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Risk-Based Framework for Developing Microbial Treatment Targets for Water Reuse
Citation:
Jahne, M., S. Nappier, J. Garland, M. Schoen, AND J. Soller. Risk-Based Framework for Developing Microbial Treatment Targets for Water Reuse. U.S. Environmental Protection Agency, Washington, DC, EPA/600/R-25/009, 2025.
Impact/Purpose:
There are increasing pressures on traditional sources of water throughout the United States, with state and local governments increasingly turning to water reuse to help meet demands. State regulators are tasked with ensuring that recycled water is treated adequately to protect public health in its intended use; this is known as “fit-for-purpose” treatment. EPA’s 2012 Water Reuse Guidelines and 2017 Potable Reuse Compendium highlighted the importance of managing acute microbial risks, particularly for applications in which human contact is likely to occur, and discussed quantitative microbial risk assessment (QMRA) approaches to define treatment targets for removing pathogenic viruses, bacteria and protozoa. However, these documents did not provide the detailed scientific information that states, Tribes and other relevant entities need to develop their own risk assessments and microbial treatment targets (log10 reduction targets (LRTs)). This document reviews the state of the science regarding the development of risk-based microbial treatment targets for a range of fit-for-purpose water reuse applications. It articulates the components of the QMRA framework and provides a rationale for input model parameters based on peer-reviewed literature to support states, Tribes and other regulatory entities interested in developing LRTs. The document is designed to provide these entities with sufficient detail to make their own informed decisions regarding the development of microbial treatment targets and provides considerations for decision-makers translating risk-based management into practical implementation. In addition, the document presents peer-reviewed LRTs for a range of alternative sources of water for both potable and non-potable applications, which were computed using the aforementioned input parameters. The QMRA framework and corresponding LRTs should be viewed as an opportunity to fill important gaps in public health protection to move water reuse forward using scientifically-defensible information. Using the QMRA framework herein, the input parameters and associated LRTs may be updated with new data as they become available to ensure that water reuse treatment decisions are made with the most current science. This state of the science review covers the following topics: · A background and introduction to the QMRA framework for water reuse (Chapter 1); · Information on bacterial, viral and protozoan enteric reference pathogens to consider when evaluating microbial risks related to water reuse (Chapter 2); · A summary of updated reference pathogen densities in different sources of water and approaches for characterizing those densities to inform water reuse QMRAs (Chapter 3); · A summary of ingestion estimates for potable reuse, unrestricted irrigation and non-potable indoor uses (Chapter 4); · An overview of the most current reference pathogen dose-response models and parameter values for determining the probability of infection and illness along with a quantitative characterization of illness severity (Chapter 5); · A description of risk characterization approaches using both infection and disease burden health metrics (Chapter 6); · A synopsis of peer-reviewed publications for water reuse treatment requirements (i.e., LRTs) that establish the current state of the science for a wide range of applications (Chapter 7); · A discussion of key policy considerations for decision-makers implementing risk-based water reuse treatment targets (Chapter 8); and · Information on research needs specific to the QMRA framework (Chapter 9).
Description:
There are increasing pressures on traditional sources of water throughout the United States, with state and local governments increasingly turning to water reuse to help meet demands. State regulators are tasked with ensuring that recycled water is treated adequately to protect public health in its intended use; this is known as “fit-for-purpose” treatment. EPA’s 2012 Water Reuse Guidelines and 2017 Potable Reuse Compendium highlighted the importance of managing acute microbial risks, particularly for applications in which human contact is likely to occur, and discussed quantitative microbial risk assessment (QMRA) approaches to define treatment targets for removing pathogenic viruses, bacteria and protozoa. However, these documents did not provide the detailed scientific information that states, Tribes and other relevant entities need to develop their own risk assessments and microbial treatment targets (log10 reduction targets (LRTs)). This document reviews the state of the science regarding the development of risk-based microbial treatment targets for a range of fit-for-purpose water reuse applications. It articulates the components of the QMRA framework and provides a rationale for input model parameters based on peer-reviewed literature to support states, Tribes and other regulatory entities interested in developing LRTs. The document is designed to provide these entities with sufficient detail to make their own informed decisions regarding the development of microbial treatment targets and provides considerations for decision-makers translating risk-based management into practical implementation. In addition, the document presents peer-reviewed LRTs for a range of alternative sources of water for both potable and non-potable applications, which were computed using the aforementioned input parameters. The QMRA framework and corresponding LRTs should be viewed as an opportunity to fill important gaps in public health protection to move water reuse forward using scientifically-defensible information. Using the QMRA framework herein, the input parameters and associated LRTs may be updated with new data as they become available to ensure that water reuse treatment decisions are made with the most current science. This state of the science review covers the following topics: · A background and introduction to the QMRA framework for water reuse (Chapter 1); · Information on bacterial, viral and protozoan enteric reference pathogens to consider when evaluating microbial risks related to water reuse (Chapter 2); · A summary of updated reference pathogen densities in different sources of water and approaches for characterizing those densities to inform water reuse QMRAs (Chapter 3); · A summary of ingestion estimates for potable reuse, unrestricted irrigation and non-potable indoor uses (Chapter 4); · An overview of the most current reference pathogen dose-response models and parameter values for determining the probability of infection and illness along with a quantitative characterization of illness severity (Chapter 5); · A description of risk characterization approaches using both infection and disease burden health metrics (Chapter 6); · A synopsis of peer-reviewed publications for water reuse treatment requirements (i.e., LRTs) that establish the current state of the science for a wide range of applications (Chapter 7); · A discussion of key policy considerations for decision-makers implementing risk-based water reuse treatment targets (Chapter 8); and · Information on research needs specific to the QMRA framework (Chapter 9).