Reducing greenhouse gas emissions and enhancing carbon and nitrogen conversion in food wastes by the black soldier fly.

Currently, sustainable utilisation, including recycling and valorisation, is becoming increasingly relevant in environmental management. The wastes bioconversion by the black soldier fly larva (BSFL) has two potential advantages: the larvae can convert the carbon and nitrogen in the biomass waste, and improve the properties of the substrate to reduce the loss of gaseous carbon and nitrogen. In the present study, the conversion rate of carbon, nitrogen and the emissions of greenhouse gases and NH during BSFL bio-treatment of food waste were investigated under different pH conditions. The results showed that the pH of the raw materials is a pivotal parameter affecting the process. The average wet weight of harvested BSFL was 13.26-95.28 mg/larva, with about 1.95-13.41% and 5.40-18.93% of recycled carbon and nitrogen from substrate at a pH from 3.0 to 11.0, respectively. Furthermore, pH is adversely correlated with CO emissions, but positively with NH emissions. Cumulative CO, NH, CH and NO emissions at pH ranging from 3.0 to 11.0 were 88.15-161.11 g kg, 0.15-1.68 g kg, 0.19-2.62 mg kg and 0.02-1.65 mg kg, respectively. Compared with the values in open composting, BSFL bio-treatment of food waste could lead greenhouse gas (especially CH and NO) and NH emissions to decrease. Therefore, a higher pH value of the substrate can increase the larval output and help the mitigation of greenhouse gas emissions.