Process modeling and sludge characterization of electrocoagulation for the removal of oil-in-water emulsions and calcium from petroleum refinery wastewater

Electrocoagulation (EC) process efficiency for treating synthetic petroleum refinery wastewater was investigated. The novelty of this study lies in the simultaneous removal of oil-in-water emulsion and calcium ions using an integrated experimental-statistical-financial approach, combining response surface methodology (RSM) optimization with COMSOL Multiphysics simulation. The impact of independent variables on the removal rates of both contaminants was studied and optimized using the central composite design method. Analysis of variance was employed to evaluate the significance of the variables and the mathematical model determined by RSM. The optimal conditions were determined to be a pH of 9, a current density of 6.123 mA/cm², an initial calcium concentration of 130 ppm, an initial oil content concentration of 588 ppm, a NaCl concentration of 2.5 g/l, and a total electrolysis time of 98 min. These conditions correspond to an oil content removal rate of 91.3% and a calcium removal rate of 72.9%. Energy consumption and total operation costs were calculated under these parameters to be 12 kWhm^-3 and 10.32 EGPm^-3, respectively. Fourier Transform Infrared spectroscopy, Energy-dispersive X-ray spectroscopy, and Scanning electron microscopy characterization were performed on the resulting sludge and scum at the optimum conditions and its utilization was discussed. Furthermore, COMSOL Multiphysics software was used to simulate the voltage distribution across the proposed cell to understand the electrochemical features. Overall, the statistical, financial, and simulated study demonstrates the feasibility of the EC technique for oil refinery wastewater treatment.