Evaluating Black Soldier FLY (Hermetia illucens) Frass and Larval Sheddings in the Production of a Quality Compost

Abstract

Black Soldier Fly (Hermetia illucens) is well-known for having a high protein and lipid content during its larval stage and is cultivated for animal feed. Rearing Black Soldier Fly larvae (BSFL) produces byproducts known as frass and larval sheddings in large volumes with limited applications. Therefore, there is a need to identify viable sustainable management strategies to prevent potential environmental issues associated with their accumulation. Accordingly, the purpose of this study was to evaluate BSFL frass and larval sheddings as viable ingredients in composts that utilize additional nitrogen feedstocks. Four experimental compost piles (22.7 m³) with different ratios of BSFL frass and sheddings were developed based on previous research; two piles included 25% frass, whereas the other two included 30% frass. Across these piles, the inclusion of wood chips, food waste, and livestock manure varied to determine the best proportions for compost. The compost piles were maintained for five months, including a curing phase. After curing, samples from each pile were collected to analyze their pH, macro- and micro-nutrients, particle size, stability, and maturity. The findings indicated that the pH levels (7.1–8.1) and carbon-to-nitrogen ratios (10.40–13.20) were within the optimal ranges for all piles. The phosphorus levels (0.75–1.30%) of each pile exceeded typical ranges, likely due to the high phosphorus content of the frass itself. The moisture content varied widely (24.5–51.7%), with some piles falling below optimal levels. Stability and maturity tests yielded mixed results, with some piles demonstrating continued decomposition activity. Overall, the findings indicated that inclusion rates of 25–30% of BSFL frass and sheddings produced compost with generally favorable characteristics when high nitrogen feedstocks were also incorporated into the compost piles. These findings align with those from previous research and highlight both the potential and challenges of incorporating BSFL frass into compost production.

1. Introduction

The growing global population, projected to reach 9.7 billion by 2050, necessitates a 70% increase in food production [1]. The concomitant rise in the demand for food, coupled with rapid urbanization and changing dietary preferences, is creating unprecedented pressure on agricultural systems and natural resources [2]. Simultaneously, waste management has emerged as a critical environmental challenge; global municipal solid waste generation is expected to increase from 2.01 billion tons in 2016 to 3.40 billion tons by 2050 [3]. The interconnection of these challenges demands innovative, sustainable solutions that can address both food security and waste management in an integrated manner [4].

Insect farming, particularly the cultivation of the Black Soldier Fly (Hermetia illucens), has garnered significant attention as a potential solution to these challenges [5]. Black Soldier Fly larvae (BSFL) are remarkably efficient bioconverters, capable of transforming a diverse range of organic substrates into high-quality protein and lipids [6] for subsequent integration into the human food or animal feed chain [7,8,9]. The efficiency of bioconversion is associated with the larvae’s unique gut microbiome and enzymatic profile, which facilitates the rapid digestion of complex organic matter [10]. The protein content of BSFL can approach 50% on a dry matter (DM) basis and is accompanied by a balanced amino acid profile that is comparable to soybean meal and other conventional protein feeds for livestock and poultry [11]. As a result, BSFL are considered to be highly effective for sustainable protein production and organic waste valorization [12].

The emphasis on BSFL as a protein source has overshadowed another potentially valuable byproduct of their cultivation—frass. Frass, a heterogeneous mixture of BSFL excrement and exuviae (shed exoskeletons), is produced in significant quantities during larval rearing. Recent studies have demonstrated that, for every kilogram of dried larvae produced, approximately 1.4–2.3 kg of frass was generated, depending on the substrate and rearing conditions [13,14]. As the insect farming industry expands, with global BSFL production estimated to reach 1.2 million tons by 2025 [15], the volume of frass produced is projected to exceed 2 million tons annually. The total global production of BSFL frass and sheddings is difficult to estimate, because the quantities of frass produced vary substantially depending on the characteristics of the original feedstock on which the BSFL were raised [16]. This anticipated increase in frass production demands innovative approaches to its utilization and management.

Recent studies have explored the potential of BSFL frass as a soil amendment and biofertilizer. Frass contains a complex matrix of macro- and micro-nutrients, including nitrogen (2–3%), phosphorus (1–2%), potassium (1–2%), and chitin, a polymer that stimulates plant defense mechanisms [17]. The presence of chitin and its derivative, chitosan, in frass is particularly intriguing due to the potential to induce systemic acquired resistance in plants, enhancing the ability of the plant to withstand pathogen attacks [18].

Previous research demonstrates that frass application can improve the soil structure, enhance microbial activity, and promote plant growth through various mechanisms, including the slow release of nutrients and the stimulation of beneficial soil microorganisms [19]. However, the direct application of raw frass to soil has yielded mixed results, with some studies reporting phytotoxic effects, possibly due to the presence of undecomposed organic matter and/or a high ammonia (NH₃) content [20]. Ammonia can be phytotoxic at high concentrations, potentially causing root burn, inhibiting seed germination, and/or disrupting plant metabolic processes [21]. Moreover, excessive ammonia can alter the soil pH, leading to nutrient imbalances and affecting the availability of essential elements for plant uptake [22]. The volatile nature of ammonia also contributes to nitrogen loss through gaseous emissions, reducing the fertilizer value of the frass and potentially contributing to environmental issues such as air pollution and greenhouse gas emissions [23].

A potential solution for addressing the variability and phytotoxic risks of raw frass is through composting. The composting process is characterized by the controlled aerobic decomposition of organic materials facilitated by a diverse community of microorganisms, ultimately creating a stable, humus-like substance that enhances the soil structure and fertility [24,25]. While composting has traditionally and primarily utilized plant residues and animal manures, there is growing interest in incorporating alternative organic materials to enhance the nutritional and biological properties of the final compost product [26] and reroute organic waste from the landfill into a valuable horticultural and agricultural product.

Utilizing BSFL frass as a compost ingredient could provide a sustainable market and application for this byproduct of insect production, contributing to its re-use and application [27]. The nutrients and chitin in frass could enhance the agronomic value of the resulting compost, potentially improving its plant growth-promoting and disease-suppressive properties [28]. Finally, the composting process itself could stabilize the frass, potentially reducing any phytotoxic effects observed with raw frass application through the degradation of harmful compounds and the humification of organic matter [29].

Recent studies have explored the potential of BSFL frass as a compost ingredient. Jasso et al. [30] investigated the use of BSFL frass and sheddings as compost ingredients, evaluating their effects on the composting process and final compost quality. Incorporating BSFL frass into compost piles at rates of up to 25% by volume did not negatively impact the composting process nor the quality of the final product; further, the compost piles containing frass reached and maintained appropriate temperatures for pathogen reduction, and the final compost products met industry standards for nutrient content and stability [30]. Importantly, including BSFL frass in compost resulted in a higher phosphorus content compared to industry standards, potentially enhancing the agronomic value of the compost, and the frass-containing composts had a lower bulk density and higher porosity [30], which are characteristics that can improve the soil structure when compost is applied to land.

