Application of the hybrid electrocoagulation–electrooxidation process for the degradation of contaminants in acidified biodiesel wastewater

Abstract

• Acidified biodiesel production wastewater was treated by the hybrid EC-EO process. • Optimum operating conditions were determined for single EC, EO processes. • For single EC, EO processes, reaction rate constants were found based on kinetic models. • The specific energy consumption of the EC, EO and hybrid EC-EO processes were calculated. • Higher COD, TSS and oil-grease removal efficiencies were achieved in the hybrid EC-EO process. In this study, the treatment of biodiesel production wastewater by the hybrid Electrocoagulation (EC) - Electrooxidation (EO) processes was investigated. Before the hybrid process, biodiesel production wastewater was acidified using H 2 SO 4 and HCl at different pH values. The highest pollutant removal efficiency was achieved at pH 6 using HCl. The chemical oxygen demand (COD), total suspended solids (TSS), and oil-grease removal efficiency were 67.2%, 65.7%, and 56.9% after the acidifying of the wastewater. After the application of the acidification technique, the operating conditions of the EC and EO processes were optimized, then the hybrid EC-EO process was applied. Different electrodes were evaluated and the Al-Al electrode pair was chosen for the EC process while Ti/SnO 2 anode was chosen for the EO process. Optimum operational conditions for the EC process were 0.25 A and 60 min whereas 0.5 A and 150 min for the EO process while pH was kept as the outlet of the acidification. The COD, TSS, and oil-grease removal efficiency of the hybrid EC opt -EO opt process was 98.9, 98.2, and 99.8%, respectively. The specific energy consumption of the EC, EO, and hybrid EC-EO processes at optimized conditions were 1.02, 43.4, and 37.4 kWh/kg COD removed , respectively. The hybrid process has a higher removal efficiency than either the EC or EO procedures alone, while it uses less energy than the EO process. The hybrid EC-EO procedure, is an effective treatment method for acidified biodiesel wastewater, according to the results of the study.