Evaluation of the efficiency of peracetic acid in the disinfection of sewage effluents

Aims: Evaluation of the efficiency of peracetic acid in the disinfection of wastewater in a large treatment plant. Methods and Results: Over a period of 18 months 30 sample collections were made, each consisting of three samples taken from: raw incoming sewage, sec ondary effluent (after 10-12 h) and secondary effluent disinfected with 1.5 -2 mg l(-1) of peracetic acid (contact time: 20 min). Total coliforms and E scherichia coli declined from 10(7) MPN 100 ml(-1) in the raw sewage to 10( 2) in the disinfected effluent and the enterococci fell from 10(6) MPN 100 ml(-1) to 702 MPN 100 ml(-1). The reduction of bacteria increased with the rise in temperature and decreased with the rise in BOD5. Conclusions: Disinfection with peracetic acid reduced levels of faecal cont amination by 97%, thus attaining the limit recommended by current Italian l aw (Escherichia coli less than or equal to 5000 MPN 100 ml(-1)) for dischar ge into surface waters. Significance and Impact of the Study: The process of disinfection with pera cetic acid is easier to manage than other more common methods and the tests performed confirm that from the bacteriological point of view good results can be obtained for urban effluents.