Single-cell Protein Bioplastic Films from Recovered Nitrogen and Carbon with High Anaerobic Biodegradability and Biogas Potential at End-of-Life

The majority of plastics used today are produced from nonrenewable resources, and, depending on the end-of-life management, they may end up in landfills or in nature, giving rise to microplastic pollution. A potential way of minimizing this is to use proteins, preferentially recovered from organic waste and residues, to make plastics. In line with this, we explored here the potential of protein-based bioplastics sourced from single-cell protein (SCP). Films of glycerol-plasticized SCPs (grown by recovering carbon from cheese whey and nitrogen from anaerobic digestate) were produced by compression molding. Electron microscopy revealed a structure of intact cells and the presence of cracks/voids, and the mechanical properties indicated a rather poor cohesion between the cells, despite the high-temperature treatment in the pressing stage. The resulting structure yielded a material that could absorb a sizable amount of both nonpolar (rapid capillary uptake) and polar liquids. The anaerobic biodegradation of the SCP films demonstrated that full biodegradability (100%) and high specific biomethane productions (471 ± 8 mL/gram of volatile solids) could be attained within operating conditions that are typical of anaerobic digestion processes in the treatment of food waste. Overall, this study highlights the potential and also the challenge of using SCP as an alternative bioplastic material in food packaging and edible coatings.