waste streams will be discharged either to a water body or a WWTP that is not under the utility’s direct control. Acceptance of the proposed discharge is not guaranteed, and gaining the necessary permits can be a lengthy process due to public consultation and regulatory approval. For example, for MWW’s UF WTP, lagoon storage and discharge of neutralized CIP waste to the Mississippi River was found to be less expensive than discharge to the sewer, however, appropriate permits were required for this option. MWW


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started the application procedure for the appropriate discharge permit early in the project to avoid possible delays. Similarly, water quality issues can arise and alter acceptable discharge options for a WTP. During the pilot plant for the Chaparral WTP in Scottsdale, Arizona, the intended disposal of MF/UF backwash was to the sewer system of a neighboring utility. However, once the volume and water quality, specifically the arsenic content, was quantified after pilot testing, sewer discharge was deemed too costly. An on-site solids handling and dewatering facility was included in the project, and residual solids will be hauled away for disposal. Restrictions on residuals disposal provide opportunities for innovation. For MF/UF processes, backwash waste is relatively simple to treat and the treated water can often be recycled. Techniques that were employed by utilities interviewed as part of this study were:

• Recycle to the head of the treatment process, where coagulation and clarification preceded membrane filtration.

• Treatment using secondary MF/UF membranes, that are operated at a lower flux due to a higher solids loading than the primary membrane filtration processes, and the filtrate from the secondary units is either recycled or sent to distribution (Clay Lane and Inverness).

• Treatment and re-use for industrial users, where a lower quality water source is acceptable.

• Treatment using conventional processes, such as coagulation, clarification, and sludge thickening.

Neutralized CIP wastes from MF/UF processes were usually discharged to sewer or to a

water body. Neutralization was achieved by either (1) adding neutralizing chemicals or (2) dilution and self-neutralization by blending chemical waste streams, e.g., alkaline and acid wastes. In one instance, neutralized CIP waste was blended with backwash waste from the secondary membranes before further treatment through a sludge thickener. This procedure ultimately led to the development of a concentration loop, which resulted in a high TDS concentration which causes poor clarification in the sludge thickener at the Ennerdale WTP. This problem was exacerbated by very low alkalinity and a lack of buffering capacity in the raw water source. To resolve this operational challenge, neutralized waste is hauled off site by tanker trucks at routine intervals, and this practice has added to the operational costs at this facility.

NF and RO waste can be more problematic to discharge, primarily due to the greater volumes and higher contaminant or TDS content in the concentrate stream. The system recoveries for utilities of this study ranged from 65 to 85 percent. PWN’s Heemskerk facility was able to use a pipeline installed by a neighboring steel manufacturer to discharge RO concentrate to the North Sea. This resulted in a considerable cost saving to PWN. Deep well injection and discharge to sewer are other disposal options for utilities that are located far from a coast.

NF processes produce waste that has a lower TDS concentration than RO, and it can sometimes be discharged to fresh water bodies, depending on volume and quality of the concentrate. NF concentrate could also be used for irrigation purposes as a non-potable source, as has been considered in more arid regions of the world. Saline tolerant grass has been developed for this very purpose.


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PUBLIC INVOLVEMENT

The degree of public involvement differs for each utility. For some, it is critical that the public be aware of treatment options, whereas for others, minimal public involvement occurs due to a lack of interest or lack of issues that normally influence the public’s opinion (e.g., location, chemical deliveries, loss of public-use lands). Examples from two of the participating utilities in this project are highlighted below.

The MWW recognized early in the planning stages that they would need to address local politics as well as follow a sound technical approach to integrate membranes for their 160-mgd (606 ML/d) facility (Kramer et al. 2001). A CAC was established to represent various stakeholders in the Minneapolis community. This Committee worked closely with the Mayor and other City offices to keep all stakeholders informed of issues, alternatives, progress, and decisions. This approach helped streamline the approval process for the City. The committee has stayed involved at key stages throughout the project, including during the design of the facility.

When the City of Scottsdale identified land for their new 30 mgd (113 ML/d) membrane WTP, they recognized the need to keep the neighborhood groups informed to avoid opposition or delays. Meetings to discuss the purpose and components of the facility and the construction schedule were held. Also, several artistic renderings of the facility, including that of the adjacent dog-walking park and ball fields, were developed to increase public awareness of the utility’s efforts to accommodate public amenities within the proposed facility.

PROCUREMENT

The methods of procurement of membrane systems depend on any relevant procurement regulations that are applicable to public projects, including policies governing equipment purchases for WTPs. The typical procurement procedure for MF/UF membrane equipment is different than for conventional WTP equipment for several reasons. First, because not all membrane systems perform similarly, pilot testing of various membrane systems may be required as part of the procurement process. Oftentimes, the results from the pilot testing are incorporated into the procurement process. In addition, pilot testing results could also be used to determine the life cycle costs of various membrane systems, and these costs can be used during bid evaluation. This impacts the schedule of the project. Second, membrane systems have different system hydraulics (i.e., encased versus submerged), foot print and ancillary equipment, resulting in a significant impact on upstream and downstream hydraulics that would affect the design of the overall facility. Because of this, some utilities prefer to select a membrane system supplier prior to the initiation of detailed design; otherwise, the facility would need to be designed to accommodate several membrane systems, increasing the cost. For NF/RO equipment, as with MF/UF, pilot testing may be required to identify suitable membranes for treating specific source water. Because NF/RO membranes are standardized in size, the supporting infrastructure could be designed prior to the final selection of the membrane facility. Examples of various procurement methods and issues are highlighted in the following text.


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Municipal Procurement

There are many approaches to procuring membranes and membrane equipment for a WTP. Procedure for selection of the membranes for installation can include pilot testing, or proof-pilot testing, as discussed earlier in this chapter. The contractual procurement procedures will vary from utility to utility, but in general, having a competitive bid for membrane equipment, with at least two vendors, is typically a requirement. Each approach has advantages and disadvantages, as illustrated in the examples below. The procurement procedure followed by MWW is perhaps the most comprehensive in the industry (Kramer et al. 2003). In 1994, a Water Quality Strategy was developed for the MWW. This Strategy outlined a program for bench- and pilot-scale testing, which resulted in the recommendation for membranes at their two conventional softening facilities. In 1999, a value engineering and peer review team recommended preliminary designs for the two WTPs. While MWW staff worked to address local political solutions for implementation of two new membrane filtration plants (discussed in Chapter 5), procurement of the equipment was initiated. Bids for full-scale membrane equipment were collected before pilot testing was performed. Procurement involved three main phases (1) evaluation of supplier qualifications, (2) performance, or pilot testing, and (3) bid evaluation. The pilot testing effort was completed in October 2001, and the Norit X-Flow UF membrane was selected for both of MWW’s WTPs. In total, the evaluation and procurement procedures for MWW encompassed seven years of effort. The procurement method used by the City of Scottsdale, Ariz., is similar to that of MWW. It is described in detail in Chapter 2. Pilot testing was used to identify membrane systems that could successfully treat canal water, and the membrane systems that demonstrated their ability to treat the canal water were allowed to participate in a bidding process. Based on life cycle cost analyses, one membrane system was procured prior to detailed design. This allowed the design of the facility to be tailored to the selected membrane supplier.

Some utilities solicit bid proposals from pre-qualified membrane system suppliers based on the available water quality data and proposed operating criteria. Based on the information provided by the membrane system suppliers, the equipment procurement contract is awarded. The successful supplier is required as part of the contract to conduct pilot testing to verify, and sometimes modify, the quoted design specifications for membrane systems. This is often referred to as ‘proof’ piloting, because the vendor is essentially proving that the system can operate at the proposed design settings (i.e., flux, backwash interval, cleaning interval, etc.). The City of Salmon, Idaho, solicited proposals for an MF or UF surface water treatment plant to replace their existing traveling bridge filters. Pilot testing was a requirement as part of the pre-qualification process (Mueller and Sloan 2001). Likewise, the Weber Basin Water Conservancy District of Utah conducted pilot trials of four membrane systems to verify the operating and design conditions where were pre-quoted for procurement (Paxman et al. 2001). In Tennessee, the South Blount County Utility District conducted a proof-pilot only after the membrane system was selected. The selection was based on an economic and non-economic review of three membrane bids (Reiss et al. 2002). For the Olivenhain Municipal Water District (OMWD) of Encinitas, Calif., pre-procurement procedures began after the pilot testing of five different membrane units in late 1998 (Thorner et al. 2001). It was necessary to pre-select membranes so that the final design could incorporate design requirements of the selected membrane. Each system submitted a statement of qualifications, and at that time, only two of the five systems were approved by the


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California Department of Health Services (DHS). OMWD sponsored the un-certified systems for DHS approval, which was ultimately granted to each system. Proposals were then submitted based on the design, operation, and costing guidelines of the OMWD. A selection panel reviewed the proposals, visited manufacturing facilities and full-scale installations for four of the five manufacturers, and selected the Zenon submerged UF for installation. This pre-procurement process was six months in duration. For other cities, two phases of pilot testing have been performed as part of the procurement process. Bexar Met, Texas, for example, used the first phase for qualification to bid, and the second phase to optimize treatment and determine design parameters (Moreno et al. 2001).

Private Company Procurement

Sometimes, water utilities are allowed to select equipment based solely on performance rather than on cost. Most utilities will, however, require a cost comparison before equipment can be procured. Having at least two eligible membrane suppliers to bid on a project offers competitive pricing for the project, and this is generally the goal of all utilities.

United Utilities in the UK solicited tenders for a groundwater MF or UF treatment facility at Ennerdale, UK. Reference sites were visited by United Utilities, and systems were evaluated based on a list of criteria (Hillis 2001). The main criteria were the existence of long-term commercial future, integrity testing, proven track record, robustness, and throughput. After the evaluation period, one system was selected for pilot testing and installation. This procedure allowed for a competitive tendering, followed by pilot testing of one system. Because the source water was a groundwater, pilot testing of one system was considered to be less risky than for surface water.

OPERATIONS AND MAINTENANCE NEEDS

One of the advantages of membrane systems are that they can be fully automated, thus requiring fewer staff for operation of the facility. Maintenance of the facility, however, will require staff time and training, and needs to be considered for any plant.

Equipment of a membrane installation that requires regular maintenance includes:

• Online instruments (particle counters, turbidimeters, conductivity probes, etc.). • Flow meters. • Valves. • Pumps. • Piping. • Fiber repair.

Piping maintenance is often overlooked, but has been reported to be a maintenance issue

for some membrane facilities. Kothari and Schideman 2002 reported that the frequent and sudden flow changes during a production cycle have caused enough physical vibration that a maintenance program of tightening connections and inspecting the integrity of pipework is necessary. Plastic piping may not be suitable for MF/UF systems that are subject to high flow rates or hydraulic fluctuations that cause vibrations.


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Fiber Repair

An additional maintenance issue for membrane plants is the effort required for locating broken fibers that cause failure of integrity tests and fixing them. The frequency of fiber repairs are beginning to be reported in the literature as many membrane facilities are aging. Kothari and Schideman 2002 presented fiber breakage occurrence data from a pressurized MF plant in Wisconsin (Table 3.4).

The Manitowoc facility comprises 13 MF units (i.e., USFilter’s CMF 90 M15C ), and each unit holds 90 membrane modules. Pressure hold tests are automated, thus requiring little operator intervention. However, any failure of the integrity test requires sonic testing and module repair, which requires a trained technician for both procedures. Several sonic tests and module repairs were conducted in 2000. In one month, 29 modules were repaired (i.e., almost one per day). It is important to recognize that maintaining the integrity of membrane systems will require operator attention and time.

Other plants have experienced higher-than-expected staffing requirements to repair and replace compromised membrane modules. Oxtoby (2003) reported that the integrity and repair procedures used at Clay Lanes WTP have required improvements to streamline the procedures and enable accurate and timely repairs to the modules. As discussed in the utility interview for this utility, a special hoist and membrane removal system have been developed for their UF system (i.e., Norit X-Flow).

The participating utilities reported different strategies to achieving their O&M goals. The implementation of membrane filtration processes had enabled almost all of the utilities to reduce operating staff hours at the WTPs. The majority of plants staffed the facilities during day shifts only, with remote coverage provided during evening hours. This trend was identified in the European and North American continents in particular. Where utilities operated more than one WTP, operational monitoring had been reduced to a regional base that served several plants. This was the case with Three Valleys Water, where staff at the regional operational center supervised three different membrane plants remotely. MWW reported that the installation of the Columbia Heights membrane filtration plant will enable them to better utilize operational staff, allowing staff to concentrate on more labor intensive tasks at the existing conventional processes of their facilities.

Table 3.4 Integrity test failures and fiber repairs for Manitowoc Public Utilities

Average Occurrence per month Maximum Occurrence per month Parameter 1999 2000 2001 1999 2000 2001

PDT failures 1.2 1.3 1.5 1.5 2.6 2.3 Sonic test failures

10 21 8 15 42 22

Repaired modules

6 12 3 8 29 8

Source: Data from Kothari and Schideman 2002


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Maintenance tasks at two of the European facilities interviewed, PWN and Three Valleys Water, have been outsourced to independent contractors on a fixed-term, contract basis. Of particular interest at these two utilities was that the membrane maintenance and repair tasks were performed as needed by a contractor.

At PWN, a contract supplied by an outside contractor exists with the membrane suppliers for both the UF and RO treatment stages. The maintenance contractor performs UF repair whenever the target log rejection for a membrane unit is reached. Routine maintenance, such seal replacement (i.e., O-rings, gaskets, etc.) and RO membrane replacement is also conducted by the contractor.

Three Valleys Water has contract staff present during most day shifts to conduct fiber repairs. This large, 42-mgd (160 ML/d) facility has a very onerous 5-log removal target for particle removal. A few fiber breaks can lead to a failure to meet this target. This utility has reported a relatively high number of fiber breaks and the cost of repair has been a significant additional cost that was not anticipated. When this utility was initially interviewed, fiber repairs were conducted by utility staff. A follow-up interview was conducted to investigate how this utility had refined its membrane maintenance strategy. They found that using contract staff dedicated to the repair of membrane fibers was more efficient than using utility staff. This also allowed utility employees to conduct maintenance activities on other parts of the WTP. As noted in Chapter 2, the purchase of vacuum testing equipment has also shortened the fault identification and testing time.

COSTS

When considering integration of membranes into WTPs, cost is an important issue in the decision making process. Cost comparisons of membranes versus conventional treatment processes, and between various membrane suppliers, are commonly performed by evaluating the capital costs as well as O&M costs. It is important to recognize that with any cost estimation, all of the included and excluded costs of the estimates need to be clearly stated and understood to allow a fair comparison. Membrane suppliers and engineering companies calculate the cost of membrane systems frequently, but are not always able to share cost information due to a competitive bidding environment or other confidentiality reasons. Some general rules of thumb for cost estimating for an MF/UF membrane installation in the USA are $0.40 per gallon treated for systems less than 10 mgd, and $0.30 or less per gallon for systems treating over 10 mgd. For example, Fuerst, Hargesheimer, and Taylor 2003 reported that costs for 8- and 10-mgd MF/UF systems were $0.39 and $0.35 per gallon (installed). The ultimate cost will depend on many factors, such as those listed in Table 3.5. Costs for the membrane facilities of participating utilities of this project are discussed in this chapter. The discussion in this section includes published cost information from other membrane installations.

The Southside WTP in Texas has both primary and secondary UF units and treats a groundwater under the influence of surface water. The construction cost for this 3.0-mgd (11.4 ML/d) plant was $3.6 million ($1.1 million for the primary equipment and $0.28 million for the secondary backwash equipment, including membranes, pumps, controls, and ancillary equipment; Lynk, Briggs, and Petry 2001). One unique aspect of this facility is the low discharge costs, which are a result of the high recovery rate (i.e., greater than 99 percent) of the plant.


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Table 3.5

Factors to be considered in estimating costs of membrane systems Need for pumping to/from membranes

Power for pumps, motors, valves, air supply, heating of cleaning solutions.

Market value of concrete and steel The value of water lost in low recovery systems.

Local construction costs Manhours for routine maintenance. Need for pretreatment Manhours for fiber repair. Need for post-treatment Level of instrumentation. Chemicals needed for CEBWs and CIP

Ability to use siphon-assisted pumping in submerged systems.

Level of competition and market value of membrane equipment

Regulatory requirement for integrity testing (i.e., downtime).

Waste hauling and/or discharge fees

Architectural treatment

Site work, foundation, access roads, grading, stormwater, etc.

O&M costs are an important consideration when evaluating membrane integration. They

include labor, chemical use, power use, equipment replacement and repair, and can include residuals disposal costs. A comparison of O&M costs for the 14-mgd (53 ML/d) Manitowoc Public Utilities WTP in Wisconsin is shown in Table 3.6 (Kothari and Schideman 2002).

The costs of Table 3.6 show that the total O&M costs for the MF facility were initially higher than those of the conventional plant. This is attributable to the higher energy costs due to higher pumping requirements. Labor costs increased in the first year of operation due to training and gaining experience with the equipment. The purchase of spare parts is evident in the equipment costs for the year 2000; however, it is lower in the subsequent year, 2001. These costs exclude membrane replacement costs.

Table 3.6

A comparison of O&M costs for a conventional versus MF full-scale plant Conventional WTP New MF WTP 1998 2000 2001 2002* Chemical $97,000 $72,000 $119,000 $79,000 Electrical $143,300 $240,000 $260,000 $199,000 Labor $174,000 $216,000 $192,000 $108,000 Equipment Repair & Replacement

$10,000 $56,000 $20,000 $31,000

Residuals Disposal

$14,000 $7,000 $17,000 $29,000

Total Cost $440,300 $591,000 $608,000 $446,000 Source: Data from Kothari and Schideman 2002 *Costs were projected to a full year from five months of data


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As expected, there are capital cost differences between submerged and encased membrane systems. For example, USFilter supplies both the encased and submerged MF system, and Sorgini 2003 reported that the capital cost for the submerged system is lower, because the membrane area per unit is higher for the submerged system, and the necessary ancillary pipework, pump, and valve requirements are lower.

The MWW was able to secure State Revolving Fund (SRF) assistance for its extensive program of improvements in Minneapolis. Following extensive study, the costs estimates for improvements totaled $140 million. This included not only membrane filtration plant procurement, design, and construction for a total capacity of 160 mgd (606 ML/d), but also additional improvements to the utility. The success of gaining the funding hinged on the MWW proving that the membrane filtration plant, including membrane cartridge replacement every seven years, was cheaper than building a conventional filtration WTP. This cost difference was easily demonstrated in Minneapolis, because filter buildings have to be enclosed to protect against freezing during the winter months, and this is a substantial cost item. As membrane filtration processes have a much smaller footprint compared to conventional filters a smaller building, and lower overall cost was demonstrated. The additional level of treatment that membranes offered also will enable compliance with the proposed LT2ESWTR.

A 30-year pro-forma was prepared to bond the capital improvements, and the MWW applied for SRF assistance. The advantage to the MWW obtaining SRF assistance is that interest payments are reduced by 1.5 percent. The assistance covers funds for capital expenditure and subsequent operation and maintenance costs, but not engineering design services. The loan repayments were factored into the annual operating costs for the MWW, which were included in the five-year rate projection that was presented to City Council for approval. The initial impact on rates for MWW customers was a 10 percent increase per annum, which will parallel the construction phases of the two plants (i.e., the financial years of 2004 through 2007).

On completion of construction, the annual rate increase will be gradually scaled back over a five-year period. The percentage increase in water rates is summarized in Table 3.7. Water rates as of 2004 charged to residential customers were $3.18 per 1,000 gallons.

Table 3.7

Impact of water treatment plant upgrades on water rates for the MWW Financial year Percentage rate increase

2003 10 2004 10 2005 10 2006 10 2007 10 2008 7 2009 5 2010 3 2011 2


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Several cost estimating models are currently available for estimating capital and operating costs of water treatment processes including membranes process. These include Water Treatment Estimation Routine (WaTER) (Chapman Wilbert et al. 2000) and the WTCost model (Moch & Associates, Inc., and Reclamation 2002). These models can be a useful budget level evaluation of the cost for membranes. As mentioned above, there can be treatment or infrastructure modifications that are necessary for a project that are not a part of the membrane system (e.g., need for pumping station or modifications to backwashing treatment), and the cost for these should be considered when making a fair evaluation.

The costs of membrane plants of the participating utilities are summarized in Table 3.8 and shown graphically on Figure 3.1. The costs are difficult to compare as there are many differences between the facilities. Some costs include office space and training rooms, and others have expensive civil construction items, such as storage reservoirs.

Similarly, operational costs also differ between WTPs due to levels of treatment and other capital expenses that are included in the overall rate structure. For example, a pipeline replacement program can easily cost more than installing a new membrane filtration plant and this will be reflected in the overall rates that are charged to customers. Some of the utilities interviewed declined to provide costs due to their particular commercial circumstances and the markets in which they operate.

Table 3.8 Costs for membrane filtration plants of participating utilities

Plant

Type of membrane

plant Capacity

(mgd) Year

constructed Construction cost

($ million)

Production costs,

($ per 1000 gallons)

San Patricio MF 7.8 1999 7.0 1.94 Torreele UF & RO 1.4 2002 7.6

(4.0 membranes only)

1.81

Bexar Met UF 9.0 1998 16 (3.8 membranes only)

1.25

Clay Lane UF 42 2000 17 NA* Inverness UF 6.8 2002 24 (9.6 membranes

only) NA

Méry-sur-Oise NF 37 1994 135 0.45 (NF stage only)

Columbia Heights

UF 70 2004 52 3.18†

Heemskerk UF & RO 15.8 2000 20 NA Chaparral UF 30 2004 60 (Engineer’s

Estimate) NA

CCK UF 96 2003 73 to 108 (Bid range)

NA

Note: The following exchange rates were used to provide comparison. 1 GB pound = 1.8 US dollar, 1 Euro = 1.20 US Dollar, 1 Singapore Dollar = 0.60 US Dollar. * NA = not available or provided during the interview. † Costs presented are rates and include all treatment and distribution costs; no figures are available for membrane only production costs.


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0

20

40

60

80

100

120

140

160

0 20 40 60 80 100 120

Plant Capacity (mgd)

Cos

t ($

Mill

ion)

Figure 3.1 Membrane system capital costs as reported by utilities Figure 3.1 shows a wide variation in the costs that were reported. Although the data were not corrected for the year or scope of work, some interesting observations were made. The outlier point (i.e., 37 mgd, $135 million) is the oldest plant included in the survey. Membrane system capital costs have decreased substantially in the last ten years and normal cost indices cannot be applied to correct these data to current values. Also of note is the extremely cost effective Clay Lane WTP (42 mgd, $17 million), which was constructed as design build, on tight budget, and within a limited time frame.

INSTALLATION AND COMMISSIONING

There are many issues and developments which occur during commissioning. Some issues or lessons learned are listed below, for reference. One of the main challenges to commission is the disposal of test water during start-up. A suitable use or disposal site is needed for the potentially millions of gallons needed for commissioning. Sometimes this water is recycled or discharged to a reservoir or other water body. The location of discharge needs to be approved by local regulatory agencies well in advance of commissioning to avoid delays to the schedule. Another issue during start-up is the presence of foreign materials or debris in piping during construction. These materials pose two potential problems. First, they can enter the membrane system and damage the membrane fibers. Some utilities (e.g., Bexar Met) install strainers upstream of membranes to help combat this potential problem.


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Preservative Rinsing

Some membranes are shipped in glycerine preservative that must be rinsed from the unit prior to putting the system into production. This glycerine waste may be discharged to a sewer, and in some cases can be discharged into a nearby stream or lake. It should be recognized that the preservative may have to be shipped off site if local agencies or regulators do not allow discharge to a sewer. The volume and timing of flushing the preservative from the membranes needs to be part of the commissioning plan. In an environmentally sensitive area, discharge limits and access to a sewer can present challenges or delays to the installation.

Wetting of Membrane

Many of the membrane surfaces are hydrophobic (e.g., PVdF), and thus are ‘water hating.’ This quality can cause problems with the membrane not ‘wetting’ properly after installation. Wetting is essentially the displacement of air bubbles or pockets within the membrane material. If wetting is not performed, the production rate of the membrane will be lower than expected, because water cannot pass through the membrane material at reasonable pressures. Likewise, if air is introduced as part of a cleaning cycle, a re-wetting procedure is sometimes necessary to ensure that the membrane is permeable to water.

Laboratory researchers can overcome the wetting problems by using an isopropanol solution for soaking, which is then removed by a distilled water rinse (Tomaszewska and Mozia 2002). In full-scale installations, the duration of the wetting period can be shortened by conducting chemical soaks, similar to chemical cleaning procedures. The type of chemical used and duration is specific to each membrane supplier and should be discussed with them prior to commissioning.

RECOMMENDATIONS TO UTILITIES CONSIDERING MEMBRANE FILTRATION

Staff that were interviewed at the participating utilities provided recommendations to utilities that are considering membrane integration. Their views are summarized in Table 3.9.

Table 3.9 Recommendations by participating utilities

WTP Recommendation Pilot testing Clay Lane; Chaparral; Inverness Pilot test with all anticipated water quality

variations that are possible. For example, if clarification is upstream, pilot test system upsets with turbidity carry over.

Inverness Pilot tests should cover all anticipated temperature variations in the feed water.

Bendigo, Columbia Heights Continue piloting during construction and operation of the membrane facility to compare (1) different chemical cleaning strategies, (2) new membrane formulations, (3) off-line virus or other microbial challenge tests, and (4) process optimization.

(continued)


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Table 3.9 (Continued) WTP Recommendation

Bexar Met Involving operational staff during piloting phases is an excellent method of introducing operators and maintainers to the concepts of membrane filtration and familiarizing them with the technology.

Selecting membranes/engineers San Patricio, Torreele Consider the importance of oxidant resistant

MF/UF membranes, particularly if bio-fouling could develop.

San Patricio; Bexar Met Evaluate previous designs produced by design engineers that are being considered and then interview operational staff at that facility.

Procurement and construction San Patricio Ensure that complete life cycle cost data are

provided to enable accurate analysis of whole life costs.

San Patricio Some utilities recommend direct purchase of membrane equipment, outside of the general contractor.

San Patricio Good planning and coordination with the contractor, membrane supplier, designer and owner is necessary for smooth start-up and commissioning.

Ennerdale Consider a staged start-up of the new facility and consider a bypass arrangement to assist commissioning.

Operations Bendigo Log all chemical cleaning sequences and check all

chemical deliveries to ensure chemical cleaning is occurring at scheduled times and at the correct concentration and temperature.

Bendigo Regularly check, calibrate, and maintain instrumentation.

Chaparral; Columbia Heights Allow for flexible chemical cleaning regimes to deal with unexpected water quality changes that could cause a fouling event.

Columbia Heights Allow for autopsies to better determine fouling materials and tailor chemical cleaning regimes to either prevent their accumulation or remove them from the membrane surface.



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CHAPTER 4 DECISION TOOL

Based on the information gathered throughout this project, a simple computer-based decision tool has been developed to illustrate the potential use of membranes to meet various water treatment goals. A general description of the decision tool is given in this chapter. The program will be referred to as “tool” henceforth for readability.

OVERVIEW OF THE DECISION TOOL

Integration of membranes with other water treatment processes requires careful consideration of various issues that include (1) historical water quality data, (2) seasonal water quality variations, (3) geographical location, (4) local regulations, (5) treatment objectives, (6) cost, and (7) feasibility. The other chapters in this report highlight each of these issues, and provide examples from studies or full-scale installations, whenever appropriate.

The objective of this tool is to illustrate how membranes could be used, either in a new facility or for retrofitting into an existing plant, to achieve specific water quality goals. The tool’s recommended treatment alternatives for a given situation are limited to membranes, with only a few occasional references to other non-membrane treatment alternatives. It is recognized that several non-membrane treatment alternatives are equally or more effective, in terms of performance and economics, and these should be further investigated by the user.

The tool is structured to allow the user to select whether the intended use for membranes is in new facility or for retrofitting an existing facility. Each of these options is discussed below.

New Facility

The options for integration membranes with conventional water treatment processes are illustrated in this option. The user is allowed to select either a surface water source or a ground water source. The user is then allowed to select any combination of five water quality parameters that are of concern. The five parameters that are listed in the tool were selected to account for the most common water quality concerns faced by utilities. The five water quality parameters for surface water sources are:

1. Turbidity and pathogens. 2. DBPs and their precursors. 3. TDS, hardness, and nitrate. 4. Pesticides and synthetic organic chemicals (SOCs). 5. Arsenic. The five parameters for groundwater sources are:

1. Turbidity and pathogens. 2. Iron and manganese. 3. TDS, hardness, and nitrate. 4. Radionuclides. 5. Arsenic.


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As an example, if the user selects the third water quality parameter listed above (i.e.,

TDS, hardness and nitrate), the raw water concentration as well as finished water quality goals for these constituents are entered by the user. The tool calculates an approximate volume of water that would need to pass through RO/NF membranes to meet the required treatment goals based on these parameters.

Depending on the water quality parameters chosen, the tool would indicate one or more treatment alternatives that could potentially meet the treatment goals. The treatment alternative which addresses the selected water quality parameters is highlighted. In addition, a brief overview of issues relating to the suggested membranes (i.e., MF/UF, NF/RO, or both) is listed.

Whenever possible, the user is reminded that only use of membranes is considered in addressing the water quality concerns that were selected and that other non-membrane alternatives should be evaluated independently. Retrofitting an Existing Facility

This option allows the user to investigate the potential integration of membranes within an existing treatment plant to meet water quality goals. Typically, retrofitting an existing facility with any treatment process requires a careful evaluation of the (1) existing facility, (2) compatibility of membranes with existing practices, such as chemical use, (3) hydraulic profile within the plant, (4) site layout, and (5) cost. Because the purpose of the tool is only to illustrate the potential use of membranes within an existing plant, the user is required to select the treatment plant type that matches their facility. The seven plant types choices are:

1. Conventional water treatment (e.g., rapid mix, coagulation, flocculation, clarification, filtration, and disinfection).

2. Direct filtration plant (e.g., coagulation, filtration, and disinfection). 3. Conventional plant using ozone (e.g., coagulation, flocculation, clarification, ozonation,

filtration, and disinfection). 4. Oxidation and filtration plant (e.g., oxidation, filtration, and disinfection). 5. Softening plant (either single stage or two stage softening plant). 6. MF/UF plant (with or without pretreatment). 7. Conventional plant with GAC contact.

Once the user selects the plant type, the user is required to select one or more of five

water quality parameters. These parameters are similar to the list for a new facility and are modified slightly depending on the type of plant that is selected. For example, if the existing plant is an oxidation and filtration plant, iron and manganese are listed as a water quality parameter in lieu of DBPs.

Once the water quality parameters are selected, the output includes a typical treatment train for the type of plant chosen, and locations where membranes could be integrated to meet the treatment objectives are highlighted. As for the new facility option, the recommended treatment alternative for each water quality parameter is identified. The remainder of the output is similar to that of a new facility and includes a listing of some issues related to implementation of membranes, as well as references to the various sections of this report which have further information on this topic.


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The output from the tool is shown in an internet browser (i.e., Microsoft Explorer®) that could be either printed or saved. The user can also access previously stored inputs and outputs for a particular plant.



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CHAPTER 5 CONCLUSIONS AND RECOMMENDATIONS

CONCLUSIONS

This study concludes that the integration of membranes into WTPs has been successful, and membranes will continue to be viable treatment alternatives for utilities around the world. The availability of practical information about the issues associated with various aspects of their implementation has been limited due to membranes being a fairly new technology for the drinking water industry. This report examines the process and design implications associated with the integration of membranes into WTPs.

It is important to recognize that there are many different reasons for membrane integration, and these reasons impact how systems are designed and operated. The most common reasons for membrane integration are:

• Regulatory compliance, in particular MF/UF for turbidity removal, Cryptosporidium removal, and NF/RO for other regulated inorganic and organic compounds.

• Asset renewal, in particular, replacement of sand filters. • Treating challenging waters that cannot be treated using conventional treatment

processes. • Sea water and brackish water desalination. • Protection against future water quality threats such as virus and chlorine-tolerant

pathogens. • Providing water treatment with limited land availability, making use of the small

footprint of membrane treatment systems. • Reuse applications for areas where water sources are limited.

The literature review and utility interviews of this study identified several issues related

to the integration of membranes into WTPs. Some of the main integration challenges were identified as:

• Variable water quality and the impacts on membrane fouling. • Pretreatment influences on stable operations. • Maintaining integrity and minimizing fiber breakage, especially with MF/UF processes. • Waste disposal, due to limitations on volume and quality of the discharge. • Translation from pilot to full scale installation, especially in larger installations. • Integrating the new operating philosophy of membranes with existing WTP processes. • Predicting staffing levels. • Anticipating training needs for new operators. • Regulatory approval of new disinfection regime with membranes. • Hydraulic considerations, such as surge issues and flow balancing throughout the facility. • Preventing bottlenecks (e.g., backwash treatment and recycling). • Short timescales to meet regulatory time limits, particularly for Cryptosporidium removal

in the UK.


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As part of this project, a simple, decision making software, or tool, was developed to assist in the evaluation of how and where to install membranes into a treatment process to achieve specific water quality goals. Issues that may impact the facility are highlighted and discussed in the tool.

RECOMMENDATIONS

Recommendations for a successful membrane integration include:

Piloting

• Pilot challenging waters (i.e., those with variable solids, organic, or inorganic content) thoroughly. Pilot through all anticipated water quality changes and keep pilot plant settings as close to full scale design settings as possible.

