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Ultraviolet disinfection
Guidance document
About Australian WaterSecure Innovations Ltd
Australian WaterSecure Innovations Ltd (trading as WaterSecure) was established in 2016 to oversee the implementation of national research outcomes, including the WaterVal™ program, one of the flagship outcomes developed by the Australian Water Recycling Centre of Excellence (the Centre), an independent research organisation established in 2009 by Commonwealth funding.
About WaterVal™
WaterVal™ is a framework that provides national consistency in the validation of water treatment technologies for the water industry. The framework, jointly developed by the Centre, regulators, water utilities, researchers and the private sector, is underpinned by protocols and agreed methods to validate pathogen removal by treatment technologies. The framework and protocols are applicable to a broad range of water sources, and give effect to key objectives of the Australian guidelines for water recycling and the Australian drinking water guidelines.
Acknowledgements
WaterSecure is grateful for the contributions made by the WaterVal™ Protocol Development Group (in particular Luc Richard and David Cunliffe), Viridis Consultants Pty Ltd (Karen Pither), Karl Linden and Cedric Robillot, and input received from external reviewers.
Citation
WaterSecure 2017, Ultraviolet disinfection, WaterVal validation guidance document, Australian WaterSecure Innovations Ltd, Brisbane.
Date of publication
February 2017
Publisher
Australian WaterSecure Innovations Ltd Level 16, 333 Ann Street, Brisbane, Queensland 4000 www.watersecure.com.au
© Australian WaterSecure Innovations Ltd
This work is copyright. Apart from any use permitted under the Copyright Act 1968, no part of it may be reproduced for any purpose without written permission from the publisher. Requests and inquiries concerning reproduction rights should be directed to the publisher.
Disclaimer
While every effort has been made to ensure the accuracy of the information contained in this document, Australian WaterSecure Innovations Ltd cannot guarantee that it is entirely accurate and error-free.
This document is intended to be used in conjunction with the WaterVal™ framework. Australian WaterSecure Innovations Ltd does not accept any legal liability or responsibility whatsoever for any injury, loss or damage, due to or arising out of any use of this document independent of that framework.
It is the responsibility of the user to determine the suitability and appropriateness of the information and its specific application.
201702_WaterVal_Guidance Document_UV Disinfection 1
Contents
1. Background and scope ............................................................................................................................... 2
2. Policy position ............................................................................................................................................ 3 2.1. US EPA guidelines ........................................................................................................................... 3 2.2. German guidelines ......................................................................................................................... 3 2.3. Operational monitoring .................................................................................................................. 4
3. Rationale .................................................................................................................................................... 5 3.1. Comparison of validation methods ................................................................................................ 5 3.2. Incorporating validation uncertainties ........................................................................................... 6
3.2.1. Protozoa ............................................................................................................................ 6 3.2.2. Viruses ............................................................................................................................... 8
Glossary and abbreviations ................................................................................................................................. 9
References ........................................................................................................................................................ 10
Tables
Table 1 UV doses required to achieve various log reduction values for target pathogens .............................. 5
Table 2 Validated Cryptosporidium dose (mJ/cm2) as a function of log reduction value and UV transmittance, based on Bacillus subtilis RED of 40 mJ/cm2 ............................................................................... 7
Table 3 Validated Giardia dose (mJ/cm2) as a function of log reduction value and UVT, based on Bacillus subtilis RED of 40 mJ/cm2 .................................................................................................................................... 7
Table 4 Minimum UVT (%) required as a function of log reduction value for a UV disinfection system validated under the German guidelines .............................................................................................................. 7
Figures
Figure 1 Overview of the validation method ..................................................................................................... 3 Figure 3 RED bias as a function of UV transmittance for a range of log reduction values (3, 3.5 and 4) of (a)
Cryptosporidium and (b) Giardia ........................................................................................................ 6
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1. Background and scope
This document provides guidance on the application of pre-validated ultraviolet (UV) disinfection systems in the United States Environmental Protection Agency (US EPA) Ultraviolet disinfection guidance manual for the final long term 2 enhanced surface water treatment rule (US EPA 2006; US EPA guidelines) and the German Association for Gas and Water UV disinfection devices for drinking water supply – requirements and testing (DVGW 2006; German guidelines).
