Integrated microalgae–insect cultivation for enhanced carbon-negative biodiesel production

Black soldier fly larvae (BSFL) are promising feedstocks for large-scale biodiesel production owing to their short growth cycle and high lipid content. However, the CO2 emissions associated with BSFL cultivation compromise the overall process sustainability. To mitigate this issue, this study used the CO2 fixation capability of Chlorella sp. HS2 by using defatted microalgae as feed for BSFL. Despite using a defatted substrate, BSFL synthesized 20.9 % lipid. Therefor, the integrated cultivation system can enhance lipid productivity by providing lipids from microalgae and BSFL. Microalgal lipids, which are rich in free fatty acids, challenge conventional alkaline-catalyzed transesterification because of the side reactions. To circumvent this, we introduced a thermally induced transesterification process, which achieved a biodiesel yield of 55.1 wt% from Chlorella lipids within 1 min at 380 °C (an eight-fold increase in yield from microalgal lipids compared with conventional catalytic methods). The same process applied to BSFL lipids yielded 87.5 wt% biodiesel, indicating greater reaction selectivity. The blended biodiesel derived from microalgal and larval lipids exhibited improved oxidative stability and flash point. The integrated cultivation system achieved a net CO2 reduction of 3.7 g per gram of biodiesel.