Key Insights
Black Soldier Fly Larvae (BSFL) can be raised on multiple waste types with varying results.
Each waste type has a distinct macronutrient composition, influencing BSFL development speed and nutrient profile. Understanding these variations is critical for optimising BSFL rearing and resource recycling.
The time it takes for BSFL to develop from larvae to prepupae varies significantly depending on the waste source. This development time can range from as little as 15 days to as long as 52 days, with factors like genetics, feeding rates, temperature, and larval density contributing to these differences.
Macronutrients play crucial roles in BSFL development.
Existing BSFL processing facilities show promise in terms of financial sustainability but rely on a mix of waste sources for long-term operation. Scaling up BSFL production to make a global impact is a potential pathway for the future.
Introduction
Black Soldier Fly Larvae (BSFL) have emerged as eco-friendly champions in the world of biowaste decomposition. These remarkable insects possess a unique ability to efficiently consume a wide range of organic waste materials, making them invaluable contributors to sustainable waste management practices. As our planet grapples with the challenges of burgeoning waste production and resource scarcity, the utilisation of BSFL in biowaste decomposition represents a promising and innovative solution. In this exploration, we delve into the fascinating realm of BSFL and their vital role in transforming organic waste into valuable biomass and sustainable products, shedding light on the remarkable potential they hold for a more environmentally conscious future.
Waste Types
There are seven common waste/side streams that are used in BSFL production. These are human manure, animal manure, fruit waste, vegetable waste, municipal organic solid waste (waste produced in urban environments), waste produced by millings and breweries, and poultry feed. These waste types are mainly used because they have very low economic value, however in the case of poultry feed, it is used as a control when experimenting with BSF feed types.
These waste types each have a different nutritional composition, which when consumed can not only affect how fast BSFL develops to the prepupa stage, but also affect their nutrient profile.
Development time
Although the BSF larvae are able to process many different waste types, because of the nutrient composition of these waste types, the length of their development period from the larval to the prepupal stage can vary significantly. For optimal use, it's essential to find a balance between nutritional richness and a low development time.
Below are the different waste types and the corresponding development time of the BSF larvae.
Animal manure (Swine) - 34 days
Human manure - 27 days
Fruit waste - 15-52 days
Vegetable waste - 16-48 days
Municipal waste - 16-37 days
Millings & brewery - 16-39 days
Poultry feeds - 15-24
Since these results were collected from different studies, there are many reasons that can be attributed to the variation in growth rates from the different waste stream types such as genetic influences, feeding rates and intervals, larval density, temperature and time of harvest.
Nutrient composition
The composition of macronutrients (proteins, carbohydrates, fibres, and lipids) in biowaste significantly affects how BSFL treatment processes perform. Different types of biowaste, like human and animal manures, milling and brewery side streams, and municipal organic solid wastes, have varying nutrient compositions.
Waste stream macronutrient composition
As previously mentioned, the different waste streams vary in their macronutrient content. These are essential substances that the body needs to grow and function properly, helping to provide energy and carry out other essential functions. The macronutrient composition of these waste streams refers to the proportion of the macronutrients it contains. For example, one waste type might be higher in proteins and fats, but low in carbohydrates, whereas another may be higher in carbohydrates but lower in proteins.
Understanding the macronutrient composition of these waste streams is crucial in ensuring that BSF can be fully utilised to their maximum effect, as these nutrient ratios can not only influence their own larval development, but also the development of any other organism that consumes them.
Table 1. Waste stream macronutrient composition measured as percentages of dry weight.
BSF Macronutrient composition according to the waste stream type
Not only can we measure the proportion of macronutrients in the different waste types, but also the proportion of macronutrients in the BSF itself. This is important as it helps to provide a more accurate representation of the nutritional value of the BSF as a whole. In addition to this, the efficiency of nutrient uptake by the BSF larvae can also be analysed.
Table 2. BSF macronutrient composition in accordance to waste type reared on.
Influence of macronutrients on BSF larval development
Proteins, carbohydrates, fibres and lipids play pivotal roles in shaping the development of the larvae. Adequate protein intake is essential for robust growth and development, while carbohydrates provide the energy needed to fuel this development. Understanding the intricate connections between these macronutrients is key to optimising BSFL development.
Carbohydrates
A lot of the biowaste consists of carbohydrates. When consumed, it is broken down by enzymatic processes. This results in the formation of simple sugars, organic acids and other metabolites. This mainly occurs in the midgut of the larvae, and once digested it can be absorbed by the gut cells for energy use.
