A dynamic quantitative microbial risk assessment for norovirus in potable reuse systems

This study describes the results of a dynamic quantitative microbial risk assessment (QMRA) for norovirus (NoV) that was used to evaluate the relative significance of foodborne, person-to-person, and person-to-sewage-toperson transmission pathways. This last pathway was incorporated into simulated potable reuse systems to evaluate the adequacy of typical treatment trains, operational conditions, and regulatory frameworks. The results confirm that secondary and foodborne transmission dominate the overall risk calculation and that waterborne NoV likely contributes no appreciable public health risk, at least in the scenarios modeled in this study. De facto reuse with an environmental buffer storage time of at least 30 days was comparable or even superior to direct potable reuse (DPR) when compound failures during advanced treatment were considered in the model. Except during these low-probability failure events, DPR generally remained below the 10-4 annual risk benchmark for drinking water. Based on system feedback and the time-dependent pathogen load to the community's raw sewage, this model estimated median raw wastewater NoV concentrations of 107-108 genome copies per liter (gc/L), which is consistent with high-end estimates in recent literature.