The WaterVal validation Protocol template (AWRCE 2015) provides a recommended approach to validation that is based on the following nine elements:
identification of the mechanisms of pathogen removal by the treatment process unit
identification of the target pathogens and/or surrogates that are the subject of the validation study
identification of the factors that affect the efficacy of the treatment process unit in reducing the target pathogen
identification of operational monitoring parameters that can be measured continually and are related to the reduction of the target pathogen
identification of the validation method to demonstrate the capability of the treatment process unit
description of a method to collect and analyse data to formulate evidence-based conclusions
description of a method to determine the critical limits, as well as an operational monitoring and control strategy
description of a method to determine the log reduction value (LRV) for each pathogen group in each specific treatment process unit performing within defined critical limits
provision of a means for revalidation or additional onsite validation where proposed modifications are inconsistent with the previous validation test conditions.
The flexibility in the US EPA guidelines provides opportunities for tailoring the validation method to specific operating conditions, including a variety of target UV doses. The methodology for validating UV disinfection systems described in the US EPA guidelines has been mapped against the WaterVal validation protocol template, showing that all nine elements are addressed appropriately (Richard 2015a); this is the methodology recommended under WaterVal.
The German guidelines present a model for certification of UV disinfection systems according to strict standards and a set target UV dose. The methodology for validating UV disinfection systems described in the German guidelines has also been mapped against the WaterVal validation protocol template, with seven of the nine elements addressed appropriately (Richard 2015b). In contrast to the US EPA guidelines, under the German guidelines, determination of the LRV for each pathogen group does not take into account biases and uncertainties involved in using experimental testing to define a validated dose and validated operating conditions. In addition, the German guidelines do not address the need for revalidation because the certification process does not allow the validated unit to be modified.
This guidance document identifies the process for applying the German guidelines to claim LRVs for UV disinfection systems in Australia.
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2. Policy position
Figure 1 depicts the process for implementing the results of validation under the US EPA guidelines and the German guidelines. Refer to Section 3 for detailed rationale.
UVT = UV transmittance
Figure 1 Overview of the validation method
2.1. US EPA guidelines
Pathogen LRVs claimed for UV disinfection systems validated using the method in the US EPA guidelines will be accepted if:
the method is applied consistently and is detailed in a validation report
operating conditions are validated in situ to demonstrate that the system achieves the required UV dose and the validation report is appropriate to the site-specific conditions
ongoing monitoring of operating parameters, as described in Section 2.3, confirms that the system is operated within the validated operation envelope
quality assurance and quality control requirements have been addressed.
2.2. German guidelines
UV disinfection systems that have been validated under the German guidelines to achieve a UV dose of 40 mJ/cm2 will be considered to be validated for inactivation of protozoa of 3 to 4 logs, depending on the UV transmittance (UVT) at which the UV disinfection system is operated.
4-log credit protozoa and
bacteria
Selection of pre-validated UV disinfection system
US EPAguidelines
Germanguidelines
US EPA validation method applied consistently
UV dose ≥ 40 mJ/cm2
UVT > 95%
3.5-log credit protozoa and
bacteria
UVT > 65%
3-log credit protozoa and
bacteria
UVT > 50%
Validated log credit accepted
201702_WaterVal_Guidance Document_UV Disinfection 4
Bacteria inactivation is considered similar to protozoa inactivation (Hijnen et al. 2006), therefore, a LRV for bacteria of 3 to 4 as a function of UVT will also be recommended (Linden 2014).
No log inactivation will be credited for viruses, since the consideration of validation uncertainty results in a validated dose below the 39 mJ/cm2 required to achieve 0.5 log reduction.
These pathogen LRVs claimed for UV disinfection systems validated under the German guidelines will be accepted if:
the validation method is applied consistently and detailed in an English language validation report
operating conditions are validated in situ to demonstrate that the system achieves the required UV dose and the validation report is appropriate to the site-specific conditions
ongoing monitoring of operating parameters, as described in Section 2.3, confirms that the system is operated within the validated operation envelope
quality assurance and quality control requirements have been addressed
2.3. Operational monitoring
Four parameters are to be monitored in real time during operations to confirm the UV dose delivery:
flow rate
lamp status
UV intensity
UVT.
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3. Rationale
3.1. Comparison of validation methods
The basic difference between the US EPA guidelines and the German guidelines is that the German guidelines adhere to a strict target UV dose of 40 mJ/cm2, whereas the US EPA guidelines allow any validated dose for a targeted log inactivation of the desired pathogen. The US EPA guidelines identify a flexible method for validating LRVs achieved by UV systems, which includes:
use of a variety of microorganisms as biodosimeters
inclusion of specific safety factors to cover a range of uncertainties
a range of target UV doses, depending on the desired LRV target (
Table 1).
