Bokashi fermentation of brewery’s spent grains positively affects larval performance of the black soldier fly Hermetia illucens while reducing gaseous nitrogen losses

• Published in: Waste management (Elmsford) 2023-11, Vol.171, p.411-420
• Main Authors: Gebiola, Marco, Rodriguez, Michael V., Garcia, Alexandro, Garnica, Andrea, Tomberlin, Jeffery K., Hopkins, Francesca M., Mauck, Kerry E.
• Format: Article
• Language: English
• Subjects: ammonia; biomass; BSF larvae; carbon dioxide; Circular economy; digestion; ecological footprint; feeds; feedstocks; fermentation; GHG emissions; greenhouse gases; Hermetia illucens; industrial wastes; larvae; larval development; N2O; NH3; nitrogen; organic fertilizers; volatilization; waste management
• ISSN: 0956-053X; 1879-2456
• DOI: 10.1016/j.wasman.2023.09.033

•Bokashi fermentation improves performance of black soldier fly larvae.•CO2 fluxes tracked black soldier fly larval growth and metabolism.•Black soldier fly rearing on brewery’s spent grains increases N2O and NH3 emissions.•Fermentation of spent grains reduced N2O and NH3 emissions from larval feeding. Digestion of waste feedstocks by larvae of the black soldier fly Hermetia illucens (Diptera: Stratiomyidae) (BSF) results in proteins for animal feed and organic fertilizer with a reduced environmental footprint, but it can still have negative environmental effects through greenhouse gas (GHG) and ammonia (NH3) emissions. Both biomass conversion by BSF larvae and associated GHG and NH3 emissions can depend on substrate properties that may be optimized through microbial inoculation pre-treatments, such as bokashi fermentation. Here, we quantified the effects of bokashi fermentation of brewery’s spent grains on BSF rearing metrics and associated GHG and NH3 emissions at benchtop scale. We found that bokashi fermentation increased larval biomass by 40% and shortened development time by over two days on average, compared with unfermented spent grains. In line with increased larval growth, CO2 emissions in BSF larvae treatments were 31.0 and 79.0% higher in the bokashi fermented spent grains and Gainesville substrates, respectively, compared to the unfermented spent grains. Adding BSF larvae to the spent grains increased cumulative N2O emissions up to 64.0 mg N2O kg substratedry-1 but there were essentially no N2O emissions when larvae were added to fermented spent grains. Bokashi fermentation also reduced NH3 fluxes from the volatilization of substrate nitrogen in the BSF larvae treatment by 83.7-85.8% during days 7 and 9, possibly by increasing N assimilation by larvae or by reducing the transformation of substrate NH4+ to NH3. Therefore, bokashi fermentation may be applied to improve performance of BSF larvae on a common industrial waste stream and reduce associated emissions.