Pure mycelium materials are a novel type of biobased materials that provide an alternative to otherwise polluting leather products and meat. Pure mycelium is considered a sustainable material as it is being produced through biofabrication while making use of renewable biomass resources or waste streams. However, the production of this pure mycelium results in a waste stream itself. This waste stream consists mostly of the spent mycelium substrate (SMS) used for its production along with a smaller share of pure mycelium waste (PMW) which cannot be used for its intended purpose due to contamination with substrate particles. The current knowledge gap with regards to the lack of appropriate options for its valorisation results in these waste streams to be composted and provides a serious burden to producers of mycelium materials as this disposal is costly. Additionally, composting of these mycelium waste streams is considered unsustainable according to the principles of the circular bioeconomy (CBE). The CBE is suggested as an alternative economic system that is to overcome the problems that are inherent to our present linear economic systems e.g., resource depletion and environmental degradation. This thesis aims to determine the potential for valorisation of these mycelium waste streams to support operationalisation of the CBE and to improve the cost-efficiency of pure mycelium materials.

To assess this potential, the characteristics of the mycelium waste streams are synthesized from the literature and various options for its valorisation are identified from the literature based on these characteristics. The environmental impacts (GWP, water- and energy consumption) and economic viability of the identified valorisation options are determined by studying available lifecycle impact assessments and techno-economic assessments of processes comparable to those for the valorisation of the mycelium waste stream. Additionally, the eco-efficiency, or the relation between the environmental costs per monetary unit benefit of these valorisation options is calculated with the idea that this provides a more straightforward answer as to what would be the most favourable options for this valorisation based on the separate assessments of environmental impacts and economic viability.

The results of this study suggest that there are several economically viable options that theoretically provide the potential to support operationalisation of the CBE through the valorisation of mycelium waste streams. These are the production of mushrooms, cellulase and fuel pellets for the valorisation of the SMS and extraction of dietary fibers and phenolic compounds from the PMW. The production of fuel pellets is considered the preferred option for valorisation of the SMS due to its fast ROI. However, it does not provide the possibility for optimalisation of biomass resource utilisation. Furthermore, the identified options for valorisation of the PMW are not desirable due to their extremely high environmental impacts. Nonetheless, the production of fuel pellets from the SMS provides the opportunity to improve the cost-efficiency of pure mycelium production as it makes up the vast majority of the mycelium waste streams.

Additionally, the novel synthesis of mycelium waste characteristics provides the potential to study additional options for valorisation of mycelium waste streams in the future. These options could potentially provide the possibility to improve the cost-efficiency of pure mycelium production while simultaneously allowing an optimisation of the utilisation of the resources used for its production. Furthermore, the findings of this study suggest that a different approach in the decision-making of appropriate options for valorisation of biomass waste streams, including mycelium waste streams, is required. An initial idea for a potential decision-making tool is therefore provided.

Lastly, the findings of this study provide the first indication of the possibility to capture economic value from a waste stream that provides a growing burden to the mycelium materials industry. This will allow reductions in the cost price of pure mycelium, making it available to a larger group of consumers and allowing the release of their full potential through increased substitution of otherwise polluting materials and meat.