Table 1 UV doses required to achieve various log reduction values for target pathogens
Target pathogens Log inactivation
0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0
Cryptosporidium 1.6 2.5 3.9 5.8 8.5 12 15 22
Giardia 1.5 2.1 3.0 5.2 7.7 11 15 22
Virus 39 58 79 100 121 143 163 186
Note: All doses are in mJ/cm2. Source: US EPA (2006)
The target UV dose of 40 mJ/cm2 accepted by the German guidelines is based on a comprehensive analysis of existing data by Oluf Hoyer in 1998 (Hoyer 1998). The German guidelines are primarily for low pressure UV lamp systems but can also be used for medium pressure systems that cut out wavelengths below 240 nm. Requirements of the German guidelines include:
the types of sensors, and their specific criteria, that can be used in UV systems
that there be 1 sensor for every 10 low pressure lamps
the way the reactor is tested, such as
o the test organism must be Bacillus subtilis ATCC6633
o a 90° elbow is used downstream of the UV reactor to make the hydraulics most challenging
o tests use a fixed lamp power of ≤ 70%
o minimising the UV intensity in the reactor through testing conditions of high lamp power coupled with low UVT, and low lamp power coupled with high UVT.
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3.2. Incorporating validation uncertainties
To account for reduction equivalent dose (RED) bias and validation uncertainty (Uval) in the German guidelines, the following equation from the US EPA guidelines can be used
Validated pathogen dose = Challenge organism RED
RED bias × (1+Uval/100) (equation 1)
In the German guidelines, the challenge organism is Bacillus subtilis and the RED is 40 mJ/cm2. A conservative uncertainty Uval of 27.6% is to be used (Wright 2007).
The US EPA guidelines provide tabulated values of RED bias as a function of UVT and challenge microorganism UV sensitivity for various LRVs for Cryptosporidium, Giardia and viruses. The UV sensitivity of B. subtilis is 14.8 mJ/cm2 per LRV and the range 14–16 can be used in the US EPA guidelines tables.
3.2.1. Protozoa
The minimum UVT in RED bias tables in the USEPA Guidelines is 65%; however, lower transmittances are commonly detected in recycled water. The relationship between UVT and RED bias can be extended to a lower UVT (down to 50%) from linear extrapolation of the RED bias values associated with the two lowest UVT values in the US EPA guidelines (Figure 2). The RED bias values and extrapolations are specific to the target pathogen and to a LRV.
Figure 2 RED bias as a function of UV transmittance for a range of log reduction values (3, 3.5 and 4) of (a) Cryptosporidium
and (b) Giardia
Based on RED biases (US EPA guidelines and extrapolated), a Uval of 27.6% for B. subtilis and a RED of 40 mJ/cm2, validated pathogen doses can be calculated for each target pathogen as a function of UVT and LRV using equation1. Tables 2 and 3 provide these validated doses, as well as the minimum UV dose requirements from Table 1.
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Table 2 Validated Cryptosporidium dose (mJ/cm2) as a function of log reduction value and UV transmittance, based on Bacillus subtilis RED of 40 mJ/cm2
UVT Log reduction value
4 3.5 3
98 27.3 26.8 26.8
95 24.5 23.6 23.6
90 21.8 19.8 19.4
85 20.5 18.1 17.2
80 19.7 17.0 16.0
75 19.0 16.2 15.1
65 18.1 15.1 13.9
60 17.7 14.7 13.3
55 17.3 14.2 12.8
50 16.9 13.8 12.4
Minimum UV dose required
22 15 12
Table 3 Validated Giardia dose (mJ/cm2) as a function of log reduction value and UVT, based on Bacillus
subtilis RED of 40 mJ/cm2
UVT Log reduction value
4 3.5 3
98 27.7 26.8 26.6
95 25.3 23.6 23.2
90 22.9 19.8 18.9
85 21.8 18.1 16.6
80 21.0 17.0 15.4
75 20.5 16.2 14.4
65 19.6 15.1 13.2
60 19.2 14.7 12.6
55 18.8 14.2 12.2
50 18.4 13.8 11.7
Minimum UV dose required
22 15 11
Based on the data in Table 2 and Table 3, minimum UVT values can be defined at which a UV disinfection system validated under the German guidelines is required to operate for a specific LRV ( Table 4). Table 4 Minimum UVT (%) required as a function of log reduction value for a UV disinfection system
validated under the German guidelines
Target pathogen Log reduction value
3 3.5 4
Cryptosporidium 50 65 95
Giardia 50 65 90
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3.2.2. Viruses
The US EPA guidelines specify a requirement of 39 mJ/cm2 for a 0.5 LRV of viruses by UV disinfection. Based on the Bacillus subtilis RED of 40 mJ/cm2, as specified under the German guidelines, a Uval of 27.6% and a RED bias of 1 (as in the US EPA guidelines), the validated dose for viruses of 31.3 mJ/cm2 is considerably lower than the target 39 mJ/cm2. Note that a less conservative Uval would lead to the same conclusion.
