Holistic effect of operating conditions and purification methods on the pollution characteristics of washing water and biodiesel quality

Abstract

This study aimed to optimize the experimental conditions in terms of converting waste cooking oil to biodiesel and minimizing contaminants in the washing water. The statistical interactions of the experimental conditions such as alcohol:oil ratio, catalyst ratio, temperature and reaction time on the biodiesel and the washing water quality were determined. Aqueous and dry washing methods were carried out and optimum alcohol:oil and catalyst ratios were obtained as 30 % (molar ratio 3:1) and 1 %, respectively, for both methods. Kinematic viscosity, density and pH of the biodiesel and chemical oxygen demand (COD), phosphate (PO4), total nitrogen (TN), conductivity, pH, absorbance values, metals and long-chain fatty acid composition of the washing water were measured. It was concluded that COD and fatty acid concentrations of the washing water have significantly decreased to 10,015 mg/L and 7 mg/L, respectively, at the optimum conditions. Long-chain fatty acid composition in the wastewater was determined to be related with the experimental conditions and the quality of produced biodiesel. It was observed that types and concentrations of the fatty acids increased in the waste washing water of biodiesel at low alcohol and catalyst ratios. As an important contribution to the literature, fatty acids passing from biodiesel into wastewater were determined by gas chromatography and their relation to COD was analyzed. Besides linear correlation was found between fatty acids and COD. The increase of metals in waste washing water thought to be as a result of frying process in the metallic containers. © 2023 Elsevier Ltd