Abstract
Methane production was carried out in two different types of reactors using a thermophilic and hydrogenotrophic methanogen, Methanothermobacter sp. KEPCO-1, which converts hydrogen and carbon dioxide into methane at 60 °C. The two reactors used for methane production were stirred-tank reactor (ST) and a bubble column reactor (BC), which were selected because they can provide a good comparison between the medium agitation type and gas–liquid mass transfer. The specific growth rate of KEPCO-1 in the ST and BC was 0.03 h−1 and 0.07 h−1, respectively. The methane conversion rate increased to 77.8 L/L/d in the ST and 19.8 L/L/d in the BC. To prevent the dilution of nutrients in the medium by the water generated during the hydrogenotrophic methanation reaction, a membrane distillation (MD) process was applied to selectively remove water from the culture medium. The MD process selectively removed only water from the medium. Fouling by KEPCO-1 had a negligible effect on flux and showed a high removal performance flux of 16.3 ± 3.1 L/m2/h. By operating the MD process in conjunction with the hydrogenotrophic methanation process, it is possible to prevent the dilution of the nutrients in the medium by the water generated during the methanation process, thereby maintaining stable microbial growth and methanation activity.
Highlights
Global warming due to greenhouse gas emissions has sparked interest in reducing the world’s carbon footprint
The membrane distillation (MD) process was applied to remove the water produced during the methanation process using two different types of mixer-operated fermenters: By a stirrer and by a diffuser. This is a feasibility study and our results suggested that the integrated system of biomethanation and MD could be applied to remove only water without losing nutrients in the methanation process
Compared with previous reports [9,31] that show a high methane production rate at high gas hourly space velocity (GHSV), the methane production rate in this study showed a convincing conversion rate at low GHSV
Summary
Global warming due to greenhouse gas emissions has sparked interest in reducing the world’s carbon footprint. As a carbon utilization method, CO2 reduction into methane (CH4 ) with hydrogen produced from electrolysis has recently emerged as a promising option to store surplus renewable electricity [1,2]. In contrast to H2 , CH4 is good for long-term storage without additional special storage materials and is already widely used as an energy carrier in compressed natural gas, transport fuel, etc. Biomethanation for microbial reduction of CO2 into CH4 with renewably produced hydrogen (H 2) is catalyzed by methanogenic archaea and operates at a lower temperature (40–70 °C) and lower pressure (≤10 bar) than chemical methanation into CH4 with renewably produced hydrogen (H2 ) is catalyzed by methanogenic archaea and operates at[2].
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