A full recycling chain of food waste with straw addition mediated by black soldier fly larvae: Focus on fresh frass quality, secondary composting, and its fertilizing effect on maize

Artificial light source combined with functional microorganism improves reproductive performance of black soldier fly

Black soldier fly (BSF, Hermetia illucens) has been recognized as a promising insect species for sustainable conversion of organic waste into valuable biomass. Many studies have focused on the use of BSF larvae to improve the recycling of organic waste. However, few studies have been conducted on the reproductive efficiency of BSF adults. In particular, the major problems with artificial systems are directed oviposition and the poor oviposition rate due to inadequate sunlight. This study aimed to address the bottleneck by developing an effective artificial source and finding effective attractants. Results showed that our homemade artificial light significantly enhanced the number of BSF eggs and elevated the egg hatching rate compared to commercial artificial light. Simultaneously, the isolated strain of Trichosporon asahii BSFL-2 can induce gravid BSF females to oviposit and the combination of homemade artificial light with BSFL-2 resulted in a notable increase in the number of eggs collected in the BSF adults rearing system. Analysis of the gas chromatography-mass spectrometry results and experimental validation showed that 2,5-dimethylpyrazine produced by BSFL-2 strain was able to attract gravid females to aggregate and oviposit. This study demonstrates that the use of effective artificial light source and attractant is a crucial element in addressing the bottleneck of efficient indoor reproduction of BSF.

Gut microbial communities and transcriptional profiles of black soldier fly (Hermitia illucens) larvae fed on fermented sericulture waste

Sericulture waste poses significant challenges to industrial and environmental safety. Black soldier fly larvae (BSFL) offer a promising solution for organic waste management by converting it into insect protein. This study aimed to develop a microbial fermented method for utilizing sericulture waste to feed BSFL and explore the underlying mechanisms. Our results showed that all fermented sericulture waste groups had positive effects on body weight, survival rate, substrate consumption rate, and substrate conversion rate. Metagenomic analysis revealed a notable increase in the abundances of commensal genera, including Sedimentibacter, Clostridium, Enterococcus, Bacteroides, and Bacillus, in the gut of BSFL fed on sericulture waste fermented with the most effective combination of microbial strains (B. subtilis, B. licheniformis, and E. faecalis). In contrast, BSFL reared on unfermented sericulture waste exhibited higher abundances of potentially pathogenic and harmful genera, including Providencia, Klebsiella, Escherichia, Brucella, and Enterobacter. Clusters of orthologous genes (COG) analysis indicated that altered microbial communities in the fermented group mainly participated in metabolic pathways, defense mechanism, and signal transduction mechanism. Transcriptome analysis further revealed that the upregulated genes were functionally associated with key metabolic pathways and immune mechanisms in the fermented group. These findings underscore the pivotal role of selected microbial fermentation in utilizing sericulture waste as BSFL feed, providing a sustainable solution for organic waste management.

Characteristics and biological mechanism of protein degradation by the black solider fly (Hermetia illucens L.) larvae gut strain Bacillus subtilis S4

The black solider fly larvae (BSFL) can efficiently convert nitrogen in organic waste into insect protein. Bacillus subtilis S4, an efficient protein-degrading bacterium from the BSFL gut, was isolated and identified to explore the mechanism of nutrient metabolism underlying BSFL nitrogen utilization. Results showed that B. subtilis S4 could effectively increase larval biomass in a bean stem bioconversion system. In vitro high-performance liquid chromatography analysis showed that B. subtilis S4 completely degraded casein into Val, Ile, Phe, Leu, Tyr, Lys, Gly, and Met. Various protease genes with secretion expression ability were annotated in B. subtilis S4. They included peptidoglycan DL - endopeptidase, aminopeptidase, extracellular metalloprotease, peptidoglycan endopeptidase, and peptidase M15. Therefore, the BSFL intestinal microbe B. subtilis S4 could effectively degrade protein and promote larval biomass accumulation, which could provide novel insights into the combined conversion of organic waste into proteins by microbes and insects.