Therefore, in this study, we asked the question, “Do BSFL frass and sheddings incorporated with other compost feedstocks produce an industry-level quality compost?” with the hypothesis that incorporating BSFL frass and sheddings with other compost feedstocks will produce a high-quality compost by industry standards. The primary objective of this study was to evaluate the potential of BSFL frass and larval sheddings as viable ingredients in compost production by compost industry standards. Specifically, this research aimed to investigate the effects of incorporating BSFL frass into compost while also utilizing nitrogen-rich feedstocks, such as livestock manure. This study assessed the impact of these combined inputs on the composting process, analyzing the physicochemical properties, nutrient content, and overall quality of the resulting compost. By examining these aspects, the suitability and effectiveness of BSFL frass as a component in producing high-quality compost for horticultural and agricultural applications can be determined.

2. Materials and Methods

2.1. Materials Collection

This study utilized the four following types of waste ingredients for compost production: BSFL frass and larval sheddings, wood chips, food waste, and livestock manure. The BSFL frass was commercially sourced from EnviroFlight Feed Company (Apex, NC, USA); pre-consumer food waste was fed to the larvae, and the resulting frass and sheddings were heat-treated for pasteurization prior to their shipment and ultimate incorporation into the research compost piles. Wood chips were procured from a local tree care company (San Marcos, TX, USA) and are a commonly used carbon source in both the small- and large-scale composting industry. The wood chips maintained relatively consistent sizes, aligning with industry standards [31]. Pre- and post-consumer food waste served as the primary nitrogen source within the compost piles and was collected from on-campus cafeterias at Texas State University (San Marcos, TX, USA). This diverse waste stream included vegetables, fruits, meat, bread, coffee grounds, and dairy products. The food waste was accumulated and stored in 363.40 L bins until the required quantity was available for pile development. To further enhance the nitrogen content and balance the carbon-to-nitrogen ratio, livestock manure was incorporated into the compost piles. Specifically, beef cow manure was collected from the Freeman Center (San Marcos, TX, USA), an on-campus working ranch at Texas State University. Recognized for its high nitrogen content, livestock manure plays a crucial role in accelerating the decomposition process [32]. The manure was collected each morning before the cattle were released to pasture and stored at room temperature for approximately two weeks before being incorporated into the compost piles.

2.2. Development of Compost Piles

The compost piles were created at the Bobcat Blend university campus composting location, an approximately five-acre plot of land on the Muller Farm owned by Texas State University. Muller Farm consists of approximately 125 acres, with approximately 2.5 acres allocated for the compost site and an additional 2.5 acres surrounding the compost site serving as run-off space and a catchment pond that can withstand environmental pressures like unprecedented flooding. The Bobcat Blend site is a fully operating municipal solid-waste-handling facility.

Four distinct piles were developed, each maintaining a consistent volume of 22.7 m³ with varied proportions of ingredients (Table 1). The inclusion levels of the four different waste ingredients were chosen based on previous research which investigated the suitability of novel compost ingredients, and particularly past research results regarding the composting of BSFL frass and the limitations and recommendations of that study [30,33,34,35]. A true control pile was not needed, since in compost quality tests, compost quality standards are measured against overall industry compost quality standards [30,35,36], and the primary objective of our study was to evaluate whether compost derived from BSFL frass and sheddings met established industry standards, specifically those set by the USCC. These standards represent a comprehensive benchmark developed through extensive research and industry consensus, effectively serving as a universal control. Our approach focused on validating the compost’s quality against these standardized parameters rather than comparing it to a single control pile.

Wood chips, serving as the primary bulking agent and carbon source, ranged from 15% to 50% of the total pile volume (3.4 m³ to 11.4 m³). BSFL frass and sheddings, the focal material of this study, were incorporated at 25% to 30% of the total volume (5.7 m³ to 6.8 m³) across all formulations, enabling a thorough evaluation of the BSFL frass performance in various compost mixtures and providing insights into its potential as a novel compost ingredient. Livestock manure, consisting of bovine cow manure, varied from 12.5% to 30% of the total volume (2.8 m³ to 6.8 m³) of the compost piles. As a traditional nitrogen source option in composting, the proportion of manure was adjusted to balance the carbon-to-nitrogen ratio with BSFL frass. Food waste, representing an additional nitrogen-rich component, ranged from 12.5% to 30% of the total volume (2.8 m³ to 6.8 m³).

2.3. Compost Development and Maintenance

Compost piles were created and then turned weekly. The turning/mixing of the piles was conducted with a front-end loader. Each pile was systematically divided into two equal sections to ensure thorough mixing, after which, the material was methodically combined to achieve the complete homogenization of the substrate. During this period, water was added to maintain optimal moisture conditions (40–60%), crucial for microbial activity and efficient waste decomposition [36]. A moisture meter (Lincoln Irrigation, Lincoln, NE, USA) and compost thermometer (ReoTemp Instrument Co., San Diego, CA, USA) were utilized to measure the moisture content and internal temperature on a weekly basis throughout the composting process. These parameters were monitored from the initial pile formation through the activation phase, characterized by the stabilization of internal pile temperatures at approximately 57 °C.

The curing phase commenced when internal temperatures declined from 57 °C to 32 °C. This temperature decrease required approximately 55–60 days on average, with notable variations observed between piles (Figure 1). Specifically, the duration ranged from 50 to 70 days across all treatments. Piles with higher percentages of frass and sheddings (30%) tended to maintain higher temperatures for longer periods compared to those with lower percentages (25%) (Figure 1). During the curing period, the piles remained undisturbed, without turning or watering, to maximize microbial functionality and achieve stability [37]. Curing was deemed complete upon the consistent maintenance of lower temperatures (<32 °C) for one week. The curing process spanned approximately two months within the total composting duration of five months.

2.4. Compost Quality Tests

Upon entering the curing phase, each finished compost pile was screened to 25.4 mm. Following screening, samples were collected from each compost pile following the protocols established by the United States Composting Council Seal of Testing Assurance program [36]. To ensure accurate representation, sub-samples were obtained from three depths and five locations within each pile. These 15 sub-samples were then combined to create a single, representative sample for each pile. This process yielded four compost samples across the four individual piles, each measuring 1.9 L.

The samples were subsequently analyzed by the U.S. Composting Council Seal of Testing Assurance program at the Agricultural Analytical Services Laboratory, Pennsylvania State University (University Park). This program adheres to industry-standard protocols [36] for assessing compost market suitability. The analysis encompassed a broad spectrum of parameters, including pH, soluble salt content (electrical conductivity), moisture content, organic matter content, total nitrogen, total carbon, carbon-to-nitrogen ratio, phosphorous, potassium, calcium, magnesium, and select metals (aluminum, copper, and zinc). Particle size, stability, and maturity were also evaluated to provide a comprehensive profile of the finished compost quality.

