Tannery wastewater treatment using combined electrocoagulation and electro-Fenton processes

Tannery wastewater was performed using electrocoagulation (EC) coupled with an electro-Fenton (EF) process and boron-doped diamond (BDD) anodes to generate hydrogen peroxide (H₂O₂), and then optimized using the response surface methodology (RSM). Effects of three independent variables (e.g., reaction time, current density and Fe²⁺ concentration) on the performance of electrochemical processes were analyzed using a statistical experimental design. Current density and reaction time were significant for total organic carbon (TOC) removal when the EC and EF processes were tested. The interaction between initial Fe²⁺ concentration (0.66 mM L^-1, the highest value) and reaction time was significant and achieved 32% TOC removal, but because it was used with the highest current density value tested (70 mA cm^-2), the energy consumption was as high as 74.5 kWh m^-3. Optimization of the process for TOC removal and energy consumption was accomplished by lowering the current density and treatment time values (40 mA cm^-2 and 217 min) during EF treatment. Under these conditions, 25% of TOC removal was achieved. The integrated EC-EF system generated 64% TOC removal using a greater current density (9.7 mA cm^-2) during the EC process, and the overall treatment energy consumption was 22.3 kWh m^-3. The sludge produced under the tested EC conditions exhibited no hazardous characteristics. The EC treatment was also faster in TOC abatement (sixth-order kinetic), compared to the EF treatment (third-order kinetic).