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The addition of 0.5–1 mm biostable biochar (10 g/L) to mesophilic anaerobic digesters inoculated with crushed granules (1 g-VS/L) and fed with 4, 6 and 8 g/L glucose shortened the methanogenic lag phase by 11.4%, 30.3% and 21.6% and raised the maximum methane production rate by 86.6%, 21.4% and 5.2%, respectively, compared with the controls without biochar. 75 μm biochar further shortened the lag phase by 38.0% and increased the methane production rate by 70.6% at 6 g/L glucose loading. Biochar also simultaneously enhanced the production and degradation of intermediate acids. The fingerprint and sequencing analysis used to examine the spatial distribution and temporal evolution of communities revealed that proportion of Archaea was higher in the biochar-added treatments and in the tightly-bound fractions. Methanosarcina located in the tightly-bound fractions on the biochar surface, and was …