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SEQUENTIAL NITRIFICATION/DENITRIFICATION - 840 SEQUENTIAL NITRIFICATION/DENITRIFICATION * IN SUBSURFACE FLOW CONSTRUCTED WETLANDS * A LITERATURE REVIEW BY I FRANK W. TITUS 3 Departmental

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  • AD-A259 840

    SEQUENTIAL NITRIFICATION/DENITRIFICATION

    * IN

    SUBSURFACE FLOW CONSTRUCTED WETLANDS

    * A LITERATURE REVIEW

    BY

    I FRANK W. TITUS

    3 Departmental Report Environmental Health EngineeringThe University of Texas at Austin

    in Partial Fulfillment DTICELECTE

    of the Requirements JANI 5 1993

    3 for the Degree of E* MASTER OF SCIENCE OF ENGINEERING.

    THE UNIVERSITY OF TEXAS AT AUSTIN

    I .December 1992

    931 03 044

  • IISS EQU ENTIAL N ITRI FICATION/D EN ITR IFICATION

    1 IN

    3 SUBSURFACE FLOW CONSTRUCTED WETLANDSA LITERATURE REVIEW3

    A/Ol O /23- 1?'?- 5-53/Accesion For

    Ips NTIS CRAMDTIC TAB

    I ~unannounced 0justification

    Distribution I

    Availability Codes

    I Avail and orDist Special

    1 VAPPROVED:

    I

    I

    I-

    I

  • III

    SEQUENTIAL NITRIFICATION/DENITRIFICATION

    I IN

    I SUBSURFACE FLOW CONSTRUCTED WETLANDSA LITERATURE REVIEW

    BY

    I FRANK W. TITUSI

    I Departmental Report Environmental Health EngineeringI The University of Texas at Austin

    in Partial Fulfillment

    I of the RequirementsI for the Degree ofI MASTER OF SCIENCE OF ENGINEERING

    THE UNIVERSITY OF TEXAS AT AUSTIN

    1 December 1992IIII

    I ii

  • I3 ACKNOWLEDGEMENTS3 I would like to thank the following: Sherwood Reed of E.E.C. in Norwich, Vermont;

    Donald Brown of the EPA in Cincinnati, Ohio; and Ancil Jones of the EPA in Dallas, Texas.

    3 The information and guidance they provided for my literature review was invaluable. Iam sincerely grateful for the time they took to talk to me whenever I called and the

    promptness in which they responded to my requests for information.

    3 I would also like to thank Dr. Neal Armstrong and Dr. Raymond Loehr forreviewing my report. Their inputs and suggestions helped me write an infinitely better

    3 report than I could have ever written on my own. I would also like to thank them both forsetting a standard of excellence and professionalism that I will take away from the

    University of Texas and will strive to achieve for the rest of my career.

    IIIIIIIII

    iii

    II

  • I3 TABLE OF CONTENTS

    SIG NATURE PAG E ............................................................................................................... iTITLE PAG E ...................................................................................................................... iiACKNOW LEDG M ENTS ...................................................................................................... iii

    LIST O F TABLES ................................................................................................................ vLIST O F FIG URES ......................................................................................................... vi

    3 SECTION I. INTRODUCTION ......................................................................................... 1A. Introduction ............................................................................. 1B. Purpose ................................................................................. 2C. Scope .................................................................................... 3

    SECTION I1. CONSTRUCTED WETLANDS: AN OVERVIEW ......................................... 4A. Natural W etlands .................................................................. 43B. SFCW Background And Process Description..................... 8

    SECTIO N II1. NITRIFICATIO N/DENITRIFICATIO N .................................................... 21A. Introduction ....................................................................... 21B. Nitrification/Denitrification ......................... 24C. Artificial W etlands In Santee CA ...................................... 26D. Discussion .......................................................................... 28E. Nutrient Plant Uptake ....................................................... 30F. SFCW Design For Nitrification/Denitrification ................... 31

