The goal of the UpWaste project is to create a modular cascading biorefinery system based on heterotrophic microalga Galdiera sulphuraria and larvae of insect (Hermetia illucens) for the upcycling of agricultural residues, to obtain higher-value products with defined composition. An industrial blueprint for such a system will be created based on metabolic modelling and experiments at lab and pilot industrial scale.

Draft metabolic models were developed for both test organisms. Full genome sequence of the species with annotation data were the basis. Validation of the model with experimental trials is ongoing. Model will allow to predict agricultural residues upcycling potential, best mixtures for high value chemical accumulation and help develop design sets for upscaling process.

A range of different waste and side streams, more than 10, were collected and characterized both chemically (nutritionally) and physically. G. sulphuraria was grown in non-sterile conditions on pure digestate at rates of 0.9 day-1 with glucose. However, a proteolytic treatment of digestate resulted in increased growth rates (1.2 day-1) and doubled cell concentrations. Furthermore, G. sulphuraria can utilize glucose obtained after straw hydrolysis. Biomass yields in glucose limited cultures were around 0.9 g per g glucose, while only 0.2 g biomass was formed per g glucose in glucose sufficient cultures, probably indicating that amino acids are simultaneously used as nitrogen and carbon sources. Biomass composition (w/w) of G. sulphuraria grown in digestate supplemented with straw hydrolysate was 20% carbohydrates, 37% proteins and 3% lipids.

Larvae of the H. illucens were reared on multiple streams, where survival, growth, feed conversion and waste reduction were determined. Survival was high on most streams, except for tomato leaves, feather meal, grain middlings and household waste. These streams likely contained substances that were toxic to the larvae or had a texture in which the larvae could not survive. The microbiological quality of a series of substrates has been screened during two seasons. The experimental set-up for the heat treatment has been developed. As side lines, we also studied Clostridium perfringens throughout H. illucens production and processing as well as the impact of heat treatment on the microbiological quality of frass.

Current legal obstructions, especially concerning the use of waste in insect feed in Europe, have been identified. From a purely scientific perspective however, no obstacles for the implementation of the system are known. From the market perspective, a large and increasing demand for protein on the world market has been highlighted. Based on the system design, economic and life cycle assessment (LCA) will be carried out to determine the economic feasibility as well as sustainability of such a system.

Ultimately, the developed system will create market opportunities for sustainable and economic production and processing of food and nonfood materials whilst at the same time reducing pollution and resource use by closing loops in the circular bioeconomy. This additional raw material source will increase the utilization of current agricultural production and take some strain off natural resources and agricultural production capacities.

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Photo: Colourbox