Phosphorus role in bioconversions of food waste by black soldier fly larvae

Black soldier fly larvae (BSFL) have emerged as a promising technology for recycling phosphorus (P) from food waste. However, the concentrations and forms of P in food waste are highly variable, and their effects on BSFL bioconversion efficiency remain poorly understood. This study systematically investigated how P concentration and form (orthophosphate vs. apatite) influence the bioconversion efficiency of food waste by BSFL, as well as the mechanisms underlying P solubilization. The results showed that adding appropriate levels of orthophosphate (TP: 12.29 ± 0.84 to 24.58 ± 1.68 g/kg DM) maintained a comparable bioconversion rate (BCR) of 22.50%-26.14%. However, excessive orthophosphate (49.17 ± 3.38 g/kg DM) significantly reduced BCR to 8.22% ± 2.40%. BCR in the apatite-added groups were consistently lower than those in the control and in groups receiving equivalent orthophosphate. Although apatite impaired larval growth and conversion efficiency, it was substantially transformed into labile forms, with nearly half of the residual P converted into bioavailable fractions. Mechanistic analyses revealed that P solubilization was driven by host-microbe interactions. The gut served as the primary site of phosphatase secretion, playing a key role in P activation. In the residual substrate, acidification (pH 4.92 ± 0.04) and elevated ammonium levels (1.46 ± 0.17 mg/g DM) were observed, which may further promote P release. These findings demonstrate that BSFL mediate P bioconversion through integrated physicochemical, enzymatic, and microbial pathways, providing a novel strategy for recycling P-rich biowastes via insect-based bioconversion.