    SECTION IV. OXYG EN TRANSPO RT ........................................................................ 35A. Introduction ...................................................................... 35B. Diffusion ............................................................................. 36C. Convective Oxygen Transport ............................................ 38D. Root Zone Oxygenation ...................................................... 40E. Discussion .......................................................................... 41

    SECTION V. DESIGN RECOMMENDATIONS ............................................................. 45A. Introduction ....................................................................... 45B. Perform ance Data Analysis .............................................. 46C. The Plug Flow First O rder M odel ..................................... 47

    D. Design Recom m endations ................................................. 49E. Design Example ................................................................. 51F. Discussion .......................................................................... 53

    SECTION Vi. CONCLUSIONS AND RECOMMENDATIONS ......................................... 58A. Sum m ary of Objectives ................................................... 58B. Conclusions ........................................................................ 58C . Recom m endations ............................................................... 60

    APPENDIX ...................................................................................................................... 62

    REFERENCES .................................................................................................................. 71

    ivI

  • I* LIST OF TABLES

    TABLE I1-1 Percent removal for several pollutants from secondary effluent in naturalw etlands .......................................................................................................................... 19

    TABLE 11-2 Summary of nutrient removal from natural wetlands ........................ 19

    I TABLE 11-3 Summary of guidelines for hydraulic loading of wastewater into naturalw etlands .......................................................................................................................... 20

    3 TABLE 11-4 Summary of guidelines for loadings of wastewater into SFCW ........ 20TABLE IV-1 Mean composition (%) of the air in different parts of reeds during light and3 dark cycle ................................................................................................................. 43TABLE V-1 Selected performance data ................................................................... 54

    3 TABLE V-2 SFCW design considerations ................................................................ 54

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    VI

  • UST OF FIGURES

    FIGURE I1-1 Typical cross section FWS wetland ...................................................... 21

    FIGURE 11-2 Typical cross section SFCW .................................................................. 21

    FIGURE I1-1 Nitrogen behavior in natural treatment systems ................................ 33

    FIGURE 111-2 Cross section of a wetland root in an anoxic sediment ......................... 33

    FIGURE IV-1 Relationship between relative humidity and convective flow ............... 44

    FIGURE IV-2 Relationship between temperature and convective flow ..................... 44

    FIGURE V-1 HLR vs. %TN Removal ............................................................................ 55

    FIGURE V-2 TN Load vs. %TN Removal ...................................................................... 55

    FIGURE V-3 NH3 Load vs. %NH3 Removal ................................................................. 56

    FIGURE V-4 HLR vs. %NH3 Removal ....................................................................... 56

    FIGURE V-5 NH3 Load vs. NH3 Effluent ..................................................................... 57

    vi

  • I. INTRODUCTION

    A. Introduction

    A need exists for the application of a low cost, low maintenance, low technology

    municipal wastewater treatment option for small rural communities. The construction,

    operation, and maintenance of a community wide managed wastewater facility is a major

    and difficult undertaking for most small (

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    Federal money is becoming difficult to obtain for small communities to fund and

    operate conventional wastewater treatment systems. As stated earlier, a need exists for a

    I low cost treatment system that is applicable to the rural environment. Subsurface flowconstructed wetlands (SFCW) may help small communities solve their wastewater

    problems. Reed and Brown (1992) report an average cost for construction of SF

    3 systems to be about $0.62/gallon (flow), and Jones reports (1992) for operation andmaintenance about $0.18/1000 gallons (flow). These low costs, coupled with the

    I reliable performance of SFCW for BOD and TSS removal, make the consideration of thesesystems a good choice.

    Even though there is currently no consensus on the design of SFCW (Reed and

    Brown 1992), the ability of constructed wetlands to meet municipal wastewater

    requirements for BOD and TSS is well documented. Nitrogen removal appears from the

    existing performance data to be one of the primary problems with these systems. The

    negative effects of excessive levels of nitrogen on the aquatic environment include

    -- eutrophication of receiving waters and the increased risk of methemoglob

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