Different ratios of this nutrient can have varying effects on overall larvae nutrient composition. Taking the example of a high-carbohydrate and low-protein diet, the BSF reared on this usually are higher in lipids, due to the conversion of carbohydrates to these organic compounds. These compounds are then stored as fat in the larval body. This is compared to BSF which are reared on a diet which is balanced in carbohydrates and proteins, where their lipid content is much lower. This means that BSF produced on higher carb diets have a higher energy content due to the higher proportion of lipids within them.
Proteins
Proteins have been identified as one of the most important macronutrients that can influence BSF larval development. They are a great source of amino acids for which the larvae need. Proteins and amino acids are degraded in the midgut by enzymes known as peptidases and are then absorbed by gut cells. Once sufficient amino acids have been obtained, larval development is then triggered by hormones secreted by cells in the body.
On low protein diets, due to the absence of sufficient amino acids, larval development is enabled by the production of molecules from carbohydrates that help to increase the amount of amino acids that can be extracted from the diet. Due to this however, the larvae are smaller and have higher development times. BSF reared on a high protein diet have been shown to produce a positive effect on process performance by having a higher larval weight, bioconversion rate, feed conversion rate, larval protein content and a lower development time, with one trade off being a lower lipid content.
Amino acid composition and digestibility are important factors that drive larval development. The amino acid requirements of BSFL can be measured and analysed using the comparative slaughter technique.This is a method of comparing the amino acid composition of the diet to the amino acid composition of the animal following its slaughter, a method mainly used to determine energy requirements of livestock. Due to some waste streams having similar amino acid compositions, formulations of biowaste with amino acids that complement each other could help to enhance overall BSFL development compared to using biowaste types individually.
Fibres
It has been shown that BSFL may not have the enzymes required to directly decompose fibres found in biowaste. Instead, the microbes present in the larval gut and biowaste can break down these fibres, making the nutrients within them available for larval development. Carbohydrates, simple sugars, and other metabolites are produced because of the microbial hydrolysis of fibres.
Fibres in biowaste are a diverse group with varying decomposition processes, and more research is needed to identify which types of fibres can be decomposed by BSFL. High levels of fibres in biowaste, such as those found in animal manures, can reduce the overall nutrient density for BSFL development, potentially impacting process performance. Potential strategies to improve BSFL process performance could include pretreating biowaste to degrade fibres before BSFL treatment or introducing microbes at the beginning of BSFL treatment that can break down fibres (co-conversion). However, future research should consider the role of different types of carbohydrates (e.g., starch, sugars, available carbohydrates) in BSFL development.
Lipids
Lipids are typically a minor component of biowaste and are broken down into free fatty acids, mono- and diglycerides in the biowaste and/or larval gut. These breakdown products are then absorbed by gut cells and used in the larval metabolism. Research suggests that lipids are unlikely to limit larval development unless provided in excess. When compared to proteins, lipids have a smaller influence on larval development. Excess lipids, such as those found in restaurant waste, can potentially hinder larval development.
Unlike carbohydrates and proteins, the composition of biowaste lipids directly affects the fatty acid composition of BSFL. Diets high in long unsaturated fatty acids produce BSFL with longer and more unsaturated fatty acid profiles, which in turn is beneficial for overall heart health. As an example, larvae fed with plant-based diets rich in long unsaturated fatty acids can lead to BSFL with phospholipids that are longer and more unsaturated. Conversely, diets with low lipid content can impact the BSFL fatty acid composition.
Sustainability and scalability
Utilising Black Soldier Fly Larvae (BSFL) biomass in food and feed production could help meet the increasing nutritional needs of the growing global population. However, it's important to note that feeds made from BSFL may not always be a lot more environmentally friendly than conventional feed sources. To ensure sustainability, it's crucial to focus on biowaste materials that are not already used for animal feed or other resource recovery methods. New methods are being developed to assess the sustainability of waste management and feed production systems based on BSFL biowaste processing.
Existing BSFL biowaste processing facilities have demonstrated financial sustainability, particularly when they process several tons of biowaste daily with high efficiency. These facilities typically rely on a mix of biowaste sources for long-term operation due to competition for access to large and continuous biowaste supplies. To have a meaningful impact on global food systems, the BSFL industry would need to produce hundreds of thousands of tons of BSFL annually, considering the vast quantities of soybean and fish meal currently produced each year.
Conclusion