Direct utilization of unprocessed food waste for black soldier fly larvae rearing

Conventional food waste (FW) management commonly relies on three-phase separation pretreatment, which divides raw waste into solid, oil, and liquid fractions for downstream treatment and resource recovery, but also increases equipment demand, energy consumption, and operational complexity. Here, we investigated the feasibility of bypassing pretreatment through the direct bioconversion of untreated food waste (UFW) by black soldier fly larvae (BSFL). Four substrate groups were compared: three-phase separation residue (TR), UFW mixed with manure (WR), the solid fraction of UFW (SR), and the liquid fraction of UFW mixed with manure (WM). By integrating growth evaluation with 16S rRNA sequencing and untargeted metabolomics, we examined how larvae adapted to these distinct physicochemical environments. The WR group showed growth performance close to the optimized TR benchmark while maintaining strong waste-reduction capacity, indicating that direct whole-waste conversion can remain effective without mechanical homogenization. Multi-omics analyses further showed active gut-ecosystem remodeling in response to substrate-specific constraints. In WR, enrichment of Turicibacter and Bacilli was associated with a synergistic defense-digestion pattern that may have supported efficient substrate depletion. In SR, Pseudomonas enrichment was linked to metabolic reprogramming and elevated lipid accumulation, yielding larvae with high fat and lauric acid content. In contrast, WM performed poorly and showed a stress-adaptive metabolic profile consistent with intensified lipid-processing demands. Overall, direct bioconversion of whole food waste represents an effective strategy for bypassing complex pretreatment, and the WR model may offer a simplified and potentially lower-input route for food waste valorization.