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

Abstract

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 %).