Evaluation of the Performance of Various Cathodes in the Treatment of Petrochemical Wastewater by Membrane-Free Microbial Electrolysis Cells

The petrochemical industry, including petrochemical processing, oil refining, and natural gas production, generates large amounts of wastewater. Thus, the petrochemical industry produces a large amount of wastewater containing a variety of pollutants. Therefore, the main objective of this study is to evaluate the treatment and simultaneous production of methane from petrochemical wastewater by different cathode materials in single membrane-less microbial electrolysis cells. Three single membrane-less microbial electrolysis cells were made of polymethyl methacrylate. The systems were 15 cm long, 15 cm wide and 10 cm deep with a total volume of 2.25 L. Anaerobic sludge was obtained from an anaerobic digester of Isfahan municipal wastewater treatment plant (Isfahan, Iran).  The anodes and cathodes were held together by plastic screws with electrodes spaced 2 cm apart. The MECs performance was described by using several main parameters, electricity generation, gas production, COD removal, and pH levels. According to the results, the removal rate of COD in microbial electrolysis cells with the SS316 cathode was higher compared to the other two systems. So that the maximum removal efficiency of COD with SS316 cathode under a voltage of 1V at HRT of 48h was 85%. Also, the results indicate that the production rate of methane and the content of methane with the system containing the SS316 was higher compared to the other two systems. The maximum methane production rate of 56 ml was with a content of 85% under a voltage of 1V at HRT of 48h. Based on the results, the microbial electrolysis cell containing the SS316 cathode was introduced as a promising system to treat and produce methane from petrochemical wastewater.