A new method for simultaneous coke oven gas (COG) biomethanation and in situ biogas upgrading in anaerobic reactor was developed in this study. The simulated coke oven gas (SCOG) (92% H-2 and 8% CO) was injected directly into the anaerobic reactor treating sewage sludge through hollow fiber membrane (HFM). With pH control at 8.0, the added H-2 and CO were fully consumed and no negative effects on the anaerobic degradation of sewage sludge were observed. The maximum CH4 content in the biogas was 99%. The addition of SCOG resulted in enrichment and dominance of homoacetogenetic genus Treponema and hydrogenotrophic genus Methanoculleus in the liquid, which indicated that H-2 were converted to methane by both direct (hydrogenotrophic methanogenesis) and indirect (homoacetogenesis + aceticlastic methanogenesis) pathways in the liquid. However, the aceticlasitic genus Methanosaeta was dominant for archaea in the biofilm on the HFM, which indicated indirect (homoacetogenesis + aceticlastic methanogenesis) H-2 conversion pathway on the biofilm. (c) 2013 Elsevier Ltd. All rights reserved.