Disinfectant demand and microbial inactivation rate are essential issues for assessing disinfection performance and proper design of disinfecting systems. In the United Kingdom and Italy, peracetic acid (PAA) has recently become an accepted disinfectant for treating wastewaters prior to reuse in agriculture, and its use is likely to spread worldwide due to its efficacy as well as the benign nature of the by-products produced. In this paper, overall PAA demand during the advanced disinfection of municipal wastewater for agricultural reuse was evaluated under different experimental conditions. Batch tests were carried out using primary and secondary settled effluents sampled at the City of Taranto municipal wastewater treatment plant. PAA dosages ranged from 1.5 to 8.5 mg/L and from 21 to 40 mg/L for the secondary and primary settled effluents, respectively. Residual PAA was measured after contact times ranging from 1 to 60 min. Results showed that after a strong and almost instantaneous initial disinfectant consumption, the PAA consumption followed first-order kinetics with both effluents. The effluent characteristics affected the values of the parameters in the consumption model. PAA disinfection efficacy was assessed in terms of total coliform and Escherichia coli indicator organism reduction; better results were achieved with the latter. The approximate solution of Hom's model established by Haas and Joffe was used to model inactivation kinetics of both microbial targets.

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