Unlocking poly(lactic acid) degradation through biochar-induced environmental shifts and functional consortia...

Despite the proven degradability of poly(lactic acid) (PLA) under industrial standards, its incomplete breakdown in real food-waste composting systems remains a major barrier to sustainable bioplastic management. This study investigated how biochar influences the physicochemical environment and microbial processes governing PLA degradation during food waste composting. A 30-day controlled composting experiment was conducted with 0%, 5%, and 10% biochar additions. Composting parameters, PLA surface properties, molecular weight evolution, and microbial community dynamics were systematically analyzed. Results showed that biochar improved aeration, moisture regulation, and pH stability, thereby enhancing early-stage hydrolysis. The number-average molecular weight (Mn) of PLA decreased by 86.6%, accompanied by a consistent reduction in weight-average (Mw) and z-average (Mz) molecular weights, indicating accelerated chain scission. Limited surface oxidation suggested that early degradation was dominated by abiotic hydrolysis, while later stages (days 16-30) were characterized by oxidative microbial activity. Biochar promoted the enrichment of Bacillus during the thermophilic phase and Pseudomonas during the cooling phase, both of which are associated with hydrolysis and oxidation of polyester polymers. Redundancy analysis revealed that pH and moisture content accounted for over 80% of the variance in degradation indicators. Overall, biochar acted as a microenvironmental regulator that coordinated abiotic hydrolysis and microbial oxidation, enhancing PLA composting efficiency under realistic composting conditions. These findings provide mechanistic evidence and practical guidance for integrating biochar into food waste composting systems to accelerate bioplastic transformation and reduce residual plastic accumulation.