Conversion of Spent Coffee and Donuts by Black Soldier Fly (Hermetia illucens) Larvae into Potential Resources for Animal and Plant Farming

SIMPLE SUMMARY: Unsustainable farming practices have depleted the quantity and quality of topsoil and, moreover, 30–40% of the food produced ends up in landfills. These issues can be simultaneously mitigated by producing black soldier fly (Hermetia illucens) larvae that convert food waste into two resources. This includes the black soldier fly (Hermetia illucens) larvae (BSFL) itself as a rich source of protein and lipid for animals as well as the “frass” which is the leftover organics that can be used as fertile compost. The aim of this study was to examine the applications of two widely available resources, spent coffee grounds and donut dough, as food for BSFL. The proximate, fatty acid and amino acid composition demonstrates that a blend of these resources produced BSFL of similar quality as soybean meal. Moreover, the left behind frass had a similar nutritional profile as many organic fertilizers. Therefore, BSFL farming yields potential resources for animal and plant farming from otherwise discarded waste. ABSTRACT: Nutritionally unbalanced organic waste can be converted into potential resources for animal and plant farming by culturing black soldier fly (Hermetia illucens) larvae (BSFL) and prepupae (BSFP). BSFL and BSFP are rich sources of protein and lipids, while the leftover excrement called “frass” can be used as an organic fertilizer. Using readily available resources, BSFL were cultured on spent coffee, donut dough or an equal blend for 35 days. Survival, productivity, daily pupation and biochemical composition of BSFL and BSFP were measured along with the nitrogen-phosphorus-potassium values of the frass. Survival was highest in the blend compared (81%) to spent coffee (45%) or dough (24%); however, BSFL and BSFP were significantly longer and heavier from dough. Stage and food significantly influenced the protein, lipid and glycogen content of the BSFL and BSFP, which tended to be higher in the latter. While fatty acids were often significantly higher in BSFL fed spent coffee, the amino acid composition of BSFL was generally higher in dough. Frass from the blend had significantly highest nitrogen content, while potassium and phosphorus were significantly higher and lower from spent coffee, respectively. Although coffee and donut dough were suboptimal substrates for BSFL, a blend of these produced BSFL and frass that were nutritionally comparable to soybean meal and many organic fertilizers, respectively.