Potential treatment of leachate by Hermetia illucens (Diptera, Stratyomyidae) larvae: Performance under different feeding conditions

In this study, the ability of H. illucens larvae (black soldier fly (BSF)) to metabolise different semisolid biowastes (e.g. kitchen waste, animal manure) has been applied to the treatment of landfill leachate. A testing programme has been developed by mixing leachate with three different solid supports: wheat bran, a biodegradable nutrient substrate, brewers’ spent grain, a biodegradable nutrient residue from the brewery industry and sawdust, a low biodegradable residue from the wood industry. Larvae growth rate was monitored in terms of weight variation, mortality and time to reach the prepupal stage. Prepupal biomass composition was analysed in terms of crude protein, lipids and fatty acids. Substrates were monitored at the beginning and the end of tests for total solids (TS), total organic carbon (TOC), total Kjeldahl nitrogen (TKN), ammonia and (whenever significant) the 7-day Respirometric Index (RI7). The best performance was observed with wheat bran and brewers’ spent grain, achieving an average larval weight ranging from 155.1 to 226.1 mg (w/w) with prepupation of more than 80% over 21 days. The initial TS, TOC and nitrogen content in feeding substrates had been metabolised (gasified and accumulated in prepupal biomass) by approximately 55%, 60% and 48%, respectively. Dry mass characterisation displayed a significant content of fats and proteins. The analysis demonstrated the suitability of BSF prepupal biomass for the production of biodiesel; however, the potential use of proteins as an animal feed needs further studies for assessing the presence of contaminants.