Two laboratory-scale up-flow anaerobic sludge blankets (UASB) reactors, one with and one without granular activated carbon (GAC)[url=www.granular-activated-carbon.com/]granular carbon price[/url] were operated for municipal sewage treatment at low temperatures (16.5 ± 2.0 °C). During the 120-day operation, the GAC-amended reactor significantly enhanced COD removal (from 62% to 75%, P < 0.05) and methane production (from 87 to 218 mg CH4-COD/reactor/d) than the non-GAC reactor. Bacterial communities were significantly different between the two reactors (P < 0.05). Geobacter, a key indicator for direct interspecies electron transfer (DIET), had the highest differential score (LEfSe analysis), showing significantly higher abundances in the GAC-amended reactor (3.7–8.8 than the non-GAC reactor (0.9–4.0. GAC also enriched syntrophic bacteria, Syntrophomonas, Syntrophus and sulfate reducing bacteria. Methanobacterium dominated the archaeal community in the GAC-amended reactor sludge (35.7 and GAC-biofilm (75.3, and was less abundant in the non-GAC reactor (9.9.[url=www.coalactivatedcarbon.com/]https://www.coalactivatedcarbon.com[/url] It indicates that GAC enriched microbial syntrophic partners with potential electro-activities in the anaerobic digestion process.