Integration of electrocoagulation and electrooxidation for continuous mode treatment of tannery effluents: Experimental, optimization, and economic analysis

Treatment of tannery wastewater presents significant challenges due to its complex composition, toxic substances, and high pollution levels. Conventional treatment methods are often inadequate for effectively treating this type of wastewater. However, hybrid processes have shown promising outcomes regarding the treatment of effluents. This study presents a novel application of combined electrocoagulation (EC) and electrooxidation (EO) processes, integrated in a once-through continuous mode, for the effective treatment of synthetic tannery wastewater (STWW). Fe/Fe electrodes were employed for EC process, whereas EO process utilized a mixed metal oxide (MMO) electrode (Ti/TiO₂-IrO₂-RuO₂) as the anode and stainless steel as the cathode. The primary objective of this study is to reduce the concentrations of 4-chlorophenol (4-CP), chromium (Cr(VI)), Chemical Oxygen Demand (COD), and Total Organic Carbon (TOC) in STWW. The Box-Behnken design was employed to optimize the effects of operating factors such as current, flow rate, and time on removing 4-CP, Cr(VI), and COD concentrations, and identify their interactions. The optimal operating conditions were determined, resulting in the following removal efficiencies: 75.97 % for 4-CP, 82.33 % for Cr(VI), 89.00 % for COD, and 37.30 % for TOC. The energy consumption was measured at 28.85 kWh/m 3 . The operating costs for the hybrid process were calculated to be 2.11 USD/m 3 and compared with literature data. Therefore, combining EC-EO could be an innovative approach for tannery wastewater treatment in continuous mode. Future studies using real tannery wastewater is recommended to better validate the efficiency and scalability of the EC–EO hybrid process under practical conditions.