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A Risk-Based Evaluation of Onsite, Non-Potable Reuse Systems Developed in Compliance with Conventional Water Quality Measures
Citation:
Schoen, M., M. Jahne, AND J. Garland. A Risk-Based Evaluation of Onsite, Non-Potable Reuse Systems Developed in Compliance with Conventional Water Quality Measures. JOURNAL OF WATER AND HEALTH. IWA Publishing, London, Uk, 18(3):331-334, (2020). https://doi.org/10.2166/wh.2020.221
Impact/Purpose:
National level water quality standards (WQSs) based on conventional water quality measures (e.g., fecal indicator bacteria (FIB)) have been used by state regulatory agencies to assess onsite, non-potable water reuse efforts. An alternative, risk-based approach was also developed based on quantitative microbial risk assessment (QMRA) to define the treatment needed for non-potable water reuse to achieve selected benchmark levels of risk. The QMRA approach has not been universally accepted by state agencies with responsibility for non-potable water reuse. This work compared these two approaches using the predicted annual infection risks for non-potable reuse systems that comply with WQSs along with the selected benchmark risk levels achieved by the risk-based systems.
Description:
National level water quality standards (WQSs) based on conventional water quality measures (e.g., fecal indicator bacteria (FIB)) have been used by state regulatory agencies to assess onsite, non-potable water reuse efforts. An alternative, risk-based approach was also developed based on quantitative microbial risk assessment (QMRA) to define the treatment needed for non-potable water reuse to achieve selected benchmark levels of risk. The QMRA approach has not been universally accepted by state agencies with responsibility for non-potable water reuse. This work compared these two approaches using the predicted annual infection risks for non-potable reuse systems that comply with WQSs along with the selected benchmark risk levels achieved by the risk-based systems. The systems that comply with WQSs include a septic tank combined with recirculating synthetic sand filter (RSF) and ultraviolet disinfection for residential reuse of wastewater and aerobic membrane bioreactor (MBR) combined with chlorination for residential reuse of wastewater or commercial reuse of greywater (e.g., multi-family housing or business park). The reference pathogen density in onsite waters was simulated (including Norovirus and Cryptosporidium spp.) and treatment performance was characterized using system performance data or removal credits for the MBR system, but no performance data was identified for the RSF system. The commercial greywater reuse MBR system had predicted annual probabilities of infection of roughly 10-4 infections per person per year (ppy) for intermediate sized applications (10-2 infections ppy) in single-family residential applications, due to exposures to viruses and protozoa in the treated, non-potable waters. To better characterize pathogen risk for non-potable reuse, improved treatment performance data are required, beyond FIB, particularly for virus and parasite removal. Given the lack of risk-based guidance for intermediate-sized systems, we proposed log10 pathogen reduction targets (LRTs) for onsite, non-potable systems treating less than 19,200 L d-1 (5070 G d-1); these targets are roughly 0.5 log10 less than those previously proposed for district-sized systems.
URLs/Downloads:
DOI: A Risk-Based Evaluation of Onsite, Non-Potable Reuse Systems Developed in Compliance with Conventional Water Quality Measures
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