Treatment of biodiesel wastewater by indirect electrooxidation: Effect of additives and process kinetics

Due to the presence of growth inhibitor and high impurity concentration in biodiesel wastewater, both biologicaln and chemical processes are ineffective for treating such wastewater. In this work, biodiesel wastewater was treated by electrooxidation via Ti/RuO2 electrodes in batch and continuous modes. Effects of the additive type, hydrogen peroxide (H₂O₂) and sodium chloride (NaCl), and concentration on the treatment efficiency, monitored in terms of the reduction in the biological oxygen demand (BOD), chemical oxygen demand (COD) and oil and grease level, were explored. The addition of NaCl gave higher treatment efficiency than H₂O₂, and both were higher than no addition, due to the continuous generation of the oxidizing chloride species. The removal of almost all the COD and oil and grease and ~95% BOD was obtained in the presence of 0.061 M NaCl at an applied current density of 4.28 mA/cm² for 7h. In continuous operation mode, the steady state condition was reached within 11 h and the treatment efficiency decreased as the wastewater feed rate increased. By using wastewater feed rate of 2mL/min, approximately 83.56, 61.43 and 91.72% of BOD, COD and oil and grease levels were respectively removed. The rate of pollutant removal fitted a first order reaction for both the batch and continuous operation modes.