Efficient co-conversion process of chicken manure into protein feed and organic fertilizer by Hermetia illucens L. (Diptera: Stratiomyidae) larvae and functional bacteria

Process efficiency and ventilation requirement in black soldier fly larvae composting of substrates with high water content

In order to transition from a linear to a circular economy in the organic waste management sector, more of the elements in waste need to be recycled. Use of black soldier fly (Hermetia illucens L.; Diptera: Stratiomyidae) larvae (BSFL) for organic waste treatment has potential to harvest more complex molecules than conventional methods. Many organic waste substrates have high water content (>80%), but the impact on BSFL treatment efficiency of substrate water contents >80% is not known. This study evaluated the impact of high water content food waste on BSFL composting efficiency in terms of waste-to-biomass conversion ratio, material reduction, larval survival and the ventilation required for enabling dry separation of larvae from residue. In total, six water contents ranging from 76% to 97.5% were evaluated in two experimental trials. It was found that increasing water content reduced biomass conversion ratio and survival rate of the larvae, from 33.4% of volatile solids (VS) and 97.2% survival in 76% water to 17.5% of VS and 19.3% survival in 97.5% water. Furthermore, we found that the ventilation requirement for achieving dry separation of larvae from residue could be modelled by estimating the amount of water that would need to be removed, taking into account the water bound in the larvae, and knowing the specifics of the ventilation set-up of the modelled system. The findings could have implications on the waste management sector interested in implementing BSFL treatment, as the findings demonstrate that it is possible to treat wet substrates (such as fruit and vegetable wastes) without any pre-treatment other than grinding and attain an adequately dry residue for enabling dry separation of the larvae from the residue.

Insects for peace

Insects such as the black soldier fly (BSF) are a nutritious feed component for livestock with high protein levels. BSF can be reared on a wide range of organic residual streams. This allows for local production within a circular agriculture, decoupling livestock production from import of expensive feed components, such as fishmeal or soymeal. Rearing of BSF can be done by smallholder farmers, thus contributing to their livelihood, economic sustainability and social status. Smallholder farmers contribute importantly to food security, which is a prerequisite for a stable society. In armed conflicts, smallholder farmers are usually the first to suffer. In countries recovering from conflict, agricultural development should focus on restoring food production by smallholder farmers, improving their socio-economic position, thereby contributing to sustainable development goals 2 (zero hunger) and 16 (peace and justice). Here, we focus on these SDGs with an example of reintegration of ex-combatants as smallholder insect producers in post-conflict Colombia.

The gut and feed residue microbiota changing during the rearing of Hermetia illucens larvae

Larvae of Hermetia illucens, commonly known as black soldier fly, efficiently convert organic waste into nutrient-rich supplements for different applications. Here we performed a preliminary experiment to investigate the dynamics of the H. illucens gut microbiota and changes in the composition of the bacterial community in the residue of the larval feed during rearing. We furthermore quantified the presence of antibiotic resistance and disinfectant genes in the gut and feed microbiota during the rearing process to elucidate if rearing leads to a reduction, increase, and/or transfer of resistance genes from the feed to larvae and vice versa. We found that the gut and feed residue bacterial communities were distinct throughout the rearing process. The gut microbiome remained more stable compared to the feed residue microbiome varying in both bacterial abundance and community structure during rearing. Antibiotic-resistance genes were present in both, gut and feed residues, with a significant increase in pupae and residue samples taken at the end of the rearing process. Disinfectant-resistance genes were present in the feed residue and even increased during the rearing process but were not transferred to the gut microbiome. We conclude that H. illucens larvae have a stable gut microbiome that does not change significantly over the course of larval development, whereas bacterial communities in the feed residue are strongly affected by rearing. If the presence of antibiotics and disinfectants during rearing, can promote the spread of antibiotic/disinfectant-resistance genes among feed and larvae needs to be evaluated in further experiments.

