Microbial transformation of lignite into methane: Insights from anaerobic-activated sludge systems

Lignite pretreated by H₂O₂ was degraded by microorganisms in anaerobic activated sludge to produce methane, and the microorganisms were analyzed by high-throughput techniques. Samples fermented for 60 days were analyzed by high performance liquid chromatography (HPLC) and gas chromatography–mass spectrometry (GC–MS). Methane production was found to reach a maximum rate of 2.25 mL/g·d⁻¹ at pH 7 and 35 °C, which was synchronized with the efficient consumption of organic acids, with a peak organic acid production of 202.13 COD/mg·L⁻¹. A total of 37 compounds including alkanes, ketones, esters and polycyclic aromatic hydrocarbons were detected in the fermentation broth, and the species compositions of anaerobic sludge microbiota were fungal, bacterial and archaeal are Ascomycota, Bacteroidetes and Methanosaeta respectively in the fermentation system. Based on the analysis of above results, it is initially speculated that the biochemical pathway for lignite degradation and methane production by anaerobic sludge microorganisms is the acetate pathway.