Effects of microplastics and salinity on food waste processing by black soldier fly (Hermetia illucens) larvae

Abstract

Background: The black soldier fly (Hermetia illucens) is gaining attention as an efficient decomposer of food waste. However, recalcitrant compounds such as plastics mixed into food waste may have negative effects on its growth and survival. Moreover, its efficiency of food waste degradation may also be affected by plastics. In addition, salt (NaCl) can also be present in high concentrations, which also reduces the efficiency of H. illucens-mediated food waste treatment. In this study, we assessed the growth of black soldier fly larvae (BSFL) reared on food waste containing polyethylene (PE) and polystyrene (PS) and NaCl. The weight of BSFL was measured every 2-4 days. Survival and substrate reduction rates and pupation ratio were determined at the end of the experiment. Results: The total larval weight of Hermetia illucens reared on food waste containing PS was greater than that of the control on days 20 and 24. However, the survival rate was lower in the group treated with 5% PS, as was substrate reduction in all PS-treated groups. The weight of BSFL reared on food waste containing PE was lower than that of the control on day 6. PE in food waste did not affect the survival rate, but the pupation ratio increased and substrate consumption decreased with increasing PE concentrations. Regardless of the plastic type, the addition of NaCl resulted in decreased larval weight and pupation ratio. Conclusions: Larval growth of black soldier fly was inhibited not by plastics but by substrate salinity. Additional safety assessments of larvae reared on food waste containing impurities are needed to enable wider application of BSFL in vermicomposting.

Microplastics affected black soldier fly (Hermetiaillucens) pupation and short chain fatty acids

“…In this preliminary study, a single MP concentration was tested against the control to determine whether MPs could potentially influence the survival, growth, development or fatty acid composition of BSFL. Both the survival and growth of BSFL were unaffected by MP exposure, which is consistent with Cho et al (2020); however, there were two contrasting findings between our study and Cho et al (2020). First, PP‐MPs had no effect on substrate reduction in this study, and second, the percentage of larvae reaching the pre‐pupae stage was significantly reduced after PP‐MP exposure in this study.…”

“…Therefore, one gram of the MP treatment would contain 26,972 particles (or 26,972,507 particles/kg) based on dividing 1,621,856 particles by 60.13 g (substrate of 0.60 g plus 0.13 of the MPs). The tested MP concentration of 0.022 g/kg in this study is a fraction of those used in other studies on insects, such as 1.25 to 20 g/kg (Silva et al, 2019) and 0.2 g/kg (Cho et al, 2020). Nevertheless, the levels used in this study are substantially higher than those found in nature ranging from 112 to 234 particles/kg in Italian lakes (Fischer et al, 2016) to 3,153 particles/ kg in Poyang Lake (Liu et al, 2019) and 91,000 particles/kg in various unmanaged landfills (He et al, 2019;Hou et al, 2021;Su et al, 2019).…”

“…The freshwater diving beetle, Cybister japonicus , had reduced feed uptake to MP‐PE‐contaminated food, but did appear to regurgitate the ingested MP fragments (Kim et al, 2018). Exceptionally high MP levels of 5, 10 or 20% (or 0.5, 1.0 or 2.0 mg/g), in the form of PS or PE, had no effect on the survival of BSFL (Cho et al, 2020). Interestingly, however, the weight of BSFL in the 10 and 20% PS‐MP treatments significantly increased (Cho et al, 2020), which likely reflected MP uptake.…”

“…Exceptionally high MP levels of 5, 10 or 20% (or 0.5, 1.0 or 2.0 mg/g), in the form of PS or PE, had no effect on the survival of BSFL (Cho et al, 2020). Interestingly, however, the weight of BSFL in the 10 and 20% PS‐MP treatments significantly increased (Cho et al, 2020), which likely reflected MP uptake.…”

Impact of Processed Food (Canteen and Oil Wastes) on the Development of Black Soldier Fly (Hermetia illucens) Larvae and Their Gut Microbiome Functions

“…Elevated salt (NaCl) content in meals is often discussed because of its adverse effect on human health (e.g., high blood pressure) and can account for up to 1.2% in hot meals and sandwiches handed out in canteens ( Rasmussen et al, 2010 ). Cho et al (2020) concluded that BSFL are suitable to treat food waste with even higher salt concentrations, since a significant inhibition of biomass gain and pupation was only observed at concentrations >3%.…”