• Perform a detailed analysis of the feed water. Anticipate likely foulants and develop chemical cleaning regimes to target these fouling compounds.

• Involve operators and maintenance staff during the pilot testing so that they gain knowledge and familiarity with the process.

• Involve regulators through the protocol and testing phases of the piloting program, even if not mandatory, to ease the transition through to full scale implementation.

• Consider retaining the pilot plant or constructing a small-scale unit for conducting additional testing once the full-scale plant is operational. This allows testing of alternative chemical cleaning regimes, alternative membrane formulations, and optimization of set-points without risk to the full-scale plant.

Planning

When planning membrane integration, the following suggestions are made: • Involve citizens through meetings, newsletters, and formation of citizens’ advisory

groups. • Talk with other utilities that have installed membranes and learn from their experiences. • Go to conferences to understand the issues and discuss them with other utilities. • Include the costs and schedule for piloting in the planning stages of the project. • Meet with regulators to discuss pilot test protocol and log removal credit criteria.

Design

The following were identified as design recommendations for successful membrane plant operation:

• Select a design flux that yields stable operation and flexibility in the event of a fouling episode.

• Size wash water recovery processes with sufficient capacity to avoid creating bottlenecks. If any backwash streams are recycled, pilot test to verify design criteria. This is particularly important when using membranes for treating the washwater.


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• Allow for flexible chemical cleaning regimes by providing space for additional chemical storage and dosing systems. Also consider provision for CIP systems even if not specifically required by the membrane system that is installed.

• Minimize hydraulic shock in the system by: - Ensuring sufficient backpressures are maintained for permeate, concentrate,

backwash, and chemical cleaning piping, as relevant - Provide smooth start and stop sequences for pumps - Perform hydraulic analysis and consider all failure modes, including power failure - Provide air release valves in piping

• Consider the hydraulic gradient and make best use of available head to minimize pumping costs.

Operation and Maintenance

O&M recommendations are as follows:

• Ensure operational staff has good process training to better understand water chemistry effects upon membrane performance.

• Involve operational and maintenance staff during the pilot, design, and construction phase so that they become familiar with the technology well in advance of start-up.

• To optimize the handling of fiber repair, O-ring and seal replacement, and membrane replacement (1) consider using contract staff for these routine tasks, if efficiency savings can be demonstrated, and (2) consider purchase of vacuum test equipment to speed up the detection of leaks and confirm successful membrane repair.



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APPENDIX A REASONS FOR MEMBRANE INTEGRATION

According to a survey conducted by United States Environmental Protection Agency USEPA (2001), the principal reasons for integrating MF/UF membranes are:

1. Compliance with existing and future regulations (with compliance being facilitated by using membrane filtration).

2. Providing an absolute barrier to protozoan cysts and bacteria (and in some cases, a significant level of virus removal by UF).

3. Improving operating efficiency through automation and ability to treat water of variable quality.

4. Using a smaller land area for the plant in comparison with a conventional filtration system.

5. Providing an additional barrier against hazards to public health. 6. Lowering both capital costs and O&M costs (in comparison with other technologies). 7. Providing a barrier for unfiltered systems that may lose unfiltered status. 8. Providing pretreatment preceding NF or RO. 9. Bolstering consumer confidence in water quality.

The main reason for installing NF and RO is to remove a dissolved contaminant or contaminants from water. Examples of these contaminants are dissolved salts or salinity, pesticides, and TOC. The most commonly cited reason for implementing membrane filtration has been to meet or exceed current and future regulatory requirements, and for MF/UF particularly the removal of particles, pathogens, and organics. However, because membrane technology has become cost competitive with conventional processes, as well as with some high rate processes, there are other factors such as elimination of operator error and smaller site requirements that are making it more attractive to water purveyors.

INTERNATIONAL WATER QUALITY REGULATIONS

Drinking water regulations and guidelines established in different countries worldwide have the common goal of protecting public health by maintaining the quality of their drinking water at an acceptable level. A full description of the entire range of drinking water regulations is beyond the scope of this project; however, the regulations pertaining to membrane integration are reviewed and discussed below.

World Health Organization

In 2004, the WHO published a set of guidelines for drinking water quality, which are based on health assessments performed by experts throughout the world. Because they are guidelines rather than regulations, they are not considered a major influence on the integration of membranes in WTPs around the world. The turbidity guidelines are fairly lenient in comparison with the criteria used by the USA and UK. The WHO guidelines for turbidity are 5 NTU to avoid customer complaints, and a median of 0.1 NTU to achieve effective disinfection


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(WHO 2004). While the intent of these values is to improve the public health in all nations, for many nations, they are a goal that can be achieved only if adequate financing is available.

The WHO guidelines address microbial contamination by establishing treatment targets for Cryptosporidium, rotavirus, and Campylobacter in raw water. The guidelines consider membranes to be effective for the removal of bacteria and protozoa, but less effective for virus removal. The guidelines are often adopted and tightened by developing nations, and the WHO recognizes the importance of supplying water with reduced health risks rather than imposing very rigorous standards that would not be affordable or enforceable in developing countries. The WHO guidelines are not viewed as the main influence in monitoring membrane filtration technology integration; however, they do parallel the regulatory direction of many countries.

United States of America

In the USA, drinking water regulations are developed and enforced by the USEPA. Individual states can adopt and enforce the regulations established by the USEPA, and they can also institute requirements or standards that are stricter than those established by the USEPA.

The passage of the Safe Drinking Water Act (SDWA) of 1974, and its amendments in 1986 and 1996, mandated improvements to water quality for the protection of public health. MCLs for individual contaminants have been established and treatment technologies to remove the contaminants have been identified. Some regulations set enforceable standards based on the level of removal that could be achieved using the "best available technology" (BAT).

The major categories of contaminants that are currently regulated in the USA, along with their effective dates, are listed in Table A.1. Pending and future regulations are listed in Table A.2.

Existing Regulations

The general regulations which are outlined below have influenced or promoted membrane integration.

Surface Water Treatment Rule. The SWTR is one regulation that has promoted the use of membranes to achieve compliance. It established inactivation and removal criteria for viruses and Giardia by requiring utilities to achieve specified levels of both turbidity removal and disinfection. Surface water plants and groundwater plants under the influence of surface water were required to achieve 3-log Giardia and 4-log removal/inactivation of viruses, as well as lower finished water turbidity levels by 1993. Some utilities struggled to meet these criteria with their existing conventional treatment processes.

In 1993, when the SWTR became enforceable, membrane technology was not widely used in North America (Freeman 2001), nor were the regulatory agencies of individual states in a position to readily approve the use of membranes to obtain log removal credit. By 1999, however, 38 membrane plants had been installed in the USA, and by 2001 this number had increased to 59 (Freeman 2001). Meeting the requirements of the SWTR had led many utilities to consider the use of membranes; however, even more utilities began to investigate membrane integration in response to the more stringent regulations that were at various stages of promulgation.


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Table A.1 Existing drinking water regulations in the USA

Regulation Proposed Final Effective Fluoride Nov. 85 April 86 Oct. 87 Trihalomethanes Feb. 78 Nov. 79 Nov. 83 8 volatile organic compounds (VOCs) (Phase I) Nov. 85 July 87 Jan. 89 SWTR Nov. 87 June 89 June 93 Coliform rule Nov. 87 June 89 Dec. 90 Lead and copper Aug. 88 June 91 Jan. 92* 26 synthetic organic contaminants, 7 inorganic contaminants (Phase II)

May 89 Jan. 91† July 92

MCLs for barium, pentachlorophenol (Phase II) Jan. 91 July 91 Jan. 93 Phase V organics, inorganics July 90 July 92 Jan. 94 Radionuclides (Phase III) - except radon April 00 Dec. 00 Dec. 07 Consumer confidence reports rule Feb. 98 Aug. 98 Sept. 98 Interim enhanced water treatment rule July 94 Dec. 98 Jan. 02‡ Stage 1 – long-term enhanced SWTR April 00 Jan. 02 Jan. 05

Disinfectants/disinfection byproducts Stage 1 July 94 Dec. 98 Jan. 02‡§ Filter backwash recycling rule April 00 June 01 Dec. 03 Arsenic June 00 Feb. 02 Jan. 06 * Starting date for tap monitoring; systems with more than 50,000 consumers; and

minor revisions effective January 2001. † MCL, MCL goal for atrazine to be reconsidered. ‡ For systems serving more than 10,000 consumers. § Effective January 2005 for systems serving fewer than 10,000 consumers.

Table A.2

Pending and future drinking water regulations in the USA Regulation Proposed Final Effective Coliform rule revisions§ - June 06 June 09* Radon Nov. 99 May 07 May 10* MCLs for aldicarb, aldicarb sulfoxide, aldicarb sulfone

May 05 May 06 May 09*

Disinfectants/disinfection byproducts Stage 2

Aug. 03 Jan. 06

Jan. 06‡

Stage 2 – long-term enhanced SWTR Aug. 03 Jan. 06 Jan. 06‡ Groundwater Rule (GWR) May 00 Jan. 06 Jan. 09 * Assumes regulation in effect three years after final promulgation. † Effective January 2005 for systems serving fewer than 10,000 consumers. ‡ Monitoring begins. § Revised Total Coliform Rule may become the Distribution System Rule.


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Interim Enhanced Surface Water Treatment Rule. The IESWTR, which was finalized in November 1998, includes numerous requirements that influenced utilities to begin seriously considering membrane integration.

1. It reduced allowable finished water turbidity from 0.5 NTU to 0.3 NTU. This standard applies to the combined filtered water, and at least 95 percent of the monthly turbidity measurements must meet the revised turbidity value. The maximum turbidity of the combined filter effluent is limited to 1 NTU.

2. Surface water systems that filter their supplies and that serve a population greater than 10,000 must achieve at least a 2-log (99 percent) removal of Cryptosporidium. Systems that meet the new turbidity limit of 0.3 NTU are to receive 2-log removal credit for Cryptosporidium.

The lower turbidity limits led many utilities to begin considering membrane processes, primarily MF and UF, for upgrading their treatment systems. Discussions in the water industry regarding the possibility of further Cryptosporidium removal/inactivation requirements caused still more attention to be focused on membranes, which were fast becoming a preferred means of achieving and maintaining compliance with IESWTR.

Stage 1 Disinfectant/Disinfection Byproducts Rule (DBPR). The Stage 1 DBPR became effective on January 1, 2002, for plants serving a population greater than 10,000.

MF and UF membranes do not actually remove DBPs, or alter the mechanism for DBP formation. However, because of their ability to remove pathogens their use could lower the required level of inactivation by a chemical disinfectant. The decision to lower the level of chemical inactivation would be governed by the appropriate State regulatory agency. Less chemical inactivation could result in reduced DBP formation. Thus, membrane filtration could help achieve the lower concentration of DBP required by the Stage 1 DBPR. It should be noted that coagulation upstream of MF/UF achieves DBP precursor removal. The amount of removal depends on the coagulant dose of coagulation conditions.

RO, and to a lesser degree, NF, can remove DBPs such as total THMs (TTHMs) and their precursors; however, the best practice is to minimize DBP formation rather than removing them after they are formed. The Stage 1 DBPR is not expected to be an incentive for facilities to add NF and RO systems.

Long Term Stage 1 Enhanced SWTR Rule (LT1ESWTR). The LT1ESWTR is aimed at protecting the public from exposure to Cryptosporidium. LT1ESWTR, which became effective in January 2005, expanded the IESWTR to cover systems serving fewer than 10,000 consumers.

The LT1ESWTR establishes a minimum 2-log removal criterion for Cryptosporidium. The IESWTR granted a 2-log removal credit for conventional and direct filtration plants that maintain their turbidity to less than 0.3 NTU; thus, well-operated plants with conventional filters could meet the requirements of the LT1ESWTR without changing their treatment practices. For plants that could not consistently meet the turbidity removal requirements of the LT1ESWTR, membrane technologies such as MF and UF became attractive means of achieving compliance.


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Pending Regulations

Two pending regulations will have an impact on the use of membrane technology in the USA. These are discussed below.

Long Term Stage 2 Enhanced SWTR Rule. The LT2ESWTR (USEPA 2003a), which is expected to be promulgated mid-2005, focuses on microbial pathogens in the source water, and is expected to become a major influence in inducing utilities to consider integration of membrane technology into their treatment train. This rule will apply to all public water systems that treat surface water or groundwater under the direct influence of surface water.

The proposed rule mandates a period of monitoring raw water for microbial content, and bases treatment requirements on the level of microbial contaminants in the supply. Utilities serving 10,000 or more consumers and using conventional treatment processes (i.e., coagulation, sedimentation, and filtration) will be required to conduct monthly monitoring of the raw water supply for Cryptosporidium, E. coli, and turbidity over a 24-month period.

Samples must be collected from the raw water supply, but after pretreatment such as presedimentation, off-stream storage, or bank filtration. As specified in the proposed rule, systems practicing conventional treatment and meeting turbidity limits will be presumed to provide 3-log removal of Cryptosporidium oocysts. Additional treatment requirements under the LT2ESWTR, based on average Cryptosporidium oocyst concentration in raw water, are summarized in Table A.3.

Systems can choose technologies to comply with additional treatment requirements from a “toolbox” of options, including improved watershed control, improved treatment system and/or disinfection performance, and additional treatment barriers such as membranes. Specific “tools” identified, and associated log treatment credits are summarized in Table A.4. It is emphasized that USEPA has requested comments on the proposed log credits presented in Table A.4, and may modify these assigned credits in the final rule based on such comments.

If the LT2ESWTR is promulgated by mid-2005, many utilities practicing conventional treatment may realize the need to provide further treatment to achieve an additional 1- to 2.5-log removal/inactivation of Cryptosporidium oocysts by mid-2011. Current research results indicate that the only serious contenders for inactivation of Cryptosporidium oocysts are ozone and UV irradiation. The proposed rule indicates that membrane filtration processes, such as MF and UF, are acceptable substitutes for inactivation processes.

Table A.3 LT2ESWTR requirements for Cryptosporidium removal or inactivation

Raw water Cryptosporidium concentration oocysts per Liter*

Additional treatment required for conventional treatment systems in full compliance with IESWTR

Cryptosporidium < 0.075/L 0.075/L < Cryptosporidium <1.0/L

1.0/L < Cryptosporidium <3.0/L Cryptosporidium > 3.0/L

No action required 1-log treatment† 2-log treatment‡

2.5-log treatment‡

Source: USEPA 2003a * Based on maximum value for 12-month running annual average, or 2-year mean if twice-monthly

monitoring is conducted. † Systems may use any combination of technologies to achieve 1-log credit. ‡ Systems must achieve at least 1-log of total treatment requirement using ozone, chlorine dioxide, UV,

membranes, bag/cartridge filters, or in-bank filtration.


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Table A.4

Microbial toolbox options, log credits, and design/implementation criteria Toolbox option Proposed log credit for Cryptosporidium inactivation

Watershed Control Program 0.5-log credit for State-approved program incorporating USEPA-specified elements. Does not apply to unfiltered systems.

Alternative Source/Intake Management

No presumptive credit. Systems may conduct simultaneous monitoring of LT2ESWTR bin classification at alternative intake locations or under alternative intake management strategies.

Off-Stream Raw Water Storage

No presumptive credit. Systems using off-stream storage must conduct LT2ESWTR sampling after raw water reservoir to determine bin classification.

Pre-Sedimentation Basin with Coagulation

0.5-log credit with continuous operation and coagulant addition; basins must achieve 0.5-log turbidity reduction based on the monthly mean of daily measurements in 11 of 12 previous months; all flow must pass through the basins. Systems using existing presedimentation basins must sample after basins to determine bin classification, and are not eligible for presumptive credit.

Lime Softening 0.5-log credit for two-stage softening (single-stage softening is credited as equivalent to conventional treatment). Coagulant must be present in both stages – includes metal salts, polymers, lime, or magnesium precipitation. Both stages must treat 100 percent of flow.

Bank Filtration (as pretreatment)

0.5-log credit for 25 ft setback; 1-log credit for 50 ft setback; aquifer must be unconsolidated sand containing at least 10 percent fines; average turbidity in wells must be < 1 NTU. Systems using existing wells followed by filtration must monitor effluent well to determine bin classification and are not eligible for presumptive credit.

Combined Filter Performance

0.5-log credit for combined filter effluent ≤ 0.15 NTU in 95 percent of samples each month.

Roughing Filters No presumptive credit proposed.

Slow Sand Filters 2.5-log credit, if used as secondary filtration step; 3-log credit if used as a primary filtration process. No prior chlorination.

Second Stage Filtration 0.5-log credit for separate second filtration stage; treatment train must include coagulation ahead of first filter. No presumptive credit for roughing filters.

Membranes Log credit equivalent to removal efficiency demonstrated in challenge test for device if supported by direct integrity testing.

Bag Filters 1-log credit, with demonstration of at least 2-log removal efficiency in challenge test. Cartridge Filters 2-log credit, with demonstration of at least 3-log removal efficiency in challenge test. Chlorine Dioxide Log credit based on demonstration of log inactivation using CT table. Ozone Log credit based on demonstration of log inactivation using CT table.

UV Log credit based on demonstration of inactivation with UV dose table; reactor testing required to establish validated operating conditions

Individual Filter Performance

1-log credit for demonstration of filtered water turbidity < 0.1 NTU in 95 percent of daily maximum values from individual filters (excluding a 15-minute period following backwashing) and no individual filter turbidity >0.3 NTU in two consecutive measurements taken 15 minutes apart.

Demonstration of Performance

Credit awarded to unit process or treatment train based on demonstration to the State, through the use of a State-approved protocol.

Source: USEPA 2003a


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A key reason for integrating membrane technology with other processes is that MF and UF are the means available to water systems to achieve compliance with the additional treatment requirements of the LT2ESWTR. It should be noted that compliance for the MF and UF systems will be based on daily integrity testing. Due to the lack of a reliable online integrity testing method, use of NF/RO membranes is not typically considered for Cryptosporidium removal.

Stage 2 DBPR. The Stage 2 DBPR, which is expected to be promulgated in 2005, utilizes a risk-targeted approach to better identify locations where consumers may be exposed to high concentrations of DBPs. Although the MCLs for TTHMs and the HAA5 will remain 0.080 and 0.060 mg/L, respectively, the monitoring and testing procedures will change to more closely represent actual long-term exposure conditions. Monitoring must include locations in the distribution system where high concentrations of TTHM and HAA5 have been detected, and compliance is based on a running annual average at those locations.

As with the Stage 1 DBPR, this rule will have little direct influence on integration of membrane technology, but it may play a part in a utility’s decision to integrate membranes to help minimize the amount of inactivation, for example by using chlorine, required during treatment.

Other Regulations. Other rules that influence the choice of membrane integration are targeted at specific contaminants. NF or RO are commonly used to remove such compounds as nitrates, sulfates, hardness, and DBP precursors such as TOC. As more rules are promulgated, the use of NF and RO would be expected to increase. The new MCL of 10 µg/L for arsenic is another example of new regulations that may impact membrane integration; however, few NF and RO systems have been installed for arsenic removal because other technologies are less expensive or less complicated to operate and maintain.

Log Removal Credits by State Regulatory Agencies

Many State regulatory agencies grant log removal credits for the removal of Cryptosporidium, Giardia, and viruses by certain membrane systems. These removals are based on pilot challenge studies, industry research, and NSF Environmental Technology Verification procedures. Sometimes, pilot testing is required on feedwater that is spiked with microbes to verify the log removal values to State officials. The log removals granted by State regulatory agencies vary from state to state, and many are specific to membranes manufactured by a particular supplier from a particular material or fiber. For example, in California, the DHS grants 2-log virus removal credit to Zenon’s Zeeweed®500 membrane system, and 3.5-log virus removal to the Zeeweed®1000 membrane and system. These two membrane systems have also been granted, or certified, in California with 4-log Giardia and 4-log Cryptosporidium removal. Other states grant these membranes similar Giardia removal credit and no virus removal credit, which illustrates the diversity of regulation on membrane technology across the country. Summaries of credits for pathogen removal by membrane systems are presented in USEPA (2001) and USEPA (2003b); however, new values are approved periodically, and individual States should be consulted to verify the current credit values.

European Union

Member States of the EU must comply with EU laws, which take precedence over the individual country’s law. Directives are one type of EU legislation, and require that each


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Member State comply with of the directive within a certain period. The methods and means of implementation are governed by each Member State.

The Member States include Austria, Belgium, Cyprus, Czech Republic, Denmark, Estonia, Finland, France, Germany, Greece, Hungary, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Poland, Portugal, Slovakia, Slovenia, Spain, Sweden, The Netherlands, and the UK. Member States must comply with Council directive 98/83/EC (Council of European Communities Directive 1998) on the quality of water intended for human consumption, which was adopted by the Council on November 3, 1998, (Epolitix 2003). Member States had to implement the water quality criteria presented in the directive into their country’s laws. The water quality limits are based primarily on the limits set by the WHO.

Criteria that might influence membrane integration pertain to the removal of turbidity and microorganisms. The directive does not include a finished water turbidity limit; however, the turbidity level must be ‘acceptable to consumers and [have] no abnormal change’ (Council of the European Union 1998). The directive also states that for ‘surface water treatment, Member States should strive for a parametric value not exceeding 1 NTU…in the water exiting the treatment works.’

Article 4, General Obligations, of the directive states that Member States shall provide drinking water that is ‘wholesome and clean.’ This definition implies that drinking water is ‘free from any microorganisms and parasites and from any substances which, in numbers or concentrations, constitute a potential danger to human health.’ This generic statement could encourage a utility to consider membranes, especially if the source water is at a known risk of microorganism contamination by Giardia and/or Cryptosporidium.

Other chemical limits specified by the directive include (1) arsenic, 10 μg/L; (2) bromate, 10 μg/L; (3) total pesticides, 0.50 μg/L; (4) TTHMs, 100 μg/L; (5) iron, 200 μg/L; and (6) manganese, 50 μg/L. For the most part, these values are similar to those used by the USA and WHO, and might impact the selection of membrane technology for a particular source water.

The effects of member State regulations on the integration of membrane technology for UK and France into water treatment processes are discussed below.

United Kingdom

The Water Quality Regulations of the UK are a set of legal standards for drinking water, which stem from the obligatory European Community (EC) directive, but some UK standards are more stringent.

The DWI is a government agency that conducts audits of water companies in England and Wales to verify that the treated water they produce is in compliance with the Water Quality Regulations. In the UK, the turbidity guideline is 0.4 NTU.

Cryptosporidium regulation. In 1999, the Water Quality Regulations were amended to include the requirements to minimize the threat to public health posed by the presence of Cryptosporidium in drinking water (DWI 2001, DWI 1999). The key components of this regulation include the following:

1. The finished or supplied water must contain an average of less than one oocyst per 10 L. This applies regardless of the viability of the oocyst (i.e., no credit is allowed for inactivated oocysts).


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2. Water that is deemed to be at significant risk of contamination by Cryptosporidium by a risk assessment must undergo continuous sampling (at a rate of 40 l/h of treated water) for Cryptosporidium and the sampling results must be reported to DWI on a daily basis.

3. If a utility installs treatment that removes particles larger than 1 micron in diameter, the continuous monitoring can be terminated (but only after a verification period).

In England and Wales, 332 sites were identified by risk assessments conducted prior to September 1999 as being at a significant risk of contamination by Cryptosporidium in the source water. About 50 percent of these sites were using groundwater supplies (DWI 2001). Continuous monitoring for Cryptosporidium began in April 2000. By September of 2002, 125,760 Cryptosporidium samples were collected from 207 sites (the remaining sites were probably removed from service because of the risk), and only seven samples collected from two sites were found to exceed the limit of one oocyst per 10 L of water (Drury 2002). The continuous sampling, or monitoring, for Cryptosporidium in the treated water is expensive. Drury (2002) reported that the capital cost of sampling equipment (including installation) ranges from $18,900 to $32,400 (£10,500 to £18,000; conversion rate = 1.8 US dollars per British pound sterling, £). The annual cost of sampling and maintenance ranges from to $13,500 to $18,900 (£7,500 to £10,500) per location per year. The analysis costs are about $75,600 (£42,000) per year per sampling location. This equates to over $100,000 per site for the first year of sampling. The high cost of monitoring for Cryptosporidium was one reason Dwr Cymru Welsh Water (DCWW) installed membranes for six of its small (0.3 to 1.3 mgd, or 1 to 5 ML/d), vulnerable sites. The average monitoring cost per site is about £80,000 per year, and the average present worth capital and O&M costs total about £500,000 (Masters et al. 2002). The payback period, once DCWW receives approval to discontinue monitoring, is expected to be six to seven years. The membrane systems listed in Table A.5 have been approved in England and Wales as “capable of continuously removing or retaining particles greater than 1 micron diameter.” The DWI does not currently recognize inactivation of Cryptosporidium as a public health measure. Instead, physical removal is required, and membranes are one of the best processes for achieving continuous removal. This regulation has been the main reason for the installation of MF and UF technology in the UK since 2000. The DWI has begun to consider the possibility of approving UV for inactivation of Cryptosporidium. Some utilities are planning to install UV downstream from conventional WTPs, regardless of whether the DWI approves it for inactivation. If UV is approved for inactivation, some utilities may choose conventional treatment followed by UV, rather than membranes. For many plants, the capital and O&M costs would be lower with UV, which may reduce the number of new membrane installations in the UK.

Daily integrity testing is required for membrane plants in the UK; however this alone is not adequate for DWI to approve the discontinuation of Cryptosporidium monitoring. A utility must first submit a Membrane Integrity Testing (MIT) proposal to DWI, along with the results of a new risk assessment (Drury 2002) before continuous monitoring can be terminated.


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Table A.5 Membrane systems approved for Cryptosporidium removal in England and Wales

Company Product AEA Technology Ltd. (Kerasep)

Cross flow filtration module (MF)

Dégrémont UK Ltd. Aquasource membrane module (UF) Kalsep Ltd. Kalmem polyethersulphone hollow fiber element (UF) Koch Membrane Systems Ltd.

Targa modules V and H (UF) TFC membrane elements (UF) 8131 membrane element (UF)

PCI Membranes Systems Ltd.

PCI membrane filtration system – spiral element (UF) PCI B1 module membrane – tubular element 1 (NF) PCI tubular C10 module and membrane system (incorporating tubular element 1)

MEMCOR CMF continuous microfiltration systems M1/M2 and M10 (MF) CMF-S continuous microfiltration system (MF)

X Flow BV X flow membrane filtration elements (UF) Pall Europe Ltd. Microza TM USV membrane Source: Data from DWI 2003

The water quality regulations for utilities in Scotland are under the authority of the Scottish Executive which has adopted European Union legislation as well as the more stringent DWI guidelines. Utilities such as Inverness strive to achieve water quality goals similar to those of the UK; however, some of the operating requirements, such as supplying secondary permeate to distribution, are different from those of the UK.

Scottish water supplies typically contain considerable color and high concentrations of TOC (e.g., 14 mg/L). The low population density has resulted in hundreds of very small water treatment plants. Scottish Water has installed several small NF facilities to remove color from upland surface water supplies to meet EU quality targets. The decision to provide membrane treatment for color removal was driven by cost factors: a membrane facility can be fully automated, thus continuous on-site staff is not required and the process can be monitored remotely. The remoteness of some of the facilities and the geology of the region has made installation of pipelines to larger, centralized treatment plants cost prohibitive.

France

In France, drinking water regulations are developed by the Environmental Ministry. The implementation of these regulations is the responsibility of prefects, who are local governing officials throughout the country. They control regional water-related issues, such as abstraction and discharge permits, flow regulation, approval of new water treatment facilities, and water quality.

Several institutions in France influence water regulations; however, the following main agencies deal with water intended for human consumption:

• Direction Regionale de l’Environnement, which is responsible for implementing European and French directives


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• Direction des Affaires Sociales et Sanitaires, which controls and monitors the quality of drinking water

In France, EU directives are implemented by the issue of décrets, arêtes, and circulaires.

Décret No. 2001-1220 (Décret 2001-1220 2001), the most recent décret, was created to comply with EU directive 98/83/EC (Council of the European Communities Directive 1998) and implements more stringent regulations pertaining to microorganisms, pesticides, and turbidity. The new regulations are for:

• E. Coli and enterococci in finished water • Sulfite-reducing bacteria in the finished water, which if detected, will trigger an

investigation for Cryptosporidium in the distribution system • Turbidity (at the entrance of the distribution system must not exceed 1 NTU)

The décret also states that water treatment plants should install the best available process,

and membrane technology is recognized as one means of achieving this goal. This, coupled with the new requirements for the removal of turbidity and microorganisms, is influencing the integration of membrane technology in France. Water companies in France view membranes as a reliable means of removing particles and maintaining safe drinking water.

Another influence contributing to the use of membrane technology in France is the low chlorine residual maintained in the distribution systems. The concentration of chlorine residual at the entrance to distribution system must be less than 0.2 mg/L (Décret 2001-1220 2001), and the regulations state that it must be as low as possible without compromising public health. The desire for a low chlorine residual is driven by taste preferences, yet the preference for membrane use is likely to be influenced by the realization that the restrictions on chlorine residual limits the effectiveness of disinfection in the distribution system.

Many WTPs and WWTPs in France use membrane technology. This is somewhat influenced by the dominance of two major water companies (Vivendi and Ondeo Dégremont) in France. A British delegation that toured several French membrane plants in 2002 compiled a list of membrane systems, which are shown in Table A.6.

This list includes membranes used by both water and wastewater industries. The findings of the delegation DTI (2001) suggested that membrane use in France is influenced by the extensive research and development by the two main water companies, their subsidiary membrane manufacturers, and several independent research institutions, including Techno-Membranes, Institut de Recherches sur la Catalyse, and the Institut Européen des Membranes. Each institution has its own research objectives, but the common objective is to facilitate and promote the use of membrane technology in various applications and industries.


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Table A.6 Membranes approved in France

Manufacturer Membrane Type SCT Membralox Ceramic MF Memtec Limited MEMCOR Organic MF 3 M Series 100 prefilter Organic MF Zenon Zeeweed Organic MF Koch Romicon PM PW Organic UF Techsep Kerasep series Ceramic MF/ UF Aquasource BCDA Organic UF Dow Chemical

Filmtec NF 70 Filmtec NF 90 Filmtec NF 200B Filmtec BW 30 Filmtec SW 30 HR

Organic NF Organic NF Organic NF Organic RO Organic RO

Eurodia NEOSEPTA ACS and CMX Organic ED EIVS AMV-CMV Sélémion Organic ED Source: Department of Trade and Industry (DTI) 2001

Australia

The private and public (i.e., government-owned) utilities of the Commonwealth of Australia strive to meet the water quality outlined in the ADWG, which were written by a joint committee of the National Health and Medical Research Council (NHMRC) and the Agriculture and Resource Management Council of Australia and New Zealand (ARMCANZ) (NHMRC and ARMCANZ 1996). These guidelines are not enforced by legislation, but by the issue of licenses, charters, contracts, and memoranda of understanding (CRC 2002), which provide the incentives for compliance in Australia.

According to the ADWG, for disinfection to be effective, the turbidity of finished water must be less than 1 NTU (NHMRC and ARMCANZ, 1996). Some utilities are following the US or UK regulations, and require a filtered water turbidity much lower than 1 NTU, and this is influencing the use of membranes in Australia.

Some guidelines applicable to specific compounds warrant the use of membranes. The ADWG for arsenic is 7 μg/L, which is lower than the limits established by the USA, UK, EC, and WHO. MF and UF membranes can be used to remove properly coagulated arsenic, or NF/RO could be used to remove dissolved, ionized arsenic.

COSTS

One of the reasons for the increasing use of membrane technology is the decline in its cost in recent years. Freeman (2001) reported that between 1995 and 2001, the bid costs for membrane equipment have decreased by about 35 percent.

Comparison between the costs of low-pressure membranes and conventional filtration systems indicates that membranes are cost-competitive. For example, the total cost of water production at Ennerdale WTP is $47 MG (£26 ML), and the operating costs of the MF plant are $40 MG (£22 ML) (Hillis 2001).


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Advances in NF and RO membrane technologies have helped reduce the costs over the past 20 years. New designs of membrane elements and new materials have lowered the driving pressure requirements for NF and RO systems without compromising rejection ability (McClellan and Johnson 2001). For example, developments in RO technology between 1980 and 1998 resulted in a decrease in driving pressure at a small RO plant in Florida from 550 psi (38 bar) to 187 psi (13 bar), which results in lower energy costs, and thus, reduces operating costs.

Some of the newer RO membranes have greater permeability, with specific flux rates 20 to 60 percent higher than older generation membranes. However, the impact of increased permeability on the overall downstream system needs to be carefully considered. For instance, when using highly permeable membranes, the brine flow may be too low, which could result in increased fouling. In addition, the flux through lead elements could be significantly higher than later stages. A thorough evaluation by computer modeling and pilot testing can verify that the use of new low pressure membranes in existing RO/NF plants can save operating costs and increase production.

DESIGN AND OPERATION ISSUES

Sometimes the decision to install membranes is influenced by factors such as space requirement or degree of automation.

Williams, Wert, and Dempsey (2002) reported that the land area of a membrane plant was smaller than that of a conventional plant, and became the determining factor in the decision to pilot test MF for treating a high-color surface water. The area was a key factor because the available space was in a floodplain, where flood protection would be costly and critical.

