Microbial community dynamics in granular activated carbon enhanced up-flow anaerobic sludge blanket (UASB) treating municipal sewage under sulfate reducing and psychrophilic conditions

Two laboratory-scale up-flow anaerobic sludge blankets (UASB) reactors treating municipal sewage were operated to test the effects of granular activated carbon (GAC) addition under sulfate-reducing and psychrophilic conditions. As compared to the non-GAC reactor, the GAC-amended reactor simultaneously enhanced chemical oxygen demand (COD) removal (from 61% to 69%) and methane production (from 11% to 20%) (all with P < 0.05). With a stepwise decrease in the hydraulic retention times, the specific methanogenic activity (SMA) using acetate as substrates decreased in both reactors (from 30 to 24 and 66 to 48 mg CH4-COD/g VSS/d, in the non-GAC and GAC-amended UASB, respectively); whereas SMA using hydrogen as substrates decreased in the non-GAC UASB (from 42 to 31 mg CH4-COD/g VSS/d), and increased in the GAC-amended UASB (from 58 to 89 mg CH4-COD/g VSS/d). Microbial community analysis revealed that Geobacter was enriched in the GAC-biofilm (4.9%), higher than that in the suspended sludge of the non-GAC UASB (0.7%) and GAC-amended UASB (1.4%) at the end of the operation. Methanobacterium, Syntrophus, and sulfate-reducing bacteria were also enriched in the GAC-amended UASB. Our results indicate that GAC may stimulate potential bio-electric active microorganisms, resulted in enhancing methanogenesis during anaerobic digestion of municipal sewage