Conversion of year-long canteen waste operated by black soldier fly larvae to assess heavy metal accumulation

Results presented at Insect to Feed the World, Canada June 2022

Partner:

F. Grosso¹, M. Meneguz¹, N. Regalli² and E. Calà²

¹BEF Biosystems, via Tancredi Canonico 18, 10156 Torino, Italy,

²Eastern Piedmont University, Via Michel 11, 15121 Alessandria,

Person of interest: Elisa Calà, Young Researcher at Eastern Piedmont University:

https://upobook.uniupo.it/elisa.cala

Summary

Worldwide, there are about 244 million t/year of waste from canteens and restaurants, and 4.7 million t/year in Italy alone. Canteen waste (CW) could be used for feeding insect larvae to obtain new marketable products (e.g., feed and bran). Black soldier fly (BSFL) larvae are voracious and polyphagous, and CW is a complete food for them. In addition, BSFLs are able to bioaccumulate some heavy metals, allowing for safe organic compost, but bioaccumulation in larvae for feeding purposes needs to be evaluated.

CW was sampled once a month, and sampling was conducted for one year at a local canteen located in the northern part of Italy. Feeding was conducted in quadruplicate in plastic containers (12 l) placed in a rack inside a climatic chamber with 27°C and 70% RH. In each box, 2,000 g of feed and 2,000 5-day-old larvae were allocated. The trial ended at 7 days, and growth performance was evaluated.

The initial diet, neonates, BSFL, and residues were sampled and dried in an oven. Each sample was treated by acid digestion and microwave. Elemental chemical analyses were performed with a mass spectrometer in triplicate to evaluate 27 elements. Results reported an average final year-long larval biomass of 227.0±114.95 g and insect frass of 378.0±140.59 g. The dry matter percentage for initial diet was 26.1±10.31%, for final larval biomass 35.3±6.55% and for residual 57.9±19.24%.

Feed ingestion for BSFLs was 298.1±168.10 g during the trial. As, Pb, Hg and Cd are regulated at the European level for feed among the heavy metals analyzed in this study. As, Pb, Hg and Cd were below the maximum levels in CW for initial diet, newborn larvae, residual frass and fattened BSFL. The use of CW seems to be available for BSFL rearing. Results showed good growth performance and heavy metal values below the maximum limits specified by EU legislation. The danger related to heavy metal accumulation operated by BSFLs was not recorded by our results.