Although compliance with turbidity limits was the primary motive for choosing membranes for expansion of the Marco Island Lime Softening Water Treatment Plant, in Florida, it was noted that the land area required for the submerged UF system was 40 percent less than would be needed for conventional sand filters (Manning, Duranceau, and Anderson 2001). Likewise, for pretreatment of seawater for RO, UF systems require up to 50 percent less land area than a conventional treatment system (Galloway and Minnery 2001).

As mentioned previously, Scottish Water relies on the high level of automation and the ability to remotely operate the small NF systems in Scotland. Being able to operate systems remotely is a driver for many utilities.



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APPENDIX B TECHNICAL ISSUES OF MEMBRANE INTEGRATION

The technical aspects of the integration of membrane technology into drinking water treatment are summarized in this chapter as a basis of understanding and a point of reference for subsequent discussions of integration issues faced by utilities. The following references provide a more comprehensive discussion of membrane systems, their operation, and regulatory aspects:

• The Desalting and Water Treatment Membrane Manual: A Guide to Membranes

for Municipal Water Treatment (2nd Edition; Chapman Wilbert et al. 1998) • Low-Pressure Membrane Filtration for Pathogen Removal: Application,

Implementation, and Regulatory Issues (USEPA 2001) • Membrane Filtration Guidance Manual (USEPA 2003b) • Integrated Membrane Systems (Schippers et al. 2004) • Chapter 11 of the Water Quality and Treatment, A Handbook of Community

Work Supplies (Taylor and Weisner 1999)

GENERAL REVIEW OF MEMBRANE TECHNOLOGY

The membranes used in water treatment can be defined as a thin film barrier that selectively removes some of the constituents such as solids particles, colloidal species, and dissolved organic and inorganic constituents from the water. The principal membrane types used in water treatment include the following:

• MF • UF • NF • RO • Electrodialysis (ED) and electrodialysis reversal (EDR)

These membranes differ from each other in several aspects (Table B.1) such as driving

force, material, configuration, removal mechanism, and rejection ability. Processes using MF, UF, NF, and RO membranes rely on pressure to move water across the membrane. Pressure is applied on the feed side of the membrane to separate the water into permeate, or filtrate that passes through the membrane, and rententate, or reject or concentrate, that does not pass through the membrane and contains the rejected constituents of the feed water.

MF and UF membranes are porous and the removal mechanism is primarily sieving. Particles and colloids that are larger than the membrane pores are retained, while smaller particles, colloids, and dissolved species pass through the membrane. RO and NF membranes are semi-permeable membranes that allow transport of water across them by diffusion, while limiting the diffusive transport of contaminants.

ED, in contrast, relies on electrical potential to transport ionic species across charged membranes. In the EDR process, the polarity of the electrodes that supply the electrical potential is periodically reversed, interchanging the fresh product water and wastewater to allow flushing


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and removal of any built-up scale. ED/EDR processes do not remove uncharged constituents and require the removal of particulates upstream.

Table B.1

General description of membrane systems commonly used in water treatment

Membrane type Driving force Mechanism of separation

Membrane structure

MF Pressure Physical sieving Macropores UF Pressure Physical sieving Macropores

NF Pressure Physical sieving +

diffusion + exclusion

Dense membrane phase & nanopores

RO Pressure Physical sieving +

diffusion + exclusion

Dense membrane phase

ED/EDR Electrical potential Diffusion Dense membrane

phase

Rejection Capabilities of Membranes

The rejection capabilities of membrane systems vary, depending on the removal mechanism and membrane material. In general, MF and UF membranes remove only particles or colloids, whereas NF, RO, and ED/EDR are used to remove dissolved species. Figure B.1 illustrates the typical sizes of various contaminants in water and the applicable particle size range for each membrane system.

MF and UF Membranes

MF and UF membranes have a macroporous structure which allows passage of water, while retaining all constituents larger than the macropore size. Because the nominal pore size differs between MF and UF membranes, it may become the determining factor in the selection of membranes for a given application. The commercially available MF and UF membranes have nominal pore sizes of approximately 0.1 µm and 0.01 µm, respectively.

MF and UF membranes are typically integrated into a WTP because of their ability to reject certain pathogens, such as Cryptosporidium oocysts and Giardia cysts. UF membranes, with their smaller pore size, are capable of achieving higher virus rejection than MF membranes, and some utilities install UF rather than MF for that reason. It should be noted, however, that virus inactivation by disinfection (e.g., chlorination) requires relatively low doses of disinfectant and contact time, and State regulatory agencies generally specify a minimum amount of disinfection downstream of membranes as part of a multi-barrier approach to treatment; therefore, the impetus for installing UF instead of MF for virus rejection is not as strong for most utilities.

The pore-size cut-off definition described above as nominal is commonly used for differentiating MF and UF; however, there is a trend to better define the difference between MF and UF by conducting challenge testing with various microorganisms (e.g., Pseudomonas


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diminuta, MS2 phase, and PRD1). Research in this area is on-going, (Mysore et al. 2003), and a more rigorous pore size determination may become an industry standard in the future.

Figure B.1 Relative sizes of various constituents in water and nominal size ranges for membrane systems (ED/EDR not shown). Source: adapted from Taylor and Weisner (1999)

NF and RO Membranes

NF and RO membranes are not characterized as having pores like MF and UF membranes, but are considered to be a dense, membrane phase. Some investigators have reported that there is a pore structure within NF membranes, and that the pore size is in the range of nanometers (nm). Due to the lack of a discrete pore structure in NF and RO membrane material, the rejection capability is identified by the MWCO size classification. The rejection of a given contaminant is dependent on its molecular weight, the degree of dissociation of the species, the polarity, its molecular structure, the membrane chemistry, and the chemistry of the feed water. In general, if a molecule is larger than the MWCO of the membrane, the molecule is rejected by the membrane. If the molecular weight of the molecule is smaller than the membrane’s MWCO, the degree of rejection depends on the variables listed above.

The main distinction between RO and NF membranes is their rejection capability. RO membranes typically achieve a high rejection of most dissolved substances, including monovalent ions. The rejection capability of NF membranes is less, particularly for the monovalent ions. NF systems are sometimes referred to as ‘loose’ RO membranes due to their ability to pass some of the dissolved species that would be rejected by RO membranes. Operation of NF membranes requires lower driving pressure when compared to RO membranes,

RelativeSizes

SeparationProcess

Molecular Weight (approximate)

Size, Microns

Ionic Range

0.001

MolecularRange

0.01

MacroMolecular

Range

0.1 1.0

Micro ParticleRange

10 100

Macro Particle Range

1000

100 1,000 100,000 500,000

BacteriaViruses

Metal Ions Algae

Clays Silt

Asbestos Fibers

Cysts SandNOM

NanoFiltration

20,000

Aqueous Salts

Molecules

Humic acids

ReverseOsmosis

Ultrafiltration

Microfiltration

Conventional Filtration

RelativeSizes

SeparationProcess

Molecular Weight (approximate)

Size, Microns

Ionic Range

0.001

MolecularRange

0.01

MacroMolecular

Range

0.1 1.0

Micro ParticleRange

10 100

Macro Particle Range

1000

100 1,000 100,000 500,000

BacteriaViruses

Metal Ions Algae

Clays Silt

Asbestos Fibers

Cysts SandNOM

NanoFiltration

20,000

Aqueous Salts

Molecules

Humic acids

ReverseOsmosis

Ultrafiltration

Microfiltration

Conventional Filtration


164

which also means that energy requirements for NF membranes are lower than for RO membranes.

When considering integration of NF and RO membranes for removal of dissolved species at a WTP, it is important to recognize the differences in performance and operating costs. With adequate pretreatment, both NF and RO can perform well to meet the treatment objectives; however, with the diversity of products available in the drinking water industry, it is prudent to research all of the available options to get the most cost-effective treatment system for a specific application. For instance, to meet a certain contaminant removal goal, use of NF membranes may result in larger flow being treated by membranes, because less bypass flow is used. The use of RO membranes may result in treatment of smaller volume of flow by membranes and a higher bypass flow. With these flow differences, the capital costs for the RO system could be lower than NF system; however, the energy costs could be higher for the RO than the NF system, countering the cost savings of initial capital investment. These issues should be considered when selecting between the two types of membranes.

NF and RO membranes are not typically installed for gaining disinfection credit (i.e., rejecting pathogens like Cryptosporidium or bacteria). This is because the current design of NF/RO membrane systems does not allow for routine verification of the integrity of the system. Even though these membranes are capable of achieving near complete removal of pathogens, disinfection removal credits are typically not accredited to them. Because, these systems typically require significant pretreatment to remove particles, removal of cyst-sized particles generally occurs upstream of NF or RO.

The following text includes examples of NF/RO integration for specific water quality goals.

Dissolved Organic Carbon Rejection. Removal of DOC by NF and RO has been researched by several investigators. Typically, DOC removals greater than 95 percent can be achieved with RO membranes (Clair et al. 1991; Lynch and Smith 1987; Veerapaneni et al. 2001; Escobar, Hong, and Randall 2000; Kouadio and Madeleine 2002). The removal is typically dependent on the charge of the organics and the character of the membrane surface. Other parameters that affect rejection of organics by RO membranes include hardness, pH, and ionic strength.

Rejection of organics by NF membranes is also high, and also depends on the MWCO of the membrane (USEPA 2000; Taylor, Thompson, and Carswell 1987; Agbekodo, Legube, and Cote 1996; Cho, Amy, and Pellegrino 1999; Hong and Elimelech 1997; Chellam and Taylor 2001; and references therein). Kouadio and Madeleine (2002) reported greater than 90 percent DOC rejection using Filmtec’s polyamide (PA) composite NF membrane, which also greatly reduced the THM formation potential of the source water. Lower DOC rejection (i.e., 30 percent) was reported by Veerapaneni et al. (2001), thus showing the variability in removal that can be obtained with NF. Total Dissolved Solids or Salt Rejection. Because of their ability to achieve removal of monovalent and divalent ions, RO membranes are commonly used for removal of TDS, particularly when the concentrations of monovalent ions are high. Depending on the salinity of the water, several types of RO membranes are commercially available for treatment, and these can be evaluated to determine the membrane that requires the lowest energy consumption. For instance, for the removal of TDS from low salinity water sources, lower pressure, brackish-water RO elements are commonly used, because their energy consumption is lower than that of typical RO elements. Use of NF membranes is also common for salinity removal from brackish water;


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however, NF membranes should be selected carefully, because their rejection of various constituents varies from 15 to 80 percent, depending on the type of the membrane. For seawater desalination, RO membranes are widely used because of their ability to reject sodium and chloride, the predominant monovalent species in seawater. Use of NF membranes for seawater desalination is also being considered. A recent study by Cheng et al. (2003) showed that dual-permeate staged NF membranes were able to lower the TDS from about 37,000 mg/L to less than 300 mg/L. Only one of four available NF membranes in the pilot trial achieved this level of salt rejection. The applied pressure in the first stage was 560 psi (37 bar), and in the second stage, 230 psi (16 bar). This type of configuration reduces the energy consumption for seawater desalination, but the drawback is that the recovery of the system is limited to 38 to 42 percent, compared to recoveries of up to 60 percent that could be achieved with seawater RO membranes. The City of Long Beach plans to conduct demonstration-scale evaluations of this system in the near future.

Hardness Rejection. Several water utilities are using NF membranes to replace conventional precipitative lime softening. For example, the City of Deerfield Beach recently installed a 10.5 mgd (40 ML/d) NF system, which comprises two different types of NF membranes (Kiefer and Jackson 2002). This plant uses a two-stage, hybrid membrane design to lower the hardness concentration from 248 mg/L as CaCO3 to about 54 mg/L as CaCO3. One of the main drivers for installing membranes at Deerfield Beach was the multiple water quality goals for the plant such as lowering the concentrations of hardness, color, and DBP precursors, and NF technology achieved those goals.

Arsenic Rejection. Both arsenite [As(III)] and arsenate [As(V)] can be removed by NF and RO membranes, and a general rule of thumb is that the ability of the membrane to remove arsenic is correlated with its ability to remove sodium chloride. This was confirmed by Yi et al. (2002). For one NF membrane with 99.5 percent sodium chloride (NaCl) rejection, 99 percent arsenate removal was achieved; however, for the membrane with only 50 percent NaCl rejection, arsenate removal was about 70 percent. Yi et al. (2002) also presented data showing that as the pH increases, arsenite and arsenate removal improves for some of the NF membranes that were tested. This pH relationship has also been observed by other researchers, and is attributed to increased repulsion by negative electrostatic charges at higher pH (Kim et al. 2002).

Perchlorate Rejection. Perchlorate removal can be achieved by NF and RO membranes; however, the cost of these systems relative to other technologies is high and relatively few membrane systems are expected to be installed for perchlorate removal. In pilot scale studies Yoon et al. (2003) reported perchlorate rejection in the range of 94 percent to almost complete removal by NF and RO membranes, respectively. However, since perchlorate represents the highest oxidation state of chlorine, its affect on NF/RO membranes over long period of time is not clear and should be further investigated. The authors stated that no change in membrane rejection ability was observed over the 30-day pilot test period.

Fluoride Rejection. NF/RO systems are rarely installed for fluoride removal; however, in Finland, the Mynämäki municipality installed a NF system (using FILMTEC NF270-400 membranes) to remove multiple contaminants, including fluoride, from a groundwater source (Keskitalo et al. 2002). The fluoride concentration was lowered from about 2.8 mg/L to less than 0.52 mg/L, and the aluminum from about 1 mg/L to less than 0.05 mg/L. TOC removal was about 89 percent, and as a result, a reduction in the chlorine demand at the plant was observed.


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Endocrine Disrupting Chemical (EDC) and Pharmaceutical and Personal Care Products (PPCPs) Rejection. EDCs and PPCPs can be removed with RO membranes. Vernon (2003) reported that RO membranes at the Water Campus in Scottsdale removed various pharmaceuticals from tertiary treated wastewater to less than detection limits. Deshmukh et al. (2003) also reported that RO lowered pharmaceuticals to less than detection limits in a reuse facility. Huang and Sedlak (2001) reported that greater than 90 percent removal of steroid hormones could be achieved with RO membranes, and Adams et al. (2002) reported good removal of several different antibiotics by RO membranes. Removal of these contaminants by NF membrane would depend on the characteristics of these compounds as well as those of NF membrane. Agenson et al. (2002) conducted bench-scale evaluations of several NF membranes to observe the rejection of EDCs such as 17β estradiol and ethylnyl estradiol. The two NF membranes tested had salt rejections near 55 to 60 percent, and achieved from 57 to 72 percent rejection of 17β estradiol and from 68 to 95 percent removal of ethylnyl estradiol. As expected, the lower the MWCO of the NF membrane, the higher the rejection of the EDCs that were tested. These results were also confirmed by bench-scale tests that were conducted by Gallenkemper, Wintgens, and Melin (2002).

Electrodialysis/Electrodialysis Reversal

ED/EDR processes are used for removal of charged, dissolved substances such as nitrates, perchlorate, or salinity, and use membranes that allow passage of either anions (anion-transfer membranes) or cations (cation-transfer membranes) as the removal mechanism. The basic module consists of alternating anion-transfer and cation-transfer membranes which are separated by a flow spacer. As the water passes between these membranes under the applied electrical potential, cations migrate towards an anode through cation-transfer membranes and anions migrate towards a cathode through anion-transfer membranes. Because the process is driven by electrical potential, ED/EDR process is not capable of removing uncharged species, such as microorganisms or uncharged, organic molecules.

ED/EDR membranes are not used for municipal drinking water plants that require particle removal for disinfection, because water does not pass through a membrane (except for a possible pre-filter upstream of the ED/EDR systems) in the process. As a result, the pressure loss through the system is relatively low (i.e., 15 psi). ED/EDR systems are usually installed for removing a particular contaminant, and are somewhat specialized membrane systems that are not typically integrated into a larger, existing WTP.

Some examples of ED/EDR integration to meet specific water quality goals are given below.

Hardness Removal. ED has also been installed for softening and TDS removal. The Foss Reservoir Master Conservancy District (FRMCD) of Oklahoma, has used ED since 1974 to effectively remove hardness, sulfate, and TDS from reservoir water (raw water quality; 900 mg/L hardness, 1,000 mg/L sulfate, and 1,600 mg/L TDS; Allison and Touchstone 2003). The ED system had performed well, but was subject to calcium sulfate scaling and poor rejection of DBP precursors. The FRMCD had also switched from coagulation with aluminum salts to ferric chloride because of residual aluminum precipitation in the ED stacks.

Perchlorate Removal. A recent development is that EDR is capable of achieving good removal of perchlorate. Based on the results from a pilot study, Booth et al. (2000) reported that perchlorate removal in the range of 70 to 94 percent is possible when using a 2 to 4 stage EDR process. Perchlorate rejection was similar to that of TDS rejection.


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Types of Membrane Systems

As discussed above, membrane systems can be grouped into two main categories (1) those that remove particulates and colloids (i.e., MF and UF systems), and (2) those that remove dissolved species (NF and RO). ED/EDR also removes dissolved species, but because of it’s specialize application, it will be discussed separately. Below, a brief overview of types of MF/UF and NF/RO systems is provided. Microfiltration and Ultrafiltration Systems The MF/UF systems that are currently available for water treatment vary significantly in terms of membrane material, membrane geometry, system configuration, and operation. These characteristics are summarized in Table B.2, and discussed in the following sections. Membrane Material MF/UF membranes are made from either organic or inorganic materials. Organic membranes are comprised of polymers such as CA, PS, PA, PES, polyacrylonitrile (PAN), PVdF, polyethylene, PP, or polycarbonate. They are typically referred to as polymeric membranes.

The most common inorganic membrane material is ceramic, which is comprised of oxides, nitrides or carbides of metals such as aluminum, zirconium, or titanium. Ceramic membranes are mechanically stronger than organic membranes, are tolerant to a variety of oxidants, such as chlorine, and can handle high or low pH and temperatures.

Ceramic membranes are primarily used in industrial applications and are not presently used for potable water production for two main reasons (1) the capital cost of ceramic membranes and their larger footprint has historically made them a less attractive alternative; and (2) recent advancements to organic membranes have increased their resistance to oxidants, and thus more versatile in drinking water applications. There are several companies that continue to research ceramic membranes, and it is possible that they may become a more cost-competitive alternative for drinking water treatment in the future.

Polymeric membranes are used almost without exception for potable water treatment, and the remaining discussion focuses on this type of membrane.

The materials that are commonly used for polymeric membranes for MF/UF systems are listed in Table B.3. The diversity of materials is reflected in the wide array of characteristics that each type possesses. For instance, PP membranes are not resistant to oxidants. CA membranes, while resistant to oxidants such as chlorine, have limited operating pH range. PVdF membranes are resistant to oxidants as well as tolerant to a wider range of pH than CA membranes. Membranes made of PS and PES materials offer the greatest pH range over any other available material (except ceramic membranes).

Each type of membrane material has several advantages and disadvantages for its use on a specific water source; thus, the selection of membrane materials is critical for the successful integration of membranes into a treatment plant. For example, in warm climate surface waters, many utilities practice the addition of an oxidant such as chlorine to control biological activity. When using membranes to treat this water, an oxidant-resistant membrane material would obviously be required. PP, for example, would not be a suitable material for this application.

The range of pH that a membrane will encounter is another consideration when selecting a membrane material. For example, membranes installed downstream of lime softening, which can have pH values as high as 11, would need to be tolerant to such a pH. CA membranes


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material can hydrolyze at high pH, and would not be suitable for application downstream of a lime softening process, unless the pH was reduced prior to MF/UF treatment.

The pH range used for cleaning membranes must also be considered and evaluated based on the types of foulants that are present in the feed water. Cleaning regimes are discussed later, but mentioned here because the cleaning regime for materials like CA is limited by a specified pH range, and cleaning within this pH range may or may not be effective in restoring membrane permeability.


Table B.2

General characteristics of commercially available drinking water membrane systems Characteristic MF UF NF RO ED/EDR Membrane material

CA, PS, PA, Polycarbonate,

PP, PVdF, Ceramic

CA, PS, PES, Polyvinylpyrolidone, PAN,

PVdF

PA, Polypiperazinamide

CA, PA Modified polystyrene

Membrane configuration

Hollow fiber, Tubular,

Spiral

Hollow fiber, Tubular, Spiral, Multibore

Hollow fiber, spiral

Hollow fiber, spiral

Plate and frame

Nominal pore size

0.075 to 8 μm 0.0015 to 0.09 μm 0.001 to 0.009 μm <0.001 μm

NA*

System configuration

Encased (Cartridge) Submerged

Encased (Cartridge) Submerged

Encased Encased Electrical/ Pressure

Operating pressure

3 to 40 psi for cartridge systems, -3 to -12 psi for vacuum systems

Approx. 100 psi Approx. 1,000 psi

15 psi

Flow regime Dead-end, Cross flow

Dead-end, Cross flow

Crossflow Crossflow Dead-end, Cross flow

* NA = Not applicable, because water is not passing through a membrane.

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Table B.3 Commercially available MF/UF membrane materials

Membrane manufacturer

Configuration Chemistry Chlorine tolerant

Flow pattern

Alignment

Aquasource (UF) Encased Cel Yes In-out Vertical Hydranautics (UF)

Encased and Submerged

PES Yes In-out Vertical

Inge (UF) Encased PES (multibore)

Yes In-out Horizontal or Vertical

Koch (UF) Encased PES Yes In-out Vertical Memcor/USF (MF)


PP No Out-In Vertical

Memcor/USF (MF)


PVdF Yes Out-In Vertical

Norit/Xflow/ (UF)

Encased PES Yes In-out Horizontal or Vertical

Pall (MF) Encased PVdF Yes Out-In Vertical Polymem (UF) Encased PS Yes Out-in Vertical Zenon 1000 (UF) Submerged PVdF Yes Out-In Horizontal

and Vertical Zenon 500 (UF) Submerged PVdF

(coated) Yes Out-In Vertical

Note: Membrane chemistry abbreviations: CA = cellulose acetate; PES = polyethersulfone; PP = polypropylene; PS = polysulfone; PVdF = polyvinylidenefluoride

Membrane materials are also categorized as hydrophilic (i.e., “water-loving”) or

hydrophobic (i.e., “water-hating”), and these properties will impact performance when treating various waters. For example, if feed water contains high concentrations of organic material, hydrophilic membranes are usually recommended, because organic compounds adsorb less onto hydrophilic membranes than onto hydrophobic membranes. Membrane manufacturers strive to balance these two properties for their membrane materials to produce a membrane with sufficient permeability to water as well as with the ability to repel compounds or constituents that tend to foul membranes. For utilities wanting to install membranes into a treatment train, a thorough knowledge of the feed water quality, as well as the characteristics of the membranes under consideration is critical to the success of membrane integration.

Microfiltration/Ultrafiltration Membrane Structure and Geometry. Membrane fibers typically have two layers of material (1) the membrane film, and (2) a sublayer support. The membrane film, or ‘skin’ acts as the filtration barrier. This thin membrane skin is supported by a thicker and more porous sublayer, which does not offer any rejection or significant hydraulic resistance.

There are two categories of these layer combinations (1) asymmetric, and (2) composite. In asymmetric membranes, the membrane skin and the support structure are made from the same material, whereas in composite membranes, the membrane skin and the supporting layer are made from different materials, which are bonded together. Typically, composite membranes


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have greater strength due to the support layer; however, there is the potential for delamination of composite membranes. In recent years, asymmetric membranes are more commonly available.

The most common MF/UF membranes in potable treatment are produced as hollow fibers, with water flowing either from the inside of the fiber to the outside, or vice versa, depending on the membrane system supplier. The diameter of these hollow fibers is typically about 1 mm, and several thousand of these hollow fibers are bundled together to make one module, or element. Modules are the smallest, replaceable unit in a membrane system. There are also spiral-wound UF membranes, but these are currently not in widespread use in the drinking water industry. Spiral-wound membranes are commonly used for NF/RO, which is discussed in a later section of this report.

Microfiltration/Ultrafiltration Membrane Developments. As more and more utilities install MF and UF systems for drinking water treatment, a specialized market is emerging for system improvements and replacement parts. For example, membrane modules have been developed for replacement in existing systems. One new design is the multipore capillary membrane fiber (Inge AG, Greifenberg, Germany), which consists of seven internal capillaries of PES membrane, which are supported by a honeycomb structure. This UF membrane has an apparent MWCO of about 100 kilo Daltons (kDa). It is claimed that the honeycomb support structure offers increased stability and durability over the traditional hollow fiber membranes which are currently available. This design is relatively new, and has been pilot-tested in Germany (Berg, Koenhen, and Wunram 2002). There are several small installations in Germany, Switzerland, and in the USA, and some can treat up to 150 NTU (Inge AG 2005).

Another new design for MF and UF systems is a capillary system developed by PURON (Aachen, Germany; Voßenkaul, and Schäfer 2002). The PURON membrane module has one end where the fibers are securely potted, and the other end of the fibers is essentially free-floating. The mechanical strength of the fibers has been improved by use of a braided membrane structure, and the intended use for these modules is both water and wastewater treatment. Diffused air is applied within each module to keep the fibers vertically aligned and to prevent tangling. These modules can be mounted with the potted end at the top position or the bottom position, depending on the application. Pilot- and demonstration-scale evaluations are being conducted, mostly in Germany and Belgium (Puron 2005).

Traditionally, MF/UF membrane manufacturers have supplied completely assembled membrane system including membrane fibers, modules, backwash systems, and controls. A recent development in the membrane industry is the availability of customized membrane systems, where membrane modules are purchased from a supplier, and the remaining infrastructure is designed by an engineering firm. The resulting design is customized for the utility and application. Roquebert et al. (2001) reported that a customized submerged UF system was evaluated, but not selected, by Sheboygan, Wisconsin, for treating Lake Michigan water. This type of system may be cost effective in some evaluations; however, having a unique and individual membrane plant may present challenges during troubleshooting of potential problems such as backwashing hydraulics, flow velocities, etc.

Microfiltration/Ultrafiltration System Configuration. MF and UF membrane systems are available in two configurations 1) encased or cartridge, and 2) immersed or submerged. These configurations are depicted in Figures B.2 and B.3. Encased systems have membrane modules that are housed in individual vessels. Water is pumped to the vessel and the applied pressure forces water through the membrane fibers either in an inside-to-outside or outside-to-


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inside flow pattern, depending on the manufacturer. The operating pressure for encased membrane systems is generally up to about 40 psi (2.8 bar).

The flow pattern used for encased or cartridge membrane systems can be either dead-end

or cross-flow. In a dead-end mode of operation, the entire feed flow passes through the membrane to become filtrate. In cross-flow mode, a percentage (e.g., 85 percent) of the feed flow passes through the membrane, while the remaining flow exits the vessel. The unfiltered portion can be wasted or recycled by blending it with the incoming feed flow. The main advantage of cross-flow operation is that it maintains a tangential velocity along the entire membrane surface, which can, in some waters, minimize the deposition of foulants on the membrane surface. Cross-flow operation obviously has a lower system recovery than dead-end flow; however, the unfiltered water can be recycled to improve the overall system recovery. Recycling in a cross-flow mode requires additional pumping which often makes this mode of operation more costly to operate than dead-end operation.

Submerged systems are configured differently. A pump or hydraulic gradient pulls water through the membrane, leaving particulates and colloids in the basin, which is open to atmospheric pressure. The basins are drained periodically to remove the particles from the system. The vacuum pressure drawn on the membranes is typically from -3 to -12 psi (-0.2 to -0.8 bar).

When investigating membranes for integration into a WTP, it is important to recognize the potential treatment and operational benefits associated with encased versus submerged systems. For feed waters with a high solids loading, submerged systems or cross-flow encased

Figure B.2 Process flow diagram for cartridge or pressure MF/UF systems

Feed Water

Dirty Backwash

Permeate

Clean Backwash SupplyMembrane(MF/UF)

Figure B.2 Process flow diagram for cartridge or pressure MF/UF systems

Feed Water

Dirty Backwash

Permeate

Clean Backwash SupplyMembrane(MF/UF)

Figure B.3 Process flow diagram for submerged MF/UF systems

Feed WaterPermeate

Dirty Backwash Clean Backwash SupplySubmergedMembrane(MF/UF)

Figure B.3 Process flow diagram for submerged MF/UF systems

Feed WaterPermeate

Dirty Backwash Clean Backwash SupplySubmergedMembrane(MF/UF)


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systems would be expected to perform well. A dead-end encased system would be a cost-effective alternative for waters with a lower solids concentration. There are differences in the performance between the various systems that are available on the market. Pilot testing of the different suppliers is recommended to determine how the systems will perform for specific feed water. Nanofiltration and Reverse Osmosis Systems Understanding how NF and RO systems differ from MF and UF systems will help utilities evaluate appropriate membrane integration options. NF and RO membranes are typically used for salinity and/or specific contaminant removal, and not for particle removal or disinfection credit.

Membrane Material. Significant improvements have been accomplished in NF/RO membrane technology over time. The earliest RO membranes were developed in the late 1950’s and were made from CA. CA membrane material is hydrophilic, which helps to limit the fouling potential, while allowing for higher water flow (i.e., flux) through the membrane, and is chlorine tolerant. It is, however, susceptible to hydrolysis (i.e., degradation) when operated outside of the pH range of 4 to 6.5, has a low temperature threshold of about 85ºF (30ºC), and is susceptible to biological degradation. Improvements to these earlier membranes included the development of newer membrane materials, such as cellulose triacetate (CTA) and CTA/CA blends. Although these new materials performed better than CA membranes, they had a low rejection capability and also required high operating pressures. These operational and performance issues have ultimately led to the development of what is currently the most commonly used RO membrane material in the potable water industry, PA.

PA membranes are thin film composite membranes. They have significantly higher rejection capability than CA and CA blend membranes, require lower operating pressure, and are stable over a wider range of pH and temperature. PA is also more resistant to bacterial degradation than CA membranes. PA membranes are not resistant to oxidants like chlorine; however, due to its other performance and operational advantages, PA-based RO and NF membranes are now widely used in drinking water applications.

Many manufacturers are researching and developing newer generation NF and RO membranes that have selective ion rejection. For example, there are PES membranes that have been recently developed and marketed as an NF membrane that is chlorine resistant. It will selectively remove organic material that has a molecular weight greater than 1,000 Da, while allowing the passage of salts or inorganic ions.

When considering NF or RO membranes for integration into a drinking water plant, the selection of the membrane type and material will be a key decision. It will be based on the water quality goals for salt or contaminant rejection, and the characteristics of the feed water. Because of the variability in performance of NF and RO membranes that are available, it is prudent to conduct pilot-scale evaluations on the feed water to be treated. Pilot testing will not only provide performance data, but also information about operation and maintenance of the NF/RO system and any pretreatment requirements.

Nanofiltration/Reverse Osmosis Membrane and System Configuration. NF and RO membranes are available in four configurations (1) plate and frame, (2) tubular, (3) hollow fiber, and (4) spiral wound. Each type of configuration is briefly described, but because spiral wound


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is the most commonly used configuration for RO and NF membranes, most of the discussion focuses on spiral wound systems.

In the spiral wound design, the membrane is formed into a shape that is similar in concept to a sealed envelope, with a supporting grid on the inside of the layers. The ‘envelope’ of membrane is then wrapped around a central collecting tube to facilitate housing into a tubular PV. Feed water flows laterally through the spiral over the membrane surface. Product water, or filtrate passes through the membrane and then travels in a circular path to the collection tube at one end of the ‘envelope.’ In NF and RO systems, the membrane modules are referred to as elements.

The hollow fiber configuration has a large number of hair-like hollow fiber membranes in a PV. Both ends of the fibers are embedded in plastic tubesheets. The pressurized feed water is introduced into the vessel along the outside of the hollow fibers. Under pressure, water permeates through the fiber walls and flows through the inside of the fibers for collection at either end.

There are other configurations of NF and RO that are being researched and developed to treat waters that are more challenging due to a higher concentration and diversity of contaminants. For example, a plate-type NF membrane with 1 mm spacing between plates has been evaluated with PAC dosing for treating landfill leachate (Meier, Neymann, and Melin 2002). Likewise, a ‘cushion’ module by Rochem UF-Systeme, is being evaluated for wastewater treatment (Brügger and Melin 2002). Also, a rotating RO system, which claims to have a lower fouling potential than spiral RO membranes has been developed (Lee and Lueptow 2003). The authors claim that the scaling is minimized, because foulants, like calcium sulfate, will crystallize in bulk solution rather than on the surface of the membrane.

A new membrane configuration being evaluated in various pilot-scale studies is the vibratory shear enhancement process (VSEP) for NF (Yi et al. 2002). Shear waves are introduced at the membrane surface to reduce the fouling potential while allowing operation at high flux rates. Pilot- and demonstration-scale trials have been conducted, but thus far testing has mostly been for industrial and remediation-type applications (New Logic Research 2005).

NF and RO spiral wound membrane elements are cylindrically shaped, available in 2.5, 4, and 8-inch (in) diameters, and are typically 40 in. long. Eight-inch diameter elements are the most commonly used in full-scale drinking water applications. Multiple elements are housed in a PV, by connecting from three to eight membrane elements in series within the PV. Several NF and RO membrane manufacturers are considering larger diameter elements of 16 and 18 in., because their application would result in a smaller facility foot print and lower initial capital cost.

