Low-cost technology for recycling agro-industrial waste intonutrient-rich organic fertilizer using black soldier fly

Efforts to recycle organic waste using black soldier fly (BSF) larvae into high-quality alternative proteiningredients in animal feeds and organic fertilizers have gained momentum worldwide. However, thereis limited information on waste manipulation to increase nutrient retention for enhanced larval perfor-mance and frass fertilizer quality. In the present study, brewer’s spent grain with a carbon to nitrogen (C/N) ratio of 11 (control) was amended with sawdust to obtain substrates with C/N ratios of 15, 20, 25 and30. The effects of substrate C/N ratios on BSF larval yield, waste degradation, biomass conversion effi-ciency, compost maturity and nutrient levels of frass fertilizer were evaluated. Substrates amended withsawdust did not significantly affect waste degradation efficiency and biomass conversion rates of BSF lar-vae. The wet and dried larval yields were significantly higher for substrates with C/N ratio of 15 comparedto the other amended substrates. An amended substrate with C/N ratio of 15 enhanced nutrients uptakeby BSF larvae, and increased nitrogen (N) and phosphorus retention in frass compost by 21 and 15%,respectively. Compost maturation time was shortened to five weeks, as indicated by the stable C/N ratiosand high seed germination indices. This study has demonstrated that the amendment of the substratewith sawdust to C/N ratio of 15 could generate compost with desirable nutrients for use as high-quality fertilizer for organic farming