All tests described were conducted by Pennsylvania State University through the Agricultural Analytical Services Laboratory. The pH measures the active acidity/alkalinity or hydrogen ion concentration in compost [36]. To test for the pH of the compost, readings were taken from a slurry of the compost taken from the samples and mixed with deionized water at a 1:5 ratio. The slurry solution was shaken and held for 20 min at room temperature, where any salts present would dissolve, after which the pH measurements were taken using an electronic pH meter. The soluble salts present in the 1:5 ratio of the compost and deionized water slurry indicated the electrical conductivity within the samples [36,38]. The solids and moisture percentages were analyzed by first taking the weight of the original compost samples. The compost samples were subsequently dried at 70 (þ5) C and re-weighed. The dried weight indicated the solids percentage, while the evaporated weights were a measure of the moisture percentage within the compost samples [36]. The organic matter percentage was calculated by examining the amounts of solid material combusted in relation to the original oven dried compost sample [36,38]. All possible forms of nitrogen are detected in measures of total nitrogen, including organic nitrogen, ammonium, and nitrate. These were identified in the samples using the Total Kjeldahl Nitrogen Semi-Micro technique. The CO₂ Detection method uses combustion, a carbon analyzer (Leo CR-12), water vapor, and an infrared detector to calculate the total amount of carbon dioxide within compost samples [36,38]. The amounts of phosphorus and potassium were measured in their total oxide form. The overall stability and maturity of the compost samples were measured using bioassay tests in combination with respirometry (CO₂ evolution). Traditionally, bioassay tests utilize cucumber (Cucumis sativus L. ‘Marketmore 760) seedling emergence and vigor to recognize the presence of potentially harmful phytotoxins within compost samples. Respirometry tests calculate the relative microbial activity in compost samples, which provides an indication of compost stability [36].

These methods are summarized in Figure 2.

3. Results

The quality measures for each pile are outlined in Table 2. For all samples, the quality measures were compared to the normal and optimal ranges defined by the United States Composting Council Seal of Testing Assurance [36] and Ozores-Hampton et al. [39]. Indices within the optimal ranges indicated that the compost met the desired criteria for quality and effectiveness.

The pH for all the compost piles was within the optimal range of 5.0–8.0 [36,39], except for the pile containing 30% frass and sheddings and 15% livestock manure (30% FRS–15% LM), which had a slightly higher pH of 8.1. The solids content was within the ideal range of 40–70% for the piles containing 25% frass and 12.5% livestock manure (25% FRS–12.5% LM), 30% FRS–15% LM, and 30% frass and 20% livestock manure (30% FRS–20% LM), ranging from 48.3% to 56.5%, while the pile containing 25% frass and 30% livestock manure (25% FRS–30% LM) was outside of this range at 75.5% [36,39]. Consequently, moisture was within the optimal range (30–60%) for the 25% FRS–12.5% LM, 30% FRS–15% LM, and 30% FRS–20% LM samples, but lower than optimal for the 25% FRS–30% LM sample at 24.5% [36,39].

Organic matter was below the optimal range (40–60%) for all piles, ranging from 26.9% to 33.5% on a DM basis. The total nitrogen (1.1–1.9%), carbon (14.7–19.8%), carbon:–nitrogen ratio (10–11.3), and potassium (0.82–0.93%) for all piles were within the optimal ranges [36,39]. The optimal ranges for total nitrogen include levels between 0.5 and 0.6, and for carbon, the optimal level is <54%. An optimum carbon–nitrogen ratio is within the range of 10–25 [36,39]. The optimal range for phosphorus is 0.2–0.3% [36,39]; samples from all piles exceeded this, with values ranging from 0.75% (25% FRS–30% LM) to 1.30% (30% FRS–20% LM).

Stability in compost determines if the compost is fully decomposed or undergoing any further rapid decomposition, and is measured as mg CO₂-C/g organic matter/day. The stability was within the optimal range (<2 mg CO₂-C/g) for 25% FRS–12.5% LM and 30% FRS–15% LM [36,39]. The stability levels were higher for the samples that included more livestock manure, including the protocols with 30% FRS–20% LM (5.0 mg CO₂-C/g) and 25% FRS–30% LM (7.7 mg CO₂-C/g). However, when stability was measured as mg CO₂-C/g solids/day, all piles except 25% FRS–30% LM were within the specification levels of <2 mg CO₂-C/g which had a reading just outside of the range at 2.4 mg CO₂-C/g [36,39]. Composts with suboptimal levels of stability are thought to be less suitable for use in potting mixes, where they may further degrade, causing a poor porosity, but are otherwise compatible for field applications [40].

Maturity measures whether there are plant volatile acids and ammonia within the compost that could kill or cause harm to plants [40]. Maturity is measured as seed emergence during testing and within the quality testing lab, as well as seedling vigor. The maturity levels were within these specifications (>90% for both seedling emergence and seedling vigor) for all piles, classifying each as “very mature” [36,39]. Therefore, the compost was ready for use in plant applications for field use.

The particle size distribution varied among the piles, with 30% FRS–15% LM and 25% FRS–30% LM having 100% of their particles below the optimal level of 9.5 mm, while 25% FRS–12.5% LM and 30% FRS–20% LM had values of 77.2% and 92.9%, respectively [36,39]. There are no established optimal ranges for calcium and magnesium content in compost; the values ranged from 9.49 to 12.39% for calcium and 0.42 to 0.49% for magnesium across all the piles.

4. Discussion

In some regions, excess BSFL frass and sheddings that cannot be immediately used as fertilizer may be disposed of through landfilling or incineration [41]. A study by Liu et al. [42] reported that, in areas without established markets for insect-based products, BSFL frass is often treated as waste. While fresh frass and sheddings have been incorporated directly into agriculture production, past research has also indicated that, in this form, they have the potential for phytotoxicity on crops [43], and that there may be value in processing them through composting to guarantee their stability and maturity [16]. With this in mind, the primary objective of this study was to evaluate the feasibility of utilizing BSFL frass and sheddings as compostable ingredients. We aimed to transform these feed manufacturing insect byproducts from a waste stream into valuable resources for horticultural/agricultural applications. To conduct this research, BSFL frass, livestock manure, food waste, and wood chips were combined in various proportions to create four experimental compost piles that cumulatively created 54.48 m³ of finished, mature compost.