A typical NF/RO process block diagram is shown in Figure B.4. Depending on the raw water quality, pretreatment may be required to remove foulants from the feed water. Subsequent to pretreatment, addition of antiscalant and acid is often needed to minimize scaling of the NF/RO membrane. Cartridge filters, which typically have 1 micron pore sizes, often serve to remove any large particulate contaminants prior to NF/RO treatment. The water is then pumped into the membrane vessels. Once inside the vessel, a portion of the feed water passes through the NF/RO membrane and emerges as low-salinity product, or permeate, water. The remainder of the feed water, which does not pass through the membrane, exits the vessel and is referred to as brine, concentrate, or reject stream because it contains the dissolved substances that could not pass through the membrane elements. Oftentimes, it is cost effective to bypass part of the feed flow around the RO/NF system if blending treated and untreated water can meet the finished


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water quality goals for the contaminant of concern. The percentage of bypass flow depends on the difference between contaminant concentration and effluent goal. The permeate flow must almost always be treated to reduce its corrosivity, and this post treatment for corrosion control can be before or after blending with any bypass water.

The amount of flow through elements within a standard eight-inch RO PV is limited (i.e., to about 50 to 80 gpm; 3 to 5 liters per second, l/s); thus, multiple PVs are operated in parallel from a single feed pump. This assembly of vessels is referred to as a stage, array, or bank. This arrangement allows for sufficient permeate production without excessively high flux through the NF/RO membrane. The amount of water that is rejected as concentrate from a single stage of treatment is typically too high, which results in a low recovery, so the concentrate from the first stage is typically sent to a second stage, where more permeate is extracted. This is referred to as reject staging, which is shown schematically in Figure B.5.

Reject staging is typically used when treating low salinity or brackish water or when needing to increase the overall treatment system recovery. When the overall system recovery needs to be greater than 75 percent, three stages of NF/RO treatment are usually required. Depending on the application, a booster pump may be required to increase the pressure of the feed to the second and third stages to balance the permeate flux and to optimize energy consumption. The energy in the high pressure concentrate stream can also be recovered using an energy recovery device. The recovered energy could be used to augment the pumping energy that is required for the first stage feed or for the inter-stage booster pump.

CartridgeFilter

Figure B.4 Typical process flow diagram for NF/RO systems

Source Water

PossiblePretreatment

NF/RO

Post-Treatment FinishedWater

Bypass

Concentrate

CartridgeFilter

Figure B.4 Typical process flow diagram for NF/RO systems

Source Water

PossiblePretreatment

NF/RO

Post-Treatment FinishedWater

Bypass

Concentrate


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In contrast, another arrangement is product staging, where product water from the one

stage is re-pressurized and further treated by another bank of membranes. Product staging is commonly used when high purity water is required or if higher rejection of poorly removed contaminants is desired. This level of NF/RO treatment is not commonly needed in drinking water plants, and not likely necessary for most fresh or brackish water integration applications. In seawater applications, product staging is used to meet treated water quality goals for poorly rejected contaminants, such as boron.

NF/RO Evaluation and Design Procedures. Design of the NF/RO system typically involves careful evaluation of feed water quality, pretreatment requirements, and post treatment. The feed water quality is first assessed to determine what level of pretreatment is needed. Almost all systems require the addition of an antiscalant and acid to control precipitation of sparingly soluble salts. Many antiscalant manufacturers provide computer programs specific to their products that help determine the maximum recovery possible when using their products. However, the sensitivity of some models is limited and scaling episodes can still occur in NF or RO plants. Pilot-testing can be used to determine which antiscalants will perform well for a certain feed water.

Once the recovery is determined from the analysis of water quality and antiscalant selection, the NF/RO system can be designed using the computer models provided by the membrane manufacturers. These models allow design of the NF/RO array, while taking into consideration the salt rejection of the specific membrane modules selected, array configuration, and hydraulics of the system, including filtrate flux. Through use of these programs, the user can determine whether NF or RO membranes of various manufacturers are suitable to meet desired water quality goals.

Depending on the water quality, pilot testing may be required to determine the fouling potential. For instance, for groundwater sources that are characterized by low turbidity and low inorganic colloids, pilot testing may not be required. For surface water sources or groundwater sources characterized by high turbidity, inorganic colloids, and organics, pilot testing may be

Figure B.5 Typical process flow diagram for concentrate staging systems

Feed

Stage 1 Stage 2 Stage 3

1st Stage Concentrate

2nd Stage Concentrate

Concentrate

1st Stage Filtrate

2nd Stage Filtrate

3rd Stage Filtrate

Bypass

RO Product(or Filtrate)

Figure B.5 Typical process flow diagram for concentrate staging systems

Feed

Stage 1 Stage 2 Stage 3

1st Stage Concentrate

2nd Stage Concentrate

Concentrate

1st Stage Filtrate

2nd Stage Filtrate

3rd Stage Filtrate

Bypass

RO Product(or Filtrate)


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required to ensure that any pretreatment provided upstream of the membranes is adequate to limit the fouling rate of the NF/RO membranes.

Pilot testing may also be required if the information about the ability of the membrane to reject specific contaminants is not available from the manufacturer. If determination of the rejection of specific contaminants is the only information required, bench-scale testing using flat membrane sheets could be adequate. For instance, bench-scale flat sheet membrane testing units, as well as pilot-scale tests, have been shown to approximate full-scale rejection to within at least 10 percent (Grooters, Summers, and Amy 2002).

When NF/RO membranes are applied to unique conditions, pilot testing may be required to evaluate their performance. For instance, the computer programs provided by the manufacturers are not accurate in predicting the performance of NF membranes to treat seawater, because NF membranes are designed to treat low salinity water. Cheng et al. (2003) reported that pilot-testing, in addition to manufacturer modelling efforts, was required to thoroughly evaluate dual-stage NF for a seawater application in Long Beach, Calif.

Post treatment of RO permeate is required to reduce the corrosivity of the permeate and to ensure that the treated water is compatible with the quality of the water in the distribution system. Post treatment typically involves aeration (particularly if acid is used upstream of RO process), pH adjustment, and addition of carbonate, if necessary to adjust alkalinity. ED/EDR Systems

EDR is an electrochemical separation process for the removal of ionic contaminants from a water supply. EDR uses membranes that allow passage of either anions (anion-transfer membranes) or cations (cation-transfer membranes).

The basic module consists of alternating anion-transfer and cation-transfer membranes separated by a flow spacer. A direct current (DC) voltage potential field is applied across the membranes. As the feed water flows through the flow spacer between the membranes, the DC voltage potential induces the cations (positively charged ions such as sodium, Na+ and calcium, Ca2+) to migrate towards the anode through the cation-transfer membrane. Likewise, anions (negatively charged ions such as chloride, Cl- and nitrate, NO3

-) migrate towards the cathode through the anion-transfer membrane. The cations and anions get trapped in the brine channel. The EDR process is schematically presented in Figure B.6.

As cations and anions are removed from the demineralized stream, the membrane surface on that side gets depleted of ions, causing significant increase in electrical resistance and current density. This eventually would lead to depolarization and dissociation of water. To eliminate this problem, the polarity of the field is reversed periodically, and the scale forming ions are flushed off the membrane surface.

The performance of EDR depends on feed water quality. As in NF and RO, scaling of sparingly soluble salts limits the level of recovery that is possible. Use of chemicals such as antiscalants is required to control the formation of inorganic scale on the membrane surface. The presence of organic matter could also affect the performance of the process. To achieve high recovery and high rejection, multi-stage systems are used. A typical multi-stage EDR facility has three stages, and recoveries as high as 90 percent are possible, depending on the water quality. It should be noted that only one manufacturer supplies EDR equipment in North America, eliminating a competitive bidding environment for similar equipment.


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The ED/EDR process does not remove uncharged contaminants such as pathogens, some organic compounds, and turbidity; thus, it should not be considered for integration when particle removal is a treatment objective.

It is important to realize that the charged ion removal capabilities of EDR are affected by temperature (i.e., at lower temperatures more anions and cations are retained in the product water). One way to combat this temperature affect is to recycle product water to the feed of the EDR system when water temperatures are low. This decreases the feed water salinity, which also decreases the product water salinity. The implications of this are that the overall system recovery is lowered proportionally, and additional pumping costs are incurred. This type of operation, however, is commonly used (e.g., Allison and Touchstone, 2003) to achieve water quality goals.

Feed Water

Concentrate

Cathode

Anode

Product

Figure B.6 Typical process flow diagram for EDR systems

Anion MembraneCation Membrane


Feed Water

Concentrate

Cathode

Anode

Product

Figure B.6 Typical process flow diagram for EDR systems

Anion MembraneCation MembraneAnion MembraneCation Membrane


Operational Definitions and Procedures

There are several operating procedures that are common to membrane systems. Many are calculated parameters which are used to gauge the performance of the membrane system. These are summarized and defined herein. Equations for parameters or procedures that require calculations are presented and described in more detail in Appendix D.

Flux

MF/UF Systems. Flux is the amount of filtered water produced per unit area of membrane per unit of time. Typical units are gfd or lmh. For MF/UF systems, flux is expressed in several ways as discussed below, and each should be fully understood to recognize what it represents.

The instantaneous flux is the flux that occurs while the unit is operating between backwash operations. It is generally the highest flux value reported for a system and used in design calculations, but should not be used to generate estimates of total production for a membrane facility. It does not account for system downtime or filtrate uses/losses during treatment.

The average flux is another design parameter that is often discussed, and it is calculated over a period of time (e.g., 24 hours) and accounts for any production downtime during the normal operating cycles. Examples of downtime include backwashing, chemically enhanced backwashing, and integrity testing.


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Net flux is defined as the total amount of water produced per unit membrane area over a given period of time by the entire system; thus it is the design value that can be used to estimate the production that can be achieved by a membrane system. It is based on the net volume of filtrate that is produced, which is calculated by subtracting any filtrate that is used for backwashes or chemically enhanced backwashes.

Sometimes, specific flux is also reported. It is essentially flux per unit TMP, which is the amount of production relative to the pressure in the system. When operating systems at a constant flux, a decrease in specific flux would be an indication that fouling has occurred.

An optimal flux for a system can be estimated based on past experience and verified with site-specific testing. Higher fluxes may increase the rate of fouling and require higher operating TMP. In addition, operation at higher pressures is likely to compact the foulant layer, which might limit the effectiveness of backwashing to dislodge the foulants. This may necessitate frequent chemical cleans, such as chemical backwashes or chemical CIP procedures, which will increase the downtime for the system and may reduce the life of membrane module.

Net flux values vary for different systems, depending on their geometry and configuration. For submerged systems, typical fluxes are in the range of 18 to 25 gfd (30 to 43 lmh) and for encased systems, the flux can vary from 50 to greater than 100 gfd (85 to 170 lmh).

NF/RO Systems. The flux for NF/RO systems is defined in the same manner as for MF/UF systems. Flux values are generally lower in NF/RO systems than in MF/UF systems. Typical flux values are dependent on the feed water quality. For source water with low fouling potential, the netflux is typically in the range of 13 to 18 gfd (22 to 31 lmh). For seawater applications, depending on the salinity of the water, net flux is in the range of 7 to 10 gfd (12 to 17 lmh).

Backwashing and Chemically Enhanced Backwashing

MF/UF Systems. As feed water is forced through the membrane, certain particles in the feed water are rejected by the membrane due to their physical size or surface charge, and these particles collect on the membrane surface. Backwashing is used to remove these particles from the surface of the membrane and to restore the permeability of the membrane. The steps of a backwashing procedure and the frequency and duration of backwashing cycles are dependent on the water quality and the membrane system. In general, as the feed water quality degrades (i.e., more foulants including turbidity and organics are present in the feed water), the frequency and duration of backwashing increases.

Membrane manufacturers have developed various backwashing techniques which are specific to their system. These techniques include pumping filtrate or air in the direction opposite to that of normal operation and use of feed water or feed water with air to scour and flush out dislodged material. Typical backwashing intervals are from 30 to 45 minutes, and durations are from 30 seconds to 2 minutes, depending on the water quality and membrane system. It is prudent to optimize backwash frequency and downtime to increase the recovery and productivity of membrane systems. Some manufacturers use chemicals, such as chlorine, during all or some of the backwashes, and these are referred to as CEBWs. For example, one system uses 200 mg/L free chlorine for CEBW which involves an extended backwash lasting up to 30 minutes. When source waters contain inorganic foulants like manganese, acid is sometimes also used for CEBWs. Other utilities have found that a combination of high temperature and chlorine


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helps minimize the rate of microbiological fouling. Kruithoff, Kamp, and Folmer (2003) reported that backwashing procedures for the UF plant at Heemskerk were modified to include 500 mg/L sodium hypochlorite (NaOCl) with an elevated temperature to lessen the impact of biological fouling, which was attributed to algal material from blooms in the feed water from a lake.

Backwashing and CEBWs have many impacts on integration of membranes into a WTP. First, in some instances, the solids concentration in a membrane system backwash can be more dilute than that of an existing plant because of a shorter time interval between backwashes in a membrane system. This results in a greater volume of backwash flow. The impact of this on existing washwater handling and treatment systems must be carefully examined if membranes are to be integrated into an existing facility. When chlorine is added to backwashes or CEBWs, neutralization may be required prior to delivering it to a washwater treatment system.

NF/RO Systems. Unlike MF/UF systems, NF/RO membranes can not be backwashed because of their design. Since their main objective is to remove dissolved substances, any suspended material in the feed water should be removed upstream of the NF/RO systems. NF/RO systems require continuous acid and/or antiscalant addition upstream of the membranes to control precipitation of sparingly soluble salts within the membrane elements. Scaling can occur when the concentration of ions increases to above the solubility limit, which results in the precipitation of compounds like calcium carbonate, calcium sulfate, barium sulfate, silica, calcium fluoride, etc.

Chemical Cleaning

Both MF/UF and NF/RO membranes require chemical cleaning, and this procedure impacts the integration of membranes into a water treatment plant in several ways:

• Operations staff are impacted because chemical feed systems must be installed,

operated, and maintained • Safety practices must be modified to account for acids, bases, oxidants, and

possible detergents that are used for cleanings • Process monitoring must be continuous to predict when cleanings are needed • Cleaning waste disposal must be carefully managed, and may impact existing

waste handling methods on-site • Downtime for cleaning must be carefully managed, because it impacts the

production at the facility

Chemical cleaning frequency is an important design parameter because it affects both the economics of production, as well as the long-term performance of the membrane system. This process is very different than backwashing procedures of conventional media plants. For these reasons, chemical cleaning is discussed in detail to provide a thorough understanding of the issues associated with cleaning membranes.

The membrane industry sometimes refers to chemical cleans as CIP, which is an acronym for ‘clean-in-place’ and a term that was developed to differentiate membrane systems that did not require module removal for cleaning. All membrane systems marketed for potable water


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treatment are now cleaned without removing the modules from the system, yet the terminology of CIP is still commonly used.

MF/UF System Cleaning Procedures. Membrane modules require periodic chemical cleans to remove foulants that are not removed by regular backwashing. The chemical cleaning typically involves use of acidic or basic pH solutions, chlorine, and sometimes detergents. In some applications, cleaning solutions are heated to 104°F (40°C) to improve the cleaning efficiency. These chemicals are pumped into the pressurized cartridges or basins, and are sometimes recirculated over a period of time. Most cleans require at least a four hour cleaning period for each of two cleaning chemicals used; thus, membrane modules are out of production for at least 8 hours or longer for each CIP.

NF/RO System Cleaning Procedures. The NF/RO membranes require periodic CIP to remove any foulants or inorganic precipitates that deposit on the surface of the membrane. Chemical cleaning typically involves the use of a low pH solution for the removal of inorganic scale and deposited precipitates. Organic and biological fouling is typically removed with high pH cleaning solutions, possibly with detergents. The cleaning solution may be heated to improve its effectiveness, depending on the ambient temperature of the water. Sometimes, the cleaning may be limited to second and third stages or to third stage alone depending on the extent of fouling.

Several indicators are used for NF/RO membrane systems to determine when a CIP is required. NF/RO membranes are cleaned whenever any of the following events occurs:

• Specific flux (see Appendix D for definition) decreases by 10 to 15 percent • Salt passage through the membrane increases by 10 percent • The pressure loss along the membrane, as determined by the difference between the feed

and concentrate pressure, increases by 15 percent

Operation of the NF/RO systems beyond these limits may cause irreversible specific flux loss; therefore, NF/RO operating parameters should be monitored continuously. Typically, most of the relevant parameters are monitored continuously using online instrumentation. In addition to the operating parameters of the NF/RO system, feed water quality should be continuously monitored for changes that may promote fouling.

Types of Fouling. Fouling of membranes is a complex subject, and many researchers and industry experts continue to investigate the sources of fouling and the means to minimize cleaning frequency. Models and algorithms remain site specific, but advancements are being made with neural networks (Shetty, Malki, and Chellam 2003; Baxter et al. 2001; Shetty and Chellam 2003; Veerapaneni et al. 2004) to optimize operations to minimize cleaning frequency. An overview of fouling and cleaning is presented in this report; however, additional information can be obtained in references such as Liu et al. 2001, Laîné et al. 2002, and Mallevialle, Odendaal, and Weisner 1996, and Howe and Clark 2002.

Fouling can be broadly categorized as follows:

1. Inorganic scaling or precipitative fouling 2. Particulate or colloidal fouling 3. Microbial fouling 4. Organic fouling


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Each type of fouling is discussed below because understanding the types of fouling for

membrane systems is critical to the successful integration into a treatment train. Inorganic Scaling or Precipitative Fouling. Inorganic scale is typically of concern for

NF/RO systems, because the rejection of dissolved substances at the surface of the membrane results in the increase in their concentration in the concentrate solution. In addition, flow through the membrane also results in localized accumulation of ions near the membrane surface, and this is referred to as concentration polarization. Concentration polarization can cause precipitation of sparingly soluble salts such as calcium carbonate, calcium sulfate, barium sulfate, calcium fluoride, strontium sulfate, and silica. To limit concentration polarization at the surface of the membrane, the element recovery should be minimized, because a higher element recovery could increase the concentration polarization, thus increasing the potential for scaling. A higher concentrate flow would increase the turbulence at the surface of the membrane, thereby limiting the thickness of the concentration polarization layer as well as flushing away any precipitates.

Precipitative fouling is typically not an issue for MF/UF membranes, because they do not reject dissolved substances. Some scaling could occur on the surface of the membrane, if the feed water is already supersaturated with salts. For example, in lime softening plants the accumulation of calcium carbonate on the surface of the membranes could occur if the feed water is not properly stabilized.

Particulate or Colloidal Fouling. Particle or colloid fouling of membranes is caused by various naturally occurring particles such as silts, clays, colloidal silica, colloidal sulphur, and oxidized forms of iron and manganese. The interactions between different constituents in the feed water can also contribute to fouling. For example, the presence of dissolved silica and metals, such as iron or aluminum, could result in fouling by aluminum or iron silicates, even at low concentrations of these metal ions. This type of fouling of MF/UF membranes is typically removed by normal backwashing and with a periodic CIP.

Particulate and colloidal fouling is very common. Iron fouling was identified as the cause of permeability loss at the Corfe Mullen treatment works (USFilter’s encased MF system; Wessex Water) in the UK (Smith 2002). Similarly, autopsies performed for UF membranes from Clay Lane identified the presence of manganese and iron foulants mixed with organic foulants (Lake et al. 2003). Khatib et al. (1997) reported fouling of UF membranes by a silica-rich, ferric gel that had deposited the surface of the membrane. These foulants were present in the source water; however, some studies have shown that pretreatment upstream of the membranes can contribute to fouling of the membranes.

The impact of pretreatment on fouling was investigated by Colas et al. (2003). The aluminum concentration of the caustic cleaning solution was measured during two CIP cycles for a UF plant. The aluminum concentration rose from zero to above 40 mg aluminum per m2 membrane area within 40 minutes of the CIP, showing that aluminum residues were adhering to the membranes, but were being removed by the caustic cleaning procedure.

Another indirect source of particulate or colloidal fouling can be the background concentrations of manganese in some coagulation chemicals (Laîné et al. 2002). Ferric chloride coagulation upstream of membranes can introduce manganese into the membrane feed water, which can precipitate on the membranes during a chlorinated backwash. A gradual build-up of manganese oxides over time can result in more extensive fouling.


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For NF/RO systems, the first means of control of colloidal fouling is maintaining a feed water turbidity of less than 1 NTU. There is also a simple test, the SDI test, which is an indicator of the fouling potential of the feed water. In this test, feed water is filtered through a 0.45 µm filter at a constant pressure of 207 kPa (30 psi). The time to filter the first 500 mL of filtrate is recorded. Filtration is continued for a specific period of time (i.e., typically15 minutes) and the time to collect another 500 mL is recorded. The SDI value is calculated using Equation B.1:

1001

×

−

=T

tt

SDI f

i

T (B.1)

where it = initial time required to collect the first 500 mL, minutes

ft = time required to collect the final 500 mL, minutes T = total elapsed time duration, typically 15 minutes In general, feed water with an SDI value greater than five is considered to have a high

tendency for fouling NF/RO membranes, whereas SDI values below three are considered suitable for NF/RO feed water. It should be noted that this test is highly empirical and does not accurately simulate actual flow conditions in a spiral wound NF/RO element. Several other modifications and alternatives for this test have been proposed, including the modified fouling index; however, to-date the SDI test is still the primary test performed to identify the fouling tendency of the feed water and is included in many equipment procurement specifications.

Microbial Fouling. Microbial fouling is caused by bacteria, algae, and biofilms, and can be challenging to manage in membrane systems. However, if the membrane material is oxidant tolerant, a disinfecting chemical, like chlorine, can be applied to minimize microbial foulant.

By-products of biological growth, particularly algal growth, can also contribute to fouling. For example, biopolymers from microbes, algae, and clams in the intake have been shown to cause rapid fouling of RO membranes during a pilot study (Gabelich et al. 2003). Freeman et al. (1997) reported flux decline as a result of algal secretions from the bag strainers upstream of an UF unit. Her et al. (2002) also reported that algal cell lysis can contribute to fouling.

Extracellular polymeric substances produced by attached biofilms can also contribute to fouling. These substances are viscous, gelatinous slimes, which usually have a negative surface charge. This slime protects bacteria from shearing forces as well as from chemical disinfectants, and it can cause severe fouling of MF and UF systems. NF and RO systems are also subject to microbial fouling, but disinfection processes upstream help eliminate the potential for this.

Another contributor to microbial fouling is chemical feed stocks used in upstream processes. Vrouwenvelder and Van der Kooij (2002) reported that impurities in the chemicals can result in rapid fouling of a membrane system. Similarly, Hong et al. (2003) measured assimilable organic carbon (AOC) concentrations in NF feed water and found that acid and antiscalant chemicals were causing as much as a 12.7 percent increase in the AOC concentration, thus promoting biological growth in the membrane system.

Organic Fouling. Organic fouling is typical of MF, UF, NF, and RO systems. It is the result of organic compounds collecting on the membrane surface or becoming embedded within the pores. Because of the complex chemical nature of organic molecules and membrane


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surfaces, it is difficult to consistently predict which types of organics (e.g., high molecular weight, low molecular weight, functional groups, charge density, UV absorbance, etc.) cause or contribute to membrane fouling. The chemistry and interactions of organics and membranes will be unique at each site, because source water and pretreatment will impact the degree of fouling.

The characteristics of the membrane material also affect the interaction of the organic matter with the membrane surface. For instance, Fan et al. (2001) reported that the fouling rate of the hydrophobic membranes was considerably greater than that of the hydrophilic membrane. They also reported that the fouling of the hydrophobic membrane was caused by high molecular weight fraction of the organic matter (i.e., >30 kDa). Likewise, Kabsch-Korbutowicz, Majewska-Nowak, and Winnicki (1999) reported that hydrophilic UF membranes exhibited less fouling by organic matter and that raising the pH from 4.6 to 7 reduced membrane fouling.

Having a better understanding of which organics cause fouling of MF/UF and NF/RO systems would help to define pretreatment alternatives for reducing the fouling potential. Research in this area is on-going. The structure and functional groups of organic compounds are quite diverse in nature, and as such, there are no consistent patterns in the evaluations of which types of organics contribute to fouling. For example, several investigators have reported that humic acid, which is more hydrophobic than fulvic acid, causes more fouling than fulvic acid (Jucker and Clark, 1994; Schafer et al. 2000); however, Carroll et al. (2000) and Amy and Cho (1999) reported that the neutral hydrophilic fraction of NOM caused more fouling.

The molecular weight of organic compounds may indicate the fouling potential of a feed water. Unfortunately, the results of research are inconsistent. Lin, Lin, and Hao (2000) reported that larger molecular weight organics caused more fouling of membranes, whereas Carroll et al. (2000) reported that the lower molecular weight fractions contributed more fouling.

It is generally accepted that pretreatment, perhaps with coagulation, can alter the form of organics and lower the fouling potential of water. Other chemical additives, however, could result in a higher fouling potential. Data presented by Kiefer, Brinson, and Suratt (2003) found that NF fouling in Boca Raton, Florida, appeared to be a result of the interaction between the antiscalant and the naturally occurring humic acids in the well supply.

The use of polymers (e.g., cationic polymer) during drinking water treatment processes that are upstream of membranes can result in excessive fouling of the membranes. This was observed during pilot studies in Appleton, Wisconsin, when cationic polymer use during upstream lime softening resulted in ten day cleaning intervals (Roquebert et al. 2002). Also, the use of some polymeric coagulants (e.g., chitosan, a cationic biopolymer for TOC removal) has been found to cause elevated fouling rates for hollow fiber UF membranes (Machenbach et al. 2002).

Another integration issue is the presence of polymers in the recycle stream from backwash treatment processes (e.g., thickeners, drying beds, etc.) and their potential impact on membrane performance. Some integration installations (e.g., Coliban, Australia, see Chapter 2), operate with polymer use in backwash treatment and have seen no detrimental impact on membrane permeability. There have also been recent project interviews with the two suppliers of submerged membrane technologies (i.e., USFilter and Zenon) where both suppliers have reported that their membranes are tolerant of low concentrations of a specific type of polymer. When evaluating membrane integration, issues like the effect of trace or residual concentrations of polymer on membrane performance should be thoroughly investigated. This is particularly


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important where membranes follow a process like Actiflo or Superpulsator that require polymer use.

Other organic compounds can also cause fouling. Bonnelye et al. (2003) reported that 134 μg/L hydrocarbons caused reversible flux decline for the cellulose derivative Aquasource membranes that were treating Gibraltar harbor water. MF/UF Cleaning Chemicals. The chemicals typically used to clean MF and UF membranes are shown in Table B.4.

Manufacturers generally specify which chemicals should be used with their membranes, and will recommend concentrations and cleaning durations. Some membrane materials are not tolerant of oxidants, like chlorine, or have restrictions on the use of extreme pH (i.e., very high or low) for cleaning. The chemical tolerance of a membrane is an important consideration when deciding which type of membrane to use for a specific application. For example, if a feed water is known to contain manganese, the membrane should be able to tolerate very low pH during cleaning for dissolution of any adsorbed manganese. Similarly, if a feed water is prone to microbial growth, the ability to clean with chlorine is necessary to maintain the membrane’s permeability.

Table B.4

Major categories of MF and UF membrane cleaning chemicals Cleaning chemical type

Major function of chemical

Type of fouling treated

Typical chemicals used

High pH Hydrolysis and solubilization

Organic and microbial

Caustic soda

Oxidants and disinfectants

Oxidation and disinfection


Sodium hypochlorite, hydrogen peroxide,

peroxyacetic acid, sodium bisulfite

Low pH Solubilization Inorganic Citric acid, sulfuric acid, hydrochloric acid

Chelating agents

Chelation Inorganic Citric acid, EDTA*

Surfactants Emulsifying, dispersion, surface

conditioning


Surfactants and detergents

*EDTA = ethylenediamine tetra acetic acid Source: Data from Liu et al. (2001)

As utilities gain experience with different cleaning regimes, new approaches to safer and

more efficient CIP are emerging. In MF pilot studies at Tempe, Arizona, membrane fouling by iron, manganese, and aluminum required cleaning with Ferrisol, which is a mixture of oxalic and citric acid, to restore membrane permeability (Huey et al. 1999).


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The preparation and temperature of cleaning chemicals is also a consideration for membrane plants. Norman, Hoang, and Leslie (1999) reported that calcium, magnesium, and iron silicates can cause fouling of MF in waters with high TDS (such as in water reuse membrane plants), and that the preparation of cleaning solutions with low TDS water helps eliminate this problem. Sometimes a softener is used for removing hardness from cleaning solutions.

It is important to recognize that sometimes high-strength chemicals are required to effectively clean membranes. For example, when silicate fouling has occurred, ammonium bifluoride (ABF) cleans and soaks are necessary to restore the system’s flux. ABF use has several safety precautions for health, reactivity, and corrosivity; thus it is preferred by most to avoid silicate-based fouling than to clean systems with ABF. NF/RO Cleaning Chemicals. NF/RO membranes can be fouled by inorganic scale, organics, biological growth and, in same instances, by colloids. The type of cleaning chemical used for these foulants varies, but in general, acid and alkaline chemicals are standard for NF/RO systems. Acidic solutions are used for cleaning inorganic scale, and alkaline chemicals are used for cleaning organic and biological fouling. Alkaline chemical cleaning solutions that are commercially available also contain detergents to aid in the cleaning process. Heating the cleaning solution to a temperature of 86 to 95ºF (30 to 35ºC) increases the efficiency of the cleaning process, and many utilities have a heater installed in the CIP tank. Many commercial formulations (Table B.5) of these cleaning solutions are available and are commonly used by utilities. The effectiveness of cleaning will vary, depending on the nature of foulants. Both high and low pH cleaning cycles are sometimes used. Manning et al. (2003) reported that in Florida, most of the 25 NF and RO plants surveyed used citric acid for the low pH clean, and proprietary or generic detergent with caustic soda for the high pH/detergent clean.

Methods for Controlling Fouling

The following discussion summarizes some of the methods for controlling membrane fouling.

MF/UF Fouling Control. Fouling of a membrane over time is inevitable, but the rate and extent of fouling can be controlled by several means. The operating conditions, for example, can be selected to help minimize the rate and extent of fouling. It is well understood that increased production (i.e., flux) through the membrane will increase the rate of fouling. One way to help control the rate of fouling, is to select a design flux that is below the limit of flux range that allows stable operation.

Operating at a lower recovery is also expected to help keep the membrane’s permeability at acceptable levels for longer periods of time. Crozes et al. (1995) reported results from a pilot study indicating that long term irreversible fouling could be controlled by limiting the short term reversible fouling by reducing the flux and increasing the backwash frequency.


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Table B.5 Cleaning chemicals used for NF/RO systems

Type of foulant Cleaning chemical

Inorganic scale (i.e., CaCO3)

Acidic solution Examples: 0.2% hydrochloric acid 0.5% phosphoric acid 2% citric acid

Metal oxides such as iron

Acidic solution Examples: 1% sodium hydrosulfite 0.5% phosphoric acid 1% sulfamic acid

Colloidal fouling

0.1% sodium hydroxide with surfactants such as 0.025% sodium laurel sulfate; Helps to heat the cleaning solution to 86ºF (30ºC)

Organics

0.1% sodium hydroxide with surfactants such as 0.025% sodium laurel sulfate or 1% sodium EDTA; Helps to heat the cleaning solution to 86ºF (30ºC)

Biological fouling

0.1% sodium hydroxide with surfactants such as 0.025% sodium laurel sulfate or 1% sodium EDTA; Helps to heat the cleaning solution to 86ºF (30ºC)

Silica

Difficult to remove. High pH cleaning solution described above could be tried. Use of hazardous chemicals such as ammonium bifluoride or even hydrofluoric acid

NF/RO Fouling Control. Several methods of helping to control NF/RO fouling have

been identified. First, all NF/RO cleaning solutions and scale inhibitors need to be prepared with water that is chemically-compatible to the goals of treatment. Freeman et al. (1997) and Laîné et al. (2002) both recommend that cleaning solutions be prepared with softened or de-ionized water to prevent inorganic scaling on the membranes. Typically, the NF/RO permeate water is used for preparation of cleaning solutions.

In situ, on-line monitoring can also be used to help identify and control fouling. Kappelhof et al. (2002) presented data showing that in situ measurement of specific oxygen consumption rate may be a useful tool in predicting biofouling of a membrane system. This equipment is still in development, but shows promise.


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It should be noted that computer models, including artificial neural networks, (Shetty and Chellam 2003) are being developed to assist with predicting fouling in membrane systems. Plottu et al. (2003) reported good results while modeling NF fouling rates for the Méry-sur-Oise WTP in France. The model showed that membrane operation time after a clean was the most important parameter, followed by temperature, particle count, SDI, and TOC. Dissolved constituents, such as hardness and sulfate, and pH had only a minimal influence on the fouling model results.

One innovative integration pilot project investigated the removal of divalent ions by ion exchange upstream of an NF system (Van Paassen et al. 2002). The exchange of monovalent sodium for divalent species helped lessen the fouling rate of the NF system. The ion exchange brine stream, which was laden with divalent species and the concentrate of the RO system, which was laden with monovalent and divalent species, were combined in a residuals treatment plant. The combined stream was treated with sodium hydroxide, and significant fractions of the divalent species (e.g., barium sulfate (BaSO4) and CaCO3) were precipitated out of solution, allowing for a recycle of the supernatant to the head of the treatment train. The total recovery achieved during this pilot trial was 97 percent.

