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Microbial Risk Assessment of Onsite Non-Potable Water Reuse: Updates and Implications
Citation:
Jahne, M., M. E. SCHOEN, AND J. L. GARLAND. Microbial Risk Assessment of Onsite Non-Potable Water Reuse: Updates and Implications. AWWA Virtual Summit: Sustainable Water, PFAS, Waterborne Pathogens, NA,OH, February 10 - 11, 2021.
Impact/Purpose:
Onsite non-potable water reuse provides an opportunity to reduce stress on both potable water supplies and wastewater collection systems; however, care must be taken to manage microbial risks. This presentation describes the use of quantitative microbial risk assessment (QMRA) to generate a matrix of pathogen log-reduction targets (LRTs) across various combinations of onsite source waters and non-potable end-uses. It focuses on recent developments in three areas of risk assessment and management: pathogen characterization, exposure assessment, and model application. Together, this body of work advances the science of risk-based treatment and facilitates the further development of onsite water reuse resources.
Description:
Onsite non-potable water reuse provides an opportunity to reduce stress on both potable water supplies and wastewater collection systems; however, care must be taken to manage microbial risks. Source waters such as graywater, blackwater, stormwater, and rainwater contain distinct microbial communities with unique pathogen characterizations driven by respective types and levels of fecal contamination. In the case of graywater and blackwater, these pathogen loadings are scale-dependent due to the stochastic nature of pathogen infections among small populations. For stormwater, risks are driven by variable contributions of human wastewater to these flows. Rainwater risks are associated with animal feces deposited on rooftop collection surfaces. Likewise, exposure levels are dependent on the specific end-use of treated non-potable waters, such as irrigation or toilet flushing. Cross-connections and treatment failures must also be considered, particularly given the generally short residence time and lower operational oversight of these systems. To address such concerns and provide appropriate treatment guidance for these systems, we used quantitative microbial risk assessment (QMRA) to generate a matrix of pathogen log-reduction targets (LRTs) across various combinations of onsite source waters and non-potable end-uses. The original set of LRTs has been adopted by the National Blue Ribbon Commission for Onsite Non-potable Water Systems and are now being implemented at state and local levels throughout the U.S. We continue to review and update the QMRA models to both ensure that they rely on the most current and applicable data and to extend their scope to additional source waters and non-potable end-uses. Recent developments have focused on three aspects of risk assessment and management: pathogen characterization, exposure assessment, and model application. Under pathogen characterization, we have collected new measurement data to verify modeled pathogen densities in decentralized collections of graywater, blackwater, and rainwater and are developing new methods for estimating wastewater contamination of stormwater. We have also included air conditioning condensate as an additional source water of interest. For exposure assessment, we have examined the impact of potential cross-connections on reuse risks and associated treatment requirements and extended end-uses to include decorative fountains and showering applications. In the latter, we have added consideration of opportunistic skin pathogens, including antimicrobial-resistant strains associated with high disease burden. Finally, we have applied the model to examine questions about impact of collection scale and to evaluate whether treatment systems complying with indicator-based standards meet acceptable levels of pathogen risk. Together, this body of work advances the science of risk-based treatment and facilitates the further development of onsite water reuse resources.