Bioconversion eficiency of livestock and aquaculture by-products through dipteran larval biomass production systems

Abstract:

Livestock processing and aquaculture operations generate organic residues that pose disposal challenges but contain recoverable nutrients. Bioconversion through dipteran larval systems in which chironomid (Chironomidae) larvae metabolise waste into high-protein biomass ofers a circular approach to waste valorisation that has received less industrial atention than black soldier fly alternatives. This research quantified the bioconversion eficiency, biomass yield, and economic viability of rearing Chironomus tentans on four by-product substrates poultry ofal, fish processing waste, dairy whey residue, and a mixed livestock blend in outdoor pilot beds at the Nakuru Research Institute of Agricultural Biotechnology, Rift Valley, Kenya, from January to June 2024. Twenty-four concrete rearing beds (each 2m×1m×0.15 m) were loaded with substrates at 2.0 kg dry mater per bed in a randomised complete block design with six replicates per treatment. Bioconversion eficiency, defined as the proportion of substrate dry mater converted to larval dry mater, was measured at weekly intervals over 12 weeks. Poultry ofal yielded the highest bioconversion eficiency (47.3%), followed by the mixed livestock blend (46.7%), fish processing waste (45.9%), and dairy whey residue (38.1%). Cumulative larval biomass production peaked at 373gDMm⁻² for poultry ofal and 224 g DM m⁻² for dairy whey. Substrate reduction rates exceeded 68% across all treatments, indicating efective organic mater removal. Proximate analysis of harvested larvae showed crude protein ranging from 57.4% to 63.8% DM and crude lipid from 7.9% to 10.6% DM. Economic analysis estimated net returns between 0.47 and 1.35 USD per kg of larval dry mater, with poultry ofa delivering the best cost-to-yield ratio. These data position chironomid-based bioconversion as a technically and economically viable waste management strategy for small and medium-scale livestock and aquaculture enterprises in East Africa.