Bioconversion of fruit waste and sewage sludge mixtures by black soldier fly (Diptera: Stratiomyidae) larvae

Microbial profiling of black soldier fly larvae reared on substrates supplemented with different mineral sources originating from phosphorus recycling technologies

BACKGROUND

Innovations to establish agricultural value chains utilising side streams and their reintegration into the feed and food supply are of great importance. Recyclates derived from biomass and waste are therefore becoming increasingly important as sources of nutrients. The larvae of the black soldier fly (BSF; Hermetia illucens) demonstrate considerable potential as livestock feed due to their ability to utilise a wide range of organic substrates. In this study, BSF larvae (BSFL) were reared on four different substrates: chicken feed diet (CD), high-fibre Gainesville fly diet (FD), or FD supplemented either with biochar (FD + BCH) or single superphosphate (FD + SSP) recyclates from sewage sludge processing. To validate the hypothesis that endogenous and substrate-associated microbiota significantly contribute to substrate conversion, the microbiota profiles of BSFL gut and frass were analysed by 16S rRNA gene amplicon sequencing. Results were associated to the different substrates as well as body composition, growth performance data, and mineral concentration of the larvae.

RESULTS

The CD substrate was superior in terms of larval growth, although it caused a lower microbial alpha diversity in the larval intestine and frass compared to FD, with a dominance of Morganellaceae and families of Lactobacillales. The addition of the two sewage sludge derived products to the FD substrate significantly increased the calcium content of BSFL, while the phosphorus content was only increased by the addition of SSP. The shifts in the microbiota profiles of BSFL gut and frass indicated that BCH contributed to the regulation of the microbial milieu with suppressing the growth of potentially pathogenic microbes. The addition of SSP resulted in an enrichment of microorganisms with attributed phosphate-solubilising properties such as Pseudomonas and fungal species, likely being responsible for improving the bioavailability of phosphorus from the substrate.

CONCLUSIONS

The results demonstrate the high adaptability of the BSFL and its ability to change the substrate through specific microbiota in such a way that conditions are created for an optimal nutrient supply and thus growth of the larvae.

Unlocking the potential of black soldier fly frass as a sustainable organic fertilizer: A review of recent studies

Using Hermetia illucens, or Black Soldier Fly (BSF) frass as an organic fertilizer is becoming increasingly popular in many countries. As a byproduct derived from BSF larvae that feed on organic waste, BSF frass has tremendous potential for preserving the environment and promoting the circular economy. Since it has diverse biochemical properties influenced by various production and environmental factors, further research is needed to evaluate its potential for extensive use in crop production and agriculture. Our review summarizes recent findings in BSF frass research by describing its composition and biochemical properties derived from various studies, including nutrient contents, biostimulant compounds, and microbial profiles. We also discuss BSF frass fertilizers' effectiveness on plant growth and contribution to environmental sustainability. Great compositions of BSF frass increase the quality of plants/crops by establishing healthy soil and improving the plants' immune systems. Special emphasis is given to potentially replacing conventional fertilizer to create a more sustainable cropping system via organic farming. Besides, we discuss the capability of BSF bioconversion to reduce greenhouse gas emissions and improve the socioeconomic aspect. The prospects of BSF frass in promoting a healthy environment by reducing greenhouse gas emissions and improving the socioeconomic aspects of communities have also been highlighted. Overall, BSF frass offers an alternative approach that can be integrated with conventional fertilizers to optimize the cropping system. Further studies are needed to fully explore its potential in establishing sustainable system that can enhance socioeconomic benefits in the future.

Performance of feeding black soldier fly (Hermetia illucens) larvae on shrimp carcasses: A green technology for aquaculture waste management and circular economy

Over 944 thousand tonnes of shrimp carcasses are produced worldwide during the shrimp production cycle, and black soldier fly larvae (BSFL) are a potential solution for this shrimp carcass accumulation. In this study, we evaluated the performance of BSFL feeding on shrimp carcasses. Six combinations of wheat bran and shrimp carcass powder (with replacement increments of 20 %) and one whole shrimp carcasses treatment were tested. The bioconversion rate (27.15 ± 3.66 %; p = 0.001), crude protein (55.34 ± 1.27 %; p < 0.001), and crude lipid (14.37 ± 1.86 %; p = 0.007) values of BSFL reared on whole shrimp carcasses were significantly higher than those of BSFL reared on wheat bran. Increasing the shrimp carcass amount in the feeding media resulted in significant increases in BSFL docosahexaenoic acid (with the highest value occurring for BSFL reared on whole shrimp carcasses; 1.46 ± 0.09 %; p < 0.001). Conversely, BSFL docosahexaenoic acid was not detected for BSFL reared on wheat bran. The detected heavy metal concentrations in BSFL were below the limits of the published international guidelines for animal feed. In the obtained BSFL, Salmonella was not detected, and the mould count was <10 CFU/g. The total bacterial count (Lg transformation) of obtained BSFL ranged from 7.88 to 8.07 CFU/g, and no significant differences among all treatments (p = 0.424). Overall, this study demonstrates that BSFL-based bioconversion presents a resource recovery technology for converting shrimp carcasses into high-value nutritional biomass.