As a result, no LRV for viruses can be allocated to UV disinfection systems validated under the German guidelines.
201702_WaterVal_Guidance Document_UV Disinfection 9
Glossary and abbreviations
LRV log reduction value A log10 reduction value is used in the physical–chemical treatment of water to characterise the removal or inactivation of microorganisms such as bacteria, protozoa and viruses (1-log10 = 90% or a 10-fold reduction, 3-log10 = 99.9% or a 1000-fold reduction, and so on). LRV = log10 (N0) – log10 (N), where N0 = concentration of infectious microorganisms before treatment and N = concentration of infectious microorganisms after treatment.
RED reduction equivalent dose
The UV dose derived by entering the log inactivation measured during full-scale reactor testing into the UV dose–response curve that was derived through collimated beam testing. RED values are always specific to the challenge microorganism used during experimental testing and the validation test conditions for full-scale reactor testing
RED bias Accounts for the difference between the dose delivered to the target pathogen and the dose measured using a challenge microorganism. If the challenge microorganism is more resistant to UV light than the target pathogen, the RED measured during validation will be greater than the dose delivered to the pathogen
US EPA United States Environmental Protection Agency
UV ultraviolet
Uval Uncertainty in validation or experimental uncertainty, expressed as a percentage.
UV dose The UV energy per unit area incident on a surface, typically reported in units of mJ/cm2 or J/m2. The UV dose received by a waterborne microorganism in a reactor vessel accounts for the effects on UV intensity of the absorbance of the water, absorbance of the quartz sleeves, reflection and refraction of light from the water surface and reactor walls, and the germicidal effectiveness of the UV wavelengths transmitted.
UVT UV transmittance A measure of the fraction of incident light transmitted through a material. The UVT is usually reported for a wavelength of 254 nm and a path length of 1 cm. If an alternate path length is used, it should be specified or converted to units of cm-1. UVT is often represented as a percentage and is related to the UV absorbance (A254) by the following equation (for a 1-cm path length): % UVT = 100 × 10-A
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References
AWRCE 2015, Protocol template, WaterVal validation, Australian Water Recycling Centre of Excellence, Brisbane.
DVGW 2006, UV disinfection devices for drinking water supply – requirements and testing. DVGW W294-1, -2, and -3, Deutsche Vereinigung des Gas- und Wasserfaches [German Association for Gas and Water], Bonn, Germany.
Hijnen WAM, Beerendonk EF & Medema GJ 2006, Inactivation credit of UV radiation for viruses, bacteria and protozoan (oo)cysts in water: a review, Water Research 40:3–22.
Hoyer O 1998, Testing performance and monitoring of UV systems for drinking water disinfection, Water Supply 16(1/2):419–442.
Linden K 2014, How the German DVGW Compares to the USEPA UVDGM, Australian Water Recycling Centre of Excellence, Brisbane.
Richard L 2015a, Example application of the WaterVal validation protocol template, using the US EPA ultraviolet disinfection guidance manual (2006), Australian Water Recycling Centre of Excellence, Brisbane.
Richard L 2015b, Example application of the WaterVal validation protocol template, using the German Association on Gas and Water’s technical rule, UV disinfection devices for drinking water supply – requirements and testing. DVGW W294-1, -2, and -3 (2006), Australian Water Recycling Centre of Excellence, Brisbane.
US EPA 2006, Ultraviolet disinfection guidance manual for the final long term 2 enhanced surface water treatment rule. Office of Water United States Environmental Protection Agency, Washington, DC.
Wright H 2007, Grandfathering other UV validation protocols to meet LT2 and groundwater rule compliance, presentation at the International Ozone Association/International UV Association Joint World Congress, August 2007 Los Angeles, USA.
