Biodiesel production from petrochemical industry sludge: Direct liquide - liquid lipid extraction method

Abstract

The oily sludges from petrochemical industry wastewater plant (WWTP) have high lipid content and can be used as lipid feedstocks. Standard drying method necessitates expensive sludge dewatering/drying steps, holding 50 % of overall biodiesel production cost, to remove high water content in sludge. This study explored lipid extraction from petrochemical industry WWTP sludges by using the novel direct liquid–liquid lipid extraction method, eliminating costly sludge dewatering and drying steps, and to compare it to standard drying method. The study also investigated the effect of pre-treatment methods on lipid and biodiesel yields of sludge samples. In both methods, hexane was used as an organic solvent. The direct liquid-liquid lipid extraction method, which does not require expensive sludge drying or dewatering steps, resulted with 53 % higher lipid and 56 % higher biodiesel yields for petrochemical industry WWTP sludges than the standard drying method. Acid pre-treatment increased lipid and biodiesel yields by using direct liquid-liquid and standard drying lipid extraction methods. The ultrasonication pre-treatment alone and microwave pre-treatment alone did not cause to an important change in lipid and biodiesel yields for the direct liquid-liquid lipid extraction method. The combined pre-treatment methods (acidification/ultrasonication and acidification/microwave) considerably increased the lipid and biodiesel yields for both extraction methods. The highest lipid (47.1 %) and biodiesel (32.6 %) yields were achieved by application of combined acidification/microwave pre-treatment to the thickener sludge samples and using the liquid-liquid lipid extraction method. Liquid-liquid lipid extraction seems to be an energy and cost efficient way of sludge management.