Double the biodiesel yield: Rearing black soldier fly larvae, Hermetia illucens, on solid residual fraction of restaurant waste after grease extraction for biodiesel production

Biodiesel is a promising alternative diesel fuel which has increased worldwide public interest in a number of countries including China. But the high cost of producing biodiesel from feedstock, predominately food grade oils, limited its economic feasibility. An alternative of using grease extracted from restaurant waste to produce biodiesel is a potential low cost approach. However, this approach generates a significant large quantity of solid residual fraction which required proper disposal. This study was conducted to evaluate the potential of a secondary biodiesel production from the solid residual fraction of restaurant waste after typical grease extraction (SRF) employing a high fat containing insect, black soldier fly, Hermetia illucens. The SRF was sampled and fed to black soldier fly larvae. The resulting larval biomass was used for crude grease extraction by petroleum ether. The extracted crude grease was then converted into biodiesel by acid-catalyzed (1% H2SO4) esterification and alkaline-catalyzed (0.8% NaOH) transesterification. About 23.6 g larval grease-based biodiesel was produced from approximately 1000 larvae grown on 1 kg of SRF. The weight of SRF was reduced by about 61.8% after being fed by the black soldier fly larvae for 7 days. The amount of biodiesel yield from restaurant waste was nearly doubled (original restaurant waste grease, 2.7%; larval grease, 2.4%). The major methyl ester components of the biodiesel derived from black soldier fly larvae fed on SRF were oleinic acid methyl ester (27.1%), lauric acid methyl ester (23.4%), and palmitic acid methyl ester (18.2%). Most of the properties of this biodiesel met the specifications of the standard EN 14214, including density (860 kg/m3), viscosity (4.9 mm2/s), flash point (128 °C), cetane number (58) and ester contents (96.9%). These results indicated that black soldier fly larval biomass obtained from larvae reared on SRF could potentially be used as a non-food feedstock for biodiesel production. This approach not only enhances the efficiency of biodiesel production from restaurant waste, it also helps to better manage and significantly reduce the large quantity of solid residual fraction produced during the process of biodiesel production using restaurant waste.