Modeling the Growth of Black Soldier Fly Hermetia illucens (Diptera: Stratiomyidae): An Approach to Evaluate Diet Quality

The black soldier fly (BSF, Hermetia illucens (Linnaeus), Diptera: Stratiomyidae) is an edible insect widely reared by using various types of organic wastes as its diet. Developing tools to evaluate the growth performance of BSF is crucial for improving its production. In this study, we monitored the daily growth of BSF larvae reared with 10 diets with diverse nutritional quality and compared 7 growth models for quantifying growth performance. We found that BSF generally exhibited an S-shaped growth curve and that the Richards model was the best-fitting growth model. We estimated asymptotic growth limit (W∞) and constructed a time-series curve of absolute growth rate (AGR) by using the Richards model. We used Gaussian functions to estimate AGR parameters (maximum AGR, m; timing of maximum AGR, T; the deviation of AGR, d) to evaluate whether these parameters adequately quantify the growth performance of BSF. Correlation analysis showed that the AGR parameters were mostly independent of W∞ but were correlated with the duration of the larval stage, indicating that W∞ and the AGR parameters respond to different dietary factors. The results of pairwise comparisons showed that the diets rich in carbohydrates and protein had high W∞, m, and d, and early T. The diets with low levels of carbohydrates had low W∞, and the diets with low levels of protein had low m and d and delayed T. We conclude that the parameters estimated by the Richards model could be effective indices for evaluating the growth performance of BSF and their diet quality.

Management of chicken manure using black soldier fly (Diptera: Stratiomyidae) larvae assisted by companion bacteria

Black soldier fly (BSF) is used for the management of organic waste, but research has hardly explored the effect of companion bacteria when chicken manure (CHM) is converted to insect biomass. In this study, we isolated nine bacterial species (FE01, FE02, FE03, FE04, FE05, FE06, FE07, FE08, FE09) from BSF eggs and one (BSF-CL) from the larval gut. These companion bacteria were inoculated into CHM along with BSF larvae (BSFL). Larval growth and manure conversion rates were determined. Results indicated that almost all bacteria individual bacteria in this study significantly promote BSFL growth. BSFL reared in manure with the species Kocuria marina (FE01), Lysinibacillus boronitolerans (FE04), Proteus mirabilis (FE08) and Bacillus subtilis (BSF-CL) had higher weight gain and manure reduction rates compared to the control. These four strains used were then examined as a poly-bacteria community experiment to determine BSFL growth and manure conversion. Manure inoculated with the poly-bacteria Group3 (FE01:FE04:FE08:BSF-CL = 4:1:1:1) and then fed to BSFL resulted in 28.6% more weight gain than the control. The greatest manure reduction rate (52.91%) was reached when companion bacteria were mixed at a ratio of 1:1:1:4. Additionally, the companion bacteria influenced the nutritional value of BSFL. Crude protein content in Group1 (FE01:FE04:FE08:BSF-CL = 1:1:1:1) was significantly larger than that of the control. Crude fat content in Group3 was significantly larger than that of the control. BSFL companion bacteria and their poly-bacteria compound improved manure conversion efficiency and nutrient accumulation in BSFL, reduced CHM quantity, increased larvae biomass, with potential economic gains in CHM management.

Performance of black soldier fly larvae (Diptera: Stratiomyidae) for manure composting and production of cleaner compost

The increasing number of livestock farms has led to a great deal of manure generation, and its improper treatment results in threats to the environment. Black soldier fly larvae (BSFL) have the potential to effectively convert manure into high-quality fertilizer. The aims of this investigation were to observe the organic matter transformation of different livestock manures and volatile fatty acids (VFAs), and to evaluate the end product quality. Three types of manure [chicken (T1), pig (T2), and cow (T3)] were inoculated with BSFL (1.2:7 ratio on fresh weight basis), three types without BSFL were used as control (T4, T5, and T6), and both were composted for 9 days. The results showed that the BSFL composting reduced the organic matter by 20.31-22.18% and the accumulation of VFAs by 25.58-80.08% as compared to the control. BSFL composting greatly decreased the nitrogen, by 6.08-14.37%. The employment of BSFL significantly increased the total phosphorous (TP), total Kjeldahl nitrogen (TKN), and total nutrients by 42.30-64.16%, 45.41-88.17%, and 26.51-33.34%, respectively. This study showed that employing BSFL could improve the quality of the product and the maturity degree of the composting. Therefore, the BSFL could be added as a high-efficiency transformation agent for converting organic manure into stable compost, especially in developing countries, where adopting technical devices for composting is expensive and difficult to manipulate.

