Innovative integrated approach of biofuel production from agricultural wastes by anaerobic digestion and black soldier fly larvae

Abstract In the present study, a new biorefinery approach for efficient conversion of chicken manure mixed with rapeseed straw was investigated through anaerobic co-digestion though digestate recycling. The liquid digestate fraction was used for straw pretreatment, while solid fraction was utilized for rearing the black soldier fly larvae. Anaerobic digestion of raw straw resulted in biomethane yield of 144.2 L kg−1 VS, while the pretreatment enhanced it to 227.6 L kg−1 VS. Co-digestion of the pretreated straw with chicken manure at different ratios of 1:1, 1:3, and 3:1 increased the biomethane yield to 323.5, 349.6, and 262.3 L kg−1 VS, respectively, with higher biomethanation efficiency. Black soldier fly larvae were grown on different ratios of solid digestate/larva (D/L) of 0.25, 0.50, 0.75 and 1.00, where it showed higher growth and faster development by increasing the digestate ratio. In addition, lipid content significantly increased by increasing the digestate ratio, reaching the maximum values of 31.8 dw% at 1.00 D/L. Therefore, the highest fatty acid methyl esters recovery of 301.8 mg g−1 dw was recorded at 1.00 D/L, with pronounced enhanced biodiesel characteristics. The suggested integrated approach using a mixture of liquid digestate-pretreated straw to manure at a ratio of 1:3 for dual purpose of biogas and biodiesel production enhanced the gross bioenergy yield by 95.7%, 24.6%, and 38.7% over those of raw rapeseed straw, pretreated straw, or chicken manure, respectively. The present study demonstrates an innovative waste-to-energy route that will have a positive impact on the future of biofuel industry.