Results indicated that although the three different HRTs provided a stable process with a steady-state of methane production, both methane yield (161Lkg-VSin−1 , 25% higher) and volatile solids removal (VS, 50%, 2-fold higher) increased during longer HRTs. Redundancy analysis results indicated that SporosarcinaandMethnosarcinapositively correlatedtoVSremovalandmethaneyield,andnegativelycorrelated to volatile fatty acids (VFAs) accumulation. The relative abundance of Coprothermobacter (>60%), syntrophic acetate oxidation bacteria (SAOB), and Methanospirillum (8–15%), increased during shorter HRTs. A slight shift to two-stage acetate conversion was observed during shorter HRTs. The results demonstrated that HRTs played a key role in shaping microbial structure, leading to a new steady-state of microbial community profiles and process performances at variable HRTs