Enhancing methane production potential of biodegradable plastics by hydrothermal pretreatment

Anaerobic digestion (AD) is considered a promising method to treat biodegradable plastic (BP) wastes, while low CH4 production yields (MPYs) of BPs limit field application of AD. To overcome such limitation, the impact of hydrothermal pretreatment (HTP) on MPYs of four commercial BPs such as polylactic acid (PLA), polyhydroxyalkanoate (PHA), polybutylene adipate terephthalate (PBAT), and polybutylene succinate (PBS) was investigated in this study. Solubilization efficiencies of BPs increased as BPs were pretreated under higher temperature and longer duration. After pretreatment at 150 degrees C for 3 hr, MPYs of PLA, PHA, PBAT, and PBS under mesophilic conditions were 450-460, 530-545, 165-175, and 460-490 L CH4/kg VS, respectively, which were significantly higher than one of untreated BPs. Pretreatment temperature was found to be the most important parameter affecting CH4 production from BPs compared to pretreatment duration and particle size. It was confirmed that HTP could depolymerize the long polymeric chain in BPs into the monomers of each BP, such as lactate, 2-butenoic acid, 1,4-butanediol, and succinic acid, together with significant changes in surface characteristics. Such changes might be the main reasons for enhancing CH4 production from BPs. These results suggest that the application of HTP to AD can potentially offer to treat diverse BP waste simultaneously with high CH4 production efficiency.