Abstract
Efforts to recycle organic waste using black soldier fly (BSF) larvae into high-quality alternative protein ingredients in animal feeds and organic fertilizers have gained momentum worldwide. However, there is limited information on waste manipulation to increase nutrient retention for enhanced larval performance 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 and 30. The effects of substrate C/N ratios on BSF larval yield, waste degradation, biomass conversion efficiency, compost maturity and nutrient levels of frass fertilizer were evaluated. Substrates amended with sawdust did not significantly affect waste degradation efficiency and biomass conversion rates of BSF larvae. The wet and dried larval yields were significantly higher for substrates with C/N ratio of 15 compared to the other amended substrates. An amended substrate with C/N ratio of 15 enhanced nutrients uptake by 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 ratios and high seed germination indices. This study has demonstrated that the amendment of the substrate with sawdust to C/N ratio of 15 could generate compost with desirable nutrients for use as high-quality fertilizer for organic farming.
Highlights
There is an increasing demand for the use of insects as highquality protein ingredients in animal feeds (Makkar et al, 2014)
Studies have shown that substrates with high carbon to nitrogen ratios such as soybean residues result in low biomass conversion rates by black soldier fly (BSF) larvae (Rehman et al, 2017), which is in accordance with the larval yields recorded from substrates with C/N ratio of 30
Substrates with lower carbon to nitrogen ratios in the present studies had higher biomass conversion rates. This implies that substrates with lower carbon to nitrogen ratios or substrates with higher nitrogen should be used in BSF rearing to achieve higher larval biomass conversion rates
Summary
There is an increasing demand for the use of insects as highquality protein ingredients in animal feeds (Makkar et al, 2014). Black soldier fly (Hermetia illucens L.) larvae have been widely advocated as an important source of proteins, fats, and vitamins in animal feeds (Shumo et al, 2019; Liu et al, 2017; van Huis, 2013). The larvae of BSF can be grown on a range of decomposable organic waste streams including human feces The degradation efficiency of these decomposable organic wastes by BSF larvae ranges from 55 to 80% (Lalander et al, 2014; Diener et al, 2011)
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