Peracetic acid for secondary effluent disinfection: a global performance assessment

The paper summarizes the results of a research work on secondary effluent disinfection by peracetic acid (PAA). The process was studied at bench and pilot scale to assess its global performances both for surface water discharge and for agricultural reuse. The purposes of the research were: 1) determining PAA decay and disinfection kinetics as a function of operating parameters, 2) evaluating PAA suitability as a disinfectant, 3) assessing long-term disinfection efficiency, 4) investigating WWTP effluent biological toxicity on some aquatic indicator organisms (Vibrio fischeri, Daphnia magna and Selenastrum capricornutum), 5) comparing PAA with conventional disinfectants (sodium hypochlorite, UV irradiation). Bacterial removal was monitored adopting Escherichia coli, faecal coliforms and total heterotrophic bacteria as indicators. The PAA disinfection resulted in strong bacterial removal, capable of complying with Italian regulations on reuse (10 CFU/100 mL for E. coli) and competitive with benchmarks. No regrowth phenomena were observed for coliform bacteria, as long as needed for agricultural reuse (29 h after disinfection), even at negligible concentrations of residual disinfectant. These results, combined with the flow cytometry ones, demonstrated good properties of PAA as bactericide. Toxic effect of PAA on aquatic environment was due to residual disinfectant in water, rather than to effluent chemical modification.