Process efficiency in black soldier fly larvae composting of plant-based food industry waste

Abstract: Black soldier fly larvae (BSFL) composting, in which biodegradable wastes are converted into animal-feed protein, is a technology that meets circular economy principles. The greatest potential BSFL composting is for mixed food waste, but only plant-based waste is permitted as feed for the larvae. It has lower biomass conversion efficiency (BCE), but this could be improved by pre-treatment.This thesis investigated process efficiency and GHG and ammonia emissions from BSFL composting using orange peel and broccoli and cauliflower, with ammonia or fungi pre-treatment. The impact of enzyme and ammonia pre-treatment time on process efficiency when using mixed lettuce and cabbage waste was also assessed. Following two weeks of substrate pre-treatment with ammonia and fungi, direct emissions of GHG and ammonia were evaluated. Lettuce and cabbage was pre-treated with enzymes or ammonia for 0-8 days prior to BSFL composting.BCE on a volatile solids (VS) basis was greater overall for food waste and lettuce and cabbage (~20%) than for orange peel and broccoli and cauliflower (~7%). The BCE was low (6%) in the orange peel control and even lower in both orange peel pre-treatments. Direct addition of enzymes at the start of BSFL composting gave 22% higher BCE compared with the control.Total emissions of N2O and CH4 were almost four-fold larger for the broccoli and cauliflower control than when pre-treated, indicating that ammonia pre-treatment significantly reduced total GHG emissions with no negative impact on BCE during BSFL composting, but with increased ammonia emissions.