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.