Biodegradability and Methane Fermentability of Polylactic Acid by Thermophilic Methane Fermentation

Polylactic acid (PLA) is considered to be a promising polymer to replace petroleum-based plastics. The aim of this study was to evaluate the biological decomposability of PLA by thermophilic methane fermentation (TMF) and to analyse the microorganisms involved in PLA decomposition. Small- and large-scale batch tests were carried out using disposable cutlery as PLA products and pure poly L-lactic acid (PLLA) pellets. It was found that 70–77% of PLA was decomposed by TMF, based on weight changes. The yield of CH4 was 321–343 mL CH4/g PLA consumed. The addition of bacteria doubled the physicochemical degradation rate of PLA. It was determined that PLA decomposition by TMF was efficient, and that it was enhanced by microbial activity. In particular, lactic acid-consuming bacteria were found to play an important role in PLA decomposition by TMF. Thus, we can conclude that TMF is potentially suitable for PLA treatment and biofuel generation.