Optimization of the electrochemical Fenton process for hexavalent chromium removal from tannery wastewater

Tannery wastewater, laden with toxic hexavalent chromium (Cr6+) and high chemical oxygen demand (COD), poses severe environmental and health risks. This study explores the electrochemical-Fenton (ECF) process as a sustainable and efficient treatment method for real tannery effluents. Unlike the conventional Fenton processes, ECF generates Fe2+ and hydroxyl radicals in situ, enhancing pollutant removal. Using hydrogen peroxide (H2O2) as the oxidant, the study evaluates four key operational parameters: pH (3–7), electrolysis time (20–60 min), current density (5–15 mA/cm2), and H2O2 concentration (200–800 mg/L), through Response surface methodology (RSM). Under optimal conditions (pH 5, 60 min, 15 mA/cm2, and 500 mg/L H2O2), Cr6+ and COD removal efficiencies of 91.25% and 96.2% were achieved, respectively. The Cr6+ concentration decreased from 170 ± 55 mg/L to ~ 15 ± 3.5 mg/L, while COD was reduced from 4200 ± 750 mg/L to ~ 160 ± 25 mg/L, closely matching RSM predictions. Kinetic analysis revealed pseudo-second-order adsorption behavior, while the Langmuir isotherm best described Cr6+ adsorption, indicating monolayer coverage with a maximum capacity of 25.39 mg/g. The study demonstrates the ECF process as a cost-effective, scalable, and eco-friendly solution for treating chromium-rich tannery wastewater, with strong model reliability and minimal residual error.