Department Sanitation, Water and Solid Waste for Development

Biowaste treatment with black soldier fly larvae (BSFL, Hermetia illucens L.) can promote a more sustainable food system by reusing nutrients that would otherwise be wasted. However, many agri-food wastes and byproducts are typically high in lignocellulosic fibers (i.e., cellulose, hemicellulose, and lignin), making it resistant to efficient larval and/or microbial degradation. Ammonia pretreatment could be used to partially degrade lignocellulose, making the biowaste more easily degradable by the larvae and/or microorganisms. This study evaluated ammonia pretreatment for lignocellulose degradation and its effect on BSFL performance on four fibrous biowastes: brewers spent grain, cow manure, oat pulp, and grass clippings. First, the optimal ammonia dose (1 % or 5 % dry mass) and pretreatment time (three or seven days) were assessed by measuring fibers after treatment and further examined using Fourier transform infrared spectroscopy (FTIR) spectra and scanning electron microscopy (SEM) images. Second, BSFL rearing performance on ammonia-pretreated substrates was assessed with a 9-day feeding experiment. Three-day pretreatment with 5 % ammonia was chosen as it decreased the total fiber content by 8–23 % for all substrates except cow manure. Contrary to expectations, ammonia pretreatment with all substates decreased BSFL rearing performance metrics by more than half compared to the untreated control. Follow-up experiments suggested that ammonia pretreatment had a dose-dependent toxicity to BSFL. Interestingly, three-day fermentation of cow manure and oat pulp increased bioconversion rate by 25–31 %. This study shows that ammonia pretreatment is not suitable before BSFL rearing. Ammonia toxicity to BSFL and other pretreatments, such as fermentation, should be further studied.

A key challenge for black soldier fly larvae (BSFL) treatment is its variable reliability and efficiency when applied to different biowastes. Similar to other biowaste treatment technologies, co-conversion could compensate for variability in the composition of biowastes. Using detailed nutrient analyses, this study assessed whether mixing biowastes to similar protein and non-fibre carbohydrate (NFC) contents increased the performance and reduced the variability of BSFL treatment in comparison to the treatment of individual wastes. The biowastes examined were mill by-products, human faeces, poultry slaughterhouse waste, cow manure, and canteen waste. Biowaste formulations had a protein-to-NFC ratio of 1:1, a protein content of 14–19%, and a NFC content of 13–15% (dry mass). Performance parameters that were assessed included survival and bioconversion rate, waste reduction, and waste conversion and protein conversion efficiency. In comparison to poultry feed (benchmark), vegetable canteen waste showed the best performance and cow manure performed worst. Formulations showed significantly improved performance and lower variability in comparison to the individual wastes. However, variability in performance was higher than expected for the formulations. One reason for this variability could be different fibre and lipid contents, which correlated with the performance results of the formulations. Overall, this research provides baseline knowledge and guidance on how BSFL treatment facilities may systematically operate using biowastes of varying types and compositions.

As the world population increases, food demand and agricultural activity will also increase. However, ~30–40% of the food produced today is lost or wasted along the production chain. Increasing food demands would only intensify the existing challenges associated with agri-food waste management. An innovative approach to recover the resources lost along the production chain and convert them into value-added product(s) would be beneficial. An alternative solution is the use of the larvae of the black soldier fly (BSFL), Hermetia illucens L., which can grow and convert a wide range of organic waste materials into insect biomass with use as animal feed, fertilizer and/or bioenergy. However, the main concern when creating an economically viable business is the variability in BSFL bioconversion and processing due to the variability of the substrate. Many factors, such as the nutritional composition of the substrate heavily impact BSFL development. Another concern is that substrates with high lignin and cellulose contents have demonstrated poor digestibility by BSFL. Studies suggest that pretreatment methods may improve the digestibility and biodegradability of the substrate by BSFL. However, a systematic review of existing pretreatment methods that could be used for enhancing the bioconversion of these wastes by BSFL is lacking. This paper provides a state-of-the-art review on the potential pretreatment methods that may improve the digestibility of substrates by BSFL and consequently the production of BSFL. These processes include but are not limited to, physical (e.g., mechanical and thermal), chemical (alkaline treatments), and biological (bacterial and fungal) treatments.

