Optimizing electrocoagulation process for treatment of biodiesel wastewater using response surface method

Abstract

The objective of this research was to determine the optimum conditions for the biodiesel waste water treatment using electrocoagulation process. Biodiesel, which is, mono alkyl esters of long-chained fatty acids, is an alternative fuel for diesel engines. It is produced by the chemical reaction of vegetable oil or animal fat with an alcohol. Commercial biodiesel production employs an alkali-catalyzed trans-esterification reaction method. This method ensures a high production of biodiesel from oil by a basic chemical reaction within a short period of time. In this process water is used to wash off impurities which is repeated 2–5 times depending on the quantity of impurities in the methyl-ester. The amount of wastewater generated in the process is very huge (20–120L per 100L of biodiesel). The wastewater is basic in nature, and contains high amounts of oil and grease. Conventional flotation techniques like Dissolved Air Floatation technique (DAF) and an oil and grease (O&G) trap unit are not good enough for removing oil emulsions without pretreating with chemicals. Electrocoagulation (EC) has, therefore, been successfully used to treat numerous wastewaters. An EC reactor is composed of an electrolytic cell with a pair of electrodes immersed in the wastewater that serves as the electrolyte. The process of pollutant removal involves the application of an electric current to electrodes which in turn leads to the dissolution of metal ions, such as iron or aluminum, from a sacrificial anode. Consequently, the metallic hydroxide, a coagulant formed by oxidation in the electrolyte in an aqueous phase, destabilizes colloidal suspension such as emulsified oil. Further, the destabilized colloids aggregate and form flocks. Finally, these colloid-adsorbed flocks can be separated by sedimentation or by floatation