Impact of biodegradable bioplastics on anaerobic co-digestion of household organic waste and wastewater sludge

The growing adoption of biodegradable bioplastics, such as Mater-Bi (MB) and Crystalline Polylactic Acid (CPLA), as substitutes for conventional plastics has raised questions about their environmental behaviour. This research investigates how these two materials de-grade during anaerobic co-digestion with organic frac-tions of municipal solid waste (OFMSW) and thickened sewage sludge (TWAS). Laboratory-scale semi-continuous tests were carried out to evaluate biomethane production, process performance, and the extent of deg-radation at different bioplastic concentrations. Results showed that both materials degrade only partially, with MB showing greater weight loss (23%) than CPLA (15%) over six weeks. The degradation of MB was mainly at-tributed to abiotic mechanisms rather than microbial activity. Additionally, increasing the concentration of bioplastics in the feed negatively influenced process stability, causing a drop in methane yield and a rise in volatile fatty acids. Despite these effects, phytotoxicity tests suggested the digestate might still be usable in agri-culture. However, the influence of bioplastics on the final digestate quality needs further investigation. Overall, the findings highlight the need for better-performing biode-gradable materials and improved strategies for managing bioplastics within anaerobic digestion systems, especial-ly when aiming for sustainable waste treatment and safe agricultural reuse.