Degradation of Multicomponent Tannery Dye Mixtures by Electrochemical Advanced Oxidation Processes

Industrial effluents containing persistent synthetic dyes represent an important environmental challenge because of their high chemical stability, low biodegradability, and potential adverse effects on aquatic ecosystems. This study evaluates electrochemical advanced oxidation processes (EAOPs) as remediation strategies for dye-contaminated tanery dyes, with particular emphasis on conditions representative of complex industrial effluents. Electrochemical oxidation (EOx), electro-Fenton (EF), and photoelectro-Fenton (PEF) processes using boron-doped diamond (BDD) electrodes were comparatively investigated for the degradation of Violet S4B and a multicomponent mixture containing Violet S4B, Brown DR, and Black NT2. The effects of current density and pollutant concentration were assessed through discoloration, pseudo-first-order kinetics, chemical oxygen demand (COD) removal, and HPLC analysis of oxidation intermediates. For the multicomponent system, PEF achieved approximately 99% discoloration after 120 min, compared with nearly 97% for EF and 95% for EOx, with apparent rate constants increasing in the order EOx < EF < PEF. More importantly, COD analysis demonstrated extensive mineralization during PEF treatment, while HPLC revealed negligible accumulation of oxalic acid, indicating effective oxidation of refractory intermediates. The results demonstrate that combining anodic oxidation, electrochemically generated Fenton chemistry, and photo-assisted reactions enhances the remediation of complex dye mixtures. These findings support BDD-based EAOPs, particularly PEF, as promising technologies for reducing persistent organic pollution associated with tannery dye solutions.