Nowadays, the disposal of livestock manure and organic fractions of municipal waste is subject to strict regulations in relation to its traceability, which prevents any alternative uses and carries considerable costs. The production of low-quality compost is currently the most common use of this organic waste.
However, these organic materials are the optimal substrate for the natural growth of some insect species with adaptive characteristics that enable them to thrive in environments rich of potentially pathogenic microorganisms. Amongst these insects is the “soldier fly”, Hermetia illucens (Diptera, Stratiomyidae), a non-pest fly (adults live for a few days only, they do not feed and do not transmit pathogens), whose larvae quickly and efficiently convert large amounts of organic waste into protein biomass rich in lipids.
Depending on the type of substrate in which the larvae grow, the prepupae (the stage that precedes adulthood) can be harvested and used for different purposes. Using insects as feed/food is allowed in some European countries, but only if they are reared on vegetable scrap or by-products. In Italy, the absence of clear legislation regarding the use of edible insects has so far hindered the industrial development of insect rearing for the food or animal feed industry.
In the agri-food and livestock industries, any solution that can reduce the mass and ammonia content of manure, on one hand, and the use of synthetic fertilizers on the other, is considered to be extremely beneficial for the environment.
The BSF larvae activity enables a 60% reduction in the dry mass of manure, and results in lower phosphorus and nitrogen content, suppressed bacterial growth (including harmful bacteria), reduced bad odours, and a smaller population of invasive domestic flies.
The residue makes good quality soil compost. It has been demonstrated (www.zeolife.it) that amending soils with zeolitite -a rock recoverred from quarry waste- makes it possible to reduce chemical fertilizers in crops by up to 50%. This is due to the high content of zeolites, minerals capable of carrying out cation exchange processes that absorb ammonia nitrogen, such as that present in sewage, releasing the cations (Na, K, Ca, Mg) naturally contained in the mineral.
The addition of this rock to animal bedding reduces the unpleasant emissions and allows the obtainment of a soil improver, whose action is inexhaustible over time.
Currently, the bioplastics used in agriculture derive from cornstarch polymers and their biodegradability is often uneven and lasting longer than the crop cycle of horticultural plants.
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The use of protein-based bioplastics could prevent the usage of plants intended for human consumption and could provide a performant alternative, ensuring biodegradation releases nitrogen in sync with the crop cycle.
The BSF prepupae reared on organic waste can be used as biofuel but they could also represent a resource for large-scale production of proteins, fats, chitin and other active biomolecules (e.g. antibiotics) to be used for different purposes. However, there are currently no sustainable industrial processes for fractionating insects into their components. The use of proteins as bioplastic components highlights some problems that limit the development of the material itself.
Starting from BSF proteins, the identification of an appropriate mixture of components and additives to improve the properties and the technological potential of the application is a key point to guarantee the real processability and the obtainment of functional bioplastics.