Dual-Path valorization of organic waste via black soldier fly: Synergistic enhancement of feed efficiency, crop quality, and climate mitigation in closed-loop aquaculture

The rapid expansion of aquaculture generates vast quantities of hyperhydrated organic waste (e.g., eel feces), posing a severe waste management challenge due to its recalcitrance and high disposal costs. This study presents a circular bio-strategy using black soldier fly (BSF, Hermetia illucens) larvae to synergistically convert aquaculture waste and agro-industrial residue (Flammulina velutipes substrate) within a closed-loop system. The process achieved 92.6 % waste utilization efficiency, yielding two valuable co-products: First, BSF larvae accumulated nutrient-rich biomass (17.9 % crude protein, 8.03 % lauric acid). As a 1.0 % supplement in broiler diets, it significantly enhanced feed efficiency by 2.6 % and increased 42-day body weight by 7.5 % (P < 0.01), demonstrating a viable fishmeal alternative. Second, BSF frass was composted into a superior organic fertilizer, which outperformed conventional composting by reducing NH₃ emissions by 34 % (P < 0.001) and increasing total nitrogen retention by 15.3 %, attributed to pH modulation and chitin-NH₄⁺ complexation. The frass also enhanced phosphorus (7.05 %) and potassium (2.76 %) bioavailability. Metagenomics analysis revealed that frass inoculation enriched functional microbes (Azoarcus, LDA > 2.5; Roseisolibacter) driving synchronized nitrogen fixation and phosphate solubilization. Field application of the compost boosted tomato yields by 12.1 % (P < 0.05) and improved fruit quality (vitamin C + 18.6 %, soluble sugars + 20 %). This work establishes a scalable waste-to-resource paradigm that concurrently addresses waste management, livestock feed security, and sustainable crop intensification.