The results showed the pH of the compost piles containing BSFL frass ranged from 7.1 to 8.1, aligning with the optimal range of 5.0–8.0 for plant growth [36]. This is consistent with previous research on BSFL frass, which typically showed a pH between 5.6 and 8.0 [22,44,45]. The slightly alkaline nature of the compost may offer advantages for soils prone to acidity, potentially reducing the need for lime applications in certain agricultural settings [24]. The ability of BSFL-frass-based compost to potentially ameliorate soil acidity is particularly significant in the context of global soil degradation, where approximately 30% of the world’s ice-free land is affected by soil acidity [46].

The total nitrogen levels (1.1–1.9%) in our samples were within the optimal ranges (0.5–6.0%) established by the U.S. Composting Council [36]. This finding aligns with previous studies reporting a nitrogen content in BSFL frass of approximately 2% [19,47].

The carbon–nitrogen ratios (10.40–13.20) were also within the ideal range of 10–25, indicating that the composts had an adequate nitrogen availability for plant uptake over time [24]. All protocols tested provided consistent measures. This consistency could be valuable for agricultural applications, where a predictable nutrient content is essential for proper soil management.

A notable observation was the elevated phosphorus levels (0.75–1.30%) in all compost piles, exceeding the typical range of 0.2–0.3% [36]. This high phosphorus content appears to be directly related to the inclusion of BSFL frass and sheddings, as previous studies have reported phosphorus levels in BSFL frass ranging from 1.0 to 2.5% [19,22]. Jasso et al. [30] investigated frass inclusion rates of 18.75%, 22.87%, 27.13%, and 31.25% in compost piles, and reported that compost piles with 31.25% frass had the highest total phosphorus content, reaching 1.75%. Our study findings corroborate their previous observations of elevated phosphorus levels and suggest that compost utilizing BSFL frass as an ingredient may be inherently high in phosphorus, which could be unavoidable.

This phosphorus-rich profile presents both opportunities and challenges for agricultural application. Phosphorus-rich compost could address deficiencies in certain soils, potentially reducing the need for synthetic phosphorus fertilizers. This is particularly significant given that phosphorus is a non-renewable resource, with estimates suggesting that global reserves could be depleted within 50–100 years [48]. BSFL frass could, thus, contribute to more sustainable phosphorus management in agriculture. Other commercially available composts created from waste byproducts such as shellfish, bonemeal, hair/feathers, or mushroom bedding are also known to have a high phosphorus content [49,50]. From a plant nutrition perspective and for many horticultural and agricultural land applications, the high phosphorus content of frass-containing compost could enhance flowering, fruiting, and root growth in various crops [51]. However, the phosphorus-rich nature of BSFL frass could also potentially alter soil microbial communities and mycorrhizal associations in perennial native plant habitat and forest situations. For instance, research has indicated that high soil phosphorus levels demonstrably reduce the colonization of plant roots by arbuscular mycorrhizal fungi [52]. Considering this, frass-containing composts may be best applied to annual agricultural and horticultural cropland.

The physical properties of the frass-containing compost, particularly its moisture content and particle size, may present challenges. The moisture levels varied across the piles (24.5–51.7%), with one sample, 25% FRS–30% LM (24.5%), falling below the optimal range of 30–60% [35,36]). Previous studies have noted similar results in composting BSFL frass [30]. Fresh, non-pasteurized BSFL frass typically has a higher moisture content than its pasteurized counterpart, potentially ranging from 65 to 80%, depending on the feedstock and processing conditions [53]; we utilized pasteurized frass, which was shown to have a DM content of 93.5% [54] in our study, as it was commercially available in large quantities and shelf-stable. The low moisture content we observed may have been a result of the proportions of frass and larval sheddings or may have been, instead, a reflection of the time involved in the sampling, shipping, and laboratory analysis, which provided an opportunity for the samples to dehydrate. In this study, efforts were made to incorporate high-moisture feedstocks, such as food waste or green waste, to achieve a more balanced moisture profile in the final compost product. Our study did show notable improvements in moisture levels from the previous Jasso et al. [30] study, where the moisture content averaged 17.5% during one sampling period and 10.6% at a later sampling. However, in practice and while using the compost, issues may be encountered in rewetting the composting and/or with excessive dust produced during use.

A high percentage of all compost piles (>77%) passed through a 9.5 mm sieve, indicating a relatively fine texture for all piles, though two piles included particle sizes that were not fully 100% below the 9.5 mm range. Additional screening or the reincorporation of larger particles into new compost piles is recommended in these situations until the particles reach ideal levels. Generally, composts with a high percentage of particles at this texture are well-suited and recommended for use as a soil amendment [39] This fine particle size could enhance the ability of the finished compost to retain nutrients and water when incorporated into soil, potentially improving its effectiveness as a soil amendment. The increased surface area may also facilitate quicker nutrient release and microbial colonization, leading to a more rapid integration of the compost with the soil ecosystem [24]. Additionally, the fine texture may contribute to rapid decomposition due to an increased surface area [31].

Stability and maturity assessments of the compost samples revealed intriguing and somewhat paradoxical results that warrant deeper analysis. The stability, measured as mg CO₂-C/g solids/day, ranged from 0.4 to 2.4, with two piles, 30% FRS–20% LM and 25% FRS–30% LM, exceeding the recommended threshold of <2 [36]. The variation in stability among the piles could be attributed to differences in the initial composition and the dynamics of microbial activity during the composting process [24]. The high CO₂ evolution in the 30% FRS–20% LM and 25% FRS–30% LM samples could indicate a period of microbial succession, where new communities were establishing and actively metabolizing previously untapped resources [55]. This microbial shift might be particularly pronounced in BSFL-frass-based composts due to the unique composition of the frass, including its high chitin content.

The chitin in BSFL frass likely played a crucial role in shaping the microbial community dynamics throughout the composting process. Chitin degradation is a complex process that requires specific enzymes produced by certain bacteria and fungi [56]. The presence of chitin may contribute to the proliferation of these microorganisms, potentially leading to a more diverse and active microbial community in the later stages of composting. This could explain the continued high microbial activity in the 30FRS–20LM and 25FRS–30LM samples, despite the advanced stage of composting.

Interestingly, despite the variations in stability, maturity indicators such as seed emergence and seedling vigor were within acceptable ranges (>90% and >95%, respectively) for all piles. This apparent contradiction between the stability and maturity results suggests that the microbial activity in the less stable piles was not producing phytotoxic compounds at levels harmful to plant growth. We hypothesize that the unique microbial community associated with BSFL frass might be responsible for this phenomenon. Recent studies have demonstrated that BSFL frass contains diverse microorganisms, including beneficial bacteria and fungi that could enhance soil health [57]. Future research may consider further investigating the microbial communities within BSFL-based compost.

