Understanding and Optimizing Peracetic Acid Disinfection Processes Using Computational Fluid Dynamics: The Case Study of Nocera (Italy) Wastewater Treatment Plant

In this paper, a modeling study focused on optimizing the PAA disinfection performance in a full-scale contact tank currently operated at the Nocera (Italy) Wastewater Treatment Plant is presented. The disinfection process was monitored for over 2 weeks by collecting full-scale data on plant variability in flow, disinfectant demand/decay and microbial concentrations. A computational fluid dynamics (CFD) model of the contact tank describing the PAA disinfection process was developed. Four disinfection scenarios were analysed using an Eulerian-Lagrangian approach: (a) PAA disinfection under the existing conditions; (b) PAA disinfection with PAA pre-mixed prior to the contact tank; (c) PAA disinfection with PAA dosed with 8 injection points distributed over the entire length of the inlet weir; (d) PAA disinfection in an optimized plug-flow contact tank. All these scenarios were analysed for the same operating conditions, i.e. fixed flow, PAA demand/decay and inactivation kinetics. The model-based analysis clearly revealed that the optimized contact tank (scenario d) was able to achieve a much higher contact and extended between microorganisms and disinfectant thus resulting into a five-fold increase in microbial inactivation.