Inactivation of Enteric Microorganisms in Secondary Treated Municipal Wastewaters with Peracetic Acid (PAA) Disinfection

The disinfection efficiency of peracetic acid (PAA) against enteric microorganisms in secondary treated municipal wastewaters was studied in pilot-scale. The aim was to get information on the level of disinfection achievable with PAA, by using different PAA doses and contact times in variable process conditions (effluent quality, temperature).Experimental pilot-plant for disinfection was fed with secondary effluent of Kuopio municipal wastewater treatment plant, which is an activated sludge plant with simultaneous phosphorus precipitation and secondary settling. The plug-flow disinfection reactor consisted of chicane tank with 5 parting walls (volume approximately 1 m3, polyethylene basin). Peracetic acid equilibrium mixture (15% PAA, 13–16 % hydrogen peroxide and 21–26 % acetic acid) was used as a disinfectant chemical. The tested PAA doses for wastewater disinfection ranged from 2 to 7 mg/l. Each sampling session involved collection of samples from secondary effluent and different stages of disinfection reactor, corresponding disinfection contact times of 4–27 min. Samples were analysed for total coliforms and enterococci as well as for some principal physico-chemical parameters.Peracetic acid was demonstrated to be an efficient disinfectant against enteric bacteria. PAA dose of 2–7 mg/l achieved 2.2–3.9 log reductions of total coliforms and 1.3–4.0 log reductions of enterococci during 27 minute of contact time. The most significant total coliform reductions occurred during the first 13 minute of contact time, showing fast disinfection action of PAA. The inactivation rate of enterococci was slightly slower, showing further microbial inactivation between 13 and 27 minute of contact time. No significant correlations between wastewater quality (SS, COD, turbidity or 253.7 nm absorbance) or temperature and microbial reductions were observed.