Integrity Testing

Integrity verification methods are required to verify that the membrane barrier is intact and thus rejecting all particles greater than the rated pore size of the membrane. As with conventional media filters, once an integrity breach has been identified, immediate action is required to remedy the failure. The methods of integrity testing or monitoring are summarized herein and discussed in sufficient detail to highlight their impact on integration issues. A more detailed evaluation is presented in USEPA (2003b) and American Society of Testing and Materials (ASTM) (2002) for MF and UF systems and in Lozier et al. (2003) for NF and RO systems. Duranceau (2004) also explains the role of integrity testing in compliance with the LT2EWSTR.

Integrity testing is different for MF/UF systems than for NF/RO systems, due to the different configuration of the membranes within the system. At this time, integrity testing is required by regulatory agencies for MF and UF systems used for potable water treatment. For NF/RO systems, currently there are no guidelines or established methods for integrity testing. This could be because these systems have been primarily used for treatment of groundwater, that does not require pathogen removal credit. However, with increased use of these systems for treatment of surface water, there is continued interest in developing integrity test methods for NF/RO systems (Lozier et al. 2003)

A breach in the integrity of a membrane can take many forms. For MF and UF hollow fibers, it can be a severed fiber, a pinhole puncture, or a weakened area due to abrasion. For NF/RO spiral wound membranes, it can be a tear or weakened area of the membrane sheet, or a compromised seal or O-ring. Detecting the breach of a MF/UF membrane fiber and its exact location within a set of membrane modules is important for those systems seeking pathogen removal credit. The importance of integrity testing was illustrated by Côté et al. (2003) when challenging a ZeeWeed® 500 immersed membrane system. The intact UF membranes achieved 7.0 log removal of Bacillus subtillis, which is used as a surrogate for Cryptosporidium, but with a pinhole puncture, the log removal was reduced to 5.2, and with two cut fibers, the log removal decreased to less than 4.0.


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MF/UF Integrity Tests

There are two types of integrity tests for MF and UF systems (1) direct, and (2) indirect. Direct methods of integrity testing involve tests that check for integrity breaches in the membrane system; whereas indirect methods involve using the filtrate water quality as an indicator of a breach. While the direct method has the advantage of being a true assessment of an integrity breach, it must be conducted while the system is offline. Indirect methods allow for continuous monitoring of the system while it is operating; however they only indicate the potential of an integrity breach and require a direct integrity test to confirm and locate any integrity breach. Direct Integrity Testing Methods. The five common methods for direct integrity screening are:

1. Pressure decay test (PDT) 2. Diffusive air flow test or water displacement test 3. Sonic sensing analysis 4. Bubble test 5. Marker-based tests

These methods are discussed in detail in USEPA (2001) and USEPA (2003b), and are

summarized below. The PDT is an on-line method that measures the membrane’s ability to maintain a certain

pressure that is generated by applying air to the membrane. The rate of pressure decay is measured over time, and if the rate exceeds a specific set value (depending on the membrane, system), the membrane integrity is deemed to be breached. For submerged systems, a vacuum pressure can be used with the same principles as described for the PDT, and is referred to as the vacuum hold test (VHT).

The diffusive air flow test and water displacement test are similar to a PDT, except that the rate of flow of either water or air is measured instead of pressure. This test is performed while the membrane system is off-line, and if the rate of flow exceeds a specific target value, the system integrity is deemed to be breached.

The sonic sensing analysis is a direct measure of the air-induced vibration within a membrane module during a PDT. This method is currently a manual procedure involving an accelerometer instrument that measures vibration. This method is used to identify which module on a unit or rack has an integrity breach.

The bubble test is used to identify which fiber in a module is breached. Pressure, which is just less than the bubble point for the membrane, is applied to the membrane module and the compromised fiber will emit bubbles into a surfactant or water solution that is applied to the open end of the fibers. Some systems use a marker-based test which uses direct particle removal measurement to establish and verify the integrity of the membrane system. For example, some Norit UF plants use the SIM, which involves the introduction of PAC (Norit’s SA Super brand) into the feed water. At least 70 percent of the PAC particles have diameters less than 1.7 μm, which is smaller than Cryptosporidium (van Hoof et al. 2002). Particle counts are measured on the feed and the filtrate water to calculate a log removal for the membrane skid. The feed stream will have as many as 1 x 107 particles/mL with diameters greater than 1 μm, which increases the sensitivity of


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the particle removal analysis. The advantage of this method is that it provides a direct measurement of the log removal of particles in this size range. The sensitivity of the SIM test was presented by van Hoof et al. (2002). In a pilot study, particle counting was used to show that a compromised fiber lowered the log removal by 0.2- to 0.3-log when treating feed water alone, whereas with the PAC feed, the reduction in log removal was 0.8-log.

The disadvantages of SIM testing are that (1) it requires an additional chemical feed system which requires maintenance, (2) it uses PAC which is a messy chemical, and (3) it relies on the proper operation and calibration of particle counters. Fiber repair is also messy as residual PAC is flushed out of the membranes on application of air. Many plants successfully use SIM tests for integrity testing; however, if particle counters are not operating properly, integrity testing cannot be performed (Franklin, Knops, and Smith 2001). Indirect Integrity Testing Methods. The indirect methods of integrity testing involve a measurement of filtrate water quality. On-line turbidity, particle counting, and particle monitoring are often used. Turbidity monitoring is generally believed to lack the sensitivity required for accurate integrity monitoring, and particle counting and monitoring, while sensitive, require maintenance and management of data. These methods are, however, typically used with one or more of the direct methods listed above. Many argue that particle counting is not a sensitive means of integrity monitoring. For example, a fiber breach study in Wisconsin showed that particle counts did not indicate integrity problems until at least 100 fibers were broken (Johnson and MacCormick 2002). This was also true for turbidity. One way to increase the sensitivity of indirect methods using water quality parameters is to increase the level of instrumentation (i.e., more particle counters per treatment train) to lower the dilution factor. However, this results in an increased cost for equipment and O&M, as well as data management and analysis.

There are examples of systems where particle counting in the filtrate was correlated to the number of compromised fibers and the log removal of particles in the membrane system. Best et al. (2003) conducted this type of analysis at Olivenhain WTP in California. Particle counts and the corresponding log removals correlated well as the membrane units were systematically compromised, with one fiber cut at a time (up to 12 fiber cuts, total). These data were used to establish conservative ‘alert’ and ‘alarm’ targets for particle counts in the membrane system. At 16 and 30 particles (with diameters greater than 2µm) per mL, the log removal values were 4-log and 3.5-log removal, respectively.

On the full-scale, the sensitivity of indirect and direct integrity methods is being investigated in the AwwaRF study, Integrity Testing of Low Pressure Membranes (Sethi et al. 2003). Results from the Manitowoc WTP in Wisconsin, showed the PDT was more sensitive at detecting the presence of broken fibers (up to 36 fibers, or 0.002 percent, in the full-scale plant). Of the indirect methods, particle counts and laser turbidity monitoring were found to be more sensitive than traditional turbidity monitoring; however, these indirect methods were not as sensitive as the PDT. Emerging Integrity Testing Methods. There has recently been some development in integrity monitoring. One example is the Medusa Integrity Monitoring System (Medusa). This system uses ‘a combination of laser turbidity and statistical signal processing to determine the integrity status of a membrane system’ (Sadar et al. 2003). The main advantage of this system is an on-line integrity test that can identify the module that is breached. This system was installed


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in the full-scale Westminster, Colorado, Pall MF system in 2002, and performed well once the membrane plant began continuous operation. Challenges include intermittent operation, the impact of bubbles during backwashing, and the flow variability in the proximity of the sensors.

Regulatory Requirements. Because membranes are typically granted removal credit for Giardia, Cryptosporidium, and in some cases, virus, the regulatory requirements for verifying a system’s integrity generally fall under the SWTR, IESWTR, and the LT2SWTR. The LT2SWTR is the latest regulation which will govern the integrity testing and monitoring requirements for MF and UF systems. NF/RO systems are not governed by drinking water regulations, because they are not installed for pathogen removal and thus not granted any removal credits. The LT2ESWTR requires the following characteristics of any direct integrity test:

1. The test must be able to detect a breach of size 3 µm or less. 2. The test must be able to verify LRV equal to or greater than the credit that had been given

to the membrane system. 3. The test must be performed on each membrane unit at least once every 24 hours.

State regulatory agencies are allowed to make state requirements more stringent than

federal regulations, so it is prudent to check with local regulatory agencies about integrity testing requirements. For example, in California, integrity testing is required every four hours during the first few weeks/months of operation, until the State agrees to lessen the frequency to once per 24 hours.

In areas prone to Cryptosporidium contamination, the frequency could be more than daily. This is the case for Manitowoc, Wisconsin, which must conduct PDTs on each of its 13 MF units every eight hours (Kothari and Schideman 2002).

For indirect integrity monitoring, the LT2ESWTR requires continuous indirect monitoring

unless continuous direct monitoring is practiced. Continuous direct monitoring is currently not available for MF/UF units, thus continuous indirect monitoring is required. The requirements are as follows:

1. The filtrates of each membrane unit must be monitored individually. 2. The monitoring must be continuous (i.e., measurements at least every 15 minutes). 3. A trigger set-point must be established, such that direct integrity testing is initiated once

the trigger is exceeded. 4. Any monitoring excursions that trigger direct integrity testing must be reported to the

State regulatory agency monthly.

In terms of integration, the regulatory requirements that need careful attention are the frequency of integrity testing, and the reporting and set-point triggers of indirect integrity monitoring. The required frequency of direct integrity tests must be known so that the loss in production can be accounted for in the overall design.


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NF and RO Integrity Tests Unlike MF/UF systems, no established methods are now available for integrity testing of

NF/RO membranes, because of their configuration, rejection abilities and lack of disinfection credit provided by regulatory agencies.

Measuring permeate water quality, and comparing it to feed water quality would seem to be a viable method of determining a membrane’s integrity. Turbidity is not a suitable indicator, because the turbidity to the NF/RO membrane feed water is required to be less than 1 NTU, and a significant number of NF/RO membrane elements will be compromised before an integrity breach could be positively identified using turbidity. Conductivity could be monitored, however, a significantly high number of membranes would have to be breached before the effluent conductivity would indicate a problem. Nevertheless, such parameters should still be monitored in the feed and permeate of NF/RO systems to monitor and track any gradual decline in removal efficiency. A significant increase in any of these parameters could indicate either compromised elements or defective seals between the membrane elements in the vessels.

Once a breach has been identified in a system, there is a simple test which can identify which element has the breach. The NF and RO system design allows for passage of a conductivity probe through the center permeate pipe of the elements. As the probe moves through the elements, data are collected to produce a graph of conductivity concentration versus location within the PV. There can be as many as eight elements in a vessel, so instead of removing and testing each element, this method can be used to identify specific elements or seals that may be faulty. Emerging Integrity Testing Methods. Several NF/RO system integrity testing methods are currently under investigation. Most of these are based on surrogate measurements and include the passage of a dye, microspheres, ultraviolet absorption at a wavelength of 254 nanometers, particle monitoring, and fluorescently labeled indicators through the system. Many of these indicators can not be used while the system is in production, due to the risk of contaminating the product water. Also, the sensitivity of some indicators is dependent on the concentration in the feed water. For example, unless the organic content in the water is very high, UV254 absorbance is not reliable indicator.

Use of dyes such as Rhodamine WT is being considered as a potential surrogate. Kitis et al. (2002 and 2003) reported that Rhodamine dye injection to the feed flow showed promise for determining compromised NF or RO membranes or defective O-rings. Staff at Heemskerk have researched integrity testing methods for their RO system. A VHT is currently used for RO to determine the viability of a newly installed vessel of membranes (Kruithof, Kamp, and Folmer 2001 and 2002). The VHT is performed when the permeate sulfate or conductivity measurements exceed a target value. Kouidio and Madeleine (2002) used fluorescent microsphere separation to evaluate the integrity of three spiral wound NF membranes. A suspension of 1 micron diameter was fed to the membranes, and the permeate and feed streams were analyzed with a fluorometer. The calculated log removal for the NF membranes was near 5.5 log. Another method to assess membrane integrity involves challenging the membrane with a combination of a highly rejected and poorly rejected compounds (Urama and Marinas 1997). For instance, NF/RO membranes exhibit high removal of divalent ions such as magnesium and sulfate, while at typical operating pH, their rejection of boron is low. When the membrane is


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challenged with these two compounds, any breach in the membrane would exhibit proportionately higher passage of divalent ions compared to boron.

Verification of Integrity Tests

Membrane systems can undergo performance testing either on pilot- or full-scale to verify that they are functioning properly. There are many types of performance testing, but one common test is a fiber breakage test, often performed on a pilot-scale. Performance of fiber breakage tests allows for the evaluations of direct integrity tests (e.g., PDT, SIM, etc.) to detect a broken fiber or fibers, as well as to observe whether or not on-line indirect methods, such as turbidity and particle count monitoring, are able to detect the breakage. These data are sometimes required by State regulatory agencies during the approval process for membrane installation.

The City of Scottsdale, Ariz., required that membrane vendors perform fiber break tests during the pilot study to demonstrate the sensitivity of the PDTs to detect them, and how the turbidity and particle counts in the filtrate increased over time (Black & Veatch 2001). For Zenon’s ZeeWeed® 500b, the rate of pressure decay during the VHT was 0.26 psi per minute (psi/min), 0.51 psi/min, and 0.11 psi/min, before, during, and after the fiber break test. For the Pall MF system, the rate of pressure decay with a broken fiber was 15 times more than the decay rate with a repaired fiber. The particle count data before, during, and after the fiber break test were inconsistent, and illustrated the concerns with using particle counts for integrity monitoring.

Kramer et al. (2003) reported similar results for fiber break tests for pilot membrane systems at MWW. The results show how a broken fiber is detected with the unit’s integrity test. The turbidity of the filtrate before and after the fiber was cut was similar; however, the particle counts after the fiber was cut increased dramatically. The PDT and diffused air flow tests showed a marked increase in pressure decay with a cut fiber. For example, the pressure loss before the fiber cut was near 0.02 psi over five minutes, where as the pressure loss was about 0.7 psi after less than two minutes. Virus challenge testing was included in the performance testing for MWW to document the log removal of virus by each membrane system.

Performance testing can also include special operating requirements, such as being able to operate at 10 percent higher flux for eight hours per filtration cycle between cleanings. This test shows how much ‘stealth’ capacity is present in the design, and if the design flux is close to the maximum flux to achieve a cleaning interval target.

When integrating membranes into a WTP, it is necessary to conduct various tests to verify system performance. These can be conducted during various stages of the project (e.g., pilot testing or start-up), and can yield information to the utility and regulatory agencies about the ability to identify integrity breaches or to operate under high-flow conditions.

PROCESS CONSIDERATIONS FOR MEMBRANE INTEGRATION

Process considerations for membrane integration include focus on the interactions between the feed water, and possibly recycled backwash water, and the membrane material. Recognizing the impacts of certain water quality characteristics on membrane system performance helps to establish a successful membrane integration.


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Pretreatment for MF/UF

When integrating MF or UF membranes into a treatment train, choices made about pretreatment can have a significant impact on the performance of the membrane system. This section highlights some of the issues associated with installing pretreatment or treating feed water with no pretreatment.

Untreated Feed Water

Waters with very low turbidity (e.g., 1 to 5 NTU) and having no other water quality concerns (e.g., iron, manganese, heavy metals, etc.) can be fed directly to the membrane system. Pre-strainers (e.g., 100 to 500 μm) are recommended to protect the membranes in the event that debris or particles enter the intake to the plant. Pre-strainers should be designed to cope with any potential water quality changes (e.g., algal blooms) so that they do not limit production and become the bottleneck during these events. These pre-strainers are often automatically backwashed, and the resulting backwash stream must be disposed of or treated appropriately.

Coagulated Feed Water

The effect of coagulation on the performance of the membranes will depend on the type and dose of coagulants used, characteristics of the source water, and the membrane type. There is conflicting information presented in the literature about the impact of coagulation on membrane performance. This emphasizes the fact that each water source is unique, and the performance of membrane systems is dependent upon many factors. Some of the results are highlighted herein. The reader is also referred to another AwwaRF report that has been published by Howe and Clark (2002) for additional information.

Type of Coagulant. Selecting the type of coagulant for pretreatment is site specific, and the selection can be driven by water quality concerns (e.g., TOC) or by performance with a certain membrane. Ferric and aluminum salts are commonly used with membrane systems, but each has distinct advantages and disadvantages, depending on the goal of coagulation.

In general, ferric salt coagulants are typically better than aluminum salts for TOC and DBP precursor removal Smith et al. (1994); however, they can be more expensive and are more corrosive than the aluminum coagulants. With aluminum based coagulants, there is the risk of dissolved aluminum being carried through the membrane if coagulation conditions are not optimized. ACH and PACl coagulants are sometimes preferred by membrane suppliers because they exhibit a lower rate of TMP rise over time when compared to aluminum sulfate, and they have less potential for aluminum residual in the filtrate (Tragellis 2003).

There may be other drivers for selecting a certain type of coagulant over another. Shorney et al. (2001) reported that ferric sulfate was required because the source water experienced seasonal fluctuations in arsenic concentrations, and the iron-based coagulant was needed for effective removal.

When integrating membranes into a treatment plant, the choice of coagulant may be dictated by reasons other than membrane performance. Understanding the benefits and disadvantages of each type of coagulant for treatment and performance with a membrane system will help yield satisfactory performance of the integrated system.


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Impact on MF/UF Flux and Fouling Rate. Coagulation can improve membrane performance by reducing the fouling nature of the organics in the feed water (Wiesner and Laine 1996; Kennedy et al. 2002; Doyen et al. 2002; Howe, Clark, and Wang 2001). This may due to the neutralization of the charge of the organics and particles in the water during coagulation. Lahoussine-Turcaud et al. (1990) reported that when coagulation and flocculation produced particles with a zeta potential near zero (i.e., no charge), the impact of coagulation on flux was minimized.

A similar result was reported by Lee et al. (2000). A lower rate of fouling was observed in the dead-end mode of operation when coagulant doses created charge-neutralization conditions. For cross-flow mode, no difference in membrane performance was observed between the two coagulation mechanisms.

The type of coagulant can also affect the rate of fouling of a membrane system. Some pilot studies have shown premature fouling in the presence of iron-based coagulants when compared to aluminum based coagulants (Crawford and Bach 2001). Other researchers (e.g., Lerch et al. 2002) have shown better performance with iron-based coagulants.

Oxidized Feed Water

Many water quality conditions warrant the use of oxidation upstream of membrane systems. Chlorine, chloramines, ozone, chlorine dioxide, and potassium permanganate can be used for oxidizing a variety of contaminates, some of which are discussed herein.

If the source water contains dissolved iron and manganese, oxidation, possibly with chlorine, chlorine dioxide, or potassium permanganate, to the particulate form would be necessary for removal by MF/UF membranes. Also, when manganese is present, there is the potential for manganese fouling of MF/UF as well as NF/RO. Manganese can be removed by oxidation and adequate contact time. Schneider, Johns, and Huehmer (2001) reported on the performance of MF in removing oxidized manganese. Chlorine dioxide or permanganate with 20 minutes of detention time upstream of MF reduced the manganese from 0.95 mg/L to less than 0.05 mg/L in the filtrate.

For arsenic removal, the oxidized form, As(V), is better adsorbed and co-precipitated during coagulation than As(III); thus, oxidation upstream of coagulation and MF/UF may be necessary. Many oxidants are disinfectants, and they can be effective at limiting the microbiological growth in a feed water. Upstream disinfection can not only minimize potential microbial growth and the resultant fouling, but also minimize the release of biopolymers from microbes. With all membrane systems, it is critical to check that membrane materials are compatible with any oxidant or disinfectant. Some membranes are not tolerant (e.g., PP) to these chemicals, and if they are exposed to oxidants, the membrane fibers can weaken or change in pore size. Most membrane materials offered for potable water treatment are, however, oxidant tolerant.

Impact of Algae in Feed Water

Many source waters are subject to seasonal algal blooms, and they can cause operational problems (e.g., clogging) with pre-filters or with membrane operations (Freeman et al. 1997; Shorney et al. 2001; Thorner et al. 2001; Williams, Wert, and Dempsey 2002). One example


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would be from a pilot-scale evaluation of Aquasource UF for treating water from the Seine River in France. When algal counts in the raw water reached 5 x 103 cells/mL, the operating flux was reduced from the normal operating range of 42 to 54 gfd (70 to 90 lmh) to 36 gfd (60 lmh; Glucina, and Laînè 2001).

Another potential problem relating to algae in the feed water is fouling due to excretion of polymeric organic compounds from the algae (Her et al. 2002). These compounds are a diverse mixture of proteins, polysaccharides, amino acids, peptides, enzymes, vitamins, and other compounds (Wetzel 1975), and can cause significant fouling.

MF and UF membranes are not normally installed for algae removal, because algae can cause rapid fouling of the membrane system. Systems are generally designed to have algae removed by automatic backwashing pre-strainers upstream of the membranes.

Softened Feed Water

Several utilities are considering implementation of low pressure membrane filtration (MF or UF) downstream of a softening process. Because the effluent of a softening process is typically characterized by a higher pH and the potential for calcium carbonate precipitation, it is necessary to carefully assess the fouling potential and treatability of softened water at a particular plant. In general, at high pH, naturally occurring organic matter (NOM) and other charged particles will have a higher negative charge. This is also true for membrane surfaces, most of which are negatively charged (although some are neutrally charged; Liu et al. 2001). Feed water with higher pH would, therefore, be expected to enhance NOM rejection due to repulsive forces between the negatively charged particles and ions and the negatively charged membrane surface. The counter argument to this, however, is that at higher pH there is a greater potential for precipitation of sparingly soluble salts such as carbonates. These factors further illustrate the complex physical and chemical interactions that occur when integrating membranes into treatment trains. Researchers continue to investigate the use of membranes for filtration after softening. Kweon and Lawler (2001) used bench-scale studies to assess the impact of different levels of softening on membrane flux. In general, softening improved the flux when compared to raw water filtration by UF, and in one study, recarbonation dramatically improved filtration, implying that increased stability by increasing alkalinity and reducing pH after softening minimizes the fouling potential of the water. There is concern that precipitation of CaCO3 during softening can occur within the membrane material. In studies by Kweon and Lawler (2002) softening for calcium removal (i.e., CaCO3 precipitation) did not impair the flux of an UF system. It was hypothesized that the precipitation occurred on the membrane surface and not within the membrane pores. The precipitation of magnesium hydroxide (Mg(OH)2) during softening reduced the fouling potential for UF, presumably because Mg(OH)2 effectively removes NOM during softening, thus reducing the fouling potential of the feed water. More and more lime softening utilities are investigating low-pressure membrane filtration as the filtration barrier at their existing WTPs. Kansas City, Miss. (Brown, Hugaboom and Crozes 2004), WaterOne of Johnson County, Kan., and Minneapolis, Minn., have all conducted pilot-scale evaluations to identify potential integration issues when softening occurs upstream of membranes.


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PAC Treated Feed Water

Pretreatment upstream of MF/UF with PAC, with or without coagulation, for the removal of either organics or taste and odor causing compounds has been considered by several investigators, because PAC addition could affect the hydraulics of the system, and could potentially shorten the production time between backwashing or cleaning. Huey et al., (1999) reported 50 percent reduction in filtration run time when PAC dose was increased from 10 to 20 mg/L upstream of a MF unit that was operated in dead end mode at a flux of 53 gfd (90 lmh). The impact of PAC addition on run length was less dramatic for the cross-flow UF system, especially at high fluxes (i.e., 65 to 68 gfd; 110 to 115 lmh). There have also been reports that PAC addition actually helps scour the surface of the membrane and keeps the membrane cleaner for longer periods of time; however, there are concerns that the long-term use of PAC could cause abrasion and weakening of the membrane materials (Huey et al. 1999).

Operating parameters, such as backwash interval and flux, may need to be modified to optimize the effectiveness of PAC in the process. Schideman, Kosterman, and Rago (2001) investigated removal of MIB using PAC during a pilot-scale study with submerged UF (i.e., ZeeWeed® 1000) to treat a low-turbidy, cold lake source. Longer backwash intervals, which translated to longer PAC contact time in the tank, improved MIB removal (e.g., 45 percent removal at a 30-minute interval versus 50 percent removal at a 180-minute interval). After pilot testing, the design flux for the system was set to 23.5 gfd (40 lmh) with a backwash interval of 180 minutes. They also reported that the membrane fouling was independent of the PAC dose.

Impact of Clarification Upstream of MF/UF

If coagulation and flocculation is required to treat a source water, the addition of a clarification process upstream of membranes lowers the solids loading on the membrane filters. This helps to minimize the rate of fouling and to increase the sustainable flux of the membrane system. Typically, clarification processes reduce the overall life cycle costs of a membrane facility, but depending on site specific conditions such as cost of construction and availability of space, some utilities treat the coagulated water directly with membranes (for example, the City of Scottsdale’s UF plant, which is discussed later in this report). If space is not an issue, in general, clarification improves the performance of the membrane system. For example, the San Patricio WTP uses coagulation and sedimentation upstream of Pall MF units, and attributes a longer than expected cleaning interval on the use of pre-sedimentation upstream of the membranes and the practice of operating at moderate flux (Roach and Vickers 2001).

One benefit of using pretreatment upstream of membranes is to reduce the variability of membrane feed water quality when treating flashy source waters. Flashy source waters are those that can experience rapid (i.e., within minutes) water quality changes (i.e., turbidity, solids, organics) in the feed water due to events in the watershed, like rainfall or mudslides. The Bexar Met facility in Texas uses a solids contact clarifier to pretreat water from the Medina River. The solids contact clarifier has been able to provide feed water to the membranes with turbidity less than 12 NTU, even when the raw water turbidity exceeded 4,000 NTU (Campos et al. 2002). This allowed for stable operation of the downstream Aquasource UF system, despite wide fluctuations in the source water turbidity. Braghetta, Price, and Kolkhorst (2001) reported that with pre-clarification during pilot studies in Texas and California, the operating flux of membrane systems was increased by 19 to


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50 percent. It should be noted that PAC was added during the pilot tests, and could have reduced fouling of the membranes by lowering the organic loading to the membranes.

Pre-sedimentation may have a lesser significant impact on the flux for submerged systems, because these systems can often operate with a higher solids loading in the process basin. Crawford and Bach (2001) reported that sedimentation improved the operating flux by less than 5 gfd (8.5 lmh) for a submerged Zenon UF system.

Tragellis (2003) described the relationship between membrane fiber packing density within the module and the membrane’s ability to cope with various coagulant dosages and the need for presedimentation. In general, a high packing density can cope with up to 20 mg/L ACH [typically 21 percent aluminum oxide (Al2O3)]. For 20 to 100 mg/L ACH, modules with an intermediate packing density would be recommended and for waters requiring greater than 100 mg/L ACH, pre-clarification is recommended upstream of a high packing density membrane module.

When integrating membranes into a treatment plant, it may be possible to treat water from a clarification process. The benefits of this are a higher sustainable flux, a more stable membrane feed water quality allowing stable membrane operation, and a lower cleaning interval. Each of these benefits translates to lower capital and operating costs. A higher flux translates to lower capital costs because fewer membranes would be installed, whereas consistent operation and fewer chemical cleans translates into lower operations and maintenance costs.

Pretreatment to NF/RO

NF and RO are being considered by several utilities for removal of DBP precursors such as TOC, hardness, SOC, and inorganic compounds, such as TDS, nitrate and perchlorate. The performance of NF/RO is highly dependent on the feed water quality and hence requires significant pretreatment. The SDI is commonly used to determine if pretreatment is required. Even though SDI values below 3 are generally recommended, studies have indicated that fouling due to organic compounds can occur. In the past, conventional treatment was typically the only pretreatment considered for NF/RO; however, with their increased acceptance, MF/UF membranes are being considered for pretreating RO/NF feed water.

Pretreatment is needed to remove particles from the NF/RO feed stream, as well as remove any other contaminants that may later precipitate as a scale in the NF/RO concentrate stream. It is important to recognize that excessive inorganic fouling can occur if conventional treatment with aluminum sulfate leaves residual dissolved aluminum in the membrane feed water. Dissolved aluminum can react with silicates to form aluminum silicate, which can serve as a nucleation site for inorganic fouling compounds, such as calcium carbonate (Gabelich et al. 2001). EDTA and citrate antiscalants may help inhibit fouling for some waters. Inorganic fouling by sulfite is also a concern for NF and RO systems. In some cases, coagulation can be used to remove colloidal and particulate sulfur in upstream processes. This was accomplished in a groundwater pilot study in Ohio. Oxidized sulfur yielded a feed turbidity of 60 to 120 NTU, which was effectively removed by UF with up to 50 mg/L ferric chloride and hydrochloric acid addition (Best, Singh, and Kendrick 2002). The lower sulfite concentration entering the NF system resulted in a decreased rate of fouling.


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Comparison of MF/UF to Conventional Pretreatment

Several studies have shown that the performance of RO/NF improves when MF/UF is used instead of conventional processes for pretreatment. Glucina, Alvarez, and Lane (2000) compared the performance of RO in treating saline water with conventional as well as MF/UF pretreatment. They reported better performance with MF/UF pretreatment; however, they noted that some fouling of RO membranes was caused by organic compounds that are not removed by MF/UF. Jacangelo, Chellam, and Bonacquisti (2000) also reported MF and UF pretreatment resulted in less NF fouling and longer cleaning intervals compared to conventional pretreatment. Kommineni et al. (2001) found similar results.

The SDI of conventional treatment is often higher than that of MF/UF, and this would suggest that MF/UF would be a better pretreatment for NF/RO. Glucina and Laînè (2001) found that the SDI of the UF filtrate was 1.2, whereas the SDI of conventionally treated water was 4.3. The authors noted that fouling of the downstream RO process still occurred after UF, possibly due to the organic compounds in the feed water (i.e., 2.4 mg/L TOC in UF filtrate versus 1.4 mg/L in conventional plant clarified water). Similarly, Galloway and Minnery (2001) reported that the SDI of water produced by a multi-media filter can be 1 to 3 SDI units higher than by UF treatment.

When integrating NF/RO into a WTP, the type of pretreatment should be considered carefully. MF and UF have been shown to perform well; however, their inability to remove organics could result in organic fouling of the NF/RO membranes. The SDI of MF/UF filtrate is usually lower than that of conventionally treated water, but as shown in the previous discussion, it should not be used to indicate the degree of fouling that can occur.

Bank Filtration

When source water quality varies seasonally, it can be challenging for a pretreatment process to provide a consistent feed water quality to membrane systems. Bank filtration has been shown to be effective at dampening seasonal water quality fluctuations to provide a consistent, and sometimes superior water quality, to a treatment plant.

Bank filtration involves drawing water from the banks of a river or from production wells near a lake. As the water passes through the subsurface media, the water quality typically improves due to microbial and physical processes, such as filtration by subsurface porous medium. Fluctuations in water quality are reduced due to retention time of the water in the subsurface, and dilution with ground water occurs, depending on the local hydrogeology. Even temperature fluctuations are dampened by bank filtration, to yield a more uniform temperature profile. A detailed description of river bank filtration can be found at Kuehn and Mueller (2000) and references therein.

Merkel, Speth, and Summers (1998) compared the performance of NF when treating conventionally treated surface water, bank filtered water, and bank filtered water blended with ground water. Results indicated that bank filtered water caused less flux decline compared to conventionally treated water. The flux loss that occurred when treating bank filtered water could be recovered with cleaning, while the flux loss with conventionally treated water could not be recovered with cleaning procedures. Higher concentrations of iron were observed in the bank filtered water than in the conventionally treated water, and this contributed to some of the fouling of the NF membrane. Speth et al. (1999) found similar results, which are summarized in Table


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B.6. The NF system required fewer cleaning cycles when the water from the two bank filtered sources was used.

MF Versus UF for Pretreatment

Both MF and UF can be used as pretreatment to NF/RO systems. The important difference between MF and UF is that the smaller pore size of UF may result in a lower SDI value of the filtrate (Harris 2001, Galloway and Minnery 2001). In general, the higher the SDI, the greater the fouling of downstream NF/RO; therefore, a lower SDI is desired. It must be noted, however, that organic compounds play a role in NF/RO fouling, and because MF/UF alone does not remove them, the fouling potential of MF/UF filtrate may still be high.

Oxidized Feed Water

As mentioned previously, many NF/RO membranes are made of PA, which is not tolerant to oxidants. Exposure to oxidants can alter the effectiveness of the membranes or cause deterioration and failure of the system. Deterioration in performance was observed by Seamans, Lozier, and Kommineni (2003) when chloramines were applied to RO feed water to control microbial fouling. The RO membranes experienced a 50 percent increase in salt passage, and the original salt rejection properties of the membrane could not be recovered.

Table B.6 Impact of bank filtration on feed water quality and cleaning frequency of NF

Feed water to NF Mean turbidity & TOC

Est. cleaning frequency

(days)

NF flux loss* (percent)

Bank-filtered water (Ohio River, Louisville)

0.1 NTU 2.2 mg/L

75 24

Conventionally treated water (Ohio River, Louisville)

0.05 NTU 4 mg/L

36 46

Conventionally treated water (Ohio River, Cincinnati)

0.23 NTU 2 mg/L

8 36

Conventionally treated water (Lake in SW Ohio)

0.5 NTU 3.2 mg/L

8 50

Bank-filtered water (Ohio River, SW Ohio)

NA 2.3 mg/L 62 12

* after approx. 62 days of operation Source: Data from Speth et al. 1999

A secondary impact of oxidation upstream of membranes is that it can change the nature of the organics in the water. Plottu et al. (2002) found that ozonated water caused a higher rate of fouling than water that was not ozonated. The authors noted that the SDI was low; however, the observed fouling indicated that SDI may not always be a good indicator of fouling for NF. Subsequent research at the same facility by Her et al. (2003) suggests that ozonation increased


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the release of proteins and polysaccharide-like substances from microbes, which have been the primary cause of fouling.

