Assessing the basis for regulatory crediting of virus LRVs for secondary biological wastewater treatment: A systematic review

•Influent concentration was not consistently correlated with LRV.•Median LRVs ranged from 0.8 for rotavirus and norovirus to 3.4 for polyomavirus.•5th percentile LRVs for robust enteric virus datasets ranged from 0.1 to 0.9.•Instead of correlations, target operational thresholds may exist for BOD and MLSS.•More data simultaneously comparing viruses, methods, and surrogates are needed. Regulatory frameworks for potable reuse often include stringent log10 reduction value (LRV) targets to ensure public health protection against exposure to viruses and protozoa. To achieve overall LRV targets and reduce associated capital and operational costs, it is important to maximize LRV credits awarded to each unit process in a potable reuse treatment train. This may include processes that are historically uncredited or undercredited, such as secondary biological wastewater treatment incorporating activated sludge and secondary clarification. To identify gaps in knowledge and inform future efforts to justify virus crediting, this systematic literature review and meta-analysis focused on characterizing virus attenuation during secondary treatment and identifying any virus characteristics, operational conditions, or water quality parameters that could serve as predictors of virus LRVs. Out of a total of 1,341 search results from three databases, this review considered 44 peer-reviewed studies that met the criteria for inclusion. LRVs as high as 5.3 log10 were reported for F-specific coliphages, but some studies reported increases in rotavirus and norovirus GI concentrations across secondary treatment. Median LRVs ranged from 0.8 log10 for rotavirus and norovirus GI (both based on molecular methods) to 2.4 to 3.4 log10 for poliovirus (culture) and polyomavirus (molecular), respectively. 5th percentile LRVs were