Promotion of polylactic acid biodegradation by a combined addition of PLA-degrading bacterium and nitrogen source under submerged and soil burial conditions

This article investigated an efficient process for accelerating polylactic acid (PLA) biodegradation. A combined use of bioaugmentation and biostimulation to faster PLA biodegradation under submerged and soil burial conditions was studied. Under submerged condition, PLA films in basal salt medium were inoculated with either Pseudomonas geniculata WS3 (PLA-degrading bacterium), manure extract, or wastewater sludge extract, with and without the addition of different nitrogen sources. The results revealed that soytone addition with the cultures of P. geniculata WS3, manure extract and wastewater sludge extract significantly increased PLA weight loss percentage and lactic acid content, indicating that soytone is an excellent nitrogen source for enhancing PLA biodegradation. These conditions were selected to evaluate PLA biodegradation under soil burial exposure. It was found that soytone with manure extract addition increased microbial activity and PLA biodegradation in soil. Moreover, the addition both soytone and P. geniculata WS3 speeded up biodegradation rate, resulting in almost 100 percent of PLA mass loss within 60 days in non-sterile soil burial. In conclusion, a combined use of P. geniculata WS3 with soytone is an efficient process for accelerating PLA biodegradation under both submerged and soil burial exposure conditions.