Treatment of Backwash Water

Many membrane facilities use a secondary membrane system for treating waste backwash from the primary membrane system. These units can effectively increase the overall recovery of a membrane filtration facility. For example, secondary treatment at Sweetwater, Texas, increases the recovery from 90 percent to as much as 99 percent (Hibbs and Kendrick 2003). The other benefits realized by implementing secondary treatment at Sweetwater were (1) a lower volume of waste being discharged to the sewer, and (2) the cost savings gained because new source development would not be required at the higher recovery.

When designing the secondary units, it is important to consider the nature and quantity of solids and colloids that will be present in the feed water. It is difficult to pilot test secondary units, because the backwash flows from membrane pilot skids are typically too low to provide continuous supply of feed water to a secondary membrane pilot skid. To account for this, a conservative design, in terms of flux, backwash interval, and cleaning interval is often used.

Flux Considerations

The design flux for treating backwash water from an MF/UF primary treatment unit or a conventional WTP is low because the solids loading on these systems is typically quite high. Operating data from the Southside WTP in Texas, (Lynk, Briggs, and Petry 2001) shows that the feed water turbidity to the secondary units (Aquasource UF) was around 1,500 NTU, which is almost 20 times more turbid than that of the feed water to the primary units (Aquasource UF; feed turbidity = 76 NTU). The design flux for the primary and secondary units is 76 gfd (130 lmh) and 47 gfd (80 lmh), respectively; however after optimizing treatment during the first four months of full-scale operation, the primary and secondary unit fluxes were increased to 80 gfd (136 lmh) and 59 gfd (100 lmh), respectively. The secondary flux is about 75 percent of that for the primary system, and both systems are operated in a dead-end configuration.

The Carmichael Water District in California, also uses secondary membranes to treat the backwash from its primary membrane system, which consists of twelve USFilter CMF units. The mean flux for the primary units is 80 gfd (136 lmh) at 68ºF (20ºC) and for the secondary units, 47 gfd (80 lmh) (Nugent, Boettcher, and Sorgini 2003).

Sometimes conventional water treatment plants install membranes for backwash water treatment. Willemse and Berkvoort (1999) reported results from pilot and full-scale treatment of backwash water from sand filters. The MF membrane was successful in recovering 93 percent of the backwash water at a flux of 94 gfd (160 lmh).

There are no regulatory limits on flux for backwash treatment, unless the filtrate from the secondary system delivered to the distribution system. If this is the case, then the flux of the secondary membrane units must be approved by the regulatory agency with primacy. Other regulatory aspects are discussed in the Recycle Alternatives section of this chapter.


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Waste Stream Contaminant Concentration

The use of membranes for treating backwash water will result in the concentration of contaminants that were in the feed water. Reissmann et al. (2002) evaluated UF for the treatment of filter backwash water at Dresden, Germany. The filter backwash contained contaminants such as arsenic, cadmium, and aluminum, and UF concentrated these contaminants to higher levels than were currently being discharged to the local WWTP. For this utility, however, the volume of water discharged was much less (i.e., 80 percent) and the cost savings for a lower discharge volume was greater than the higher fee for elevated contaminant concentrations.

Regardless of the application, the waste stream of any membrane facility needs to be assessed to identify the type and concentration of contaminants and solids. This information is used to identify feasible disposal, handling, and/or treatment options for the backwash waste streams.

Recycle Alternatives

The filtrate from the secondary membrane system is often recycled to the head of the plant. This is due to concerns of potential integrity breaches in the secondary system. Because the secondary system treats backwash water that is concentrated by the primary membrane system, the concentration of pathogens is likely to be several orders of magnitude higher than that of the primary system, as reported by Schaefer, Reiss, and Malmrose (2004). They report that Giardia and Cryptosporidium can be concentrated 7 to 50 times in MF/UF backwash flow. Any integrity breach in the secondary system could result in higher risk of pathogen break-through. Many regulatory agencies are reluctant to allow WTPs to put filtrate from secondary systems into the finished water supply, and require that secondary filtrate be recycled to the head of the treatment plant, sometimes to a location upstream of coagulant addition. The USEPA’s Filter Backwash Recycling Rule (FBRR) of 2001 does not have flow restrictions or water quality requirements for filter backwash recycle streams. Instead, the FBRR outlines how and what to monitor for local State agencies to review. Some states, however, do have guidelines for recycle streams. The California DHS follows guidance from Appendix K of the State’s Surface Water Treatment Rule (DHS 1994), which limits recycle flow to 10 percent of plant incoming flow. Although these guidelines were developed for conventional filter WTPs, utilities and engineers follow these guidelines for membrane systems as well.

Also in California, the CAP recommends that any recycle stream be chemically treated (e.g., by coagulation) and have a turbidity of less than 2 NTU. Although secondary membrane systems would not necessarily use a chemical treatment process for solids removal, it will be easy for these systems to meet the 2 NTU turbidity requirement for recycled water. In areas where water is scarce, utilities strive to increase the total system recovery to minimize the quantity of wasted water. Some facilities closely monitor integrity of their secondary systems so that the filtrate can be supplied as finished water. One utility, Carmichael Water District in California, has collected data to justify to the California DHS that their secondary permeate is suitable for supply (Nugent, Boettcher, and Sorgini 2003). The high quality source water, which is from collector wells in a river alluvium (i.e., similar to bank filtration, as discussed previously), will be a factor in the regulatory agency’s decision. Monitoring of the source water has shown no Cryptosporidium and only two Giardia cysts in over 100 samples collected.


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Sometimes recycle alternatives are investigated, because the options for waste discharge are limited. For example, the Summit County MF plant in Utah, is investigating recycle options to reduce the volume of water being sent to the water reclamation district (Campbell 2003). The plant was operating with about 90 percent recovery, but alternatives to increase the recovery to 98 percent were investigated. The two alternatives investigated included:

1. Backwash from the primary system is treated by coagulation, inclined plate sedimentation, and secondary membrane filtration. The filtrate would be used for backwashing the primary units, and the secondary backwash, cleaning chemicals, and settled solids would be delivered to the sewer.

2. The same as alternative No. 1, except that the filtrate from the secondary membrane system would be delivered to supply.

Both of these alternatives would provide 98 percent recovery. Summit County is

collecting data to verify that safe water would be delivered in alternative No. 2. Another option is to recycle the secondary membrane units instead of primary units, as at

the Ennerdale WTP (Hillis 2001). At this facility, a thickener treated backwash from the secondary membranes and the decant form the thickener is recycled to the secondary units. The filtrate form the secondary membrane is delivered to distribution.

In some instances, it may be possible to return waste backwash water from the MF/UF treatment process back to the head of the treatment plant, without chemical treatment or filtration. This can be considered if sufficient pretreatment is available upstream of the primary membrane units to provide removals of particulates from the treatment system. The MWW utilizes this approach at its Columbia Heights WTP.

Variability in Source Water Quality

Although membranes will provide a consistent water quality (as long as the integrity of the system is maintained), their ability to reliably produce water depends on the variability of the source water quality. For example, if the turbidity in the feed water increases dramatically, MF/UF systems will continue to produce high quality water; however, water production may be restricted due to the need to increase the backwash and cleaning frequencies or to lower the flux to limit the fouling rate.

It is important to determine all possible changes to water quality when integrating membranes into a water treatment system. For example, Kiefer, Brinson, and Suratt (2003) reported that during a drought in Boca Raton, Florida, well water quality deteriorated, and well field cycling increased. The combined effect was high hydrogen sulfide and entrained air in the feed water. The NF pilot plant was able to treat the feed water; however, the fouling rate was high due to colloidal sulfur and iron in the feed water. Although adverse water quality can sometimes be unavoidable, anticipating and planning for it can provide utilities with alternative sources or practices to minimize its impact on the membrane’s production capability.

Wastewater as Feed Water (i.e., Reuse)

Reuse of wastewater is becoming increasingly common, especially in regions where water is scarce. Membranes offer a robust treatment technique with unique challenges for


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treating WWTP effluent. This is because of the variability in water quality (e.g., nutrient loads, alkalinity, solids, etc.), which can affect membrane performance. Wastewater also tends to contain biopolymers, such as polysaccarides, that cause premature fouling of membranes and promote biofilm development (Laab et al. 2002). Although these challenges persist, lower flux and more frequent CEBWs are typically used to maintain performance.

Membranes can also be used to treat raw, untreated wastewater in submerged configuration, which are referred to as membrane bioreactors (MBRs). These systems generally operate at a low flux, and sometimes use continuous air agitation for aeration, depending on the process needs. This discussion focuses on membranes in reuse applications, because they relate to the potable water industry more directly than MBRs.

The Luggage Point reuse facility, which has MF followed by RO in Brisbane, Australia treats nitrified and denitrified secondary effluent. This plant has experienced (1) algal blooms and occasional scum carry-over which clogged pre-screens, (2) high rates of biofouling, and (3) variable alkalinity which caused inorganic fouling of the RO (Hopkins and Barr, 2002). Although these challenges persist, the system is effectively filtering the water to the desired water quality.

In some cases, NF/RO treatment of WWTP effluent is not necessary for achieving specified water quality goals. Bergman and Porter (2002) reported that demonstration- and pilot-scale testing at Gwinnet County, Georgia, showed that conventional tertiary treatment using coagulation and clarification for phosphorus removal, followed by MF/UF, ozone, GAC, and post-ozone achieved the water quality targets as specified for the discharge permit. NF had also been evaluated downstream of MF/UF, and even though ammonia levels were lower after NF treatment, the MF/UF treatment train achieved compliance.

Post Treatment Requirements

Post treatment includes disinfection downstream of filtration and stabilization of the water, in terms of pH and alkalinity, to minimize corrosion control. The requirements differ for MF/UF versus NF/RO, as discussed below.

MF/UF Post Treatment

For corrosion control, MF/UF systems typically have the same post treatment requirements as conventional media filters. If pH adjustment and alkalinity enhancement are necessary after media filtration, it is likely that it will also be needed after membrane filtration. This post treatment depends on the water chemistry during the treatment process, and varies considerably from site to site.

Despite their proven ability to achieve higher removals of pathogens than required by regulations for Giardia cysts and Cryptosporidium oocysts, many state regulators require disinfection downstream of membranes as an additional barrier of protection. Typically, 0.5-log Giardia and 2-log virus inactivation through disinfection is required downstream of membrane processes.


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NF/RO Post Treatment

Post treatment of NF/RO product water typically involves a reduction of corrosivity of the filtrate, which is devoid of ionic constituents. This is accomplished by adjustment of pH, alkalinity, and hardness, and is referred to as stabilization. The stabilization requirements will depend on the NF/RO permeate quality, extent of bypass and blending of the system, and quality of the water from other sources in the distribution system.

In general, the objectives of post treatment are to produce a positive Langelier saturation index (LSI) and a positive calcium carbonate precipitation potential. Otherwise, the finished water is likely to dissolve the protective layer of carbonate scale which typically exists in the distribution system and protects against corrosion of the distribution system infrastructure. Typically, addition of lime or caustic soda is practiced to increase the pH of finished water. In some cases, addition of sodium carbonate or carbon dioxide is also required to increase the alkalinity of the water to ensure its compatibility with the existing water in the distribution system. Another way to assess adequacy of post treatment would be to conduct corrosion testing using pipe loop systems with existing pipes, as was done by the City of Scottsdale, Ariz., (Kommineni et al. 2003). In their study, blending of RO permeate with bypass water reduced the corrosivity of the finished water, and a phosphate-based corrosion inhibitor was not deemed necessary.

DESIGN CONSIDERATIONS FOR MEMBRANE INTEGRATION

Design issues, such as hydraulics and footprint, must be considered when evaluating membrane integration into a WTP. Sometimes, these are the most important issues in the decision making process. The following section includes examples of plants where the design issues have been carefully considered.

Retrofitting Existing Infrastructure

One of the benefits of membrane integration is the possibility of re-using existing infrastructure for the new equipment. Sometimes existing buildings or even process trains may be retrofitted to allow integration of membrane processes. One common design consideration is the installation of submerged membranes in existing filter bed basins.

When examining a retrofit alternative for any plant, the cost of alternative membrane locations, as well as applicable alternative processes, must be considered to make the most cost-effective decision for a particular plant. For example, in an evaluation of processes to improve pathogen control for Sheboygan, Wisconsin, a new ozone contactor was found to be less expensive than a submerged (customized or proprietary) membrane retrofit option (Roquebert et al. 2001). Ozone was identified as a process alternative to membranes because ozone could yield the necessary disinfection by inactivation for the WTP. At this facility, land space was available for new processes; but in other instances, the lack of available land area may limit the viable alternatives, making retrofitting existing filter basins with membranes the most technically feasible solution.

There are few examples of retrofitting membrane equipment into an existing filtration bed. One such example is the Marmagen municipality in Germany (Mende, Ohle, and


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Lehmkühler 2002) where a Zenon ZeeWeed® 1000 has been installed into the existing sand filter bed basin to treat a groundwater that is subject to turbidity spikes. This successful integration has established a firm 0.26 mgd (1 ML/d) capacity in only half of the existing filter bed area, leaving space for future expansion. The City of Kennewick, Washington, is also installing submerged membranes into existing filter beds and this will help to double the plant’s capacity (Norton et al. 2004). This WTP should be producing water in late 2005.

Limited Footprint

Membrane processes often require a smaller footprint than conventional processes, and when utilities have limited space available for an upgrade or expansion, membranes are often considered. For example, the smaller footprint of membranes was one of the main drivers for considering UF membranes at the Southside WTP in Texas (Lynk, Briggs, and Petry 2001) and MF membranes at the Duncannon Borough Water System in Pennsylvania (Williams, Wert, and Dempsey 2002). The Second Taxing District Water Department (STWD) of Norwalk, Conn., investigated several treatment alternatives, including encased and submerged membranes, for an upgrade to the existing conventional facility (Bonett et al. 2001). The process alternatives included various combinations of pretreatment and low-pressure membranes for filtration. It was concluded that the process alternatives using membranes could easily fit within the available land area, while allowing remaining space for use during future expansions. The other alternatives required too much land space, limiting space for future expansion. Membrane suppliers continue to develop membrane designs to minimize land space requirements. Sorgini (2003) reported that USFilter’s submerged MF system has a footprint that can be 55 to 75 percent smaller than USFilter’s encased MF system. Small footprint was one of the main design challenges for installation of UF membranes by Severn Trent Water, Ltd., at four of their sites deemed at risk from Cryptosporidium oocyst contamination (de Lande Long 2002). For example, the Llandinam WTP, UK, treats 6.3 mgd (24 ML/d) in less than 4,300 ft2 (400 m2) of land area.

Capacity Requirements

When integrating membranes into WTPs, the future capacity needs of the full-scale membrane facility need to be carefully evaluated. If possible, space for additional membrane units should be allocated in the design for future capacity expansion or to add modules in the event that source water quality changes to the extent that additional membrane area is needed.

One example is Yorkshire Water, which experienced their worst flood in over 400 years during the weeks prior to commissioning their Keldgate facility. The turbidity in their wells increased to 16 NTU, which was higher than ever recorded (Franklin, Knops, and Smith 2001). Membrane systems provide consistent water quality, regardless of the feed water quality; however, deterioration in feed water quality can result in increased frequency of backwashing and chemical cleaning and may even be accompanied by a decrease in sustainable operating flux.

Some utilities have installed additional capacity during construction to minimize the risk of lower-than-expected production and to allow greater flexibility in plant operations. When the San Patricio WTP was constructed, an additional Pall MF membrane unit with a capacity of 1.3 mgd (4.9 ML/d) was installed. This additional capacity afforded the utility increased assurance


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of meeting the water demands of the service area, as well as allowing the plant to operate at a moderate flux (52 gfd; 88 lmh), that helped extend the cleaning interval for the system (Roach and Vickers 2001).

Waste Stream Treatment Capacity

The integration of waste recovery treatment systems is critical to the stable operation of the membrane process. If the backwash equalization basin capacity is not adequate, overall plant production capacity could be limited. Where secondary membrane units are installed to recover waste, the operating flux has to be carefully selected and the equalization tanks must be designed with sufficient volume to account for the system shutdown during backwashing, fiber repair, and integrity testing. The Clay Lane WTP in England, found that frequent integrity testing and fixing of fibers in the secondary units limited the production through the plant. This is because integrity testing is an off-line procedure and, if defects were found, the rack on the unit would need to be removed from service until repairs were made, further limiting production (Oxtoby 2003). The permeate from the secondary units is delivered to the head of the WTP, so the need for stringent integrity in the secondary units was not as great as for the primary units. Once the frequency of integrity tests on the secondary units was reduced, more stable operations of the whole plant were achieved. This illustrates the importance of balancing of waste stream management with the production of the entire plant.

Regulatory Compliance

The integration of membranes into a WTP may impact how a utility monitors and reports regulatory compliance for disinfection and turbidity removal.

Impact on Disinfection

Integration of membranes can impact disinfection practices at a treatment plant. For example, if membranes are installed at an existing facility, the disinfection credit gained via the removal mechanism of membrane filtration could increase substantially. Other chemical disinfection practices at the plant, either in pretreatment basins or in downstream basins could also be reduced due to removal credit by membranes, and this would translate into lower operating costs, as well as lower DBP formation if chlorine is used.

The overall disinfection regime at a WTP must be approved by the governing regulatory agency. State regulatory agencies require multiple barriers and any changes to existing disinfection practices are generally discouraged. This section highlights examples of some of the impacts of membrane integration on disinfection practices. The City of San Diego, Calif., carefully examined the total disinfection requirement needed if membranes were to be integrated into their Otay facility (Alspach et al. 2001). The existing facility uses coagulation, sedimentation, and filtration. MF/UF was evaluated as a replacement for the existing media filters. One of the water quality goals was to minimize TTHM and HAA5 concentrations in the finished water, and lowering the chlorine dosage at the plant was identified as one method to achieve lower DBP concentrations. The California DHS required multiple barriers for Giardia and virus inactivation/removal and requested that a


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scientific assessment be conducted. Bench-scale studies were performed to determine the optimum disinfection scheme to maximize inactivation while minimizing DBP formation. The recommended design included chlorination of settled water upstream of membranes followed by chloramination in a clearwell downstream of membranes. This example illustrates that although membrane integration incorporates a rugged disinfection barrier, some utilities may still need to include multiple barriers of chemical inactivation to meet regulatory requirements. As with conventional treatment processes, when a chlorine residual is carried through a membrane process, disinfection credit for virus or other pathogens may be granted, depending on approval from the presiding regulatory agency. One of the challenges faced by utilities using chlorine, for example, for disinfection credit is that short-circuiting can occur within a basin, thus limiting the disinfection capability of the process. Submerged membranes, with their unique flow pattern and inherent hydraulic mixing, have been shown to yield a high degree, the T10/Ttheor ratio (0.77), which is the ratio of contact time for 10 percent of the flow versus the theoretical contact time for a basin which is higher than most contact basins, USEPA (1989); Martin et al. (2003). This would be beneficial for utilities wishing to minimize the contact time with chlorine, and could possibly be used to achieve a portion of the chemical disinfection requirement. MF Versus UF for Disinfection Credit. The decision to use UF versus MF treatment should not be solely dependent on the fact that UF can achieve greater virus removal than MF. As mentioned previously, some states require a certain level of inactivation downstream of treatment (regardless of log removals granted for MF or UF), and virus inactivation can be readily achieved when using common disinfectants (e.g., chlorine, chloramines, etc.). There are enough differences in performance and operation of the various MF and UF systems in the drinking water industry, and each should be carefully considered to select the most suitable system for a specific water quality or location.

Although some utilities will choose to inactivate viruses by chlorine or other disinfectants in the WTP, some facilities rely on the virus removal of membranes to meet removal and disinfection requirements. The Heemskerk WTP in The Netherlands, for example, integrated UF followed by RO to achieve adequate disinfection without chemical addition (Kruitof, Kamp, and Folmer 2001). The required level of virus removal was 3.6-log, and UF followed by RO accomplished as much as 8-log removal when the integrity of both membrane systems was not compromised. Extensive pilot testing was performed with MS2 bacteriophage spiking to verify the virus removals. It should be noted that this utility does not apply chlorine as a matter of policy and is not required to do so by regulations that apply to utilities in The Netherlands.

Pathogen Removal by NF/RO. Most regulatory agencies do not give removal credits for NF/RO membranes; however, these membranes have been shown to achieve certain levels of pathogen removal in research studies. Lovins and Taylor (2003) reported that composite thin-film NF membranes achieved about 5.5-log removal when challenged by several different microorganisms in a pilot study. CA NF membranes achieved only about 2.1-log removal. Lovins and Taylor (2003) also reported that the use of MF or UF followed by NF provided significant log removals of virus (e.g., from 5.1- to 12.8-log). For some applications, the log rejection is not relevant as a portion of the flow typically bypasses the NF/RO treatment process. The bypass flow would need to be treated further to achieve similar log removals. This is particularly true for softening applications.


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NF/RO membranes are not recognized by the SWTR as alternative filtration technologies, and receive no credit in the USA for pathogen removal. Other countries (e.g., The Netherlands) do grant removal credits for viruses.

Turbidity Monitoring and Reporting

Having both media and membrane filters at a WTP may require different monitoring and reporting requirements for compliance with turbidity requirements. In Canada, two separate turbidity limits were established for a WTP with a membrane train and a media filter train. The turbidity limit for the media filter train is <0.03 NTU 95 percent of the time, and for the membrane train, <0.1 NTU, 95 percent of the time (Suthaker and Drachenberg 2003). Canada’s Federal-Provincial-Territorial Committee set up this technology specific guidelines because it was recognized that the two technologies could achieve different turbidity levels.

NF/RO Concentrate Disposal

NF/RO membranes, as discussed earlier, generate a concentrate stream that needs to be disposed of in an acceptable manner. Typically, the amount of concentrate flow is dependent on the feed water quality and varies from 10 percent to 25 percent of the feed flow. The quality of the concentrate depends on the feed water quality. In general, the concentration of various charged constituents in the concentrate is 3.5 to 5 times as that in feed water, depending on the recovery and membrane rejection capability. In addition, chemicals, such as antiscalants and acid, are added upstream of the NF/RO process and these chemicals are also concentrated in the concentrate steam. Concentrate disposal is an important issue, because failure to find an acceptable means of concentrate discharge may prevent implementation of NF/RO membrane processes.

A good review of these regulations and current practices can be found in Mickley (2000), Mickley (2001), and AWWA (2004). Concentrate from the NF/RO systems is typically disposed of either by direct or indirect (i.e., via sewer) discharge to a water body, underground injection, management in lagoons, and land disposal/application. Of all these alternatives, disposal to a surface water, sewer, or to a WWTP are the most common options.

Deep well injection, typically an expensive alternative compared to surface discharge, is primarily used in Florida, and environmental concerns with deep well injection make it a less desirable option for many utilities. Some industrial users implement zero liquid discharge (ZLD) technologies, which use thermal processes on a small-scale.

Each of these means of disposal is regulated by one or more of federal and state regulations. Federal regulations that govern these discharges include Clean Water Act’s National Pollutant Discharge Elimination System (NPDES) program, Dredge and Fill program and Resource Conservation Recovery Act, Safe Drinking Water Act’s Underground Injection Control Program, and the Clean Air Act. In addition, if the effluent is known to contain an identified pollutant such as radionuclides or arsenic, then an effluent limit is typically set for the known pollutants in the discharge permits. To determine the toxicity effects of constituents in the effluents, many utilities are now requiring performance of whole effluent toxicity (WET) tests, and in recent years, several utilities that use advanced processes such as RO are failing those tests, requiring the utilities to determine the cause of failure, with Toxic Identification Evaluations. In addition, applicable state regulations differ from federal regulations in some


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important aspects that include surface water quality standards, regulation of solid waste landfills, protection of local aquifers, and other land application activities.

Because of these regulatory issues and due to increasingly limited concentrate disposal alternatives, in recent years there has been significant interest in use of ZLD volume minimization technologies for eliminating or reducing concentrated residuals from advanced processes. However, ZLD volume minimization technologies still can generate some residuals that need to meet the regulatory requirements for their disposal. Even an ideal ZLD technology generates solid residual whose disposal, particularly if no beneficial use is identified, needs to be disposed of in an acceptable manner. In some instances, complete ZLD may not be feasible, either due to the nature of the concentrate or due to the cost.

As mentioned previously, the simplest alternative is disposal to the sanitary sewer, and a few examples are listed below. This was the only feasible option for the Village of Chelsea in Michigan, (Wagenmaker et al. 2003). Concentrate from the low pressure RO softening plant is expected to contain greater than 1,000 mg/L TDS, and the local WWTP will treat the concentrate. Other utilities around the country have also opted for sewer disposal (Ratzki 2003; Manning et al. 2003). In Florida, many facilities use deep well injection for concentrate disposal, although this practice is sometimes criticized for the resulting degradation of groundwater (Manning et al. 2003).


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APPENDIX C AwwaRF PROJECTS RELATED TO MEMBRANE INTEGRATION

AwwaRF

No. Title

90595 Evaluation of Particle Counting as a Measure of Treatment Plant Performance

90603 Low Pressure Membrane Filtration for Particle Removal

90637 Membrane Concentrate Disposal

90639 Evaluation of Ultrafiltration Membrane Pretreatment and Nanofiltration of Surface Waters

90674 A Practical Guide to Online Particle Counting [#835]

90706 Arsenic Removal by Enhanced Coagulation and Membrane Processes [#935]

90715 Membrane Filtration for Microbial Removal

90716 Water Treatment Membrane Processes

90719 Selective Alum Recovery From Clarifier Sludge Using Composite Membranes [#732]

90746 Cryptosporidium: Answers to Questions Commonly Asked by Drinking Water Professionals

90775 Development of Particle Counting Technology for Water Treatment Studies

90807 Fundamentals of Drinking Water Particle Counting

90808 Flat sheet, Bench, and Pilot Testing for Pesticide Removal using Reverse Osmosis

90809 Development and Verification of Information Collection Rule (ICR) Membrane Protocol

90813 Current Management of Membrane Plant Concentrate

90820 Evaluation of Membrane Technologies for Removal of Atrazine and Other synthetic organic chemicals (SOCs)

90824 Major Ion Toxicity in Membrane Concentrate


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AwwaRF No. Title

90832 Treatment Options for Giardia, Cryptosporidium, and other Contaminants in Recycled Backwash Water

90837 NOM Rejection by, and Fouling of, NF and UF Membranes

90840 Nonthermal Technologies for Salinity Removal

90851 Laboratory Test of New Membrane Material

90890 A Study of Low Level Turbidity Measurements

90894 Combining Adsorbents with Membranes for Water Treatment

90899 Integrated Membrane Systems

90900 Treatment of MF Residuals for Contaminant Removal Prior to Recycle

90920 Coagulation Pretreatment for Membrane Filtration

90932 Treatability of Perchlorate-Containing Water by RO, NF, and UF Membranes

90937 Integrated Water Treatment: Softening and Ultrafiltration

90942 Microbial Removal and Integrity Monitoring of High-Pressure Membranes

90952F Biological Fouling of Separation Membranes Used in Water Treatment Applications (Project #904)

91032F Assessment and Development of Low Pressure Membrane Integrity Monitoring Tests

91059F Development of a Microfiltration and Ultrafiltration Knowledge Base


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APPENDIX D OPERATIONAL DEFINITIONS

Basic operational definitions used for membrane systems are summarized and defined in this Appendix. Definitions are separated by technology (i.e., by MF/UF versus NF/RO technologies) to provide a clear description of operational definitions for that technology.

MF/UF SYSTEMS

Design and operation of MF/UF systems requires evaluation of several parameters that include system pressure, recovery, rate of fouling, and cleaning interval. This section gives a brief overview of basic principles of MF/UF filtration and a description of various operating parameters.

Flux

Transport of water across porous MF/UF membranes can be described using Darcy’s law as follows:

mmembrane

p

RTMP

AQ

Jμ

== (D.1)

where J = the permeate, or filtrate, flux through the membrane, gfd or lmh pQ = the flow rate of filtrate, gallons per day (gpd) membraneA = the area of the membrane, ft2 TMP = TMP, psi or bar μ = the absolute viscosity of the water, centipoise (cp) mR = the hydraulic resistance of the membrane, psi/gfd-cp As is evident in the above equation, the transport of water across MF/UF membranes is directly proportional to the TMP and inversely proportional to the absolute viscosity.

Transmembrane Pressure

Transmembrane pressure is the pressure gradient across the membrane surface that drives the transport of water through the membrane. It is the difference between the average pressure on the feed water side of the membrane and the filtered water side and is calculated by using Equation D.2. TMP = 1/2 * (Pf + Pr) – Pp (D.2) where Pf = the average pressure in feed manifold, psi or bar Pr = the average pressure of the reject stream, psi or bar Pp = the average pressure in the product manifold, psi or bar


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Temperature Effects

As discussed above, the permeation of water through the membrane is directly proportional to driving pressure and inversely proportional to the viscosity of the water. Because the viscosity of water decreases with decreasing temperature, the flux through the membrane also decreases at lower temperatures, under a constant TMP. To accurately interpret membrane performance when the feed water temperature is varying, the effect of temperature should be taken into consideration, by normalizing to a reference temperature. Several expressions have been proposed for taking temperature effects into consideration; however, all these typically yield similar results. The following expression can be used for normalizing the flux to a reference temperature, which is typically 20ºC. ( )( )REFAMB TT

AMBREF JJ −= 03.1 (D.3) where JREF = Flux at reference temperature, gfd or Lmh JAMB = Flux at ambient temperature, gfd or Lmh TREF = Reference temperature, °C TAMB = Ambient temperature, °C

Recovery

The recovery of a membrane system is the percentage of net filtrate water produced as a percentage of the total feed flow. Feed and filtrate water used during backwashing are incorporated into the recovery calculation. Recovery is typically calculated over a 24-hour period as follows:

Recovery = 100- [100* (Qf – Qp)/Qf] (D.4) where Qf = the feed flow over 24 hours, gpm or cubic meters per hour (m³/h) Qp = the net filtrate flow over 24 hours, gpm or m³/h Typically, the recovery can be increased by lowering the backwash frequency or increasing the flux. The optimal backwash frequency and flux are typically dependent on the feed water quality; so modifications to these variables to improve system recovery may be limited. Another way to increase the overall recovery of the plant would be to recycle the backwash water to the head of the plant, which is practiced at many conventional water treatment plants. It should be noted that some state regulatory agencies require treatment or monitoring of any backwash water that is recycled.

RO/NF SYSTEMS

RO and NF are pressure driven membrane processes, and the typical design parameters for NF/RO system are net driving pressure, flux, and recovery.


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Net Driving Pressure (NDP)

RO and NF membranes are semi-permeable, allowing the passage of water and preventing the passage of certain solutes (e.g., dissolved organic and inorganic species). When a solution with a high solute concentration is separated from a low solute concentration solution by a semi-permeable membrane, the water naturally flows from the low solute concentration side to the high concentration side. This phenomenon is called osmosis. The passage of water continues until a concentration equilibrium is established, and the pressure difference between the two sides of the membranes at equilibrium is equal to the osmotic pressure difference. A pressure that is greater than the osmotic pressure is needed to reverse direction of water flow through the membrane, and this is referred to as reverse osmosis. NF follows the same principles, but has a lower rejection of solute and operating pressure than RO.

The net driving pressure across NF/RO membranes can be estimated from the following relation.

( ) permeateconcavepermeatebrinefeed PPPNDP ππ −−−+= −2 (D.5)

where NDP = net driving pressure, psi or bar feedP = feed pressure, psi or bar brineP = concentrate pressure, psi or bar permeateP = permeate pressure, psi or bar concave−π = the average osmotic pressure on the feed side, psi or bar permeateπ = the osmotic pressure of the permeate, psi or bar

The average osmotic pressure on the feed side of the membrane ( )concave−π can be estimated from the log-mean average of the dissolved solids concentration on the feed side of the membrane, which can be calculated as follows:

Rec

1Rec11

⎟⎠⎞

⎜⎝⎛

−×== − LnCCsidefeedonionconcentratAverage feedavefeed (D.6)

where Rec = the recovery of the system, percentage feedC = Dissolved solids concentration of the feed water, moles/L avefeedC − = Average concentration of dissolved solids on the feed side of membrane

system, moles/L

The osmotic pressure (π) of a saline solution can be calculated using Equation D.7. π = R (T + 273) Σmi (D.7)

where π = osmotic pressure, bar T = temperature, degrees Kelvin (°K)


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Σmi = summation of molarity of all ionic and non-ionic dissolved solids R = constant, 0.0821 liter-bar/( ºK- mole)

For solutions with TDS less than 5,000 mg/L, the above formula can be approximated by Equation D.8.

π = (0.01)(TDS) (D.8)

where π = osmotic pressure, psi TDS = TDS concentration, mg/L

Flux

The flux through NF and RO membranes is calculated in the same manner as for MF and UF systems (see Equation D.1), and is expressed in the same units of gfd or lmh. Typically, the productivity of the membrane is monitored in terms of specific flux, which is flux divided by net driving pressure. Specific flux is also sometimes referred to as the mass transfer coefficient.

