Remediation of biodiesel wastewater by chemical- and electro-coagulation: a comparative study

The remediation of biodiesel wastewater was carried out using chemical and electrochemical techniques. Initially the fatty acid methyl esters (FAME or biodiesel) and free fatty acids (FFA) were chemically removed from the wastewater using three types of mineral acids, H(2)SO(4), HNO(3) and HCl, at different pH values within the range of 1.0-8.0. Optimally, approximately 24.3 ml/l of FAME/FFA were removed from the wastewater when using H(2)SO(4) to set a final pH of 2.5 for 7 min. All pollutant levels were markedly reduced during this step. That is, approximately 38.94%, 76.32% and 99.36% of COD, BOD5 and oil & grease were respectively removed. The acidic aqueous phase left after the removal of the FAME/FFA phase was then treated by chemical- and electro-coagulation processes. The results demonstrated that both investigated treatment processes were effective for treating wastewater from a biodiesel production plant. The chemical coagulation provided a lower operating cost (1.11 USD/m(3)) compared with the electro-coagulation process (1.78 USD/m(3)). However, the latter process provided a better quality of wastewater compared with the former process, with the exception of the BOD levels.