Risk-based enteric pathogen reduction targets for non-potable and direct potable use of roof runoff, stormwater, and greywater

Abstract

This paper presents risk-based enteric pathogen log reduction targets for non-potable and potable uses of a variety of alternative source waters (i.e., locally-collected greywater, roof runoff, and stormwater). A probabilistic Quantitative Microbial Risk Assessment (QMRA) was used to derive the pathogen log 10 reduction targets (LRTs) that corresponded with an infection risk of either 10 −4 per person per year (ppy) or 10 −2 ppy. The QMRA accounted for variation in pathogen concentration and sporadic pathogen occurrence (when data were available) in source waters for reference pathogens in the genera Rotavirus, Mastadenovirus(human adenoviruses), Norovirus, Campylobacter, Salmonella, Giardia and Cryptosporidium. Non-potable uses included indoor use (for toilet flushing and clothes washing) with occasional accidental ingestion of treated nonpotable water (or cross-connection with potable water), and unrestricted irrigation for outdoor use. Various exposure scenarios captured the uncertainty from key inputs, i.e., the pathogen concentration in source water; the volume of water ingested; and for the indoor use, the frequency of and the fraction of the population exposed to accidental ingestion. Both potable and non-potable uses required pathogen treatment for the selected waters and the LRT was generally greater for potable use than non-potable indoor use and unrestricted irrigation. The difference in treatment requirements among source waters was driven by the microbial quality of the water-both the density and occurrence of reference pathogens. Greywater from collection systems with 1000 people had the highest LRTs; however, those for greywater collected from a smaller population (~ 5 people), which have less frequent pathogen occurrences, were lower. Stormwater had highly variable microbial quality, which resulted in a range of possible treatment requirements. The microbial quality of roof runoff, and thus the resulting LRTs, remains uncertain due to lack of relevant pathogen data.

Assessment of Water Quality in Roof-Harvested Rainwater Barrels in Greater Philadelphia

“…Additional information is needed regarding the feasibility, cost, and health risk-reduction benefits of point-of-use devices or other interventions such as first-flush devices, cleaning and disinfecting rain barrels, and using mesh screens to prevent debris from entering the barrel in these small-scale systems under varied environmental conditions and maintenance schemes. Although the risk from enteric pathogens is likely to be low for municipal irrigation [64,65], risks due to opportunistic pathogens may be higher due to non-potable uses such as gardening, and further investigation would be beneficial.…”

A review on microbial contaminants in stormwater runoff and outfalls: Potential health risks and mitigation strategies

“…Cryptosporidium spp. : toilet flushing 0.8-3.8, unrestricted Schoen et al, 2017Schoen et al, et al, 2012aSchoen et al, , 2012bMcBride et al, 2013;Sales-Ortells and Medema, 2015), limiting the ability to capture the large variability in stormwater pathogen concentrations due to potentially diverse fecal contamination sources (human and multiple animal fecal wastes, affecting the types of index pathogens chosen for the QMRA), rainfall patterns, decay rates, and other factors.…”

“…Limited information is available for pathogen removal by stormwater treatment barriers and would be informative for conducting risk analyses. Additionally, these values can be compared with theoretical LRVs necessary to meet health risk targets (NRMMC-EPHC-AHMC, 2009;Page et al, 2015;Schoen and Garland, 2015;Schoen et al, 2017).…”

Enterobius vermicularis as a Novel Surrogate for the Presence of Helminth Ova in Tertiary Wastewater Treatment Plants

“…Deposition of eggs on the perianal skin also means that E. vermicularis eggs may become associated with clothing and bed linens, where these ova may be washed into gray water through clothes washing. This suggest that there may be not only a reuse risk associated with black water but also a reuse risk associated with gray water (49,50). Due to the ability of E. vermicularis ova to be aerosolized, this might pose a risk for transmission and should be investigated (32).…”