Biological upgrading of biogas assisted with membrane supplied hydrogen gas in a three-phase upflow reactor

Biogas upgrading via CO₂ conversion to CH₄ is an emerging technology for renewable natural gas production and carbon management, but its development is limited by the low H₂ gas to liquid phase transfer. Herein, an innovative biogas upgrading system employing a three-phase design was studied for CO₂ conversion with H₂ supply via gas-permeable membrane. The system produced biogas consisted of 74.1 ± 7.1 % CH₄ and 25.9 ± 7.1 % CO₂ with intermittent injection of H₂. When H₂ supply was continuous, the CH₄ content increased to 91.6 ± 2.2 % at a H₂:CO₂ ratio of 4.4. Although a higher ratio of 5.5 could result in a higher CH₄ percentage of 95.2 ± 2.5 %, biogas production rate started to decrease. The removal efficiency of organic contents remained above 90 % throughout the experiment. Microbial community analysis corroborated the findings, showing that hydrogenotrophic Methanobacteriaceae was more prevalent in the biofilm (71.9 %) compared to that in anaerobic digestion (15.8 %) and effluent (14.1 %).