Insect frass from upcycling vegetable by-products with cereals: Effects on the soil properties, plant development and soil invertebrate fitness

The use of insects in organic management systems is expanding due to their ability to recycle waste into valuable co-products for agriculture, notably frass, constituted by the insect's excrements, larval exuviae, and remaining undigested feedstock. This study aimed to assess the effects of different application rates of frass (0.16, 0.32, 0.64, 1.28, 2.56 and 5.12%) produced by black soldier fly Hermetia illucens larvae (BSFL) on the survival and reproduction of two non-target invertebrate species, the enchytraeid Enchytraeus crypticus and the collembolan Folsomia candida, and early development of three representative species of crops as onion Allium cepa, turnip Brassica rapa and tomato Solanum lycopersicum. Chemical analyses were conducted to evaluate changes in the soil properties. Results showed that BSFL frass did not impact the invertebrates' survival while significantly enhancing the production of E. crypticus juveniles (after 21 days). F. candida juveniles remained similar (after 28 days). Seed germination decreased at the highest frass rate (5.12%), while the development was promoted at intermediate rates (0.64%-1.28%). The different outcomes may be linked to changes in certain soil parameters, such as the soil pH and electrical conductivity, the soil organic matter, and the availability of nutrients. In summary, frass posed no risk to the tested invertebrate species but may hinder seed germination at high rates, representing a risk for agricultural production. Nevertheless, intermediate rates of BSFL frass promoted plant development, showing potential as a sustainable alternative to conventional fertilizers. Further research is needed to ensure its safe and efficient application in agriculture.

Unraveling the role of black soldier fly larvae in chicken manure conversion: Facilitating maturation and enhancing humification

Black soldier fly larvae (BSFL) have garnered considerable attention for their efficacy in mitigating waste management challenges. However, their potential in treating antibiotics contaminated chicken manure remains uncertain. This study investigates the physicochemical properties changes and nutrient dynamics during the composting of contaminated-chicken manure using BSFL. The results indicate that BSFL treatment reduces electrical conductivity (by 6.01-58.09 %), organic matter, and dissolved organic carbon content in chicken manure throughout the composting process, while maintaining a more stable pH value (pH ∼ 6.0-8.0). This is attributed to the consumption of organic matter by BSFL and the subsequent promotion of organic acid formation. Additionally, BSFL treatment improves the degree of aromatization of dissolved organic matter (DOM) in chicken manure and increases the proportions of fulvic acid (up to 48.77 %) and humic acid (maximally 14.27 %) within the DOM. The germination index and pot experiments indicated improved compost maturity and plant growth in BSFL-treated composts. Furthermore, BSFL meal demonstrated high protein and essential fatty acid content, highlighting its potential as a protein supplement in animal feed. This study underscores the efficacy of BSFL in enhancing compost quality and nutrient availability, offering a sustainable solution for waste management and animal feed production.

Effects of black soldier fly larvae on biotransformation and residues of spent mushroom substrate and wet distiller's grains

Black soldier fly larvae (BSFL) could convert a variety of organic wastes, including spent mushroom substrate (SMS) and wet distiller's grains (WDG). Nevertheless, little is known about the conversion of these wastes by BSFL. Thus, this study investigates the conversion of SMS and WDG in five different proportions by BSFL. This study demonstrates that BSFL can convert SMS, WDG, and their mixtures. It can also encourage the humification of the substrate, increasing the amount of element in the residues. It is evident that there were differences in the carbon and nitrogen element fractionation mode as well as the microbial community present in the residue. The microbial community of the substrate and the physiochemical parameters are intimately related to this. Although the mixture treated with BSFL helps to generate a residue with more humus, it might not be stable.

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.

