Methane production and microbial community characteristics in the co-digestion of biodegradable plastics with lignite

Both biodegradable plastics and lignite are rich in organic matters, but there are still bottlenecks in the process and efficiency of generating clean energy from them. This research discussed the feasibility of anaerobic co-digestion of biodegradable plastics (BP) and lignite for methane production. Polylactic acid (PLA), poly (butyleneadipate-co-terephthalate) (PBAT), polyhydroxyalkanoates (PHA) and lignite raw materials were adopted as fermentation substrates and domesticated biogas slurry was applied as bacteria source. Biogas production experiments, infrared spectroscopy and metagenomic analyses were employed to evaluate the effects of anaerobic co-digestion of BP and lignite on methane production and changes of microbial community structure characteristics. The results revealed that anaerobic co-digestion of different BPs and lignite significantly increased biomethane production. Among them, co-digestion of 5 g PLA and 10 g lignite had the highest biomethane production (56.28 mL), which was 56.90 % higher than the sum of single PLA and lignite (35.87 mL). Synergistic degradation of BP and lignite accelerated the conversion of aromatic substances into small molecular weight substances, resulting in the production of several easily degraded oligomers. Co-digestion also enhanced the diversity of microbial communities and significantly increased the abundance of Bacteroidales and Methanothrix. Co-digestion of BP and lignite was found to enhance the activity of key enzymes and abundance of typical functional genes in the metabolic processes of aromatic compounds. Research results provided a new idea for clean conversion and utilization of BPs and lignite.