Application of solar photo-electro-Fenton technology to petroleum refinery wastewater degradation: Optimization of...

Industrial and agricultural advances have led to global issues such as contamination of water sources and lack of access to clean water. Wastewater from petroleum refineries must be subjected to treatment as it poses a significant environmental threat. The present research aimed to reduce the level of chemical oxygen demand (COD) of an effluent from Bijee petroleum refinery plant, Iraq, using solar photo-electro-Fenton (SPEF) process operated in a batch recycle model. The electrochemical reactor used in the present research was of a tubular design with an anode composed of porous graphite rod and a concentric cylindrical cathode made of the same material. The impacts of operating parameters such as current density (10-50 mA/cm²), Fe²⁺ concentration (0.2-0.8 mM), NaCl addition (0-1 g/L), and time (30-90 min) on the COD removal efficiency were explored based on the response surface methodology (RSM). Results showed that the impact of Fe²⁺ concentration was most prominent, with an effective contribution of 47.7%, followed by current density, with a contribution of 18.26%, and the addition of NaCl, with a contribution of 11.20%. COD removal was found to increase with an increase in current density, Fe²⁺ concentration, NaCl addition, and time, respectively, while energy consumption was found to increase significantly with an increase in current density and a decrease in Fe²⁺ concentration, respectively. The optimum conditions were observed to be an initial pH of 3, current density of 10 mA/cm², Fe²⁺ concentration of 0.8 mM, NaCl addition of 0.747 g/L, and a duration of 87 min, upon which 93.20% COD removal efficiency was achieved, with an energy consumption of 15.97 kWh/kg COD.