Sustainable Conversion of Fat, Oil and Grease Wastes Produced by Municipal Wastewater Treatment Plant into Biofuels

Fat, oil and grease produced by oil/water separation at the wastewater treatment plant of Bari West (Southern Italy) were taken, characterized and converted. After chemical activation of this fatty fraction, with the aim of converting the starting calcium soaps into the respective free fatty acids, a direct esterification was carried out under very mild conditions. Working at 345 K under atmospheric pressure, the thermodynamic conversion (more than 90%) of the free fatty acids into the respective methyl esters was obtained in less than 2 h, by using AlCl3·6H2O as catalyst. Fundamental parameters, such as kinetic and equilibrium constants at different temperatures and activation energy correlated to the use of this catalyst, were also calculated. The biodiesel was purified with a distillation under vacuum, providing a final product conformed to the EN14214 requirements. The convenience of the overall process in terms of costs (0.45 EUR L-1) and specific thermal energy supply (5.02 MJ KgFAMEs-1) make such a process a really sustainable and effective example of valorization of a waste.