The treatment of biodiesel wastewater using an integrated electrochemical and adsorption process

Abstract

The production of biodiesel is an energy and water intensive process. The wastewater that is produced during this process is high in concentrations of COD, BOD, FOG and various other contaminants. Since it contains low levels of nutrients, it is difficult to degrade using natural processes such as conventional activated sludge wastewater treatment. The discharge of untreated biodiesel wastewater also raises serious environmental concern. It interferes when remediated with biological processes and results in additional costs during the production of biodiesel when penalties and fines are applied. Conventional treatment processes are not capable of treating contaminants and pollutants in biodiesel to satisfactory concentrations and hence advanced treatment processes are necessary. In this research, a lab scale integrated treatment process was used to investigate the successful reduction of contaminants, in particular COD, BOD and FOG. The integrated treatment process used in this study consisted of three consecutive steps; acidification, electrochemical oxidation and adsorption using chitosan as an adsorbent. The electrochemical oxidation process with IrO2-Ta2O5/Ti anodes was applied to treat biodiesel wastewater. Different operating conditions were tested to establish favourable conditions. The current density applied as well as the concentration of NaCl as the supporting electrolyte greatly affected the process. A NaCl concentration of 0.08M was deemed sufficient, whereas a current density of 1 mA/cm² showed superior performance compared to lower or higher current densities. Adsorption of pollutants in biodiesel wastewater was investigated using Chitosan as the adsorbent. Various chitosan concentrations, initial pH of the wastewater and repetitive adsorption stages were investigated. It was discovered that all three operating conditions greatly affect the performance of the process. The three consecutive adsorption stages using a chitosan concentration of 4.5 g/L at a pH of 2 resulted in the highest pollutant removal. It was observed that the integrated treatment process could reduce COD, BOD and FOG levels by 94%, 86% and 95% respectively. This concludes that the treated effluent complies with local industrial effluent discharge standards, which could be disposed safely without further treatment.