Feasibility of housefly larvae-mediated vermicomposting for recycling food waste added digestate as additive

Growth and metabolic performance of house fly and black soldier fly larvae differ across densities and waste-based growth substrates

Large scale production of insect larvae is considered a sustainable way to upcycle various organic waste- and by-products into more valuable food and feed products. The sustainability of insect larvae production depends on the substrates and species being used, but comparative studies that include both growth and efficiency are lacking. Here we compare larval fitness, including survival, development time, weight, substrate conversion efficiency, substrate reduction, and metabolic parameters across different combinations of densities and waste- and by-product-based substrates on the two fly species, the house fly (Musca domestica) and the black soldier fly (Hermetia illucens). The waste- and by-product-based substrates were a brewer's spent grain-based substrate, a digested sludge-based substrate, and a wheat bran/deproteinized grass-based substrate all highly abundant and of low value. Substrate and density significantly impacted on most larval growth and metabolic performance traits, but dependent on species. The brewer's spent grain-based substrate generally gave the highest performance in terms of larval weight, larval yield, and substrate conversion efficiency for both species, while a high density gave a higher larval yield and substrate conversion efficiency, but lower larval weight. Generally, black soldier fly larvae showed lower metabolic costs and higher net growth efficiency than house fly larvae. Altogether, our results demonstrate that both larval species, substrate, and larval densities affect larval growth and metabolic performance, and subsequently the scope for valorizing waste- or by-products to achieve a sustainable production of food and feed.

Material flow analysis and global warming potential assessment of an industrial insect-based bioconversion plant using housefly larvae

The significant increase in the demand for biomass waste treatment after garbage classification has led to housefly larvae treatment becoming an attractive treatment option. It can provide a source of protein while treating biomass waste, which means that nutrients can be returned to the natural food chain. However, the performance of this technology in terms of its environmental impacts is still unclear, particularly with regards to global warming potential (GWP).This study used a life cycle assessment (LCA) approach to assess a housefly larvae treatment plant with a treatment capacity of 50 tons of biomass waste per day. The LCA results showed that the 95% confidence intervals for the GWP in summer and winter were determined to be 24.46-32.81 kg CO2 equivalent (CO2-eq)/ton biomass waste and 5.37-10.08 kg CO2-eq/ton biomass waste, respectively. The greater GWP value in summer is due to the longer ventilation time and higher ventilation intensity in summer, which consumes more power. The main GWP contributions are from (1) electricity needs (accounting for 78.6% of emissions in summer and 70.2% in winter) and (2) product substitution by mature housefly larvae and compost (both summer and winter accounting for 96.8% of carbon reduction).