Temperature Correction

Similar to MF/UF, the flux through NF/RO membranes needs to be normalized to a reference temperature to accurately evaluate performance when the water temperature varies with time. The same expression used for MF/UF can be used for NF/RO temperature correction.

Recovery

Recovery of an NF/RO system is calculated in the same manner as for MF/UF systems using equation D.4.


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APPENDIX E NOTES FROM MEMBRANE INTEGRATION WORKSHOP

The workshop conducted on April 23-25, 2003, in Amsterdam in The Netherlands. This 2.5-day workshop was moderated by Jonathan Clement and Jonathan Pressdee. Attendees were introduced. The following were attending: Jonathan Pressdee, Black & Veatch Jonathan Clement, Black & Veatch Eric Baars, Amsterdam Water Jan Peter van der Hoek, Amsterdam Water Jean-Christophe Schrotter, Vivendi, Anjou Récherché Peter Hillis, United Utilities, United Kingdom, PAC Jack DeMarco, Cincinnati Water Works Jan Cromphout, Water Company of Flanders Jim Taylor, University of Central Florida Adam Kramer, Director Minneapolis WaterWorks, PAC Michelle Chapman, Bureau of Reclamation, Denver Vasu Veerapaneni, Black & Veatch Holly Shorney, Black & Veatch Emmanuel van Houtte, IWVA Kim Linton, AwwaRF Jan Hoffman, Amsterdam Water Supply (day two only)

The workshop was hosted by Jan Peter van der Hoek and the Amsterdam Water Supply (AWS), and began with a description of the AWS. It is the only municipal water supply in The Netherlands, and is the oldest company (150-year anniversary in 2003). They produce 92 to 93 million m3 per year.

Project Description

Jonathan Pressdee provided a brief description of the project. There are three main components to the project: Manual, Utility Interviews, and Decision Tool. This is an 18-month project, and we are currently in about the twelfth month. The literature review is mostly completed and the majority of utility interviews have been drafted. The decision tool has been started, but consensus must be reached on the final scope of this tool.

Workshop Objectives

Holly Shorney explained the objectives of the workshop. The first objective is to facilitate a workshop to foster open discussions about the issues of membrane integration. Information obtained in the workshop will be included in the synthesis portion of the manual, which will discuss and summarize all of the membrane integration issues identified in the literature review and the utility interviews. A second objective of the workshop is to reach consensus on the scope and direction of the decision tool.


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Discussion of Membrane Integration

The attendees reiterated that multiple barriers are the key to protecting public health. In The Netherlands and many parts of Europe, multiple barriers and processes are used to lower the risk of pathogens and to lower the concentration of organics and contaminants in the distribution system. Coupled with this, there seems to be a preference in some parts of the world for UF integration rather than MF integration; however, the regulatory structure and common use of chlorine in places like the USA are fostering the integration of both UF and MF.

Log removal to eight or nine is achievable for water systems using membranes. This level of removal is excellent; however, log removal by membranes is not infinite, and the concept of membrane integration as part of a multiple barrier approach should be promoted.

The attendees discussed how membranes are the single, best unit operation for producing high quality water.

General Technology Reviews

Jim Taylor provided a general technology review of reverse osmosis and nanofiltration, and Vasu Veerapaneni lead discussions on MF/UF. Much of the material presented by Jim and Vasu is incorporated into the General Technology Review section of the report (Appendix B).

The main challenges to membrane integration were identified to be cost, waste disposal, and public acceptance. The relative significance of these differs from country to country, region to region, and from application to application. These factors are very site specific.

The project covers MF, UF, NF, RO and ED/EDR. ED/EDR was briefly discussed. ED/EDR is primarily used for contaminant removal and not for water production, but that perception is gradually changing as more systems are installed. A description of the system, its capabilities, and its limitations are presented in Appendix B.

Discussion

The following sections cover the various issues that were discussed during the workshop. The information is not presented in the order in which it was generated during the workshop, but was re-arranged into topic areas for brevity and clarity. The majority of discussions over the two full days of the workshop are summarized below.

Membrane Productivity

Both Jim and Vasu stressed that monitoring productivity of a membrane system over time is necessary to establish any changes in membrane performance, possibly due to fouling and inefficient cleaning. Although historically a pressure drop parameter has been widely used, the mass transfer coefficient (gfd/psi) is the best parameter for monitoring productivity.

In general, it was viewed to be more difficult to maintain capacity at an MF/UF plant than to maintain quality. Some key benefits of MF/UF (when compared to conventional media filters) are that there is no filter-to-waste for membrane systems and there is no turbidity breakthrough after backwashing.


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Fouling

Fouling of membranes was discussed throughout the workshop. RO fouling is primarily due to precipitation (e.g., BaSO4) and biological fouling. In the AWS pilot trials, biofouling was controlled by lowering the feed water AOC concentration and by using chloramines upstream of the membranes. Other methods include removing dissolved oxygen (to minimize precipitation of iron) or installed an organics removal process (i.e., adsorption onto GAC or resin).

Pathogen Rejection

The attendees discussed pathogen rejection by membranes in great detail. In trials by Jim Taylor, a composite mixture of pathogens was introduced to different membrane systems in a controlled trial. The results showed no differentiation in organism size rejection by UF, MF, or NF; thus, pore size distribution may be the parameter that most affects rejection. The attendees concluded that studies which correlate pathogen removal to membrane systems should be viewed with careful scrutiny, because many times the data set is too small to generate a comprehensive assessment.

Some are led to believe that membranes can provide absolute rejection; however, this can give them a false sense of security about having infinite control over pathogen removal, and again, the benefits of multiple barriers must be emphasized. In general RO/NF rejection is 4 to 5 log, whereas MF/UF can achieve higher removals (e.g., 7 to 8 log).

With respect to UF, it is important to note that there are some viruses that could be smaller than the pore size for some UF membranes. Also, the influence of flow direction (inside-out versus outside-in) on pathogen rejection and performance was also discussed, but no conclusive agreement was made.

The USA regulatory practice of giving log removal credits to specific membrane systems was compared to methods used in other countries. For example in Europe, systems perform challenge testing to develop log removal performance for their own system. The results are often used to establish targets within integrity tests to determine when to remove a module from production.

Integrity Testing

Integrity testing was discussed briefly because it is discussed in Appendix B, and because AwwaRF is funding a project devoted solely to integrity testing methods. One issue, however, that was discussed was that establishing the integrity of a membrane systems is a much more stringent requirement than is currently required by conventional media filters. There was no doubt among the attendees that membranes provide a more rugged barrier than media filters, and that integrity testing of membranes was a necessary element of design.

The mechanical stability of the membrane material in its configuration (i.e., hollow fiber versus spiral wound) is a key issue to consider. Some companies are performing stress tests on fibers to better understand the limits of their system.


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Water Quality Targets

The attendees discussed differences in water quality targets for membrane permeate for various countries and regions. Many of the differences are driven by regulations, but also by customer preferences. The aspect of the biostability of membrane treated water was discussed in detail, because there were many attendees with differing views on this topic. For example, in The Netherlands, AOC levels are kept low, because of the desire to have no disinfectant in the distribution system. Biodegradable dissolved organic carbon (BDOC) is not as sensitive as AOC, and the stability of the water is determined, in part, by the AOC concentration. RO can produce biologically stable water, but although NF has been found to improve the biostability, it did not perform as well as RO for AOC removal.

Pilot Testing

The issue of pilot testing a representative system was discussed. RO pilot results from 4-inch-diameter, 40-inch-length elements tend to mimic full-scale 8-inch diameter, 40-inch- length membranes. The 2.5-inch diameter, 40-inch elements have produced variable results and are not recommended for pilot studies.

With respect to MF/UF, pilot testing can be used for many reasons. For example, Minneapolis will continue using their demonstration scale project while the water works is being constructed. Piloting can be performed in initial planning of the project, and then after commissioning to optimize the installed system. In an ideal situation, two of the same pilot units should be trialled (in parallel), with one as control and one for experimental trials.

Pilot tests can be performed to optimize operations. One key unknown for many plants is the balance between CIP frequency and the use of a chemically enhanced backwash.

Piloting can also be viewed as research and development. For example, there are studies of flat sheets of MF/UF in a submerged basin rather than tubular, encased system.

The pilot plant can also serve as a training tool for the operators and laboratory. This happened at many of the utilities in the study. This is also happening at MWW, where the operators are actually going to take control of operations of the pilot plants.

Eric Baars, of AWS, presented suggestions and ideas for membrane pilot testing. The first suggestion was to not be afraid to make mistakes in the pilot plant. Mistakes made in the pilot will translate to better designs and eventually profit in the full-scale plant. This approach also fosters a self solving philosophy, which will continue into operation of the full-scale plant.

Pilot tests are used for many reasons: trouble shooting, optimization, selection of a new process, or innovation in improving other downstream processes. Some states in the USA have requirements for pilot testing, thus it is important to assess all testing parameters before beginning a study.

When possible, also consider using pilot testing for research and development. An example is to improve the design of RO spacers for reduced fouling rates. Pilots can be used to establish a performance based level of comparison for procuring membranes in a competitive environment.

In Europe, there is a long-term commitment to pilot testing, because of the valuable knowledge gained by long term tests. For example, a three year testing duration is recommended for integration of membranes into water treatment. The first year is for start-up issues and


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pretreatment optimization, the second year is for optimization of the membrane system, and the third year is for design and further optimization.

The attendees also discussed that sharing pilot knowledge helps the water industry as a whole, because it acts as a quality assurance check for everyone. It allows you to view your data from a different perspective, which may lead to further optimization or design improvements.

Another innovation to consider is virtual pilot testing, which is performed with modeling. Using computational fluid dynamics (CFD) and for virtual process and control to get preliminary design and operating information can be valuable for the early stages of planning.

The minimum time for pilot testing depends on the study objectives, the site specific design and water quality issues. Sometimes budget limitations will keep pilot testing to a very short time frame (e.g., less than three months). If the source water quality varies significantly over a year, then a minimum of one year is recommended. If the water can change dramatically from year from year, a minimum of three years would be recommended. Also, mistakes will be made, and certain trials will fail; therefore allow flexibility in schedules is necessary. For any major capital spending project, the longer the pilot testing phase, the better.

For groundwaters with minimal water quality and temperature variation, a single element NF/RO pilot test should be at least 2000 hours in duration.

The attendees discussed that any pilot testing is better than no pilot testing, and that objectives of the pilot must be clearly defined for a successful outcome. The pilot plant is used to eliminate risk in the full-scale plant; therefore, the pilot plant should be designed to represent full-scale.

Another pilot testing issue is who takes control of the pilot plant? Is it the utility, vendor(s), and/or consultants? Leaving decisions to vendors may not meet the utility’s needs or expectations for the plant. Also, the frequency of changing operating conditions (flux, pretreatment, backwash frequency, etc.) during pilot testing also needs to be managed.

When planning for a pilot program, a feasibility study or assessment is required. If there is uncertainty about the type of membrane or pretreatment for a particular integration situation, then a very short, possibly one to three-month pilot study (with bench-or pilot-scale membranes) can be conducted. After this initial assessment, then a more detailed study is recommended. Details such as type of membrane material, membrane system, pretreatment, cleaning regime etc., can be evaluated.

Specific Contaminant Removal

Other aspects of NF and RO treatment are that they are sometimes integrated for specific contaminant removal. Depending on the membrane, up to 95 percent removal can be achieved by RO. Other contaminants to be removed by RO and NF include algal toxins and endocrine disrupters.

Cost

The approach for comparing costs for membrane integration was discussed. In the manual, some general cost information will be included; however, the attendees recognized the site specific nature of cost estimates, as well as the difficulty in separating other project costs (i.e., building, pipelines, pumping stations, etc.) from membrane costs. It was decided that in the manual, a list of possible costs (both capital items and O&M costs) would be provided as a guide for utilities to follow when establishing their cost estimates. The manual will include a


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description how to develop life cycle costs. Also, examples of the increased competitiveness of membranes are prevalent in the literature and will be included in the manual.

Flow Configuration

The majority of MF/UF systems operating today are dead-end. But some systems (e.g., Pall) have a partial, cross-flow (or recycle) to better utilize the length of the entire module by spreading evenly the deposits. The drawback to this configuration is higher pumping costs. Likewise, the decision to use inside-out or outside-in flow configurations is complicated, and best decided with a pilot testing program.

Vasu reported that there are new membrane products being developed. For example, a spiral wound submerged UF is being introduced to the market and replacement fibers for existing membranes systems are starting to be evaluated.

Pretreatment

Pretreatment alternatives and their impact on downstream membrane performance are discussed in detail in Appendix B of the manual. Some basic concepts were discussed at the workshop. For example, the trade-off between reduced flux due to the particle loading that is fed to the membrane plant and cost savings for no pre-sedimentation was discussed. This is site- specific and impacts many factors that may be critical to the success of the project. For example, a small footprint may dictate that no pre-sedimentation can be integrated.

The concept of having multiple barriers will also dictate the amount of pretreatment that is needed for a specific application. Pretreatment to protect membranes from pollutants and chemical spills is also a consideration. The pretreatment provided will also be dictated by the water quality goals of the water plant. For example, in The Netherlands, there are multiple pretreatment steps to remove pesticides and organics prior to membranes. Although there is a cost associated with this level of pretreatment, the benefits are that less chemical is used for membrane cleaning, there is a reduced risk of fouling the membranes by chemical spills, and the permeate water quality is well-suited for the customer’s preferences of no chlorine residual.

The pretreatment for MWW was discussed and is also a case study in the manual. At this facility, there has been no change to the pretreatment (softening followed by clarification), as the UF replaced the existing filters. The existing sand filters; however, will be available for use as needed. It is possible that in the winter when the flux is lower due to very low temperatures, the sand filters can be used to lower the solids loading to the membranes, to possibly improve performance.

Design Considerations

There are several design considerations that must be identified during the integration of membranes into a WTP. One key issue is process control, which needs to be linked to the other processes in the WTP. PLC programming and integration into WTP should also be evaluated for a smooth transition during integration. It should be noted that it takes a long time to fully integrate the SCADA control system for the membranes into the system. It is a real issue for membrane plants because they are fully automated.


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Other key design issues include wash water recovery and how to dispose of all residuals. This topic will be addressed in the manual, as it is sometimes the one issue that limits membrane use or is most costly to the project.

The operating philosophy must also be considered. Typically a membrane unit will operate at fixed flow, with a variable speed pump to maintain the flow. Units are switched in and out of service as production varies. The designer should carefully assess the surge and hydraulics of systems. There are site specific issues related to layout, equipment access, available space, and valve access. Chemical storage, although already incorporated into any WTP, is also an issue because many of the cleaning chemicals are new to existing plants.

Surge analysis should be conducted to minimize the risk of fiber breaks. The speed of closure of butterfly valves is different on full-scale than on pilot scale, and can have a significant impact on a membrane’s life. Power cuts can also cause pressure waves through the system. This requires careful planning of back-up power. Also, any possibility of negative pressures can be detrimental to membrane life. There have been issues with air entrainment in full-scale membrane systems.

Environmental design factors also exist for membrane facilities. Security, sunlight exposure, frost protection is needed. Dehumidification is also required in many locations, and this impacts long term reliability of the system.

The myth in the industry is that there are no chemicals in membrane treatment. Although there are sometimes no chemicals associated with the actual process of creating permeate by membranes, cleaning and maintenance can use significant amounts of chemicals. Some of these chemicals are very aggressive (e.g., acids, bases, chlorine). Some utilities are not used to using these chemicals, and frequency and quantity are also issues. Segregation and ventilation are also considerations. Vapor control and accessibility for O&M is also needed.

The issue of manual versus automatic control must be addressed. Because of the number and complexity of valve movements in membrane plants, it is sometimes difficult to operate in manual mode. This issue relates to the stand-by power generation capacities available for the membrane system.

Non-Technical Issues

For some utilities, public perception of the expenditure on membranes relative to conventional methods may become a barrier. MWW is an excellent example of one approach to gaining not only technical support and verification, but also public support and participation in the integration of membranes into their treatment system. Various aspects of their approach were discussed intermittently throughout the workshop, and the overall approach is summarized in the case study of Chapter 2.

Brainstorming Session

An important part of the workshop was a brainstorming session. The goals of this session were to generate a list of integration issues to be considered.


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Integration Issues

The attendees provided their two most important considerations for integration of membranes into water treatment. The following list summarizes these issues (similar concepts were combined as they were listed):

1. Selection of the membrane (which membranes work well with your water?). 2. System integration of control systems for membranes and other processes. 3. Establishing a knowledge base (do your homework and listen to experience of others). 4. Cost effectiveness (membranes are still expensive with respect to other technologies

and life cycle costs should be carefully estimated, and there may be cost benefits from reduced solids, etc.).

5. Design integration, control systems and everything related to design. 6. Understanding the feed water and the impact on the membrane. 7. Answering the question: Why do I need membranes in my treatment train? (What are

the decision factors?). 8. Use pilot testing to verify feasibility (evaluate fouling). 9. Recognize the lack of standardization with membranes compared to conventional

treatment equipment (using one supplier is a huge investment/risk, and if they go bankrupt, then there is trouble).

10. Evaluate potential points of membrane integration within a treatment plant, and understand the impacts on operation at each point of application.

11. Recognize the benefits of using a model as the first step of membrane integration. 12. Evaluate raw water quality and establish finished water goals, then leverage that

balance against the age of existing infrastructure and look at potential benefits. 13. Membrane processes offer flexibility as they can combine in different ways to solve

problems. 14. Automation/staffing levels may not necessarily be less with an automated membrane

plant (pretreatment, monitoring, and complexity of system will also influence requirements).

15. Maintain control of the pilot testing and/or design, as the contractors will not necessarily design with your best interests as a priority.

16. Carefully plan for and design ways to minimize biofouling. 17. Gaining public involvement and participation through public relations. 18. Security issues with integrated system. 19. Reliability (what are the risks to production capabilities in adverse water quality

conditions?). 20. What synergistic benefits are gained by including membranes?

Integration Topic Categories The attendees then grouped the important issues into four main categories (see below): feasibility, selection of membranes, design, and operation. A. Feasibility. Whether membranes are applicable or not.

Knowledge base Cost assessment


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Understanding feed water What benefits, why integrate Assess points of application and impacts on ops Age of infrastructure Flexibility Integration with customer confidence Reliability and security

B. Selection of the membrane process Understanding feed water Fouling control Flexible

C. Design and Procurement Control System Integration Cost assessment Design integration Industry standardization Automation and staffing System operation and flexibility Reliability and security

D. Operate Cost assessment Automation and staffing System operation and flexibility Reliability and security

The attendees were separated into two groups. Group 1 focused on feasibility and selection, including initial screening phase and the pilot testing. The members were Jonathan Clement, Jim Taylor, Jan Hoffman, Jean-Christophe, Holly Shorney, Kim Linton, Jan C, and Jan Peter van der Hoek. Group 2 focused on the design, cost, and procurement, construction and operation. The following questions were to be answered: what are the steps needed for each of these issues and what are the considerations? Group 1. As with any water treatment study, the following steps are recommended during the feasibility stage:

1. Identify the problem (water quality, expansion, environmental impact), 2. Evaluate alternative solutions (including other processes and membranes),

-assuming membranes are selected at this stage, and then the following steps should be taken:

3. Define other criteria and impacts (environmental impacts, brine disposal, operational

impacts, consumer confidence),


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4. Define preliminary design criteria, 5. Determine budget level costs (and plan for piloting), and 6. Pilot testing.

Once the need for pilot testing has been established, the following issues/considerations are recommended:

1. Understand the feed water quality (identify the worst condition). 2. Define what kind of membrane is needed. 3. Not all membranes are equal, so need to compare the different suppliers. 4. Decide where to put membranes in the train. 5. Does it work in this location? 6. Duration (depends on feed water, challenging water, the urgency of the project). 7. Parallel or series testing. 8. Control of the pilot testing (vendor or utility). 9. Optimizing pretreatment. 10. Pilot testing as a role in procurement. 11. Make sure the pilot represents the full-scale system. 12. Test the most representative feed water. 13. There can be multiple trains and sequencing. 14. What is your budget? 15. Chemical compatibility. 16. Some type of paper study may be needed to narrow the options. 17. A short term initial membrane selection. 18. A longer term evaluation. 19. Using a membrane element of the full-scale size. 20. When to pilot (maybe at worst water quality, maybe a periods through the year

wet/dry, cold/hot). 21. Flat sheet membranes (hydraulic issues).

Group 2. Many times, the design of a membrane facility will be influenced by the results of pilot testing. Therefore, it is important to be involved in the pilot testing and to help develop the protocols so that various design aspects can be investigated. Examples include backwash, CIP, integrity testing, and SCADA programming. Design should also be influenced by the experience of others. The utility interviews of the manual will contain information about experiences of existing facilities. The information will include lessons learned, successes, research efforts, considerations, recommendations, and expectations of staffing, chemical use, etc. This information should be processed and the various concepts should be considered into a design. Developing cost estimates is difficult, even for professional estimators. Many factors affect costs, and therefore putting general cost estimates into the manual and model will not be accurate for individual cases. Instead, the approach to cost estimating will be presented. It will include all of the possible factors affecting cost. Life cycle cost will be presented, and resources for getting costs estimates will be listed. There will also be examples of less obvious costs, such as future waste disposal, chemical use, hauling etc. The case studies will include examples of costs, where appropriate and available.


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Procurement methods and requirements differ from utility to utility, but there are some general recommendations for consideration. There are at least two case studies that highlight their method of procurement (Milwaukee Water Works and the City of Scottsdale). There is no ideal model for procurement, but the procedures should be defined so that the utility receives the equipment and facility that they desire. There are key pieces of equipment that may warrant special procurement considerations: valves, membrane warranty, and membrane system. During construction and commissioning, the integration of membranes requires the same consideration of quality, quantity, environmental aspects, and co-ordination as other treatment processes. Staff should be trained on the SCADA, which can be more complex, and should have the skill set for operations. It is helpful if they can be involved in planning and pilot testing, also. The main operational issues identified were reliability and maintaining production. Fiber breakage has been an issue at some facilities. Maintaining accurate monitoring by maintaining all instruments is vital, especially for instruments associated with integrity monitoring. Having a safe shutdown system, and the ability to operate manually is also important.

Utility Presentations

Four utility presentations were provided during the workshop, as well as a site visit to the UF/RO PWN facility. These not only provided a global perspective of membrane integration, but also stimulated much discussion about various aspects and drives of integration.

IWVA, Emmanuel van Houte

IWVA is a small company located close to the sea, and space is limited in the area. Drinking water is historically based on dune water, which is located in a region between the sea and a brackish water polder area. There was a need for sustainable groundwater management by artificial recharge. It was decided to take waste water effluent, treat it by RO, and recharge the aquifer. The flow is 285 m3/h. The WWTP has secondary treatment with phosphorus removal. There is no filtration at the WWTP.

The project started with a feasibility study and the pilot test. Emmanuel recommended that utilities considering membranes should be in control of the pilot study and gather as much independent information as possible.

They evaluated different feed waters for possible recharge sources. First, surface water was treated with MF systems. WWTP effluent was evaluated next, but biofouling was an issue. Then surface drainage water was evaluated. In the end, WWTP effluent was treated with MF/RO. Over five years of pilot testing was conducted on different waters (e.g., surface drainage, effluent, and surface water).

They have tested four different MF/UF membranes for treating WWTP effluent. The main findings were that outside-to-inside membrane filtration in the vertical position with air was very important. Also, the finer pore sizes of UF produced only slightly better quality but fouled sooner, requiring more cleaning. Using different systems made the utility staff familiar with the systems. Pre-screening was found to be more challenging than operation of the membrane system, and 500 to 1,000 µm pre-strainers were found to be sufficient for treating WWTP effluent.

There is a critical flux for every membrane system. IWVA began with a conservative flux, and optimized the system later.


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For RO, biofouling occurred, and upstream chloramination and de-chloramination proved effective. Scaling was easy to control with pH adjustment and a scale inhibitor. The RO membranes are standardized, and this makes an equal comparison with respect to fluxes. Several cleaning strategies were tested, and a biocide was also tested.

The cartridge filter upstream of RO provides extra security, and can be a indicator of biofilm development.

It was recommended that all staff should be involved from piloting to full-scale design. Their input is vital to the successful design of a membrane project. Taking responsibility of the piloting and analyzing the results is recommended. This helps eliminate risks associated with operations.

All of the pumps and mechanical equipment are in the basement, and the membranes are on the main, ground floor. The Zenon membranes are used for pretreatment. They achieve 87 percent recovery. Air is injected into the Zenon basins 50 percent of the time. There is a chlorinated backwash after 30 normal (30 second) backwashes. Valve selection is very important because there are quick sequences within a backwash sequence. Having high quality valves, with spare valves and parts is recommended.

Discussion following the presentation suggested that iron and biological fouling could be controlled if the feed water is anaerobic, but this was not deemed possible in the feasibility study. A low dosage of chlorine is in the Zenon system, and then converted to chloramines prior to RO. Bisulfite is dosed upstream of the RO system, and the dose is controlled from a redox measurement.

IWVA started full-scale operation with three, 5-µm cartridge filters upstream of the RO plants, and they have been changed to 15 µm screens. IWVA has had trouble with too high a loading rate for the area provided in the cartridge filters.

The RO system is a two stage system, with two trains. DOW ultra-low pressure membranes are used at 75 percent recovery. Each skid can treat 180 m3/h. The flow split for recharge is 90 percent of RO filtrate and 10 percent MF filtrate. This flow is dosed with UV irradiation before being infiltrated. The plant operates 24 hours per day, seven days per week.

Turbidity is monitored for permeate of each MF skid. There is pH, conductivity, temperature monitoring on the RO feed and filtrate. SDI, conductivity, and pH are also monitored on the MF filtrate.

The brine is disposed to a drainage canal which flows to the sea. This is a challenge, because the permit is for three years, and there may be problems getting the permit renewed.

The overall cost is about 0.4 euros per m3 of infiltration water. This includes investment, personnel, electricity, and chemicals, but does not include maintenance contracts, charges, and concentrate disposal. Chemical use with the RO system is lower than expected, but acid consumption is higher than expected and must be optimized. The capital cost was 2.5 million euros for the building and MF/RO capital costs were 3.5 million euro.

MF upstream of RO has performed well, however MF is an expensive treatment system. Rapid sand filtration may have been acceptable, however it was not pilot tested. The sand filter effluent would have a higher particulate loading, and the quality would be less; however, there may be an economical trade-off with increased RO cleaning.

It’s very difficult to compare costs for submerged and encased systems. The philosophies are different, and the long-term costs must be considered. One related challenge is that MF/UF systems are not standardized. Once the patents have expired, there may be replacement equipment that will benefit membranes in the future.


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The MF plant was more expensive than the RO equipment. This surprised the attendees, but after discussion, the TDS was 1,500 mg/L, and low pressure RO is used. Also, the costs for RO membranes continue to decline.

Amsterdam Water Supply, Jan Hofman

The integration experience at AWS is all pilot-scale. In the early 1990s, AWS started research to evaluated membranes for expanding their capacity for production. Recently, the demand for drinking water has stopped increasing, and no extra capacity is needed and there are no immediate plans for installing a full-scale membrane treatment plant.

The AWS has two treatment plants. One treats water from the River Rhine with a design capacity of 70 m3 per year, and the other plant has a capacity of 31 m3 per year, and treats water from seepage/canal. Treatment consists of pretreatment, recharge to dunes or reservoir storage and then post-treatment. The river water is delivered to dunes to the west of Amsterdam, and extracted for treatment.

AWS is considering membrane integration to increase production capacity, improve water quality, and provide an environmentally friendly treatment alternative. The challenges are system selection, fouling/scaling, concentrate disposal and integration location.

The pretreatment is coagulation, sedimentation, and filtration. From the dunes, rapid sand filtration (RSF), ozone, softening, BAC, and slow sand filtration. There is no chlorine in the system. The water is biologically stable.

AWS is considering direct treatment of the Rhine River. The water quality requirements are adequate disinfection, organic contaminants removal, and softening. Some additional benefits to be realized are desalination and corrosion control.

Two pilot trials have been performed. Over 40 percent of AOC in the full-scale plant is removed in the pellet softening. The remainder is removed in the downstream biological processes. Bromate is formed in the ozone; however, ozone is used for disinfection and to stimulate biological activity.

Ionics and Eurodia ED/EDR were evaluated. Other pilot units for ozone, GAC, and slow sand filtration were also used.

The key aspects of the research were investment costs, operating costs, process stability, fouling, scaling, desalination and hardness, bromate control, disinfection, organics removal, and environmental impacts.

The RO cost estimate was 27 million Euro with 0.56 euro/m3 and the EDR was 30 million euros for 0.56 euro/m3. (These estimates are a few years old, and for a 13 million m3 per year). The recovery for EDR was 90 percent, and for RO, 85 percent. Three stages were tested for RO, and two stages for EDR. The TDS is about 800 mg/L, and the hardness is about 2.5 mmole/L.

Fouling consisted of particulates, organics, biofouling and metallic fouling. The goal was to have less than 2 mg/L DOC and AOC less than 10 µg/L to prevent organic fouling and biofouling. Acid adjustment was used for controlling metallic fouling.

AWS were able to operate for over one year without cleaning. In the initial pilot studies, there was a high rate of fouling and cleaning frequencies. The fouling was introduced by the biodegradable anti-scalant, and biofouling was occurring on the membranes. After changing the anti-scalant, the stability was improved greatly. Optimizing the anti-scalant and acid dosage has improved barium sulfate control. The Permatreat 191 anti-scalant is used now.


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The preferred solution was ozone, BAC, slow sand filtration, and RO. This provided a dual barrier with ozone and BAC for organic micro pollutants. This extensive pretreatment also provided a stable operation of the RO. The costs were comparable between EDR and RO. The RO system had less temperature dependency than the EDR system, and the EDR did not remove as much salinity/hardness.

The Ionics EDR was cleaned once per month because of organic fouling. This fouling caused poor salinity removal. The Eurodia system was more subject to fouling for this source water.

Pilot trials at the second plant are being conducted to evaluate methods to prevent eutrophication of a storage basin (removal of N and P). They also wanted to stimulate self purification (i.e., low turbidity), additional disinfection capacity, flexibility, and the reduction of waste production (currently a ferric coagulant waste sludge). The pretreatment is coagulation, sedimentation, reservoir storage, and rapid sand filtration. The alternatives for upgrading the plant included dynamic sand filtration (i.e., DynaSand® and MF/UF). This water contains almost 2 mg/L of iron.

The trials showed less fouling when a coagulant was used. The chemistry is very complex between the water constituents, coagulant, and the membrane, and generalizations about performance with certain coagulants can not be made. Iron precipitation can be controlled with pH control and DO control. In some trials, dissolved iron was still in the system during backwashing, and causing precipitation of iron on the permeate side of the membrane.

Other research topics were phosphate removal, effect of pretreatment on the nitrification capacity of the rapid sand filters, removal of pathogens, reduction of sludge production, minimization of chemical use, process stability, investment costs, and the ability to expand capacity. UF looked promising because of less energy consumption and a higher disinfection capacity. More research is necessary to increase stability and to lower the operating costs.

Two new pilot plants will begin in 2003. These pilots will trial different types of UF systems and coagulant addition. MF had a four to five fold higher operating costs because of air in the backwash and operating at a higher pressure. AWS uses ferric-salt coagulants and not aluminum-based coagulants due to restriction with aluminum-based coagulants. Biopsy results show that iron is precipitating within the membrane fiber. A CEBW at pH 2 is conducted every three hours.

In general, integration of membranes at the existing plants offers a promising solution for expanding capacity and improving water quality. The direct treatment of surface by MF/UF requires much research to optimize the system and achieve stable operations.

AWS is evaluating the costs. Coagulation and sedimentation in The Netherlands is very inexpensive compared to MF/UF. The benefits of treatment of MF/UF to other parts of the treatment plant. The impacts and synergy of membrane integration is difficult to justify based on cost alone.

Minneapolis Water Works, Adam Kramer

In the early 1990s the MWW identified the need to upgrade two major WTPs. One plant is a softening plant that achieves about 50 percent TOC removal, and other plant is conventional coagulation plant. The main challenges for deciding the processes and approach were both technical and political.

A feasibility study was conducted to assess existing facilities and their ability to comply with existing and future regulations. A value engineering assessment was conducted using


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several experts from the water industry. This group was called the peer review panel, and they discussed vulnerability, source water quality, and treated water quality.

Ozone and BAC, membranes, and UV were assessed in the VE study. Membranes were evaluated, with the anticipation of adding them for only additional summer capacity.

The political solution to membrane integration at the MWW involved various stakeholders: city engineers, university experts, Minn. Health Department, Minneapolis Health Advisory Board, Minn. AIDS project, and the Capital Long Range Improvements Committee. Other stakeholders that attended meetings were the mayor’s staff, council members’ staff, finance/budget staff, and legal staff. Their buy-in helped keep the project on schedule.

Pre-procurement procedures were developed during this project. A memorandum of understanding was issued with the State regulatory agency. Water quality goals were established. The City’s procurement requirements were that there was no pre-qualification phase, no vendor contact, no negotiations, and the low bid wins. As a result, the procurement process was based on qualifications, performance testing, and bid evaluation and award. A detailed explanation of how the low bid would be evaluated and selected was also provided to the vendors.

