At the genus level (Figure 4b), the dominant microorganisms included Methanothrix, Methanospirillum, Methanobacterium, Methanosphaerula and Methanomassiliicoccus. The relative abundances of Methanothrix at different OLR (R2-2, R2-3, R2-4) were, 45.16%, 38.76% and 41.75%, respectively. In the...