Abstract
Black soldier fly (BSF) (Hermetia illucens L.) is one of the most efficient bio-waste recyclers. Although, waste substrate amendments with biochar or gypsum during composting process are known to enhance nutrient retention, their impact on agro-industrial waste have not been documented. Hence, this study focuses on a comparative effect of agro-industrial waste amended with biochar and gypsum on BSF larval performance, waste degradation, and nitrogen (N) and potassium retention in frass fertilizer. Brewery spent grain was amended with biochar or gypsum at 0, 5, 10, 15 and 20% to determine the most effective rates of inclusion. Amending feedstock with 20% biochar significantly increased wet (89%) and dried (86%) larval yields than the control (unamended feedstock). However, amendment with 15% gypsum caused decrease in wet (34%) and dried (30%) larval yields but conserved the highest amount of N in frass. Furthermore, the inclusion of 20% biochar recorded the highest frass fertilizer yield and gave a 21% increase in N retention in frass fertilizer, while biomass conversion rate was increased by 195% compared to the control. Feedstock amendment with 5% biochar had the highest waste degradation efficiency. Potassium content in frass fertilizer was also significantly enhanced with biochar amendment. At maturity, frass compost with more than 10% inclusion rate of biochar had the highest cabbage seed germination indices (>100%). The findings of this study revealed that initial composting of biochar amended feedstocks using BSF larvae can significantly shorten compost maturity time to 5 weeks with enhanced nutrient recycling compared to the conventional composting methods.
Highlights
There was a significant effect of rearing substrates on the wet and dry yields of Black soldier fly (BSF) larvae (Fig 1a and 1b)
Effect of biochar and gypsum amendments on black soldier fly larval yields The present study revealed higher yields of wet and dried BSF larvae from biochar-amended substrates, especially at inclusion levels of 15 and 20%
The results of this study indicate that the N concentration in frass fertilizer generated from all amended substrates were within the recommended standards of > 1% N according to the Kenya Bureau of Standards (KEBS) guidelines for optimal commercial organic fertilizer [63]
Summary
The efforts to recycle organic wastes using black soldier fly (BSF) (Hermetia illucens L.) larvae into high-quality sustainable protein to substitute fishmeal in animal feeds. Amended waste improves larval yield and organic fertilizer quality. 08.250.202) through the International Centre of Insect Physiology and Ecology (icipe). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript
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