The MWW required oxidant compatibility, NSF 61 certification, system experience, membrane experience, and potable water experience. Two phases of bidding were used. The first phase was technical bidding, and the second bid was the cost. The cost bids were sealed to maintain a competitive price. Three systems (Aquasource, Ionics, and Koch) were selected to pilot. If the membrane system required pretreatment, it had to be included in the bid and overall plant design. Ionics and Koch were the only systems that conducted pilot trials.

The systems had to verify 4-log virus removal, both with data and with performance testing on three occasions. The membrane needed oxidant compatibility and PAC compatibility. The pilot units also had to use full-scale membrane modules.

The pilot trials were performed in three phases over nine months. In the first stage, the membrane suppliers had the ability to operate their system at any rate. In the second phase, the City operated the membranes with guidance from the suppliers. In the third stage, the City operated the membranes at a single, optimized condition. A stipend of $30,000 was provided to systems that completed the pilot trials.

The cost bids were not opened, and were returned to the supplier un-opened. No exceptions were allowed in the technical bids.

The cost for the membrane plant was $0.21/gpd for capital costs, and $17 million was for the membranes. Three prices were requested from vendors. This was for 10 units, 11 to 35 units, and over 35 units. The cost bids were based on an estimated flux. After performance testing, the costs were adjusted to account for any flux difference (resulting from pilot testing). The flux at 68ºF (20ºC) for Koch was 67.4 gfd and for Ionics, 56.8 gfd. The recoveries were greater than 90 percent.

Performance testing included integrity monitoring, virus rejection, membrane performance, and fouling potential. There was also a limit in permeability loss over the nine-month trial.

For both systems, the virus removal was greater than 5-log removal in the pilot trials. The Norit membranes performed well and maintained stable operations with a cleaning interval greater than 30 days. The flux was 120 percent of the estimated flux in the bid.

The City included a 12-month warranty immediately after performance testing. The module warranty was to be not less than 36 months and no more than 120 months.


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Norit will be installed in the Columbia Heights (water softening plant) WTP at 70 mgd. The schedule is to have the project constructed and completed in December 2004.

PWN, Peer Kamp and Joop Kruithoff

In the 1980s, PWN identified increasing salt concentrations in the Rhine River as a potential water quality problem. PWN uses about 88 percent surface water and 12 percent groundwater, so PWN staff began investigating methods of lowering the salt concentration in finished water. They first contacted industries along the Rhine River, but soon realized that the salt concentration was not going to decrease, so treatment alternatives for salt removal were investigated. In 1988, bentazone, a pesticide, was discovered in the Rhine water. With improved analytical capabilities and further investigations, an additional 150 pesticides were discovered in the Rhine, and improved treatment was required. PWN also required additional capacity. The existing works consists of screens, ferric coagulation, flocculation, sedimentation, rapid sand filtration with GAC, infiltration, pellet softening, aeration, rapid sand filtration, and chlorine dioxide disinfection. No residual disinfectant is used in the distribution system. PWN had some pilot testing experience from the 1970’s with cellulose acetate RO. They experienced some fouling problems and could not maintain a CIP frequency of once per month. They realized that better pretreatment would be needed. Two treatment schemes were identified, and funded for testing. One included RO, ozone, and GAC, downstream of the infiltration of the existing treatment train. Rapid sand filtration upstream of the RO was necessary for improved pretreatment. This train was compared to an ozone and GAC train. Staff at PWN tried to simplify these trains, but KIWA mandated that these trains be tested. In 1990, PWN learned that bromate would be regulated (EU standard is 5 µg/L). This created a treatment challenge for ozone in both of the pilot treatment trains. The on-going pilot trials provided data showing that these trains were not meeting the treatment goals (CIP once per month) or water quality goals (bromate less than 5 µg/L), so the proposed treatment trains were considered a failure. PWN staff had learned about microfiltration in a previous trip to the United States, and in 1993 began pilot testing two units (AquaSource and Memcor) upstream of RO. The use of MF/UF upstream of RO was compared to ozone and GAC upstream of infiltration in the existing treatment train. The UF pretreatment to RO was selected because it achieved more virus removal. In this treatment train, the RO treatment targets were achieved. In late 1993, an engineering design team was selected, but with the Cryptosporidium problems in Milwaukee, KIWA and the Dutch Health Minister had reservations about using membranes as a drinking water barrier. Pilot testing of MS2 phage spiking was performed to establish the log removal values of the membranes. MF achieved from 1- to 2.3-log removal, UF from 5.4- to 5.8-log removal, and RO from 3.8- to 4.8-log removal. With these data, PWN was allowed to proceed with design of UF followed by RO. Initial designs were unfortunately not efficient and too costly, but with perseverance and further innovations and investigations, the final design was approved. During this time, additional UF suppliers were in the market, and this allowed for a competitive bid. Ultimately, Norit’s X-Flow membranes were selected. There are some unique design features at PWN. Each skid for UF and RO has a dedicated pump to eliminate hydraulic influences of valve changes on production. The pumps


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are also in sound-proof containers to improve the working environment. There are no pipe trenches in the floor. Instead, the plant is built on two floors, with all pipes being directed to the lower floor, where all valves, connections, and meters are installed. This lower floor was designed ergonomically. In the summer of 1995, the design team faced delays because the building site had to be changed. During this delay, PWN staff were able to simplify the RO design by reducing the stages from three to two. There are eight UF units. A CEB is performed three times per day using 100 mg/L (and sometimes 500 mg/L) free chlorine. The flux is 113 lmh. The UF units have not been cleaned in two years. A warm water chlorinated CEB is performed in the winter. PWN was one of the first large installations of the Norit X-Flow membranes, and has worked with Norit to improve integrity testing (via vacuum testing). PWN staff are also included in some patents for Norit, as they have helped re-design the hydraulics in the modules. There are also eight RO units. These operate at 30 lmh and achieve 80 to 82 percent recovery. A two-stage design is used, and these units have not been cleaned for the first three years of operation. The brine is delivered to the sea. PWN provided a tour of the facility to the attendees.

Decision Tool

Vasu Veerapaneni explained the scope and preliminary flow chart for the decision tool component of the AwwaRF project. The user enters raw water data and the target concentrations. Seven parameters can be selected, and turbidity is common to any system, as well as pathogen removal.

There are two main types of integration: a new plant or into an existing plant. The new plant design of the decision tool is fairly straightforward. The retrofit option is more difficult, because getting all of the information about the existing treatment into program will be nearly impossible.

The current version of the decision tool also includes notes to the user about other available processes (e.g., UV for disinfection). Does the tool lead the user down a ‘dangerous’ path? This was discussed at length. Some attendees felt the tool should not include any opinions or recommendations about investigating other processes. For example, including alternatives for issues like DBPs is too difficult because there are too many alternatives for these complex issues.

Who is the intended user? It is a person that is looking at the options for their water treatment plant. It’s additional information for the user, but not a design tool.

Others thought the main benefit of the decision tool is that it gives a different perspective for the user. The user can easily change one input and observe the impact on the decisions that are made. This type of analysis would serve as a guide for later decision making.

There was on-going discussion as to whether it is dangerous to use this tool in the event that the information is used incorrectly. However, if this type of tool is not available, people can still make a wrong decision, rather than making a wrong decision with the tool. This tool will not be 100 percent perfect, but the user can get a perspective.

In previous PAC meetings, some cost data was preferred to be presented in the tool; however, recognizing the complexity of cost information and rapid changes and market influences, it was decided that in the tool, cost should not be the driver for the decision.


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In general, this tool should suggest where you can put membranes, but will not include the other alternatives for achieving water quality goals. This program should tell you where membranes can be integrated into a WTP. With this simplified approach, the following questions should be answered:

1. Do we need membranes? 2. What kind of information do we need to make this decision? 3. What is the process of decision making?

This is a decision tool for identifying the possible locations of integrating membranes in a water system. A decision tool for identifying the technology, but not the actual membrane or supplier.

Can we take the water quality numbers out of the program? This would make the tool a generic decision tree format listing pros and cons of integration. The user would select water quality concerns, and the tool would provide information and references to case studies that faced similar challenges.

The case studies should be linked to the tool, and the focus should be kept positive so that people looking into it are not scared away by high costs or complicated pilot tests, etc.

The tool could include a series of process train examples. With the identified water quality concerns, the tool could identify opportunities to use membranes. It would answer the question, if I include membranes, how will they be used?

It was decided that relative costs will go in the case studies and not in the tool. Also, the tool should prompt users to get more knowledge about the process of integration (e.g., pilot systems, conferences, etc.).


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APPENDIX F UTILITY QUESTIONNAIRE FORM


236

Name of the project personnel conducting interview: ___________________________________

Name and location of the utility: ___________________________________________________

Utility contact person name, address and phone number: ________________________________

______________________________________________________________________________

Email address: _________________________________________________________________

Date: ___________________

Is the utility willing to be referenced? _______________________________________________

Does the utility want to remain anonymous? (For example, if the utility chooses to remain anonymous, it will be referred to as Utility A, Region, Country)

Yes _________ No

AwwaRF Project #2765 Integration of Membrane Filtration into Water Treatment Systems

The American Water Works Research Foundation Research Project "Membrane Integration Study" is moving forward. One important objective of the study is to gain knowledge of membrane experience through utility interviews. The questionnaire is to be completed by the project personnel during the utility interviews. The purpose of the questionnaire is to ensure that there is consistency between various interviewers.


AwwaRF Project #2765: Integration of Membrane Filtration Into Water Treatment Systems Black & Veatch Fall 2002

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Background Information This section will provide basic information about the utility. Please answer questions as thoroughly as possible. Contact information:

Name of Utility: ________________________________________________________________

Address of Utility: ______________________________________________________________

______________________________________________________________________________

______________________________________________________________________________

Contact name and phone number (person completing survey)

Name: ________________________________________________________________________

Phone Number: ________________________________________________________________

Engineering Firm and Contact information: __________________________________________

Size of population served by plant: _________________________________________________

Characteristics of service area (urban, rural, etc.): _____________________________________

Is water blended with another system? If yes, please give details: _________________________

______________________________________________________________________________

Describe geography and environment : ______________________________________________

______________________________________________________________________________

______________________________________________________________________________

Type of utility, please circle one of the following: Municipal Private Public



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Regulatory Involvement:

List Regulatory Agencies involved, applicable regulations and their requirements for this project:

______________________________________________________________________________

______________________________________________________________________________

______________________________________________________________________________

______________________________________________________________________________

______________________________________________________________________________

______________________________________________________________________________

Public Involvement – Planning, Construction and Operational:

Describe: ______________________________________________________________________

______________________________________________________________________________

______________________________________________________________________________

______________________________________________________________________________

______________________________________________________________________________

______________________________________________________________________________

______________________________________________________________________________



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Decision Making Process List major influences: ___________________________________________________________

Ultimate decision maker: _________________________________________________________

Is this a new plant or upgrade or expansion of an existing plant? __________________________

Reason for the new or upgrade/expansion of an existing plant (for example, more demand, meet

new regulations): _______________________________________________________________

______________________________________________________________________________

______________________________________________________________________________

List various alternate technologies considered: ________________________________________

______________________________________________________________________________

List technologies shortlisted: ______________________________________________________

______________________________________________________________________________

Issues raised and resolved with respect to each alternate technology: _______________________

______________________________________________________________________________

______________________________________________________________________________

List reasons why other alternate technologies were not implemented: ______________________

______________________________________________________________________________

______________________________________________________________________________

Groups involved in decision making: _______________________________________________

______________________________________________________________________________



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Reason(s) for selecting membranes: ________________________________________________

______________________________________________________________________________

______________________________________________________________________________

Regulatory issues involved when selecting membranes: _________________________________

______________________________________________________________________________

Issues raised and resolved concerning membranes: _____________________________________

______________________________________________________________________________

______________________________________________________________________________

Life cycle cost analysis conducted? _________________________________________________

Recommendations for other utilities:

Design issues: __________________________________________________________________

______________________________________________________________________________

Start up/commissioning: _________________________________________________________

______________________________________________________________________________

Operations: ____________________________________________________________________

______________________________________________________________________________

Regulatory Agencies: ____________________________________________________________

______________________________________________________________________________

Procurement Process: ____________________________________________________________



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Pilot Performance This section will provide information about the membrane pilot, if applicable. Any membrane experience is beneficial to the utility and will provide us with additional information regarding the performance of the membrane units. Was piloting of membrane unit(s) conducted? ________________________________________

Duration of pilot: _______________________________________________________________

Reasons for choosing or not choosing to pilot test: _____________________________________

______________________________________________________________________________

If no piloting was performed, proceed to next section. Otherwise continue…..

Description of the pilot program:

Objectives of the pilot study (for example, is it to meet future regulations, asset renewal, or to

determine design parameters to be used for bidding purpose, etc.): ________________________

______________________________________________________________________________

How many membrane systems were selected for piloting? _______________________________

Side by side testing?: Yes No

Flow rate: _____________________________________________________________________

Continuous 24hr/day operation? ___________________________________________________

Manufacturer & membrane material: ________________________________________________

Describe process for selecting membranes for pilot study: _______________________________

______________________________________________________________________________

Who performed the pilot study? ___________________________________________________

______________________________________________________________________________

Duration of pilot study or studies & dates: ___________________________________________



242

Equipment cost: ________________________________________________________________

Engineering fees: _______________________________________________________________

Facilities cost: _________________________________________________________________

Laboratory costs: _______________________________________________________________

% of total budget: _______________________________________________________________

% of time devoted by the plant personnel: ____________________________________________

Have all pre-selected membranes completed the pilot study? _____________________________

Parameters evaluated during pilot study (flux, permeability, backwash/CIP interval, waste

disposal, recovery, integrity test procedure, upset conditions, etc.): _______________________

______________________________________________________________________________

______________________________________________________________________________

Have pilot reports & papers been written? ___________________________________________

Can they be provided to the project team? ____________________________________________

Miscellaneous comments on pilot program:

______________________________________________________________________________

______________________________________________________________________________

______________________________________________________________________________

______________________________________________________________________________



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Bidding process This section will provide information about the bidding process for the procurement of the membrane equipment.

Please describe the procurement process (Design & build, traditional (detailed design & bid),

EPC, BOO, BOOT): ____________________________________________________________

______________________________________________________________________________

______________________________________________________________________________

Role of pilot plants in bidding process: ______________________________________________

Membrane warranty: ____________________________________________________________

______________________________________________________________________________

Describe the criteria used for bid evaluation: _________________________________________

______________________________________________________________________________

______________________________________________________________________________

______________________________________________________________________________

Briefly describe the membrane suppliers’ scope of services: _____________________________

______________________________________________________________________________

______________________________________________________________________________

______________________________________________________________________________

Engineer: _____________________________________________________________________



244

Plant Characteristics This section will provide information regarding the water quality associated with the membrane application. The range of water quality between membrane utilities is a valuable component of the study as it will provide a representation of the water which will be used to construct the final database.

Capacity of existing plant (mean, min, max) (mgd): ____________________________________

Capacity of new or expanded plant (mean, min, max) (mgd): ____________________________

Current capacity (mean, min, max) (mgd): ___________________________________________

Future expandable capacity: ______________________________________________________

Is plant capacity same as membrane capacity? ________________________________________

Plant Status: ___________________________________________________________________

Plant start-up date: ______________________________________________________________

Source water: __________________________________________________________________

Environmental impacts on water source (e.g. farming activity): ___________________________

______________________________________________________________________________

______________________________________________________________________________

Industrial & municipal impacts on water source (e.g. effluent discharges): __________________

______________________________________________________________________________

______________________________________________________________________________

Criticality of source to supply: _____________________________________________________

Allowable shutdown period: ______________________________________________________

Climatic events (known seasonal occurrences, e.g. snow melt): ___________________________

______________________________________________________________________________

______________________________________________________________________________



245

Water quality concerns (e.g. virus, arsenic, endocrine disruptors): _________________________

______________________________________________________________________________

______________________________________________________________________________

Raw water quality information (if historical data is available, please provide in a disk)

Any raw water quality concerns (high TDS, DBPFP, arsenic, taste, odor etc): _______________

______________________________________________________________________________

______________________________________________________________________________

Upset conditions: _______________________________________________________________

______________________________________________________________________________

______________________________________________________________________________



246

Raw Water Quality Data

Any raw water quality concerns (high TDS, DBPFP, arsenic, taste, odor etc):

Parameter Minimum Maximum Average Standard

Deviation

pH

Alkalinity, mg/L

Hardness, mg/L

Temperature, oC

Turbidity, ntu

Total organic carbon, mg/L

Dissolved Organic Carbon, mg/L

Color

UV 254, cm-1

Ammonia, mg/L

Nitrate, mg/L

Chloride, mg/L

Sulphate, mg/L

Total Dissolved Solids, mg/L

Iron, mg/L

Manganese, mg/L

Cryptosporidium, No./L

Giardia, No./L

E. Coli, No./L

Total Coliforms, No./L

Clostridia, No./mL

Plate counts, 22oC

Plate counts, 370C



247

Membrane Feed Water Quality


Deviation

pH

Alkalinity, mg/L

Hardness, mg/L

Temperature, oC

Particle counts, <2 µm, No./mL

Turbidity, ntu



Color

UV 254, cm-1

Chlorine (free or total), mg/L

Ammonia, mg/L

Nitrate, mg/L

Chloride, mg/L

Sulphate, mg/L


Iron, mg/L

Manganese, mg/L


Giardia, No./L

E. Coli, No./L


Clostridia, No./mL



248

Membrane Permeate Water Quality


Deviation

pH

Alkalinity, mg/L

Hardness, mg/L

Temperature, oC

Particle counts, <2 µm, No./mL

Turbidity, ntu



Color

UV 254, cm-1

Chlorine (free or total), mg/L

Ammonia, mg/L

Nitrate, mg/L

Chloride, mg/L

Sulphate, mg/L


Iron, mg/L

Manganese, mg/L


Giardia, No./L

E. Coli, No./L


Clostridia, No./mL



249

Process Description

Please provide a process schematic showing elements of the treatment train, including membranes, pre, post treatment, and recycle streams. Also include process parameters such as detention time, mixing intensity, filter loading rate, etc. Note whether new or existing processes.

(example flow diagram)

Describe membrane process control: (Fixed flow, variable flow, temperature compensated): ___

______________________________________________________________________________

Any by-pass: __________________________________________________________________

Describe Neutralization Process Control: ____________________________________________

______________________________________________________________________________

______________________________________________________________________________

Pre-screening upstream of membrane: _______________________________________________

______________________________________________________________________________

Downstream disinfection requirement: ______________________________________________

______________________________________________________________________________

Raw Water

Chemical Addition

Flocculation Sedimentation Membrane

Chlorine

Distribution System



250

Plan area (ft2 or m2 ) of membrane plant: _____________________________________________

______________________________________________________________________________

List monitoring devices upstream and downstream of process:

Raw water: ____________________________________________________________________

______________________________________________________________________________

Pretreatment: __________________________________________________________________

______________________________________________________________________________

Membrane effluent monitoring:

Permeate: _____________________________________________________________________

______________________________________________________________________________

Concentrate: ___________________________________________________________________

______________________________________________________________________________

Side or waste streams: ___________________________________________________________

______________________________________________________________________________

Post membrane treatment: ________________________________________________________

______________________________________________________________________________

Chemical Applications

Please list and identify any chemicals added prior to the membranes. This will help to evaluate the membrane performance and to compare data between utilities.



251

Pretreatment (any treatment prior to membrane filters) chemical addition:

List chemical, typical dose, addition point in the treatment train and the purpose for addition: ___

______________________________________________________________________________

______________________________________________________________________________

______________________________________________________________________________

______________________________________________________________________________

______________________________________________________________________________

______________________________________________________________________________

Post-treatment (any treatment after membrane filtration):

List chemical, typical dose and the purpose for addition: ________________________________

______________________________________________________________________________

______________________________________________________________________________

______________________________________________________________________________

______________________________________________________________________________

______________________________________________________________________________



252

Membrane process Information

Membrane characteristics (please include all information available)

Membrane Element Characteristics

Manufacturer Module Model Number No. of modules Dimensions of module Active Membrane Area (Feed Surface) Molecular Weight Cut Off (Daltons) or Pore Size (µm)

Membrane Material Membrane Configuration Membrane Hydrophobicity/ Hydrophilicity

Membrane Charge

Maximum Allowable Operating Pressure

Allowable Operating pH Range

Allowable Cleaning pH Range

Maximum Allowable Feed Turbidity

Chlorine/Oxidant Tolerance

Prescreen size: _________________________________________________________________

Mode of operation: (circle one) direct crossflow

Number of skids/trains: __________________________________________________________



253

Describe configuration, include area of element and number of elements per skid or train: _____

______________________________________________________________________________

______________________________________________________________________________

______________________________________________________________________________

What is the instantaneous maximum operating flux and corresponding temperature? _________

______________________________________________________________________________

What is the net operating flux? ____________________________________________________

Is this different from the design flux? _______________________________________________

If yes, Why? ___________________________________________________________________

______________________________________________________________________________

Average transmembrane pressure? _________________________________________________

Design and operating recovery of water: _____________________________________________

Any biopsies performed on the membranes? __________________________________________

______________________________________________________________________________

Flux attainment after chemical clean: _______________________________________________



254

Integrity Test

Integrity Test Method: ___________________________________________________________

Integrity Test Frequency: _________________________________________________________

Is it determined by state regulators or selected by utility? ________________________________

What initiates integrity test? ______________________________________________________

Test impact on recovery and/or permeability? _________________________________________

Diagnostic Procedure for Locating Defective Membrane: _______________________________

______________________________________________________________________________

______________________________________________________________________________

Number of Breaks Permitted Before Cartidge/Module Replaced: _________________________

Number of breaks permitted before repair: ___________________________________________

Number of fiber breakages per year: ________________________________________________

Is that higher than that specifies in the bid document? __________________________________

______________________________________________________________________________

Possible causes for fiber breakage, if known? _________________________________________

______________________________________________________________________________

______________________________________________________________________________

Backwash Information

List and describe the backwash regime:

What is the backwash criteria and operating frequency? _________________________________

______________________________________________________________________________



255

Is this different than the design frequency? ___________________________________________

If yes, Why? ___________________________________________________________________

______________________________________________________________________________

Frequency: ____________________________________________________________________

Pressure: ______________________________________________________________________

Describe the whole process listing flow rates (liquid and/or air), durations, recycle location in

process: ______________________________________________________________________

______________________________________________________________________________

Recycle rate, instantaneous & mean: ________________________________________________

List chemicals used (type and dose): ________________________________________________

______________________________________________________________________________

______________________________________________________________________________

Disposal of backwash waste: ______________________________________________________

______________________________________________________________________________

Permits if any were required: ______________________________________________________

______________________________________________________________________________

Extended Backwash Information (for example, chemically enhanced backwash): Duration of extended backwash: ___________________________________________________

Frequency: ____________________________________________________________________

Pressure: ______________________________________________________________________



256

Describe the whole process listing flow rates (liquid and/or air), durations, etc: ______________

______________________________________________________________________________

______________________________________________________________________________


______________________________________________________________________________

______________________________________________________________________________

Disposal of backwash waste: ______________________________________________________

______________________________________________________________________________


______________________________________________________________________________

Membrane Preservation:

Chemicals used: ________________________________________________________________

______________________________________________________________________________

Storage duration: _______________________________________________________________

______________________________________________________________________________

CIP Frequency of CIP: ______________________________________________________________

Duration of CIP: ________________________________________________________________

Is the CIP frequency same as the design? ____________________________________________

If no, Why? ___________________________________________________________________

______________________________________________________________________________

Pressure: ______________________________________________________________________



257

Describe the whole process listing flow rates (liquid and/or air), durations, etc: ______________

______________________________________________________________________________

______________________________________________________________________________

______________________________________________________________________________

______________________________________________________________________________


______________________________________________________________________________

______________________________________________________________________________

______________________________________________________________________________

Disposal of CIP waste: ___________________________________________________________

______________________________________________________________________________


______________________________________________________________________________

Chemicals recovered: ____________________________________________________________

Operating and Maintenance Costs

Please specify currency: __________________________________________________________

Please specify current staffing: ____________________________________________________

Normal Operation Shift Number

Duration (example, 7AM to 3PM)

# of operators Average hourly salary per operator including overhead

Qualifications

1

2

3



258

Maintenance & Special reqirements (such as during CIP, repairs, etc.) Frequency & task Example: CIP once every 45 days

Total hours

# of operators in addition to those listed above

Average hourly salary per operator including overhead

Any staffing changes necessary vs predicted & increase/decrease from previous:

______________________________________________________________________________

Capital costs:

Installed pretreatment cost (from raw water pumping station to upstream of membranes: _______

______________________________________________________________________________

Installed post treatment cost (from downstream of membranes to high service pump station: ____

______________________________________________________________________________

Training conducted: _____________________________________________________________

Research & piloting conducted after installation: ______________________________________

Membrane equipment cost: _______________________________________________________

Membrane equipment installation cost: ______________________________________________

Engineering fees: _______________________________________________________________

Ancillary equipment cost if not included in membrane system cost: _______________________

Any other additional costs: _______________________________________________________

Total plant cost (estimate does not include land acquisition, engineering, or site development): _

______________________________________________________________________________



259

Operating costs per year: (if possible, split the cost between membranes and rest of plant)

Membrane module replacement cost and life of membrane module:

Chemical _______________________________________________________________

Energy__________________________________________________________________

Labor __________________________________________________________________

Replacement parts ________________________________________________________

Maintenance _____________________________________________________________

Waste disposal ___________________________________________________________

Other __________________________________________________________________

Describe how the project was funded: _______________________________________________

______________________________________________________________________________

Actual expenditure vs. predicted: __________________________________________________




261

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Cho, J., G. Amy, and J. Pellegrino. 1999. Membrane Filtration of Natural Organic Matter: Initial Comparison of Rejection and Flux Decline Characteristics With Ultrafiltration and Nanofiltration Membranes. Water Research, 33(11):2517-2526.

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ABBREVIATIONS ABF ammonium bifluoride ac-ft acre-feet ACH aluminum chlorohydrate ACOE Army Corps of Engineers ADWG Australian Drinking Water Guidelines AIT air integrity test Al2O3 aluminum oxide AM membrane area Amembrane area of feed side of membrane Amod membrane area in one module AMW apparent molecular weight AOC assimilable organic carbon AP anionic polymer APHA American Public Health Association ARMCANZ Agriculture and Resource Management Council of Australia and New Zealand AS air scour As(III) arsenite As(V) arsenate ASTM American Society of Testing and Materials atm atmosphere ATR-FTIR attenuated total reflectance Fourier-transform infrared AWS Amsterdam Water Supply AWWA American Water Works Association AwwaRF Awwa Research Foundation µ absolute viscosity BaSO4 barium sulfate BAC biological activated carbon BAT best available technology BDOC biodegradable dissolved organic carbon Bexar Met Bexar Metropolitan Water System BMA Bexar-Medina-Atascosa BMDC Bexar Metropolitan Development Corporation BOOT build–own-operate-transfer BW backwash °C degrees Celsius CA cellulose acetate CAC Citizens Advisory Committee CaCO3 calcium carbonate CAP Central Arizona Project or Cryptosporidium Action Plan CBU City of Bloomington Utilities CCAP capital costs


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CCI construction cost index CCK Choa Chu Kang CEBW chemically enhanced backwash CFD computational fluid dynamics cfm cubic feet per minute Cfeed dissolved solids concentration of the feed water Cfeed-ave average concentration of dissolved solids on the feed of feedwater CGE Compagnie Générale des Eaux CIP clean-in-place cm centimeters CM membrane equipment costs cm² square centimeters Cmod cost of one membrane module CO2 carbon dioxide COD chemical oxygen demand cp centipoise CP cationic polymer CP non-membrane capital costs CTA cellulose triacetate CU color units CWW Greater Cincinnati Water Works Da Daltons DAF dissolved air flotation DBP disinfection by-product DBO design-build-operate DBPR Disinfectants/Disinfection Byproducts Rule DC direct current DCWW Dwr Cymru Welsh Water DHS Department of Health Services District San Patricio Municipal Water District DOC dissolved organic carbon DTI Department of Trade and Industry DWI Drinking Water Inspectorate E. coli Escherichia coli EBCT empty bed contact time EC European Community ED electrodialysis EDC endocrine disrupting chemical EDL electric double layer EDR electrodialysis reversal EDTA ethylenediamine tetra acetic acid ENR Engineering News Record EU European Union


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ºF degrees Fahrenheit FA fulvic acid FBRR Filter Backwash Recycling Rule FRMCD Foss Reservoir Master Conservancy District FRP fiberglass reinforced plastic ft feet ft² square feet G velocity gradient (mixing energy) GAC granular activated carbon gfd gallons per square foot per day gpd gallons per day gpm gallons per minute GWR Groundwater Rule h hour HA humic acid HAA haloacetic acid HAA5 regulated five haloacetic acids (dibromo-, dichloro-, monochloro-, monobromo-

and trichloro-) HCl hydrochloric acid hp horsepower HPC heterotrophic plate count HPLC high-pressure liquid chromatography HPSEC high-performance size-exclusion chromatography HS humic substances ICP inductively-coupled plasma-emission spectroscopy ICR Information Collection Rule IDEM Indiana Department of Environmental Management IDNR Indiana Department of Natural Resources IESWTR Interim Enhanced Surface Water Treatment Rule IR infrared IWVA Intermunicipal Water Company of the Furnes Region IX ion exchange J flux JAMB flux at ambient temperature JCR clean water flux after chemical cleaning JF final flux JHR clean water flux after rinsing JO initial membrane permeability JREF flux at reference temperature


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ºK degrees Kelvin kDa kilo Daltons kg/d killograms per day km kilometer kPa kilo Pascal kW kilowatt L liter LDPE low density polyethylene lb/day pounds per day L/h liters per hour lmh liters per square meter per hour l/s liters per second LRV log removal value LSI Langelier saturation index LT1ESWTR Long Term Stage 1 Enhanced SWTR Rule LT2ESWTR Long Term Stage 2 Enhanced SWTR Rule m meter M molar m² square meters m3 cubic meters m3/h cubic meters per hour mbar milli bar MBR membrane bioreactor MCESD Maricopa County Environmental Services Department MCL maximum contaminant level MDH Minnesota Department of Health MF microfiltration mg milligram MG million gallons mgd million gallons per day mg/L milligrams per liter Mg(OH)2 magnesium hydroxide MIB 2-methylisoborneol mJ/cm2 milli-joules per square centimeter MIEX magnetic ion exchange MIT Membrane Integrity Testing mL milliliter ML million liters ML/d million liters per day mm millimeter mS milli-Siemens MSDS material safety data sheet MWCO molecular weight cut-off MWW Minneapolis Water Works


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µg/L micrograms per liter µm micrometer μS microsiemens NaCl sodium chloride NaHSO3 sodium bisulfite NaOCl sodium hypochlorite NDP net density pressure NES nominal effective size NF nanofiltration ng/L nanograms per liter NH2Cl monochloramine NHMRC National Health and Medical Research Council NKWD Northern Kentucky Water District nm nanometer nmod number of modules NOM natural organic matter NPDES National Pollutant Discharge Elimination System NSF NSF International NTU nephelometric turbidity units O&M operation and maintenance OMWD Olivenhain Municipal Water District π osmotic pressure πave-conc osmotic pressure, average on feed side of membrane πpermeate osmotic pressure of permeate PA polyamide PAC powdered activated carbon PACl polyaluminum chloride PAN polyacrylonitrile Pbrine concentrate pressure PDT pressure decay test PEG polyethylene glycol PES polyethersulfone Pfeed feed pressure PLC programmable logic control PP polypropylene ppb parts per billion PPCP pharmaceutical and personal care products Ppermeate permeate pressure PS polysulfone psi pounds per square inch psi/min pounds per square inch per minute PUB Public Utilities Board PV pressure vessel


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PVC polyvinyl chloride PVdF polyvinylidenefluoride PVP Process Verification Plan PWN Provinciaal Waterleidingbedrijf van Noord-Holland ΔP pressure difference Q plant flowrate Qf feed flow QP permeate flowrate R gas constant or recovery Request Statements of Interest RF reverse flow Rm hydraulic resistance of membrane RO reverse osmosis rpm revolutions per minute SAT soil aquifer treatment SCADA supervisory control and data acquisition SDI silt density index SDS sodium dodecyl sulfate or simulated distribution system SDWA Safe Drinking Water Act sec seconds SEDIF Syndicat des Eaux d’Ile de France SEM scanning electron microscopy SIM spiked integrity monitoring SOC synthetic organic chemicals SRF State Revolving Fund SUVA specific ultraviolet absorption SRP Salt River Project STWD Second Taxing District Water Department SWTR Surface Water Treatment Rule T temperature TAMB Ambient temperature TCEQ Texas Commission on Environmental Quality TDS total dissolved solids TFC thin film composite THM trihalomethane TMP transmembrane pressure TOC total organic carbon TREF reference temperature TSS total suspended solids TTHM total trihalomethanes


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UF ultrafiltration UIC underground injection control UK United Kingdom USA United States of America USEPA United States Environmental Protection Agency UV ultraviolet UV254 ultraviolet absorption at a wavelength of 254 nanometers VHT vacuum hold test VOC volatile organic compound VSEP vibratory shear enhancement process VTD vacuum test device WaTER Water Treatment Estimation Routine WET whole effluent toxicity WHO World Health Organization WTP water treatment plant WTW water treatment works WWTP wastewater treatment plant ZLD zero liquid discharge





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