Granular activated carbon and exogenous hydrogen enhanced anaerobic digestion of hypersaline phenolic wastewater via syntrophic acetate oxidation and hydrogenotrophic methanogenesis

[Display omitted] •Acetoclastic methanogenic activity was inhibited by high salinity.•Degradation rate and methane yield of phenol were increased by GAC and H2.•The syntrophic acetate-oxidizing bacteria were enriched on the GAC surface.•H2 enhanced hydrogenotrophic methanogenesis pathway. High salinity in phenolic wastewater inhibited anaerobes' metabolic activity, thereby affecting the anaerobic biotransformation of phenol. In this study, granular activated carbon (GAC) coupled with exogenous hydrogen (H2) was used to enhance the anaerobic digestion of phenol. The GAC/H2 group's accumulative methane production, coenzyme F420 concentration, and interspecies electron transfer system activity increased by 24 %, 53 %, and 16 %, respectively, compared with the control group. In the floc sludge of the GAC/H2 group, the relative abundance of syntrophic acetate-oxidizing bacteria such as Syntrophus and Syntrophorhabdus were 18.7 % and 1.1 % at genus level, respectively, which were around 93.5 and 7.5 times of that of the controlgroup. Moreover, Acinetobacter (77.6 %), Methanobacterium (44.0 %), and Methanosarcina (34.2 %) were significantly enriched on the GAC surface in GAC/H2 group. Therefore, the coupling of GAC and H2 provided a novel attempt at anaerobic digestion of hypersaline phenolic wastewater via syntrophic acetate oxidation and hydrogenotrophic methanogenesis pathway.