Optimisation of lipid extraction from primary sludge by soxhlet extraction

Abstract

Domestic sewage sludge is a potential raw material to produce energy in the form of renewable biofuels (biodiesel) due to the high amount of lipid content in the sludge. Soxhlet extraction is commonly used in extracting lipid from primary sewage sludge. Different solvents and extraction parameters in Soxhlet extraction may affect the lipid yield. Hexane, methanol and toluene were evaluated in extracting lipids from primary sewage sludge. Methanol was identified as the most suitable solvent to be used in lipid extraction due to its high polarity. Extraction parameters such as temperature, extraction time, and sludge-To-solvent ratio were investigated in order to optimise the lipid extraction process from primary sewage sludge. The extracted lipid yield was observed to be optimum at 40.21 wt% when the temperature and extraction time were at 86 °C and 7.45 h. A sludge-To-solvent ratio of 2:1 was determined to be the optimum value in extracting lipid yield. The optimisation process was conducted using response surface methodology (RSM) and was analysed using ANOVA with R2 of 0.8146 for lipid concentration. The analysis of free fatty acid content in the lipid extracted from primary sewage sludge revealed that the composition of free fatty acid was dominated by monounsaturated oleic acid.