Abstract

Lipids of sewage scum and primary sludge taken from several wastewater treatment plants were quantified and characterised. In sewage scum, lipids represented 36–50% of total solids and were primarily composed of free fatty acids (45–60%) and calcium soaps (27–35%). In primary sludge, total lipids were 20–24% of total solids, and 71–82% of these were calcium soaps. Estolides and 10-hydroxystearic acid (prevalently present as R enantiomer, with an enantiomeric excess >92%) were also identified and quantified. A scheme of valorisation was then specifically designed and positively tested for both the sludge. Lipids were first recovered (92–99%), activated and finally reacted with methanol and AlCl3∙6H2O (343 K, 2 h, yield >96%). Besides biodiesel, methyl estolides and methyl 10-hydroxystearate were efficiently isolated and purely separated in different fractions. A preliminary feasibility study was finally conducted and a possible integration of processes into a wastewater treatment plant was proposed and positively evaluated.

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