Recirculating frass from food waste bioconversion using black soldier fly larvae: Impacts on process efficiency and product quality

Biowaste generation is increasing worldwide and inadequate disposal has strong negative impacts on food systems and ecosystems. Biodigestion of biowaste using black soldier fly (Hermetia illucens) larvae (BSFL) generates valuable by-products such as animal feed (larval biomass) and organic fertiliser (frass). However, the latter is typically unstable immediately after waste conversion and is thus unsafe for use as a fertilizer in terms of maturity. This study evaluated recirculation of frass within bioconversion of post-consumer food waste (FW) as a dietary component for BSFL to improve the quality of the subsequent frass obtained. Frass was introduced at increasing inclusion levels replacing food waste (2.5-100% on wet-weight basis) as part of the larvae's feeding substrate. Bioconversion efficiency and material reduction were significantly reduced by frass inclusion, while larval yield per experimental unit remained unchanged. When considering only the waste component in the larval diet, larval yield (dry-weight basis) ranged between 207 (0% frass inclusion) and 403 (40% frass inclusion) kg tonne FW-1, thus increasing by up to 94% at higher frass inclusion. With increasing dietary inclusion rate of frass from 0% to 100%, crude protein content of larval biomass increased by 41%, while fat content was reduced by 32%. The recirculated frass (obtained after including frass in the larval diet) had elevated concentrations of P, K, S, Na and B and around 6% lower organic matter content, demonstrating a higher degree of decomposition. Frass inclusion in the larval diet generated recirculated frass that were more stable and mature, as indicated by self-heating capacity, CO2 and NH3 volatilisation, seed germination bioassays and other parameters. It was concluded that frass recirculation improves waste bioconversion efficiency in relation to food waste unit, as well as larval biomass and frass quality, ensuring safer use as a fertilizer.

Protaetia brevitarsis larvae produce frass that can be used as an additive to immobilize Cd and improve fertility in alkaline soils

Bioconversion of agricultural waste by Protaetia brevitarsis larvae (PBL) holds significant promise for producing high-quality frass organic amendments. However, the effects and mechanisms of PBL frass on Cd immobilization in an alkaline environment remain poorly understood. In this study, three types of frass, namely maize straw frass (MF), rice straw frass (RF), and sawdust frass (SF), were produced by feeding PBL. The Cd immobilization efficiencies of three frass in alkaline solutions and soils were investigated through batch sorption and incubation experiments, and spectroscopic techniques were employed to elucidate the sorption mechanisms of Cd onto different frass at the molecular level. The results showed that MF proved to be an efficient sorbent for Cd in alkaline solutions (176.67-227.27 mg g-1). X-ray absorption near-edge structure (XANES) spectroscopy indicated that Cd immobilization in frass is primarily attributed to the association with organic matter (OM-Cd, 78-90%). And MF had more oxygen-containing functional groups than the other frass. In weakly alkaline soils, MF application (0.5-1.5%) significantly decreased Cd bioavailability (5.65-18.48%) and concurrently improved soil nutrients (2.21-56.79%). Redundancy analysis (RDA) unveiled that pH, CEC, and available P were important factors controlling Cd fractions. Path analysis demonstrated that MF application affected Cd bioavailability directly and indirectly by influencing soil chemical properties and nutrients. In summary, MF, the product of PBL-mediated conversion maize straw, demonstrated promise as an effective organic amendment for Cd immobilization and fertility improvement in alkaline soils.

Microbial fermentation and black soldier fly feeding to enhance maize straw degradation

This study used an innovative synergistic microbial and insect approach to treat maize straw and kitchen waste substrates, including cyclic microbial fermentation and feeding of black soldier fly larvae (BSFL) using the fermented substrate. Increasing cycle numbers led to significantly increased cellulose, hemicellulose, and lignin degradation rates (DR) in the maize straw, which increased by 68.28%, 81.43% and 99.95%, respectively, compared to those in the blank group without frass addition. Moreover, according to the experimental results, it was revealed that the structure of lignocellulose, the composition and structure of the bacterial community in the BSFL gut and frass changed significantly after the addition of the previous cycle of frass treatment. Moreover, the differences in amplicon sequence variants (ASVs) between the gut and frass further increased. The relative abundances of Enterococcus and Actinobacteria in the gut and Gammaproteobacteria_unclassified and Dysgonomonas in the frass increased significantly, which may play a more positive role in lignocellulose degradation. In conclusion, this study showed that frass fermentation + BSFL feeding to degrade straw is a promising method and that frass fermentation is beneficial for the whole cycle. Furthermore, these findings underscore the beneficial impact of frass fermentation on the entire cycle.