Bioconversion of Meat and Fish-Based Former Foodstuffs by Black Soldier Fly Larvae: A Sustainable Pathway for Reducing Food Waste, Enhancing Nutrient Recovery, with a Circular Economy Approach

: Food waste containing meat and fish presents a considerable environmental challenge due to regulatory constraints preventing its use in industrial insect farming. Although substrates derived from meat and fish are not currently approved for industrial insect feed production due to regulatory constraints, this study explores their potential in bioconversion through Hermetia illucens larvae. In this study, five different former foodstuffs containing meat and/or fish were tested to evaluate their suitability for BSFL rearing. The substrates included pizza with salami (PIZZA), cheeseburger (CHB), pasta Bolognese with meat (PASTA), chicken salad (CHISA), and fish salad (FISA). Results showed that BSFL successfully developed on all tested substrates. The highest performance was observed for FISA, with a total larval weight of 35.21 ± 3.91 g, dry matter yield of 11.21 ± 0.45 g, survival rate of 96.63 ± 0.40%, and the most efficient feed conversion ratio (FCR, 4.11 ± 0.59). Heavy metal analysis revealed substantial bioaccumulation of lead (Pb) and cadmium (Cd) in larvae. In particular, larvae reared on PIZZA showed a Pb concentration of 4.68 μg/100 g, with a corresponding bioaccumulation factor (BAF) of approximately 1.5. Cadmium accumulation was most notable in larvae fed CHB, with a Cd concentration of 0.41 ± 0.33 μg/100 g and a BAF of about 2.1. Despite this bioaccumulation, all detected concentrations remained well below the regulatory limits set by the European Union for animal feed, indicating not only the feasibility of H. illucens larvae in sustainable waste management but also its use as a safe protein source in animal feed. This research highlights the viability of integrating such food waste into insect bioconversion systems. With appropriate risk management, this practice could significantly improve nutrient recycling, waste management, and the circular economy, urging a regulatory review to allow broader substrate utilization. These positive outcomes underscore the potential of integrating currently restricted animal-derived food waste streams into H. illucens-based bioconversion systems, unlocking additional value for the circular economy and contributing to more efficient waste management practices.