Use of black soldier fly (Hermetia illucens (L.), Diptera: Stratiomyidae) larvae (BSFL) is among the solutions being explored to shift the value chain in organic waste management by producing valuable products. Although BSFL consume a range of substrates, nutrient-imbalanced materials with high hemicellulose and lignin content, e.g. manure and banana peel, yield low conversion into larval biomass. This study explored pre-treatment methods to improve the nutrient composition and digestibility of banana peel to achieve higher substrate conversion into BSFL biomass. The pre-treatment methods evaluated were microbial, chemical (non-protein nitrogen), heat-based, and combinations of these. All pre-treatments tested except heating resulted in more efficient BSFL conversion in terms of final larvae weight. The low BSFL responses in pre-treatments were caused by the observed high amounts of tannins and phenolic compounds mainly from the heating pre-treatment. Waste to biomass conversion ratio correlated negatively with substrate volatile solids (VS) and positively with the decrease in VS in pre-treatment. Microbial - 14 days pre-treatments provided the optimum pre-treatment time for the microorganisms to achieve maximum degradation of the substrates, facilitating larval assimilation of the released nutrients. Rhizopus oligosporus-14 days and ammonia + Rhizopus resulted in the most efficient BSFL treatment, measured as protein produced per kg incoming material.

Global population growth has led to an urgent need for more efficient food production systems. Moreover, as income levels increase, dietary preferences are shifting to more animal-based products. However, current feed protein sources deplete wild fish populations and contribute to rainforest deforestation. Capturing the resources in organic waste could help alleviate environmental impacts of food production. The larvae of the black soldier fly (Hermetia illucens) are ferocious feeders on decomposing organic material and could be used as protein source in animal feed. This study evaluated development of black soldier fly larvae on eight urban organic waste fractions and two control substrates. Principal component analysis was conducted to identify substrate properties that contributed to treatment efficiency and larval development. The main treatment factors found to be affected by substrate were waste-to-biomass conversion ratio, larval development time and final prepupal weight. The substrate properties with the greatest impact on biomass conversion ratio and larval development time were content of total volatile solids and protein content, while only total volatile solids content affected final prepupal weight. It was concluded that black soldier fly larvae are versatile in their feedstock preferences and can be used to treat a variety of organic waste streams, provided that the total volatile solids and nitrogen content are sufficiently high to support larval development. Abattoir waste, food waste, human faeces and a mixture of abattoir waste e fruits & vegetables are waste streams that are highly suitable for fly larvae treatment.

Black soldier fly (BSF) larvae composting is a promising waste treatment that can add value to available biodegradable waste. However, substrates that have low protein content and contain complex molecules (e.g. fruit peels) are not easily degraded by the larvae. This study evaluated the impact on the BSF larvae composting efficiency of co-composting different mixtures of banana and orange peels with incremental increase of fish waste. Mixtures (in total 50 distinct mixtures) of varying proportions of banana peels, orange peels and fish waste were evaluated. BFSL fed on orange peel and banana peel mixtures, containing no fish waste, resulted in a lower biomass conversion efficiency (4.5% ± 1.3) on a volatile solids (VS) basis (BCE_vs). Co-composting the fruit peels with fish waste increased the biomass conversion efficiency and the highest BCE_vs (25%) was attained when 75% fish waste was included. However, the BCE_vs varied greatly (18.0% ± 5.8), likely due to varying fish waste composition. A 25% fish waste inclusion resulted in more than twice as high BCE_vs (12.3% ± 2.1) compared to when no fish waste was included. As the conversion efficiency variance increased with increasing fish waste inclusion, it was recommended to keep the inclusions of the fish waste to around 25% of the total mixture, in order to increase the reliability of the BSF larvae composting efficiency.

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.

Black soldier fly larvae (BSFL) waste processing has proven to be a promising approach, which can be applied in centralised or decentralised settings. Financial considerations however still remain undisclosed given business secrecy. Building on the experiences of a facility and operational setup in Indonesia, this study conducted an indepth cost analysis using methods such as time motion studies, activity based costing and a mass flow balance to evaluate business models. Thereafter followed an analysis of different scenarios on how to integrate the approach into the solid waste management system of Surabaya, Indonesia assuming different degrees of decentralisation with market rates and prices from 2020. Results show that a centralised plant, managing all steps of the BSFL process (Scenario 1), achieves the highest net present value (NPV), mainly through the economy of scale. When BSFL waste treatment is conducted using a decentralised approach, close to the waste sources, and the nursery and postprocessing of larvae remains at a central location (Scenario 3), other benefits besides the still positive NPV can be shown. Such a scenario for instance would reduce the spatial footprint of the central facility, create jobs within the communities and reduce the transport costs and total costs for the municipality. Another scenario (Scenario 2) hypothesises a decentralised waste treatment as well as post-processing of larvae at the same decentralised location increasing storability and the value of products. Although this achieves higher NPV values compared to Scenario 3, it requires larger scale units to achieve financial viability. Coordination and facilitation by local government can further strengthen a network of decentralised BSFL treatment plants, as the city authorities could focus on operating a centralised nursery (Scenario 2), supplying young larvae at low cost or free of charge to increase the financial viability of the decentralised plants treating the waste.

