Optimization of a combined electrocoagulation-electro-oxidation process for the treatment of Al-Basra Majnoon Oil field wastewater: Adopting a new strategy

•A synergistic combination of EC and EO for oilfield effluent treatment was studied.•Current density has the main effect on the COD removal in comparison with pH.•Current ratio (IAl/IGr) depends on the total current, pH, and NACL addition.•EC consumes higher current than EO but effect of EO on COD removal is higher than EC.•High COD removal (93.4%) occurred at current density of 26.77 mA/cm2 and pH of 7.6. The performance of a synergistic combination of electrocoagulation (EC) and electro-oxidation (EO) for oilfield wastewater treatment has been studied. The effect of operative variables such as current density, pH, and electrolyte concentration on the reduction of chemical oxygen demand (COD) was studied and optimized based on Response Surface Methodology (RSM). The results showed that the current density had the highest impact on the COD removal with a contribution of 64.07% while pH, NaCl addition and other interactions affects account for only 34.67%. The optimized operating parameters were a current density of 26.77 mA/cm2 and a pH of 7.6 with no addition of NaCl which results in a COD removal efficiency of 93.43% and a specific energy consumption of 128.6 kWh/kg COD. The most new findings of this research was that currents provided for the two anodes (Al and Graphite having the same surface area) were not equal between them and the current ratio (IAl/IGr) depends on the intensity of current, pH, and addition of NaCl. Besides, higher removal of COD occurs at a lower value of (IAl/IGr). The COD removal reaction was found to be pursued a second-order kinetic with a reaction rate constant (k) of 7.5847 × 10−5 (mg/L)−1/min. [Display omitted]