While Jasso et al. [30] demonstrated the potential of incorporating BSFL frass into compost, our study extends this knowledge in several ways. We examined the composting process at a larger industrial scale, with our piles measuring 22.7 m³ compared to 6.12 m³. This substantial increase in scale provides crucial insights into the practical challenges and opportunities of large-scale BSFL frass composting. Our research also investigated the effects of varying frass-to-bulking agent ratios on compost quality and maturation time, offering optimized guidelines for commercial applications. These findings contribute valuable data to support policy-making and industry best practices as insect farming continues to expand globally. By building upon the foundational work of Jasso et al. [30], our research offers practical insights and data to support the transformation of BSFL frass from a waste product into a valuable horticultural and agricultural resource, paving the way for more sustainable and economically viable insect farming operations.

Furthermore, BSFL-frass-based compost could be used as an alternative to synthetic fertilizers in some production situations. The high phosphorus content of the compost, while challenging from a regulatory standpoint, could be particularly beneficial in regions with phosphorus-deficient soils or for crops with high phosphorus requirements [48]. In this context, BSFL-frass-based compost could serve as a crucial alternative phosphorus source [58].

5. Conclusions

This study provides valuable insights into the potential use of BSFL frass and sheddings as compost ingredients. While challenges exist, particularly with phosphorus levels, the overall results suggest that BSFL frass can contribute positively to compost quality when used at appropriate inclusion rates. Our findings indicate that inclusion rates of 25–30% of BSFL frass and sheddings can produce compost with generally favorable characteristics when high nitrogen feedstocks are also incorporated into compost piles. This range offers a balance between utilizing a significant amount of frass while maintaining the overall compost quality. However, the upper limit of inclusion should be approached cautiously, particularly in areas with strict phosphorus regulations. The maximum inclusion rate may vary depending on local regulations, soil conditions, the intended use of the compost, and the actual frass itself.

Our study was limited to protocols of inclusion rates of ingredients based on past research and recommendations and comparisons to overall U.S. compost industry standards. Additionally, while compost quality tests indicated good seedling emergence when utilizing the compost, our finished compost was not evaluated for use in growing a crop to observe the compost’s effect on plant health or growth. Further research is recommended to investigate the impact of compost created incorporating BSFL frass and sheddings on crop health and growth in comparison to other composts or fertilizers, especially in relation to phosphorus levels, which may offer advantages or disadvantages to particular crops.

Author Contributions

D.K.: Data curation, Investigation, Formal analysis, Writing—original draft. T.M.W.: Conceptualization, Formal analysis, Resources, Supervision, Writing—review & editing. M.L.D.: Conceptualization, Funding acquisition, Supervision, Writing—review & editing. All authors have read and agreed to the published version of the manuscript.

Institutional Review Board Statement

Not applicable.

Informed Consent Statement

Not applicable.

Data Availability Statement

The original contributions presented in this study are included in the article. Further inquiries can be directed to the corresponding author(s).

Conflicts of Interest

The authors declare no conflict of interest.

Footnotes

Disclaimer/Publisher’s Note: The statements, opinions and data contained in all publications are solely those of the individual author(s) and contributor(s) and not of MDPI and/or the editor(s). MDPI and/or the editor(s) disclaim responsibility for any injury to people or property resulting from any ideas, methods, instructions or products referred to in the content.

Figures and Tables

Figure 1. Temperature profile over time of the four comparison compost piles containing Black soldier fly larvae frass and sheddings.

Figure 2. Summary of methods implemented in the study of the us of Black soldier fly larvae frass and sheddings in the production of quality compost.

Table 1

Composition of experimental compost piles containing Black Soldier Fly larvae frass and sheddings.

	Wood Chips	Frass and Sheddings	Livestock Manure	Food Waste	Total
25% FRS a–12.5% LM b
Inclusion	50%	25%	12.5%	12.5%	100%
Amount	11.4 m3	5.7 m3	2.8 m3	2.8 m3	22.7 m3
30% FRS–15% LM
Inclusion	35%	30%	15%	20%	100%
Amount	7.9 m3	6.8 m3	3.5 m3	4.5 m3	22.7 m3
30% FRS–20% LM
Inclusion	25%	30%	20%	25%	100%
Amount	5.7 m3	6.8 m3	4.5 m3	5.7 m3	22.7 m3
25% FRS–30% LM
Inclusion	15%	25%	30%	30%	100%
Amount	3.4 m3	5.7 m3	6.8 m3	6.8 m3	22.7 m3

^a FRS = Black soldier fly frass and sheddings. ^b LM = Livestock manure.

Table 2

Quality of finished compost piles containing varying proportions of black soldier fly larvae frass and sheddings.

Variable (Units) a	25% FRS b–12.5% LM c	25% FRS b–30% LM c	30% FRS b–20% LM c	30% FRS b–15% LM	Optimal Range d
pH	7.7	7.1	7.3	8.1	5.0–8.0
Solids (%)	50.1	75.5	48.3	56.5	40–70
Moisture (%)	49.9	24.5	51.7	43.5	30–60
Organic matter (%)	29.2	31.0	33.5	26.9	40–60
Total nitrogen (%)	1.9	1.1	1.7	1.5	0.5–6.0
Carbon (%)	19.8	14.7	18.2	16.9	<54
Carbon–nitrogen ratio	10.40	13.20	10.50	11.30	10–25
Phosphorus (%)	1.17	0.75	1.30	0.91	0.2–0.3
Potassium (%)	0.89	0.82	0.90	0.93	0.10–3.5
Calcium (%)	10.22	10.79	9.49	12.39	--
Magnesium (%)	0.48	0.42	0.49	0.46	--
Particle size (% <9.5 mm)	77.2	100.0	92.9	100.0	--
Stabilitymg CO2-C/g solids/daymg CO2-C/g organic matter/day	0.5 1.8	2.4 7.7	1.7 5.0	0.4 1.4	<2<2
MaturitySeed emergence, % controlSeedling vigor, % control	96.67 100	10096.67	96.67 96.67	100 100	>90>95

^a pH, solids, moisture, and particle size are reported on an as-is basis while the remaining variables are reported on a dry matter basis. ^b FRS = Black soldier fly frass and sheddings. ^c LM = Livestock manure. ^d Optimal ranges established by U.S. Composting Council or Ozores-Hampton [36,39].

References

1. United Nations. Global Sustainable Development Report 2019; Department of Economic and Social Affairs: New York, NY, USA, 2019; Available online: https://www.un.org/en/desa/global-sustainable-development-report-2019 (accessed on 25 November 2024).

2. Godfray, H.C.J.; Beddington, J.R.; Crute, I.R.; Haddad, L.; Lawrence, D.; Muir, J.F.; Toulmin, C. Food Security: The Challenge of Feeding 9 Billion People. Science; 2010; 327, pp. 812-818. [DOI: https://dx.doi.org/10.1126/science.1185383]

3. Kaza, S.; Yao, L.; Bhada-Tata, P.; Van Woerden, F. What a Waste 2.0: A Global Snapshot of Solid Waste Management to 2050; World Bank Publications: Washington, DC, USA, 2018.

