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 CO₂ from raw biogas, novel biological CO₂ biomethanation can convert CO₂ present in raw biogas into CH₄ by hydrogenotrophic methanogens in presence of exogenous H₂. In this study, CO₂ biomethanation process with intermittent pulse H₂ injection was experimented with ex-situ condition with externally supplied CO₂ in a batch mesophilic continuously stirred tank reactor (CSTR) with nutrient-enriched inoculum adapted in H₂-CO₂ environment. Gas composition, CH₄ yield, CO₂ utilization efficiency and volatile fatty acid (VFA) profile were examined. The result indicates final CH₄ composition of 82.71% with H₂ injection. The net CH₄ yield from biomethanation was found to be 0.78 mmol (0.20 mmol_CH4/mmol_H2). The CO₂ utilization efficiency of 74.53% was achieved with CH₄ yield of 80.21% of theoretical potential of supplied H₂. 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 H₂ supply during biomethanation process. CO₂ biomethanation can serve as a H₂ end-use application, carbon capture and utilization method in addition to biological biogas upgradation.