Single-cell\nProtein Bioplastic Films from Recovered\nNitrogen and Carbon with High Anaerobic Biodegradability and Biogas\nPotential at End-of-Life

The majority of plastics used today are produced from\nnonrenewable\nresources, and, depending on the end-of-life management, they may\nend up in landfills or in nature, giving rise to microplastic pollution.\nA potential way of minimizing this is to use proteins, preferentially\nrecovered from organic waste and residues, to make plastics. In line\nwith this, we explored here the potential of protein-based bioplastics\nsourced from single-cell protein (SCP). Films of glycerol-plasticized\nSCPs (grown by recovering carbon from cheese whey and nitrogen from\nanaerobic digestate) were produced by compression molding. Electron\nmicroscopy revealed a structure of intact cells and the presence of\ncracks/voids, and the mechanical properties indicated a rather poor\ncohesion between the cells, despite the high-temperature treatment\nin the pressing stage. The resulting structure yielded a material\nthat could absorb a sizable amount of both nonpolar (rapid capillary\nuptake) and polar liquids. The anaerobic biodegradation of the SCP\nfilms demonstrated that full biodegradability (100%) and high specific\nbiomethane productions (471 ± 8 mL/gram of volatile solids) could\nbe attained within operating conditions that are typical of anaerobic\ndigestion processes in the treatment of food waste. Overall, this\nstudy highlights the potential and also the challenge of using SCP\nas an alternative bioplastic material in food packaging and edible\ncoatings.