4. Lal, R.; Brevik, E.C.; Dawson, L.; Field, D.; Glaser, B.; Hartemink, A.E.; Hatano, R.; Lascelles, B.; Monger, C.; Scholten, T. et al. Managing Soils for Recovering from the COVID-19 Pandemic. Soil Syst.; 2021; 4, 46. [DOI: https://dx.doi.org/10.3390/soilsystems4030046]

5. Huis, A.V.; Itterbeeck, J.V.; Klunder, H.; Mertens, E.; Halloran, A.; Muir, G.; Vantomme, P. Edible Insects: Future Prospects for Food and Feed Security; FAO: Rome, Italy, 2013; Available online: http://www.fao.org/docrep/018/i3253e/i3253e.pdf (accessed on 25 November 2024).

6. Müller, A.; Wolf, D.; Gutzeit, H.O. The Black Soldier Fly, Hermetia illucens–A Promising Source for Sustainable Production of Proteins, Lipids and Bioactive Substances. Z. Für Naturforschung C; 2017; 72, pp. 351-363. [DOI: https://dx.doi.org/10.1515/znc-2017-0030] [PubMed: https://www.ncbi.nlm.nih.gov/pubmed/28742526]

7. Fukuda, E.P.; Cox, J.R.; Wickersham, T.A.; Drewery, M.L. Evaluation of Black Soldier Fly Larvae (Hermetia illucens) as a Protein Supplement for Beef Steers Consuming Low-Quality Forage. Transl. Anim. Sci.; 2022; 6, txac018. [DOI: https://dx.doi.org/10.1093/tas/txac018] [PubMed: https://www.ncbi.nlm.nih.gov/pubmed/35233513]

8. Tasci, K.D.; Wickersham, T.A.; Drewery, M.L. Acceptance and Forage Utilization Responses of Steers Consuming Low-Quality Forage and Supplemented Black Soldier Fly Larvae as a Novel Feed. J. Anim. Sci.; 2024; 102, skae168. [DOI: https://dx.doi.org/10.1093/jas/skae168]

9. Carrasco, M.N.; Drewery, M.L. Mealworm Larvae and Black Soldier Fly Larvae as Novel Protein Supplements for Cattle Consuming Low-Quality Forage. Transl. Anim. Sci.; 2024; 8, txae122. [DOI: https://dx.doi.org/10.1093/tas/txae122]

10. Bruno, D.; Bonelli, M.; De Filippis, F.; Di Lelio, I.; Tettamanti, G.; Casartelli, M.; Caccia, S. The Intestinal Microbiota of Hermetia illucens Larvae Is Affected by Diet and Shows a Diverse Composition in the Different Midgut Regions. Appl. Environ. Microbiol.; 2019; 85, e01864-18. [DOI: https://dx.doi.org/10.1128/AEM.01864-18]

11. Barragan-Fonseca, K.B.; Dicke, M.; van Loon, J.J. Nutritional Value of the Black Soldier Fly (Hermetia illucens L.) and Its Suitability as Animal Feed—A Review. J. Insects Food Feed; 2017; 3, pp. 105-120. [DOI: https://dx.doi.org/10.3920/JIFF2016.0055]

12. Gasco, L.; Biancarosa, I.; Liland, N.S. From Waste to Feed: A Review of Recent Knowledge on Insects as Producers of Protein and Fat for Animal Feeds. Curr. Opin. Green Sustain. Chem.; 2020; 23, pp. 67-79. [DOI: https://dx.doi.org/10.1016/j.cogsc.2020.03.003]

13. Fowles, T.M.; Nansen, C. Insect-Based Bioconversion: Value from Food Waste. Food Waste Management: Solving the Wicked Problem; Springer: Cham, Switzerland, 2020; pp. 321-346. [DOI: https://dx.doi.org/10.1007/978-3-030-20561-4_12]

14. Schmitt, E.; de Vries, W. Potential Benefits of Using Hermetia illucens Frass as a Soil Amendment on Food Production and for Environmental Impact Reduction. Curr. Opin. Green Sustain. Chem.; 2020; 25, 100335. [DOI: https://dx.doi.org/10.1016/j.cogsc.2020.03.005]

15. Chia, S.Y.; Tanga, C.M.; van Loon, J.J.; Dicke, M. Insects for Sustainable Animal Feed: Inclusive Business Models Involving Smallholder Farmers. Curr. Opin. Environ. Sustain.; 2019; 41, pp. 23-30. [DOI: https://dx.doi.org/10.1016/j.cosust.2019.09.003]

16. Lopes, I.G.; Yong, J.W.H.; Lallander, C. Frass Derived from Black Soldier Fly Larvae Treatment of Biodegradable Waste. A Critical Review and Future Perspectives. Waste Manag.; 2022; 142, pp. 65-76. [DOI: https://dx.doi.org/10.1016/j.wasman.2022.02.007] [PubMed: https://www.ncbi.nlm.nih.gov/pubmed/35176600]

17. Poveda, J.; Jiménez-Gómez, A.; Saati-Santamaría, Z.; Usategui-Martín, R.; Rivas, R.; García-Fraile, P. Mealworm Frass as a Potential Biofertilizer and Abiotic Stress Tolerance-Inductor in Plants. Appl. Soil Ecol.; 2019; 142, pp. 110-122. [DOI: https://dx.doi.org/10.1016/j.apsoil.2019.04.016]

18. Chandra, S.; Chakraborty, N.; Dasgupta, A.; Sarkar, J.; Panda, K.; Acharya, K. Chitosan Nanoparticles: A Positive Modulator of Innate Immune Responses in Plants. Sci. Rep.; 2015; 5, 15195. [DOI: https://dx.doi.org/10.1038/srep15195]

19. Beesigamukama, D.; Mochoge, B.; Korir, N.K.; Fiaboe, K.K.; Nakimbugwe, D.; Khamis, F.M.; Subramanian, S.; Dubois, T.; Musyoka, M.W.; Ekesi, S. et al. Exploring Black Soldier Fly Frass as Novel Fertilizer for Improved Growth, Yield, and Nitrogen Use Efficiency of Maize Under Field Conditions. Front. Plant Sci.; 2020; 11, 574592. [DOI: https://dx.doi.org/10.3389/fpls.2020.574592] [PubMed: https://www.ncbi.nlm.nih.gov/pubmed/33072150]

20. Alattar, M.A.; Alattar, F.N.; Popa, R. Effects of Microaerobic Fermentation and Black Soldier Fly Larvae Food Scrap Processing Residues on the Growth of Corn Plants (Zea mays). Plant Sci. Today; 2016; 3, pp. 57-62. [DOI: https://dx.doi.org/10.14719/pst.2016.3.1.179]

