Degradation/mineralization of carwash wastewater by coupled process electrocoagulation/electro-Fenton

The importance of this work lies in the application of a combined electrocoagulation/electro-Fenton (EC/EF) treatment for carwash wastewater, offering a cost-effective and efficient remediation approach. During electro-coagulation (EC), experiments were carried out in a cylindrical cell containing 450 mL of carwash wastewater. This process promotes the formation of $$Fe\left( {OH} \right)_{n}$$ (n = 2 or 3) as coagulants, along with $${\text{Fe}}^{3 + } {\text{/Fe}}^{2 + }$$ ions acting as catalysts. The effects of key operating parameters, including applied current, electrode material (Fe and Al), and initial pH, were evaluated, and both COD removal and energy consumption were assessed. In the EF stage, comparative trials were performed in stirred reactors equipped with a Pt anode and a carbon-felt cathode under O₂ bubbling to generate H₂O₂ at the cathode. The hydroxyl radicals produced at the anode surface through water oxidation and in the bulk solution via Fenton’s reagent (Fe2⁺/H₂O₂) promote the oxidative degradation of organic contaminants. The effects of the supporting electrolyte, applied current and the catalytic activity were investigated to optimize electro-Fenton efficiency. Under optimal EC conditions (I = 1 A, Fe electrode, pH = 5.7), 76.58% COD removal was achieved with an energy consumption of 0.987 kWh·m⁻3. Nearly complete COD removal (97.8%) was obtained using the combined process, where residual organics after EC were removed during electro-Fenton treatment at 0.3 A for 360 min.