Managing high fiber food waste for the cultivation of black soldier fly larvae

Increases in global human population are leading to increasing demands for food production and waste management. Insect biomass is a sustainable alternative to traditional animal feeds when insects are produced on lignocellulosic by-products. Resources high in lignocellulose have high carbon to nitrogen ratios and require nitrogen supplementation to accelerate bioconversion. Here we report on studies that examine the influence of nitrogen supplementation of almond hull-based feedstocks on black soldier fly larvae (Hermetia illucens L.) cultivation and composition. Decreasing carbon to nitrogen ratio from 49 to 16 increased larvae harvest dry weight, specific larvae growth, and yield by 36%, 31%, and 51%, respectively. However, the decrease in carbon to nitrogen ratio decreased larvae methionine and cysteine contents by 11% and 13%, respectively. The findings demonstrate that carbon to nitrogen ratio can be managed to enhance bioconversion of lignocellulose to larvae, but that this management approach can reduce larvae amino acid content.

Greenhouse gas emissions from small-scale fly larvae composting with Hermetia illucens

Fly larvae composting is an emerging waste treatment alternative with great potential to increase revenue from food waste management. For wider implementation, fly larvae composting has to be evaluated in comparison with conventional systems, based on direct greenhouse gas (GHG) emission data for the treatment process, which are currently limited. This study evaluated direct emissions of CO₂, CH₄, N₂O and NH₃ from composting of food waste using black soldier fly (BSF) larvae (Hermetia illucens). Use of BSF larvae-associated bacteria in 7-day pre-treatment and seeding at larvae treatment start were evaluated and compared to larvae treatment without bacteria addition. The treatments were performed in a set of 14-day laboratory-scale experiments. Mean substrate reduction was 49 ± 8% and bioconversion ratio was 24 ± 8% (both dry matter basis). Direct GHG emissions from the fly larvae treatment process were generally very small, with emissions of CH₄ and N₂O equivalent to 0.38 kg CO₂-equivalents per ton food waste treated assuming global warming potential over 100 years, while mean total CO₂ emissions were 96 g CO₂ per kg food waste treated. Additional emissions could be expected to occur in the pre-treatment process, which did not provide any significant improvement in bioconversion ratio or reduction in total GHG emissions during treatment. Similarly, use of BSF larvae-associated bacteria did not significantly improve process efficiency. No NH₃ emissions were detected, as reflected in total N mass balance over the treatment cycle. The results show that total direct GHG emissions from food waste treatment by fly larvae composting are lower than those from conventional food waste treatment, and that pre-treatment and seeding of food waste with BSF larvae-associated bacteria do not further reduce total GHG emissions.

Insects for Food and Feed-Safety Aspects Related to Mycotoxins and Metals

Edible insects as an alternative source of protein are discussed as an important contribution to future feed and food security. However, it has to be ensured that the consumption is non-hazardous. This systematic review summarizes findings concerning contaminations of insects with mycotoxins and heavy metal ions (SciFinder, Pubmed, until 26 June 2019). Both kinds of contaminants were reported to reduce growth performance and increase mortality in insects. There was no evidence for accumulation of various mycotoxins analyzed in distinct insect species. However, further research is necessary due to limitation of data. Since the gut content contributes relevantly to the total body burden of contaminants in insects, a starving period before harvesting is recommended. Contrary, accumulation of heavy metal ions occurred to a varying extent dependent on metal type, insect species, and developmental stage. Examples are the accumulation of cadmium (black soldier fly) and arsenic (yellow mealworm). The reported species-specific accumulation and metabolism patterns of contaminants emphasize the importance to assess potential safety hazards in a case-by-case approach. Subject to regular monitoring of contaminants, the general ban in the European Union to use waste in animal feed should also be questioned regarding insect farming.

Enhanced bioconversion of dairy and chicken manure by the interaction of exogenous bacteria and black soldier fly larvae

