Carbon Bioavailability Correlates with Bioconversion Efficiency and GHG Emissions in Hermetia illucens Larvae Treatment of Chicken Manure

Bioconversion of chicken manure by Hermetia illucens (black soldier fly, BSF) larvae offers a sustainable route for organic waste disposal and protein production, yet how carbon source bioavailability regulates this process remains unclear. We conducted 13-day trials on chicken manure across 27 combinations of three supplement-to-manure mixing ratios (SMMRs, 3:1, 1:1, and 1:3, dry weight basis) and nine carbon blends (sawdust, straw, and corn flour). Measured endpoints included larval yield, substrate temperature dynamics, GHG emissions, global warming potential (GWP), ammonia volatilization, carbon–nitrogen fixation, and frass characteristics. Carbon source identity showed a much stronger association with performance than did the manure-to-supplement mixing ratio. Dry-basis larval yield ranged from 3.5% to 13.2% (mean 7.4%), total GWP ranged from 5105.6 to 8737.2 mg kg−1, and ammonia emissions from 419.6 to 1114.1 mg kg−1. Optimal larval yield was combined with a 3:1 SMMR with corn-flour-rich blends, which boosted productivity and C-N retention. Labile carbon was associated with enhanced lipogenesis, amino acid accumulation, C-N sequestration, and reduced GHG emissions. In contrast, recalcitrant carbon (sawdust) restricted degradation, intensified microbial competition, and induced energy shortage and nutrient losses, impairing conversion efficiency. These findings are consistent with carbon bioavailability rather than C/N, being a key correlate of BSF performance through energy–microbe–substrate interactions. We further propose that substrate formulation targeting labile carbon enrichment can serve as a practical strategy to simultaneously improve larval production and mitigate environmental impacts, though the inferred mechanisms await direct microbiological validation.