Efficient conversion of brown grease produced by municipal wastewater treatment plant into biofuel using aluminium chloride hexahydrate under very mild conditions

•Efficient valorization of urban wastewater FOG under mild conditions.•AlCl3··6H2O as an effective catalyst in direct esterification of free fatty acids.•Biofuels and high value chemicals efficiently obtained from waste.•An energetically/economically competitive production of FAMEs from brown grease.

Wastes produced by oil/water separation at the wastewater treatment plant of Bari West (Southern Italy) were taken, characterized and converted. About 12% of this material was composed of greases, mainly made of free fatty acids (50%) and soaps (34%), and was easily separable by the aqueous phase through a hot centrifugation. After chemical activation of this fatty fraction, a direct esterification was carried out under very mild conditions (320 K and atmospheric pressure), converting more than 90% of the original free fatty acids into the respective methyl esters in less than 4 h, by using AlCl3··6H2O. The activation energy correlated to the use of this catalyst was also calculated (Eaest = 43.9 kJ mol−1). The very low cost of the biodiesel produced (0.45 € L−1) and the associated relevant specific energy (5.02 MJ kgFAMEs-1) make such a process a really sustainable and effective example of valorization of a waste.