Disinfecting behaviour of peracetic acid for municipal wastewater reuse

Following an increased interest in the last decade to employing peracetic acid (PAA) as an alternative disinfectant to chlorination, a study was started to investigate the technical, economic and chemical suitability of PAA for disinfecting municipal wastewater to be reused in agriculture. Laboratory and pilot-scale (10 m3/h) experiments of disinfecting secondary settled effluent from the municipal wastewater treatment plant of Taranto (S. Italy) were made where, under the experimental conditions investigated, the disinfection process was addressed by modelling PAA consumption and microbial inactivation by zero-order kinetics.

The suitability of PAA-based advanced wastewater disinfection of secondary settled municipal effluent was assessed at pilot-plant scale (10 m3/h) at the Taranto municipal wastewater treatment plant. Irrespective of PAA dosage investigated (4–8 mg/l), E. coli for the Italian MAC for wastewater reuse was achieved after a #10-min contact time under the experimental conditions investigated. In spite of the fast and effective inactivation of both microbial indicators monitored (E. coli and total coliforms), very low and slow PAA consumption occurred, regardless of initial PAA concentration according to a zero-order kinetics towards PAA. Accounting for the complex chemical equilibrium in the commercial disinfectant used (Oxystrong® is an aqueous mixture of PAA, H2O2 and acetic acid in equilibrium), other chemical intermediates such as hydroxyl radicals (*OH) must presumably play a leading role during microbial inactivation with PAA. Both E. coli and total coliforms inactivation in SSE, indeed, were fast and effective and the experimental results fitted a Monod-type decay model very well, ensuring a 2-log inactivation for total coliforms under the conditions investigated. Quite higher total coliforms inactivation (3.5 log units) was achieved in corresponding batch laboratory experiments, demonstrating the importance of specific hydrodynamic conditions. Further investigation is in progress in order to assess process performance and kinetics of PAA disinfection as well as to model hydraulic behaviour of the plug-flow pilot plant.