The main goal of this study was to compare the component and yield of biodiesel obtained by different
methods from different sludge in a wastewater treatment plant. Biodiesel was produced by ex-situ and
in-situ transesterification of scum, primary and secondary sludge respectively. Results showed that scum
sludge had a higher calorific value and neutral lipid than that of primary and secondary sludge. The lipid
yield accounted for one-third of the dried scum sludge and the maximum yield attained 22.7% under
in-situ transesterification. Furthermore the gas chromatography analysis of fatty acid methyl esters
(FAMEs) revealed that all sludge contained a significant amount of palmitic acid (C16:0) and oleic acid
(C18:1) regardless of extraction solvents and sludge types used. However, the difference lay in that oleic
acid methyl ester was the dominant component in FAMEs produced from scum sludge while palmitic
acid methyl ester was the dominant component in FAMEs from primary and secondary sludge. In addition,
the percentage of unsaturated fatty acid ester in FAMEs from scum sludge accounted for 57.5–64.1%
of the total esters, which was higher than the equivalent derived from primary and secondary sludge. In
brief, scum sludge is a potential feedstock for the production of biodiesel and more work is needed in the
future.