Methane Yield, Substrate Conversion, Microbial Community Structure and Metabolic Pathways During Anaerobic Digestion of Natural Cellulosic Biomass

Three natural celluloses (softwood pulp, straw grass pulp, and degreased cotton) were used for anaerobic digestion tests to research methane yield, substrate conversion and microbial community structure, and further supplemented and clarified the metabolic pathway mechanisms of anaerobic digestion of cellulosic biomass. The results showed that natural cellulose could be significantly degraded and converted into methane by anaerobic microorganisms. The cumulative specific methane yields of wood pulp fiber (F1), straw pulp fiber (F2), and degreased cotton fiber (F3) were 373.57 ± 10.70 mL/g VS, 349.15 ± 13.20 mL/g VS and 346.16 ± 1.60 mL/g VS, respectively. The corresponding biodegradability values were 93.97%, 85.95% and 84.32%. Although the fermentation cycles in F1, F2, and F3 were identical (T95 was 12 days), the three groups exhibited distinct biogas production patterns. Metagenomic analysis indicated that F1 and F2 were dominated by the acetoclastic methanogenesis pathway, while the proportion of the hydrogenotrophic methanogenesis pathway increased in F3. Meanwhile, the cell motility pathway category was significantly enriched in F3. These results supplement the existing research on the anaerobic digestion of natural cellulose and provide theoretical support for the efficient anaerobic bioconversion of natural cellulosic biomass.