Effects of straw addition on the physicochemical and microbial features of black soldier fly larvae frass derived from fish meat and bone meal

Black soldier fly larvae (BSFL) hold great promise for sustainable management of meat and bone meal (MBM), a kind of organic waste. Harvested BSFL frass can be used as soil amendment or organic fertilizer. This study evaluated the quality and microbial profile in the frass of BSFL, fed with fish MBM containing 0% (CK), 1% (T1), 2% (T2) and 3% (T3) of rice straw. Results suggested straw addition into fish MBM had no significant impacts on BSFL weight; however, straw addition remarkably affected waste reduction and conversion efficiency, as well as physicochemical properties including electric conductivity, organic matter (OM) and total phosphorus contents in frass. Fourier transform infrared analysis indicated that increasing levels of cellulose and lignin might not be fully degraded or transformed by BSFL when more straw was introduced into substrates. Straw addition had hardly significant influences on microbial richness or evenness in BSFL frass, only T3 treatment remarkably elevated the phylogenetic diversity value more than the control. Bacteroidetes, Proteobacteria, Actinobacteria and Firmicutes were the most dominant phyla. Genera Myroides, Acinetobacter and Paenochrobactrum maintained high abundances in all frass samples. Elements including OM, pH and Na were key factors in shaping the microbiological characteristics of BSFL frass. Our findings helped to understand the effects of fish MBM waste manipulation on BSFL frass qualities and contributed to the further application of BSFL frass.