Kinetic Insights and Process Selection for Electrochemical Remediation of Industrial Dye Effluents Using Mixed Electrode Systems

The discharge of dye-laden effluents remains an environmental challenge since conventional treatments remove color but not the organic load. This study systematically compared anodic oxidation (AO), electro-Fenton (EF), and photoelectro-Fenton (PEF) processes for three representative industrial dyes, such as Coriasol Red CB, Brown RBH, and Blue VT, and their ternary mixture, using boron-doped diamond (BDD) and Ti/IrO2–SnO2–Sb2O5 (MMO) anodes. Experiments were conducted in a batch reactor with 50 mM Na2SO4 at pH = 3.0 and current densities of 20–60 mA cm−2. Kinetic analysis showed that AO-BDD was most effective at low pollutant loads, EF-BDD became superior at medium loads due to efficient H2O2 electrogeneration, and PEF-MMO dominated at higher loads by fast UVA photolysis of surface Fe(OH)2+ complexes. In a ternary mixture of 120 mg L−1 of dyes, EF-BDD and PEF-MMO achieved >98% decolorization in 22–23 min with pseudo-first-order rate constants of 0.111–0.136 min−1, whereas AO processes remained slower. COD assays revealed partial mineralization of 60–80%, with EF-BDD providing the most consistent reduction and PEF-MMO minimizing treatment time. These findings confirm that decolorization overestimates efficiency, and electrode selection must be tailored to dye structure and effluent composition. Process selection rules allow us to conclude that EF-BDD is the best robust dark option, and PEF-MMO, when UVA is available, offers practical guidelines for cost-effective electrochemical treatment of textile wastewater.