Recycling nitrogen in livestock wastewater for alternative protein by black soldier fly larvae bioreactor

Protein from livestock cannot meet the increasing demand of the growing global human population. Therefore, identifying safe sources of protein is essential for food security. Converting the nitrogen in livestock wastewater into insect protein is now gaining attention due to efficient and safe methods being developed. In this study, we designed a novel black soldier fly larvae (BSFL) and microbial bioreactor that converts nitrogen in the wastewater to bacterial and insect proteins concurrently. We determined that the introduction of nitrifying bacteria isolated from the BSFL gut into the conversion system of the BSFL and microbial bioreactor increased the weight, biomass, and protein gain of resulting BSFL as well as the nitrogen use efficiency by 11.3% compared with the BSFL group. The conversion system of the bioreactor (BSFL+NB group) could not only effectively remove 80% of the total nitrogen (TN) from the wastewater, but also effectively reduced ammonia (NH3) emissions from 54.6% to 33.5% compared with the CK group. Bacteria utilized inorganic nitrogen in wastewater through nitrification and denitrification. The functional genes of BSFL+NB group primarily comprised Klebsiella sp. were enhanced as revealed by the increase in the abundance of ammonia monooxygenase gene(amoA) that was a critical enzyme in nitrification, nitrate reductase gene (narG), and nitrite reductase gene (nirS) that were critical enzyme in denitrification. This study identified a new method for converting the nitrogen in wastewater to insect protein, providing a new approach to produce alternative protein to ensure strategic food security. [Display omitted] •A novel black soldier fly larvae (BSFL) and microbial bioreactor.•The bioreactor can upcycle nitrogen in livestock wastewater to insect protein.•Nitrifying bacteria can increase the BSFL conversion efficiency of wastewater.•The BSFL and microbial bioreactor can reduce ammonia (NH3) emissions.