A Comparison Between Coagulation and Ultrafiltration Processes for Biodiesel Wastewater Treatment

Abstract

The progressive increasing on biodiesel production has been generating a large amount of wastewater due to the biodiesel purification process. The present work aims to develop and evaluate different processes to improve the quality of biodiesel wastewater to achieve legislation requirements for its final disposal. In order to do that membrane filtration and coagulation processes were tested. Micro and ultrafiltration ceramic membranes obtained by isostatic pressing were used for the cross-flow filtration process and tannin coagulant (Tanfloc SG) was employed in the coagulation process. A pre-treatment for grease removal was accomplished by adding sulfuric acid the wastewater until pH 2.5. Ultrafiltration membrane (alumina-zirconia and sintered at 1,500 °C) showed better results for color, turbidity and Chemical Oxygen Demand (COD) removal. These tests were conducted at a transmembrane pressure of 2 bar and keeping constant the other operational parameters. Once the best membrane was determined, the variation of transmembrane pressure was investigated by increasing it to 3 bar. The alumina zirconia ultrafiltration membrane, using the pre-treated wastewater, had a COD, color and turbidity removal of 19.5, 74.1 and 100%, respectively. The biodiesel wastewater was submitted to coagulation experiments for different pH values and tannin concentration. Through the coagulation tests, the pre-treated effluent with the higher tannin concentration, at pH of 8, had better results when compared to the untreated wastewater. The best coagulation results showed a COD, color and turbidity removal of 73, 69 and 75%, respectively. Both ultrafiltration and coagulation presented good efficiency for organic matter removal, but the coagulation process reached higher COD removal.