Evaluation of Biogas Production from Anaerobic Digestion of Biopolymeric Films and Potential Environmental Implications

The increasing environmental pollution resulting from plastic waste and the need to reuse agro-industrial wastes as a source of discarding has led to the development of innovative biobased products. In the frame of this context, the use of neat polylactic acid (PLA) and its blend with polybutylene succinate (PBS) with or without cellulose nanocrystals (CNCs) extracted from hemp fibers is explored here. This study aimed to assess the biogas production of different biopolymeric films. In parallel, life cycle assessment (LCA) analysis was performed on the same films, focusing on their production phase and potential end-of-life scenarios, regardless of film durability (i.e., single-use packaging) and barrier performance, to counteract possible soil health threats. Specifically, this study considered three specific systems: PLA, PLA_PBS (PLA/PBS blend 80:20 w/w), and PLA_PBS_3CNC (PLA/PBS blend + 3% CNCs) films. The assessment involved a batch anaerobic digestion (AD) process at 52 °C, using digestate obtained from the anaerobic treatment of municipal waste as the inoculum and cellulose as a reference material. The AD process was monitored over about 30 days, revealing that reactors containing cellulose showed inherent biodegradability and enhanced biogas production. On the other hand, biopolymeric films based on PLA and its blends with PBS and CNCs exhibited an inhibitory effect, likely due to their recalcitrant nature, which can limit or delay microbial activity toward biomass degradation and methanogenesis. LCA analysis was performed taking into consideration the complex environmental implications of both including biopolymers in the production of renewable energy and the use of post-composting digestate as an organic fertilizer. Remarkably, the PLA_PBS_3CNC formulation revealed slightly superior performance in terms of biodegradability and biogas production, mainly correlated to the presence of CNCs in the blend. The observed enhanced biodegradability and biogas yield, coupled with the reduced environmental impact, confirm the key role of optimized biopolymeric formulations in mitigating inhibitory effects on AD processes while maximizing, at the same time, the utilization of naturally derived energy sources.