Optimization of a Fenton-based process as a tertiary treatment of tannery wastewater through response surface methodology

Nowadays, the implementation of effective advanced oxidation systems in wastewater treatment plants (WWTPs) as tertiary treatment represents an urgent need and current topic of interest in the literature. The aim of this study was to identify the optimal operating conditions of an electrochemical peroxidation (ECP) process to maximize COD and color removals from tannery secondary effluents at neutral pH, as well as improve the cost-effectiveness of the ECP process by avoiding the addition of chemicals commonly used in conventional electro-Fenton process, which can increase the overall concentration of chlorides and sulphates in high-salinity effluent. To the best of our knowledge, no study in the literature has focused on the optimization of the ECP process for tannery wastewater treatment. Therefore, the influence of the independent variables (current density, electrolysis time and H2O2 concentration) and best parameter setting were investigated through a central composite design combined with response surface methodology (CCD-RSM). Under optimal conditions (36 mA/cm2, 19.7 min and 9.9 g/L of H2O2), 74 % of COD and 96 % of color were removed by ECP. The optimized conditions for the ECP treatment were verified and tested on photo-electrochemical peroxidation (PECP) and photolysis processes. The irradiation with UV-C light in PECP and photolysis processes did not significantly improve the removal efficiency, while increasing the energy demand. This study provides a new engineering approach for the removal of recalcitrant COD, addressing key factors that limit the application of the conventional electro-Fenton process in WWTPs. Future research should improve the sustainability of the process for full-scale application.