Cities of low and middle-income countries face severe challenges in managing the increasing amount of waste produced, especially the organic fraction. Black Soldier Fly (BSF) biowaste treatment is an attractive treatment option as it offers a solution for waste management while also providing a protein source to help alleviate the rising global demand for animal feed. However, to-date very little information is available on how this technology performs with regard to direct greenhouse gas (GHG) emissions and global warming potential (GWP).
This paper presents a study that uses a life cycle assessment (LCA) approach to assess the GWP of a BSF waste treatment facility in the case of Indonesia and compares it with respective values for an open windrow composting facility. Direct CH₄ and N₂O samples were extracted from BSF treatment units and analyzed by gas chromatography. Results show that direct CO₂eq emissions are 47 times lower the emissions from composting. Regarding the overall GWP, the LCA shows that composting has double the GWP of BSF treatment facility based on the functional unit of 1 ton of biowaste (wet weight). The main GWP contribution from a BSF facility are from: (1) residue post-composting (69%) and (2) electricity needs and source (up to 55%). Fishmeal production substitution by BSF larvae meal can reduce significantly the GWP (up to 30%). Based on this study, we conclude that BSF biowaste treatment offers an environmentally relevant alternative with very low direct GHG emissions and potentially high GWP reduction. Further research should improve residue post-treatment.

In developing countries, effective waste management strategies are constrained by high collection costs and lack of adequate treatment and disposal options. The organic fraction in particular, which accounts for more than 50% of the waste production, constitutes a great, yet mostly neglected, reuse potential. Concomitantly, the demand for alternative protein sources by the livestock feed industry is sharply increasing. A technology that effectively transforms organic waste into valuable feed is therefore a timely option. Larvae of the non-pest black soldier fly,Hermetia illucens L. (Diptera: Stratiomyidae), may be used to reduce the mass of organic waste significantly. Concurrently, larval feeding converts organic waste into prepupae (last larval stage) which is high in protein. In combination with a viable market, this potential animal feed may cover the waste collection costs and thus promote innovative, small-scale entrepreneurs to establish a profitable business niche. Organic waste, however, often contains persistent pollutants, such as heavy metals, that may accumulate in the larvae and prepupae of black soldier flies and consequently in the food chain. In this study, we fed black soldier fly larvae chicken feed spiked with heavy metals (cadmium, lead and zinc at three concentrations each) to examine the extent of metal accumulation in the different life stages and the effect of heavy metal concentration in the feed on the life cycle determinants of the flies. The cadmium accumulation factor in prepupae (metal concentration in the body divided by metal concentration in the food) ranged between 2.32 and 2.94; however, the lead concentration remained well below its initial concentration in the feed. The bioaccumulation factor of zinc in prepupae decreased with increasing zinc concentration in the feed (from 0.97 to 0.39). None of the three heavy metal elements had significant effects on the life cycle determinants (prepupal weight, development time, sex ratio).

The recycling of organic waste worldwide is not effective, which leads to water pollution and loss of potential crop fertilizers. Available resources have to be used more efficiently as the world population increases. An innovative solution is to use insects for the management of organic waste. Here, we used black soldier fly to convert organic waste into animal feed protein, as fly larvae, and plant fertilizer, as compost residue. A continuous fly reactor was monitored for 9 weeks. We analyzed physicochemical and microbial parameters, and we evaluated the sanitary risk. Results show 55.1 % of material degradation and 11.8 % of biomass conversion based upon total solids. We observed higher levels of N and P in the treatment residue than in the inflow material. Results also show a lower concentration of Salmonella spp. and viruses. Compost treatment with black soldier fly is therefore an efficient system for nutrient recycling.

Inadequate and lacking sanitation and wastewater treatment systems can lead to the spreading of diarrhoeal diseases. One contributing factor in the lack of such treatment systems is the lack of economic incentives for stakeholders throughout the service chain. However, the organic fraction of the waste is high in valuable plant nutrients and could be reused in agriculture and as animal feed. For example, grown larvae of the black soldier fly, Hermetia illucens L. (Diptera: Stratiomyidae), make an excellent protein source in animal feed, while the feeding activity of the larvae substantially reduces the dry mass of the treated material. This study examined the effect of black soldier fly larvae on the concentration of pathogenic microorganisms in human faeces and found a 6 log₁₀ reduction in Salmonella spp. in human faeces in eight days, compared with a < 2 log₁₀ reduction in the control. No increased reduction was observed for Enterococcus spp., bacteriophage ΦX174 or Ascaris suum ova.

