Evaluation of biomethanation process with intermittent hydrogen purging

Biogas upgrading has been intensively investigated to use biogenic carbon sources to produce biomethane. Unlike conventional upgradation practice, which separates CO 2 from raw biogas, novel biological CO 2 biomethanation can convert CO 2 present in raw biogas into CH 4 by hydrogenotrophic methanogens in presence of exogenous H 2 . In this study, CO 2 biomethanation process with intermittent pulse H 2 injection was experimented with ex-situ condition with externally supplied CO 2 in a batch mesophilic continuously stirred tank reactor (CSTR) with nutrient-enriched inoculum adapted in H 2 -CO 2 environment. Gas composition, CH 4 yield, CO 2 utilization efficiency and volatile fatty acid (VFA) profile were examined. The result indicates final CH 4 composition of 82.71% with H 2 injection. The net CH 4 yield from biomethanation was found to be 0.78 mmol (0.20 mmol CH4 /mmol H2 ). The CO 2 utilization efficiency of 74.53% was achieved with CH 4 yield of 80.21% of theoretical potential of supplied H 2 . VFA analysis shows total VFA concentration of 5.10 mg/L and the pH was maintained at 7.53. This suggests that there is no accumulation of VFAs, supporting pulse injection as an effective remedial approach to mitigate the effects of H 2 supply during biomethanation process. CO 2 biomethanation can serve as a H 2 end-use application, carbon capture and utilization method in addition to biological biogas upgradation. • CO 2 biomethanation with pulse H 2 injection was investigated. • The experiment is performed in mesophilic ex-situ condition with continuous stirring. • CH 4 content, CH 4 yield, and CO 2 utilization efficiency were calculated. • Validated CO 2 conversion into CH 4 from hydrogenotrophic methanogenesis.