Green Route for the Upcycling of Urban Bioplastic Waste: A Biotechnological Resource Recovery Strategy toward Medium-Chain Fatty Acids Production

High Resolution Image Download MS PowerPoint Slide Bioplastics are expected to represent an expanding fraction of urban waste. Recycling and upcycling remain still limited, yet bioplastics are suitable feedstocks for producing value-added products. Developing circular valorization pathways is essential to prevent resource loss and environmental degradation. This study presents an integrated chemo-biotechnological strategy to upcycle bioplastic waste toward medium-chain fatty acid production. Hydrothermal pretreatments were optimized to chemically recycle typical domestic items, such as thermoplastic starch-based bags and poly(lactic acid)-based cups. The yield of carbohydrates extracted from the bag was 86 wt % at 134 °C, 20 min, while the yield of lactic acid from the cup was around 40 wt %. The resulting enriched hydrolysates were utilized in cascade fermentation batch tests using a mixed microbial culture. The system successfully converted the recycled carbohydrates into ethanol, acetate, and butyrate, subsequently leveraging the recycled lactate as an electron donor for anaerobic chain elongation toward medium-chain fatty acids. This process yielded caproate and caprylate concentrations of up to 3000 mgCOD/L and 1300 mgCOD/L, respectively. By decoupling chemical deconstruction from microbial synthesis, this integrated approach enables the recovery of strategic building blocks that are otherwise lost in incineration or landfilling practices. Overall, this study establishes a robust groundwork for transitioning from fossil-dependent chemical production to a waste-based circular bioeconomy, offering a proof of concept to demonstrate the feasibility of upcycling mixed urban bioplastics into platform chemicals.