Significant economic, environmental, and social impacts are associated with the avoidable disposal of foods worldwide. Mass-rearing of black soldier fly (Hermetia illucens) larvae using organic wastes and food- and agro-industry side products is promising for recycling resources within the food system. One current challenge of this approach is ensuring a reliable and high conversion performance of larvae with inherently variable substrates. Research has been devoted to increasing rearing performance by optimizing substrate nutrient contents and ratios, while the potential of the substrate and larval gut microbiota to increase rearing performance remains untapped. Since previous research has focused on gut microbiota, here, we describe bacterial dynamics in the residue (i.e., the mixture of frass and substrate) of black soldier fly larvae reared on two food wastes (i.e., canteen and household waste). To identify members of the substrate and residue microbiota, potentially associated with rearing performance, bacterial dynamics were also studied in the canteen waste without larvae, and after inactivation by irradiation of the initial microbiota in canteen waste. The food waste substrates had similar microbiota; both were dominated by common lactic acid bacteria. Inactivation of the canteen waste microbiota, which was dominated by Leuconostoc, Bacillus, and Staphylococcus, decreased the levels of all rearing performance indicators by 31–46% relative to canteen waste with the native microbiota. In both food waste substrates, larval rearing decreased the bacterial richness and changed the physicochemical residue properties and composition over the rearing period of 12 days, and typical members of the larval intestinal microbiota (i.e., Providencia, Dysgonomonas, Morganella, and Proteus) became more abundant, suggesting their transfer into the residue through excretions. Future studies should isolate members of these taxa and elucidate their true potential to influence black soldier fly mass-rearing performance.

Large-scale insect rearing for food and feed production can be improved by understanding diet digestion and host–microbe interactions. To examine these processes in black soldier fly (Hermetia illucens L.; Diptera: Stratiomyidae) larvae, two protocols were developed. Protocol 1 describes a method to produce viable, sterile black soldier fly larvae and a gentle method for diet sterilization. Sterile black soldier fly larvae can be used to study the diverse role of microbes in larval development. Nutrient requirements of sterile black soldier fly larvae are met only through diet. Viable sterile black soldier fly larvae were consistently generated using a four-step treatment with alternating immersions of eggs for 2 min each in ethanol (70%) and sodium hypochlorite (0.6%), over two cycles. A nonthermal method of diet sterilization, namely high-energy electron beam (HEEB) treatment, was introduced. Subsequently, growth of sterile black soldier fly larvae was observed on the HEEB-treated diets (40, 60, and 40% of replicates with poultry feed, liver pie, and an artificial diet, respectively) but not on autoclaved diets. In Protocol 2, we propose a novel method to collect frass from individual larvae. We then measured the metabolites in frass, using high-pressure liquid chromatography. Results on metabolites confirmed the influence of digestion. For instance, succinate increased from 1 to 2 and 7 μmol/g sample from diet to gut homogenate and frass, respectively. The collection method is a promising tool to estimate the diet and nutrient requirements of black soldier fly larvae, thus increasing the performance and reliability of black soldier fly larvae rearing. We discuss in detail the possible applications and limitations of our methods in black soldier fly larvae research.

Black soldier fly larvae treatment is an emerging technology for the conversion of biowaste into potentially more sustainable and marketable high-value products, according to circular economy principles. Unknown or variable performance for different biowastes is currently one challenge that prohibits the global technology up-scaling. This study describes simulated midgut digestion for black soldier fly larvae to estimate biowaste conversion performance. Before simulation, the unknown biowaste residence time in the three midgut regions was determined on three diets varying in protein and non-fiber carbohydrate content. For the static in vitro model, diet residence times of 15 min, 45 min, and 90 min were used for the anterior, middle, and posterior midgut region, respectively. The model was validated by comparing the ranking of diets based on in vitro digestion products to the ranking found in in vivo feeding experiments. Four artificial diets and five biowastes were digested using the model, and diet digestibility and supernatant nutrient contents were determined. This approach was able to distinguish broadly the worst and best performing rearing diets. However, for some of the diets, the performance estimated based on in vitro results did not match with the results of the feeding experiments. Future studies should try to establish a stronger correlation by considering fly larvae nutrient requirements, hemicellulose digestion, and the diet/gut microbiota. In vitro digestion models could be a powerful tool for academia and industry to increase conversion performance of biowastes with black soldier fly larvae.