A new disinfection system for wastewater treatment: performic acid full-scale trial evaluations

To evaluate the efficiency and effect of a new disinfection technology in wastewater treatment, batch and full-scale experiments were performed between winter 2005 and summer 2011. The system, developed by Kemira Oyj, produces a disinfection solution containing performic acid (PFA) by mixing hydrogen peroxide and formic acid. A preliminary study in batch reactors established the suitability for wastewater disinfection; three subsequent full-scale plant experiments conducted at two municipal wastewater treatment plants (120,000 and 32,000 equivalent inhabitants) discharging in sensitive areas demonstrated its effectiveness and reliability in this application field. The disinfection power of the system was measured using faecal coliforms, Escherichia coli and faecal enterococci; additional water quality parameters included total organic carbon, suspended solids, eco-toxicity and disinfection by-products. Full-scale experiments indicated that PFA has a high disinfection power, always ensuring over 3 log of faecal coliforms and E. coli reductions at CT over 60 mg/L min (CT: disinfectant initial Concentration (mg/L) x contact Time (min)). The final production system yielded even better performance, with E. coli and faecal enterococci reductions ranging from 2 to 4.2 and from 0.7 to 3.2 log, respectively, at CT conditions lower than 23 mg/L min. There were no eco-toxicological effects measured by Vibrio fischeri or by-product formation.