Direct Liquid–Liquid Lipid Extraction Method for Biodiesel Production from Sewage and Petrochemical Industry Sludges

Abstract

Municipal wastewater treatment plant sludge (sewage sludge) has gained importance in biodiesel production due to its high lipid content. The oily sludges from petrochemical industry wastewater treatment plants (WWTPs) have high concentrations of phospholipids, free fatty acids, neutral lipids and can also be used as efficient feedstocks for biodiesel production. Lipid extraction is the first step of biodiesel production from sludges. Standard drying lipid extraction method necessitates expensive sludge dewatering/drying steps, holding almost 50% of overall biodiesel production cost, to remove high water content in sludge. The aim of this study was to explore lipid extraction from municipal and petrochemical industry WWTP sludges by using the novel direct liquid–liquid lipid extraction method, which does not require expensive sludge dewatering/drying steps, and to compare it to standard drying method. The study also investigated the effect of acid pre-treatment on lipid yields of the sludge samples. In both methods, hexane was used as an organic solvent. Acid pre-treatment increased the lipid yields noticeably. The highest lipid yield of 31.2% (dry sludge) was obtained from pre-acidified petrochemical industry WWTP sludge by using liquid–liquid lipid extraction method. Compared to standard drying method, direct liquid–liquid lipid extraction method resulted with 53% higher lipid and 56% higher biodiesel yields for petrochemical industry WWTP sludge sample. However, liquid–liquid lipid extraction method caused to a very slight increase in the biodiesel yield of primary municipal WWTP sludge samples.