Generation of insects' biomass from lignocellulose rich organic wastes is of significant challenges in reducing the environmental impact of wastes and in sustaining feed and food security. This research looked at the effects of lignocellulotic exogenous bacteria in the black soldier fly (BSF) organic waste conversion system for biomass production and lignocellulose biodegradation of dairy and chicken manures. Six exogenous bacteria were investigated for cellulolytic activity with carboxymethyl cellulose and found that these tested bacterial strains degrade the cellulose. In this study; a co-conversion process using Hermetia illucens larvae to convert the previously studied best mixing ratio of dairy manure (DM) and chicken manure (CHM) (2:3) and cellulose degrading bacteria was established to enhance the larval biomass production, waste reduction and manure nutrient degradation. BSF larvae assisted by MRO₂ (R₅) has the best outcome measures: survival rate (99.1%), development time (19.0 d), manure reduction rate (48.7%), bioconversion rate (10.8%), food conversion ratio (4.5), efficiency of conversion of ingestion (22.3), cellulose (72.9%), hemicellulose (68.5%), lignin (32.8%), and nutrient utilization (protein, 71.2% and fat, 67.8%). By analyzing the fiber structural changes by scanning electron microscopy and Fourier-transformed infrared spectroscopy (FT-IR), we assume that exogenous bacteria assist the BSF larvae that trigger lead to structural and chemical modification of fibers. We hypothesized that these surface and textural changes are beneficial to the associated gut bacteria, thereby helping to larval growth and reduce waste. The finding of the investigation showed that enhanced conversion of DM and CHM by BSF larvae assisted with lignocellulotic exogenous bacteria could play key role in the manure management.

Assessing the Microbiota of Black Soldier Fly Larvae (Hermetia illucens) Reared on Organic Waste Streams on Four Different Locations at Laboratory and Large Scale

This study aimed to gain insight into the microbial quality, safety and bacterial community composition of black soldier fly larvae (Hermetia illucens) reared at different facilities on a variety of organic waste streams. For seven rearing cycles, both on laboratory-scale and in large-scale facilities at several locations, the microbiota of the larvae was studied. Also samples of the substrate used and the residue (= leftover substrate after rearing, existing of non-consumed substrate, exuviae and faeces) were investigated. Depending on the sample, it was subjected to plate counting, Illumina Miseq sequencing and/or detection of specific food pathogens. The results revealed that the substrates applied at the various locations differed substantially in microbial numbers as well as in the bacterial community composition. Furthermore, little similarity was observed between the microbiota of the substrate and that of the larvae reared on that substrate. Despite substantial differences between the microbiota of larvae reared at several locations, 48 species-level operational taxonomic units (OTUs) were shared by all larvae, among which most belonged to the phyla Firmicutes and Proteobacteria. Although the substrate is assumed to be an important source of bacteria, our results suggest that a variety of supposedly interacting factors-both abiotic and biotic-are likely to affect the microbiota in the larvae. In some larvae and/or residue samples, potential foodborne pathogens such as Salmonella and Bacillus cereus were detected, emphasising that decontamination technologies are required when the larvae are used in feed, just as for other feed ingredients, or eventually in food.

Influence of Lactobacillus buchneri on soybean curd residue co-conversion by black soldier fly larvae (Hermetia illucens) for food and feedstock production

Black soldier fly larvae (BSFL), Hermetia illucens (Diptera: Stratiomyidae) can reduce environmental pollution and convert organic wastes into biomass that is rich in protein and fat. The influence of the nutritional characteristics of organic waste on BSFL characteristics relevant for food and feed safety remains poorly understood. To evaluate the conversion of soybean curd residues (SCR) into high-quality animal-derived proteins and fats for human and livestock consumption, this study assessed the co-conversion efficacy, nutrient composition, safety, and anti-nutritional factor concentrations in BSFL after the development on SCR with Lactobacillus buchneri (L3-9). SCR was pretreated with L. buchneri (108 cfu/ml), and then BSFL was employed for conversion. BSFL fed with SCR and L. buchneri had a significantly higher dry mass reduction (55.7 ± 0.9%), bioconversion rate (6.9 ± 0.3%), crude protein content (55.3 ± 0.6%), and fat content (30.0 ± 0.6%) than SCR (49.0 ± 0.7%, 5.0 ± 0.3%, 52.8 ± 0.3%, and 26.1 ± 0.8%, respectively) and artificial feed (43.9 ± 0.8%, 3.9 ± 0.1%, 50.3 ± 0.4%, and 24.3 ± 0.4%, respectively). However, the feed conversion ratio (8.0 ± 0.3), of BSFL fed with SCR and L. buchneri was lower than that of the BSFL fed with SCR (9.8 ± 0.1) and artificial feed (11.1 ± 0.5). In addition, BSFL had satisfactory concentrations of all essential amino acids and fatty acids required for human consumption as recommended by WHO/FAO/UNU. The heavy metals and anti-nutritional factor concentrations were within the safety intake levels for food and feedstock. Therefore, the addition of L. buchneri with BSFL on SCR did not only increase co-conversion performance but also enhanced the nutritional value of BSFL.

