Treatment of biowaste commingled with biodegradable bioplastic films using Black Soldier Fly larvae: Generation and fate of micro-plastics

The use of Black Soldier Fly (BSF) larvae is emerging as a promising alternative for biowaste (i.e. food waste) treatment, generating larval biomass and process residues, suitable for use as animal feed and fertilizer, respectively. In line with an increasing use of starch-based bioplastics in food packaging, the presence of these biopolymers and associated biodegradable microplastics (BMPs) in food waste is expected to rise. Knowledge of the generation of BMPs and their fate in the BSF treatment process is scarce, or indeed, completely lacking in the case of small-sized BMPs (<50 mu m). The present study aims to investigate the generation and potential accumulation of BMPs in BSF larvae process. Food waste mixed with starch-based bioplastic films was fed to larvae and BMPs of two particle sizes (inferior to and exceeding 10 mu m in diameter) were monitored over time in rearing substrate and larval biomass. BMPs concentrations in substrate were compared with larvae-free control tests. The presence of larvae favoured the generation of BMPs. Concentrations of smaller-sized BMPs (<10 mu m) increased by approximately 172% in the final substrate, and accumulated in the larval biomass with a peak exceeding the initial larval concentration by over 1000% just before prepupation, which is the typical stage they are collected when used as animal feed. These results indicate a potential risk of soil contamination by BMPs when final substrate is used as fertilizer and a risk of biomagnification phenomena when larvae are used as animal feed.