21. Brito, L.M.; Mourão, I.; Coutinho, J.; Smith, S.R. Simple Technologies for On-Farm Composting of Cattle Slurry Solid Fraction. Waste Manag.; 2012; 32, pp. 1332-1340. [DOI: https://dx.doi.org/10.1016/j.wasman.2012.03.013]

22. Gao, S.; DeLuca, T.H.; Cleveland, C.C. Biochar Additions Alter Phosphorus and Nitrogen Availability in Agricultural Ecosystems: A Meta-Analysis. Sci. Total Environ.; 2019; 654, pp. 463-472. [DOI: https://dx.doi.org/10.1016/j.scitotenv.2018.11.124]

23. Chen, S.; Wang, F.; Zhang, Y.; Qin, S.; Wei, S.; Wang, S.; Liu, B. Organic Carbon Availability Limiting Microbial Denitrification in the Deep Vadose Zone. Environ. Microbiol.; 2018; 20, pp. 980-992. [DOI: https://dx.doi.org/10.1111/1462-2920.14027]

24. Bernal, M.P.; Alburquerque, J.A.; Moral, R. Composting of Animal Manures and Chemical Criteria for Compost Maturity Assessment. A Review. Bioresour. Technol.; 2009; 100, pp. 5444-5453. [DOI: https://dx.doi.org/10.1016/j.biortech.2008.11.027]

25. Li, Z.; Lu, H.; Ren, L.; He, L. Experimental and Modeling Approaches for Food Waste Composting: A Review. Chemosphere; 2013; 93, pp. 1247-1257. [DOI: https://dx.doi.org/10.1016/j.chemosphere.2013.06.064] [PubMed: https://www.ncbi.nlm.nih.gov/pubmed/23876506]

26. Lohri, C.R.; Diener, S.; Zabaleta, I.; Mertenat, A.; Zurbrügg, C. Treatment Technologies for Urban Solid Biowaste to Create Value Products: A Review with Focus on Low-and Middle-Income Settings. Rev. Environ. Sci. Bio/Technol.; 2017; 16, pp. 81-130. [DOI: https://dx.doi.org/10.1007/s11157-017-9422-5]

27. Mertenat, A.; Diener, S.; Zurbrügg, C. Black Soldier Fly Biowaste Treatment–Assessment of Global Warming Potential. Waste Manag.; 2019; 84, pp. 173-181. [DOI: https://dx.doi.org/10.1016/j.wasman.2018.11.040] [PubMed: https://www.ncbi.nlm.nih.gov/pubmed/30691890]

28. Kebli, H.; Sinaj, S. Agronomic Potential of a Natural Fertiliser Based on Fly Larvae Frass. Agrarforschung Schweiz 2017. Available online: http://www.researchgate.net/publication/316631389_Agronomic_potential_of_a_natural_fertilser_based_on_fly_larvae_frass (accessed on 25 November 2024).

29. Bernal, M.P.; Sommer, S.G.; Chadwick, D.; Qing, C.; Guoxue, L.; Michel, F.C., Jr. Current Approaches and Future Trends in Compost Quality Criteria for Agronomic, Environmental, and Human Health Benefits. Adv. Agron.; 2017; 144, pp. 143-233. [DOI: https://dx.doi.org/10.1016/bs.agron.2017.03.002]

30. Jasso, B.; Quinchia, L.; Waliczek, T.M.; Drewery, M.L. Black Soldier Fly Larvae (Hermetia illucens) Frass and Sheddings as a Compost Ingredient. Front. Sustain. Food Syst.; 2024; 7, 1297858. [DOI: https://dx.doi.org/10.3389/fsufs.2023.1297858]

31. Rynk, R.; Schwarz, M.; Richard, T.L.; Cotton, M.; Halbach, T.; Siebert, S. Compost Feedstocks. The Composting Handbook; Academic Press: Cambridge, MA, USA, 2022; pp. 103-157. [DOI: https://dx.doi.org/10.1016/B978-0-323-85602-7.00005-4]

32. Bai, L.; Deng, Y.; Li, J.; Ji, M.; Ruan, W. Role of the Proportion of Cattle Manure and Biogas Residue on the Degradation of Lignocellulose and Humification During Composting. Bioresour. Technol.; 2020; 307, 122941. [DOI: https://dx.doi.org/10.1016/j.biortech.2020.122941]

33. Hustvedt, G.; Meier, E.; Waliczek, T. The Feasibility of Large-Scale Composting of Waste Wool. Green Fashion; Springer: Singapore, 2016; Volume 1, pp. 95-107. [DOI: https://dx.doi.org/10.1007/978-981-10-0111-6_4]

34. Walsh, K.T.; Waliczek, T.M. Examining the Quality of a Compost Product Derived from Sargassum. HortTechnology; 2020; 30, pp. 331-336. [DOI: https://dx.doi.org/10.21273/HORTTECH04523-19]

35. Waliczek, T.M.; Drewery, M.; McMoran, A.; Eriksen, M.; Hale, J. Assessing the Quality of Compost Produced from Human Hair and Pet Fur Waste. Compost. Sci. Util.; 2021; 29, pp. 57-64. [DOI: https://dx.doi.org/10.1080/1065657X.2023.2167749]

36. United States Composting Council Seal of Testing Assurance. Certified Compost STA; US Composting Council: Raleigh, NC, USA, 2010; Available online: https://www.compostingcouncil.org/page/CertifiedCompostSTA (accessed on 25 November 2024).

37. Pace, M.G.; Miller, B.E.; Farrell-Poe, K.L. The Composting Process; Utah State University Extension: Logan, UT, USA, 1995; Available online: https://digitalcommons.usu.edu/cgi/viewconent.cgi?article=1047&context=extension_histall (accessed on 25 November 2024).

