A Bayesian Model for Estimation of Virus Reduction in Potable Reuse Treatment Trains and Quantitative Microbial Risk...

Understanding virus occurrence and reduction at advanced treatment facilities for potable water reuse constitutes a high-priority research need to protect human health and to enhance available water supply alternatives. The objectives were to (1) determine log reduction values (LRVs) of 15 viruses by advanced wastewater treatment; (2) evaluate suitability of the final wastewater effluent for potable reuse; (3) evaluate viruses or groups of viruses as indicators of wastewater treatment efficiency. Reduction data of seven human enteric and eight surrogate viruses were obtained from three potable reuse facilities. LRVs were estimated using a Bayesian model that can handle nondetects and identifies groups of viruses with similar LRVs. Quantitative microbial risk assessments were conducted for adenoviruses, enteroviruses, and noroviruses GI and GII. Mean total LRVs ranged from 5.4 to 11 log_10. Required mean total LRVs for the four pathogenic viruses ranged from 11.3 to 13.4 log₁₀. Both male-specific and somatic coliphages, detected by classical enumeration of infectious virions, are recommended as indicator viruses. Of the pathogenic viruses, adenovirus was found to be the most effective indicator for virus reduction. At all facilities, infection risks were higher than 10^-4 per person per year, implying that the finished water may not comply with existing safety standards. Infection risks may have been overestimated by 2-4 log₁₀ because only a fraction of the detected virus was infectious. Nevertheless, achieved LRVs were still too low and given the uncertainty on infectious virus fraction, one may accept overestimation of risks to stay on the safe side.