Multielectrode Advanced Oxidation Treatment of Tannery Wastewater: Mass Transfer Characterization, Process Performance, Kinetic Modeling, and Energetic Analysis

Tannery wastewater from textile-related industries poses treatment challenges due to its high load of recalcitrant pollutants. Various advanced hybrid treatments, such as electro-oxidation (EO), have been proposed but mainly focus on electrode material development. Several studies on EO using multiple electrode pairs with large electroactive surface areas exist, however, none have reported on mass transfer characterization. This study addresses these gaps by investigating the electro-degradation performance of active (mixed-metal oxide, MMO) and non-active (boron-doped diamond, BDD) anodes paired with carbonaceous (graphite) and non-carbonaceous (stainless steel, SS) cathodes under applied current densities of 2 to 6 mA/cm2. A 2 L volume of simulated tannery wastewater containing recalcitrant tannic acid was treated using three electrode pairs with a total surface area of 500 cm2. Results showed optimal condition was identified at 4 mA/cm2 across all electrode combinations and better degradation using BDD anodes and SS cathodes, with total organic carbon (TOC) removed up to 500 mg/L (98% removal). Adopting the 3-electrode configuration, mass transfer coefficients ranged from 4.15 to 5.18 × 10−6 m/s. Energy consumption evaluation suggested MMO as a more cost-effective option, while BDD remained preferable for highly recalcitrant waste. Higher currents show diminishing returns due to mass transfer and parasitic reactions.