Insect protein in animal nutrition

Global meat consumption per capita is expected to increase ~40% from 2019 to 2050. Over 30% of the total cropland worldwide is currently being used to produce either livestock and poultry feed or silage to meet the demand. One solution to reduce cropland use for animal feed is to increase the production of alternative protein sources. The primary protein sources for animal nutrition, including soybeans, peas and fish meal, are of increasing demand and are subsequently becoming more expensive, making their long-term use unsustainable. Insects such as the black soldier fly larvae (Hermetia illucens), crickets (Gryllus testaceus Walker) or mealworms (Tenebrio molitor) offer a viable addition to the feed sources and can provide valuable, high-quality energy, protein and fat to an animal’s diet. Here, we review the environmental benefits of insect feedstuff, current research findings related to the use of insects for animal nutrition, and outline additional products that can generate benefits to insect producers.

Decomposition of biowaste macronutrients, microbes, and chemicals in black soldier fly larval treatment: A review

Processing of biowaste with larvae of the black soldier fly, Hermetia illucens L. (Diptera: Stratiomyidae), is an emerging waste treatment technology. Larvae grown on biowaste can be a relevant raw material for animal feed production and can therefore provide revenues for financially viable waste management systems. In addition, when produced on biowaste, insect-based feeds can be more sustainable than conventional feeds. Among others, the scalability of the technology will depend on the availability of large amounts of biowaste with a high process performance (e.g. bioconversion of organic matter to proteins and lipids) and microbial and chemical product safety. Currently, in contrast to other waste treatment technologies, such as composting or anaerobic digestion, the process performance is variable and the processes driving the decomposition of biowaste macronutrients, inactivation of microbes and fate of chemicals is poorly understood. This review presents the first summary of the most important processes involved in black soldier fly larvae (BSFL) treatment, based on the available knowledge concerning five well-studied fly species. This is a starting point to increase understanding regarding the processes of this technology, with the potential to increase its efficiency and uptake, and support the development of appropriate regulations. Based on this review, formulating different types of biowaste, e.g. to produce a diet with a similar protein content, a balanced amino acid profile and/or pre- and co-treatment of biowaste with beneficial microbes, has the potential to increase process performance. Following harvest, larvae require heat or other treatments for microbial inactivation and safety.

Effects of waste stream combinations from brewing industry on performance of Black Soldier Fly, Hermetia illucens (Diptera: Stratiomyidae)

BACKGROUND

In recent years, there has been a rapidly growing demand for readily accessible substrates for mass production of Black Soldier Fly, Hermetia illucens Linnaeus. Beer production results in various by-products that typically end up in uncontrolled dumpsites constituting pollution problems, which merits urgent attention. The present study investigated whether the 12 formulated diets composed of brewers' spent grains (BSGs), brewers' yeast and cane molasses can serve as substrate for H. illucens production.

METHODS

Four different BSGs were selected and formulated into 12 diets, aiming at varying protein and net energy levels. The diets were offered to newly hatched (∼1 h old) H. illucens larvae and the influence on developmental duration, survival, wet weight, pre-oviposition time, fecundity, and longevity were compared.

RESULTS

Developmental duration of the larvae (16-21 days) and pre-pupae (8-11 days) differed significantly across the different diets. The developmental duration of the pupae (8.7-9.1 days) was not affected by diet. The larval (86-99.2%), pre-pupal (71-95%), and pupal (65-91%) survival rates varied significantly between flies reared on the different diets. The pre-oviposition time was similar for flies provided with water (7-11 days) and 10% sugar solution (8-14 days) or across the different diets. The mean fecundity per female ranged from 324-787 eggs and did not differ between females provided with water or sugar solution. However, the number of eggs laid per female varied significantly across the different diets when provided with water. The longevity of starved H. illucens adults was significantly lower (5 days) compared to those provided with water (11-14 days) or sugar solution (14-15 days).

DISCUSSION

The implications of these findings as part of a quality control procedure for commercial production of high-quality H. illucens larvae as an alternative protein ingredient in livestock and aquaculture feed are discussed.