Disinfection of secondary effluents by peracetic acid: influence of the initial flash-mixing step

The influence of a flash-mixing step before two in series chicane contact tanks on peracetic acid (PAA) disinfection was evaluated through a pilot-scale experimentation, varying contact time, disinfectant dose and initial bacterial concentration. Preliminarily, a series of tracer tests was performed varying flow-rate and water level to identify the hydrodynamic conditions that best simulate a plug-flow regime into the contact tanks. Residual PAA concentration and two indicator microorganisms (faecal coliforms and Escherichia coli) were monitored during disinfection tests to assess PAA disinfectant effectiveness. Experimental results, analyzed through Generalised Linear Models, showed that a flash-mixing phase before contact tanks do not affect PAA consumption but, in specific operating conditions, can increase disinfection effectiveness; moreover, both PAA decay and bacterial inactivation depend on initial bacterial concentration. The most used models were also evaluated to describe PAA decay and disinfection kinetics, investigating the influence of operating parameters.