In Ontario, Canada, information is lacking on chlorine and ultraviolet (UV) light disinfection performance against enteric viruses in wastewater. We enumerated enteroviruses and noroviruses, coliphages, and Escherichia coli per USEPA methods 1615, 1602, and membrane filtration, respectively, in pre- and post-disinfection effluent at five wastewater treatment plants (WWTPs), with full-year monthly sampling, and calculated log10 reductions (LRs) while WWTPs complied with their monthly geometric mean limit of 200 E. coli/100 mL. Modeling of densities by left-censored estimation and Bayesian inference gave very similar results. Polymerase chain reaction (PCR)-detected enteroviruses and noroviruses were abundant in post-disinfection effluent (mean concentrations of 2.1 × 10+4–7.2 × 10+5 and 2.7 × 10+4–3.6 × 10+5 gene copies (GC)/L, respectively). Chlorine or UV disinfection produced modest LRs for culture- (0.3–0.9) and PCR-detected enteroviruses (0.3–1.3), as well as noroviruses GI + GII (0.5–0.8). Coliphages and E. coli were more susceptible, with LRs of 0.8–3.0 and 2.5, respectively. Sand-filtered effluent produced significantly higher enteric virus LRs (except cultured enteroviruses). Coliphage and human enteric virus densities gave significantly positive correlations using Kendall's Tau test. Enteric viruses are abundant in wastewater effluent following routine chlorine or UV disinfection processes that target E. coli. Coliphages appear to be good indicators for evaluating wastewater disinfection of enteric viruses.

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Peracetic acid (PAA) has been used as a municipal wastewater disinfectant for over 2 decades, but information about its virucidal performance is limited. Here, we report on a 2 year study of virus disinfection with PAA and chlorine as hypochlorite (NaClO) in a secondary wastewater treatment plant. During year 1, we conducted a side-stream comparison of PAA dosed at 4 mg/L (minus a demand of about 10%) and NaClO at 7.3 mg/L against indigenous enteroviruses and noroviruses, as well as coliphages and Escherichia coli, while assessing PAA fish toxicity under flow-through conditions. During year 1, PAA and NaClO produced poor median log10 reductions (LRs) against enteroviruses and noroviruses, although NaClO LRs were significantly higher. PAA and NaClO performed better against coliphages, but differences were not significant. Against E. coli, PAA and NaClO performed well. 96 hour toxicity testing was done only during year 1, revealing that PAA residual was lethal to rainbow trout only prior to quenching. The PAA dose was reduced to 3 mg/L (minus a demand of about 10%) during year 2 when we enumerated only coliphages and E. coli. F+ male-specific coliphage LRs significantly dropped from 1.2 to 0.5, while E. coli LR remained unchanged. To ensure protection of aquatic life, an interim 0.27 mg/L PAA residual discharge limit was derived.