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Valorization of Wheat-Bran Substrate with Microplastic Inclusions Using Black Soldier Fly (Hermetia illucens) Bio-processing and the Effect on Frass and Larval Development
Summary
Black soldier fly larvae were able to process wheat-bran substrates containing polyethylene microplastics at up to 0.8 g/kg without mortality, though larval weight gain and development were progressively retarded as microplastic concentration increased. This research is relevant to microplastic pollution because insect-based bioconversion is a growing food and feed production method, and microplastic retention in frass and larvae raises questions about contamination entering animal feed and human food chains.
The formation and distribution of microplastics are alarming and could have adverse effects on the food sources for insects, fish, animals and human beings. The bio-recycling processes, such as the black soldier fly (BSF) technology, are evolving with great prospects. The BSFL technology is a potential biological resource recovery method that is known to valorize organic substrates, but the larvae’s growth and development on substrates with microplastic inclusions is not well known. Therefore, this study investigates the valorization of wheat-bran substrate with microplastic inclusions using the BSFL technology and assessed the effect on frass and larval development. Substrates were prepared from milled wheat-bran mixed with microplastics of 1 mm particle-sized sourced from waste sachet water plastic films. Substrate treatments were prepared and labelled P1, P2 and P3 according to the inclusion level of the microplastic. Thus, P1 had 0.2 g/kg of microplastic, while P2 and P3 had 0.4 and 0.8 g/kg respectively. The control P4 had no microplastic in the substrate. Samples of BSFL and frass were collected and analyzed at the end of the study for proximate composition. The control (P4) recorded the highest larval weight gain curve while P3 had the lowest curve. This demonstrated that the wheat-plastic inclusion substrate did not cause any larval mortality but had a retardation on the larvae development. Results also showed that the highest percentage crude protein in BSFL from the wheat-plastic inclusion substrate occurred at P1 (26.77 ± 8.71%) while the lowest at P3 (24.0 ± 8.71%). Percentage increment occurred in all proximate parameters of the frass, with the exception of Total organic nitrogen (TON), crude protein and crude fiber, which recorded a reduction. Present study has therefore demonstrated the effect of microplastic in wheat-bran substrate on BSFL growth and development as well as on frass quality.