Ultraviolet disinfection. Guidance document

Transcription

1 Ultraviolet disinfection Guidance document

2 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 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 errorfree. 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.

3 Contents 1. Background and scope Policy position US EPA guidelines German guidelines Operational monitoring Rationale Comparison of validation methods Incorporating validation uncertainties Protozoa Viruses... 8 Glossary and abbreviations... 9 References Tables Table 1 UV doses required to achieve various log reduction values for target pathogens... 5 Table 2 Validated Cryptosporidium dose (mj/cm 2 ) as a function of log reduction value and UV transmittance, based on Bacillus subtilis RED of 40 mj/cm Table 3 Validated Giardia dose (mj/cm 2 ) as a function of log reduction value and UVT, based on Bacillus subtilis RED of 40 mj/cm 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 _WaterVal_Guidance Document_UV Disinfection 1

4 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 _WaterVal_Guidance Document_UV Disinfection 2

5 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. Selection of pre-validated UV disinfection system US EPA guidelines German guidelines US EPA validation method applied consistently UV dose 40 mj/cm 2 UVT > 95% UVT > 65% UVT > 50% Validated log credit accepted 4-log credit protozoa and bacteria 3.5-log credit protozoa and bacteria 3-log credit protozoa and bacteria 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 German guidelines UV disinfection systems that have been validated under the German guidelines to achieve a UV dose of 40 mj/cm 2 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 _WaterVal_Guidance Document_UV Disinfection 3

6 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/cm 2 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 _WaterVal_Guidance Document_UV Disinfection 4

7 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/cm 2, 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 Cryptosporidium Giardia Virus Note: All doses are in mj/cm 2. Source: US EPA (2006) The target UV dose of 40 mj/cm 2 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 _WaterVal_Guidance Document_UV Disinfection 5

8 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 Challenge organism RED Validated pathogen dose = RED bias (1+Uval/100) (equation 1) In the German guidelines, the challenge organism is Bacillus subtilis and the RED is 40 mj/cm 2. 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/cm 2 per LRV and the range can be used in the US EPA guidelines tables 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/cm 2, 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 _WaterVal_Guidance Document_UV Disinfection 6

9 Table 2 Validated Cryptosporidium dose (mj/cm 2 ) as a function of log reduction value and UV transmittance, based on Bacillus subtilis RED of 40 mj/cm 2 UVT Log reduction value Minimum UV dose required Table 3 Validated Giardia dose (mj/cm 2 ) as a function of log reduction value and UVT, based on Bacillus subtilis RED of 40 mj/cm 2 UVT Log reduction value Minimum UV dose required 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 Cryptosporidium Giardia _WaterVal_Guidance Document_UV Disinfection 7

10 Viruses The US EPA guidelines specify a requirement of 39 mj/cm 2 for a 0.5 LRV of viruses by UV disinfection. Based on the Bacillus subtilis RED of 40 mj/cm 2, 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/cm 2 is considerably lower than the target 39 mj/cm 2. 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 _WaterVal_Guidance Document_UV Disinfection 8

11 Glossary and abbreviations LRV RED RED bias US EPA UV Uval UV dose UVT log reduction value A log 10 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-log 10 = 90% or a 10-fold reduction, 3-log 10 = 99.9% or a 1000-fold reduction, and so on). LRV = log 10 (N 0) log 10 (N), where N 0 = concentration of infectious microorganisms before treatment and N = concentration of infectious microorganisms after treatment. 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 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 United States Environmental Protection Agency ultraviolet Uncertainty in validation or experimental uncertainty, expressed as a percentage. The UV energy per unit area incident on a surface, typically reported in units of mj/cm 2 or J/m 2. 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. 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 (A 254) by the following equation (for a 1-cm path length): % UVT = A _WaterVal_Guidance Document_UV Disinfection 9

12 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): 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 _WaterVal_Guidance Document_UV Disinfection 10