Performic Acid Versus Sodium Hypochlorite for Municipal Wastewater Effluent Disinfection: Bench-Scale Tests Using New...

Alternatives to chlorination are needed for wastewater effluent disinfection to improve microbial inactivation, while reducing concerns associated with chlorinated disinfection byproducts (DBPs) and total residual chlorine (TRC). Performic acid (PFA) is a strong disinfectant, yet comparative USA data linking disinfection performance to matrix-dependent oxidant demand and residual behavior in wastewater remain limited. Here, PFA and sodium hypochlorite were evaluated in bench-scale batch experiments using final settling tank effluent (FSTE) from two New York City wastewater resource recovery facilities (WRRFs) with different biological configurations: Wards Island (step-feed BNR) and Newtown Creek (conventional secondary). Dissolved metals were also screened in Wards Island samples. At 1 mg/L and 10-min contact time, PFA achieved strong inactivation in both effluents, with log reductions of 2.8 and 3.5 for fecal coliforms and 2.5 and 2.9 for enterococci in Wards Island and Newtown Creek, respectively. Under the tested conditions, 1 mg/L of hypochlorite (as Cl₂) generally produced comparable fecal coliform reductions but substantially lower enterococci log reductions. In Newtown Creek FSTE, 1 mg/L of PFA exceeded enterococci inactivation achieved by 2 mg/L of hypochlorite (2.9 versus 1.7 after 10-min contact time), indicating higher enterococci efficacy at a lower dose. Disinfectant initial demand with PFA was generally higher, and PFA decayed faster than hypochlorite. The higher TRC observed with hypochlorite may necessitate dechlorination prior to discharge, whereas this concern is not associated with PFA. Dissolved metals did not differ significantly between PFA-treated and hypochlorite-treated Wards Island samples under the tested conditions, although minor increases in Ni and Zn relative to the control were observed and warrant further investigation. Future work should evaluate continuous-flow conditions and confirm performance across seasons and a wider range of effluent matrices.