Biodegradation of Poly(lactic acid) in Soil Microcosms at Ambient Temperature: Evaluation of Natural Attenuation, Bio-augmentation and Bio-stimulation

Biodegradation of poly(lactic acid)-PLA-films in soil matrix under mesophilic conditions was evaluated using natural attenuation, bio-augmentation and bio-stimulation. Rate of mineralization was found to be very slow as 10% in soil at 150 days and there was no evidence of abiotic degradation of the polymer at 30 A degrees C. Bioaugmentation with previously isolated PLA-degrading bacteria, Sphingobacterium sp. strain S2 and Pseudomonas aeruginosa strain S3 and stimulating the native microbial community with 0.2% sodium lactate significantly enhanced the mineralization rate of PLA to 22 and 24%, respectively at 150 days. No adverse effect on soil health as well as its nitrification potential was observed in response to biodegradation and bioremediation strategies. Bio-stimulation and bio-augmentation enhanced more the rate of mineralization of PLA in soil than the natural rate of degradation, and both strategies have no ecotoxic effect on soil microbial population; hence, they can be considered as potential routes to enhance the degradation of PLA at ambient temperature.