Side-Stream Comparison of Peracetic Acid and Chlorine as Hypochlorite for Disinfection of Municipal Wastewater Effluent at a Full-Scale Treatment Facility, Ontario, Canada

Abstract

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.