38. Etheredge, C.L.; Waliczek, T.M. An Analysis of the Quality of Compost Produced from Vermicomposting Fresh Cut Flower Waste. J. Environ. Hort.; 2022; 40, pp. 87-93. [DOI: https://dx.doi.org/10.24266/2573-5586-40.2.87]

39. Ozores-Hampton, M. Guidelines for Assessing Compost Quality for Safe and Effective Utilization in Vegetable Production. HortTechnology; 2017; 27, pp. 162-165. [DOI: https://dx.doi.org/10.21273/HORTTECH03349-16]

40. Wichuk, K.M.; McCartney, D. Compost Stability and Maturity Evaluation—A Literature Review. Can. J. Civ. Eng.; 2010; 37, pp. 1505-1523. [DOI: https://dx.doi.org/10.1139/L10-101]

41. Basri, N.E.A.; Azman, N.A.; Ahmad, I.K.; Suja, F.; Jalil, N.A.A.; Amrul, N.F. Potential Applications of Frass Derived from Black Soldier Fly Larvae Treatment of Food Waste: A Review. Foods; 2022; 11, 2664. [DOI: https://dx.doi.org/10.3390/foods11172664] [PubMed: https://www.ncbi.nlm.nih.gov/pubmed/36076850]

42. Liu, T.; Klammsteiner, T.; Dregulo, A.M.; Kumar, V.; Zhou, Y.; Zhang, Z.; Awasthi, M.K. Black Soldier Fly Larvae for Organic Manure Recycling and Its Potential for a Circular Bioeconomy: A Review. Sci. Total Environ.; 2022; 833, 155122. [DOI: https://dx.doi.org/10.1016/j.scitotenv.2022.155122] [PubMed: https://www.ncbi.nlm.nih.gov/pubmed/35405225]

43. Song, S.; Ee, A.W.; Tan, J.K.; Cheong, J.C.; Chiam, Z.; Arora, S.; Lam, W.N.; Tan, H.T.W. Upcycling food waste using black soldier fly larvae: Effects of further composting on frass quality, fertilizing effect and its global warming potential. J. Clean. Prod.; 2021; 288, 125664. [DOI: https://dx.doi.org/10.1016/j.jclepro.2020.125664]

44. Ritika, P.R.; Rajendra, S.S.P. Study on Occurrence of Black Soldier Fly Larvae in Composting of Kitchen Waste. Int. J. Res. Biosci.; 2015; 4, pp. 38-45. Available online: https://www.ijrbs.in/index.php/irjbs/article/view/170/113 (accessed on 25 November 2024).

45. Klammsteiner, T.; Turan, V.; Fernández-Delgado Juárez, M.; Oberegger, S.; Insam, H. Suitability of Black Soldier Fly Frass as Soil Amendment and Implication for Organic Waste Hygienization. Agronomy; 2020; 10, 1578. [DOI: https://dx.doi.org/10.3390/agronomy10101578]

46. Von Uexküll, H.R.; Mutert, E. Global Extent, Development and Economic Impact of Acid Soils. Plant Soil; 1995; 171, pp. 1-15. [DOI: https://dx.doi.org/10.1007/BF00009558]

47. Kawasaki, K.; Toshimitsu, K.; Matano, M.; Fujita, M.; Fujii, M.; Togasaki, K.; Ebisundani, T.; Shimokawa, M.; Takano, A.; Takahashi, S. et al. An Organoid Biobank of Neuroendocrine Neoplasms Enables Genotype-Phenotype Mapping. Cell; 2020; 183, pp. 1420-1435. [DOI: https://dx.doi.org/10.1016/j.cell.2020.10.023]

48. Cordell, D.; Drangert, J.O.; White, S. The Story of Phosphorus: Global Food Security and Food for Thought. Glob. Environ. Change; 2009; 19, pp. 292-305. [DOI: https://dx.doi.org/10.1016/j.gloenvcha.2008.10.009]

49. Nayaka, S.; Vidyasagar, G. Development of Eco-Friendly Bio-Fertilizer Using Feather Compost. Ann. Plant Sci.; 2013; 2, pp. 238-244.

50. Wei, Y.; Zhao, Y.; Xi, B.; Wei, Z.; Li, X.; Cao, Z. Changes in Phosphorus Fractions During Organic Wastes Composting from Different Sources. Bioresour. Technol.; 2015; 189, pp. 349-356. [DOI: https://dx.doi.org/10.1016/j.biortech.2015.04.031] [PubMed: https://www.ncbi.nlm.nih.gov/pubmed/25912971]

51. Bhadouria, J.; Giri, J. Purple Acid Phosphatases: Roles in Phosphate Utilization and New Emerging Functions. Plant Cell Rep.; 2022; 41, pp. 33-51. [DOI: https://dx.doi.org/10.1007/s00299-021-02773-7] [PubMed: https://www.ncbi.nlm.nih.gov/pubmed/34402946]

52. Smith, S.E.; Jakobsen, I.; Grønlund, M.; Smith, F.A. Roles of Arbuscular Mycorrhizas in Plant Phosphorus Nutrition: Interactions Between Pathways of Phosphorus Uptake in Arbuscular Mycorrhizal Roots Have Important Implications for Understanding and Manipulating Plant Phosphorus Acquisition. Plant Physiol.; 2011; 156, pp. 1050-1057. [DOI: https://dx.doi.org/10.1104/pp.111.174581]

53. Lalander, C.H.; Fidjeland, J.; Diener, S.; Eriksson, S.; Vinnerås, B. High Waste-to-Biomass Conversion and Efficient Salmonella spp. Reduction Using Black Soldier Fly for Waste Recycling. Agron. Sustain. Dev.; 2015; 35, pp. 261-271. [DOI: https://dx.doi.org/10.1007/s13593-014-0235-4]

54. Rea, J.C. Evaluating Multiple Edible Insects as Feed for Cattle: An In-Vitro Analysis; Texas State University: San Marcos, TX, USA, 2022; Available online: https://digital.library.txstate.edu/handle/10877/16144 (accessed on 25 November 2024).

55. Neher, D.A.; Weicht, T.R.; Bates, S.T.; Leff, J.W.; Fierer, N. Changes in Bacterial and Fungal Communities Across Compost Recipes, Preparation Methods, and Composting Times. PLoS ONE; 2013; 8, e79512. [DOI: https://dx.doi.org/10.1371/journal.pone.0079512] [PubMed: https://www.ncbi.nlm.nih.gov/pubmed/24278144]

56. Kaur, S.; Dhillon, G.S. Recent Trends in Biological Extraction of Chitin from Marine Shell Wastes: A Review. Crit. Rev. Biotechnol.; 2015; 35, pp. 44-61. [DOI: https://dx.doi.org/10.3109/07388551.2013.798256]

57. Klammsteiner, T.; Walter, A.; Bogataj, T.; Heussler, C.D.; Stres, B.; Steiner, F.M.; Schlick-Steiner, B.C.; Insam, H. Impact of Processed Food (Canteen and Oil Wastes) on the Development of Black Soldier Fly (Hermetia illucens) Larvae and Their Gut Microbiome Functions. Front. Microbiol.; 2021; 12, 619112. [DOI: https://dx.doi.org/10.3389/fmicb.2021.619112]

58. Schoumans, O.F.; Bouraoui, F.; Kabbe, C.; Oenema, O.; van Dijk, K.C. Phosphorus Management in Europe in a Changing World. Ambio; 2015; 44, pp. 180-192. [DOI: https://dx.doi.org/10.1007/s13280-014-0613-9] [PubMed: https://www.ncbi.nlm.nih.gov/pubmed/25681976]