Enteric Pathogen Treatment Requirements for Nonpotable Water Reuse Despite Limited Exposure Data

Abstract

Exposure factors (e.g., ingestion volume and frequency) are required to establish risk-based treatment requirements (i.e., log 10 reduction targets (LRTs)) for enteric pathogens using quantitative microbial risk assessment (QMRA). However, data to Wastewater characterize nonpotable exposure factors are sparse. We calculated graywater and wastewater nonpotable LRTs (corresponding to 10 −4 infections per person per year) for uses missing detailed exposure data (including showering and decorative fountain) and across a range of exposure factors. The LRTs decreased linearly toward zero as the log 10 transformed volume or the frequency of reuse decreased. When nonroutine exposure was included, representing either accidental ingestion from misuse or cross-connection between potable and nonpotable waters, the LRTs remained high, even as the routine ingestion volume decreased. Therefore, uses with small anticipated routine ingestion volumes (i.e., roughly <10 −5 L), e.g., domestic indoor or decorative fountain uses, share common LRTs, and further refinement of the routine exposure is of limited value. Additional data to characterize nonroutine exposures and uses with high routine ingestion, e.g., showering, remain valuable to better estimate LRTs. These results will assist regulators in the selection of LRTs for nonpotable uses that lack detailed exposure factor characterizations.

Towards risk assessment for antibiotic resistant pathogens in recycled water: a systematic review and summary of research needs

“…Therefore, it is an additional research need to identify additional approaches for incorporating ARG monitoring data into a risk assessment framework and to operationalize these approaches for a specific example within a QMRA. Additionally, once specific ARB are identified as monitoring targets, a reverse QMRA approach similar to those applied for previous studies of recycled water (Schoen et al ., 2017, 2020) could be applied to calculate associated log reduction targets (LRT) or monitoring concentrations for a given benchmark infection risk (e.g. 1 in 10 000 per person per year).…”

“…are identified as monitoring targets, a reverse QMRA approach similar to those applied for previous studies of recycled water (Schoen et al, 2017(Schoen et al, , 2020) could be applied to calculate associated log reduction targets (LRT) or monitoring concentrations for a given benchmark infection risk (e.g. 1 in 10 000 per person per year).…”

Quantitative Microbial Risk Assessment of Antimicrobial Resistant and Susceptible Staphylococcus aureus in Reclaimed Wastewaters

“…We used QMRA to model the annual probability of colonization and subsequent infection risk and disease burden for healthy adults from exposures to MRSA or MSSA resulting from residential and municipal nonpotable and potable uses of reclaimed water. We considered a range of S. aureus treatment log 10 reduction values (LRVs) that included the bacteria log 10 reduction targets (LRTs) for nonpotable indoor GW and WW reuse of 3.5 and 6.0, respectively, 33,34 for reuse of GW for showering of 5.7, 31 as well as an estimated LRV for potable reuse of 15. 35 We adopted the conservative exposure assumption of daily immersion for all residential and municipal nonpotable and potable uses (described further in Section 2.1.1).…”

“…We considered a range of S. aureus treatment log 10 reduction values (LRVs) that included the bacteria log 10 reduction targets (LRTs) for nonpotable indoor GW and WW reuse of 3.5 and 6.0, respectively, , for reuse of GW for showering of 5.7, as well as an estimated LRV for potable reuse of 15 . We adopted the conservative exposure assumption of daily immersion for all residential and municipal nonpotable and potable uses (described further in Section ).…”

“…The objective was to estimate the probability of nasal colonization and subsequent delayed infection and disease burden resulting from exposures to MRSA and MSSA in reclaimed WW and GW, considering a range of treatment levels. In doing so, we evaluated whether risk-based reuse treatment requirements based on enteric pathogens for nonpotable reuse 33,34 and potable use 35 are also protective against S. aureus. A secondary objective was to identify the dominant mechanisms that influence MRSA exposure in a reuse scenario with HGT occurring in treatment.…”