Anaerobic biodegradation of PLA at mesophilic and thermophilic temperatures: methanation potential and associated microbial community

Polylactic acid (PLA) is the most promising bio-based alternative to traditional petrochemical plastics across diverse applications. In this study, the biodegradation performance of PLA plastic under two potential end-of-life scenarios: mesophilic and thermophilic anaerobic digestion (AD) were investigated. The biotic and abiotic influence factors were evaluated through short-time exposure experiments. The potential bacteria and archaea involved in PLA anaerobic biodegradation were identified by high-throughput 16S rRNA sequencing analysis. The results showed that PLA had different biodegradation performance at mesophilic and thermophilic digestion (the biogas yield: 36.70 ± 0.2vs 398.6 ± 1.1 mL/g VS). The increased temperature at thermophilic conditions improved the biodegradability of PLA, but an attack by microorganisms was more crucial for biodegradation. The bacteria engaged in PLA hydrolysis and acidification were closely associated with proteolytic microbes. Mesophilic biodegradation of PLA involved <i>Clostridia</i> (14.94%), <i>Anaerolineae</i> (22.6%) and acetoclastic <i>Methanothrix</i> (53.0%). Thermophilic biodegradation of PLA was mainly accomplished by syntrophic microbes, <i>Clostridia</i> (38.2%), <i>Synergistia</i> (18.99%) and <i>Thermotogae</i> (17.82%), in tandem with hydrogenotrophic <i>Methanothermobacter</i> (20.5%). The results provide some insights for understanding mechanisms governing PLA biodegradation under AD conditions.