| dc.description.abstract | Underground Hydrogen Storage (UHS) in reservoirs and caverns is a possible solution for large-scale and long-term storage of hydrogen (H2) in the subsurface. As the cost of tech- nology installation and electricity from renewable energy, such as solar and wind energy, continues to decrease, utilization and storage of H2 can accelerate the energy transition. H2 and UHS can also contribute to energy security and a more sustainable energy system. How- ever, it is essential to understand the potential implications the microbial processes in the subsurface can cause in the UHS. This thesis quantifies and studies the impacts of different H2 concentrations and pressures on the microbial H2 consumption by two metabolic groups; sulfate-reducers and methanogenesis. The sulfate-reducing bacterium (SRB) and the methanogen used in this experiment are Desulfohalobium retbaense and Methanocalculus halotolerans, respectively. In addition, the microbial H2 consumption by the SRB was also studied in the micromodel experiment to observe the behavior in porous media. The metabolic processes of the SRB were inhibited by the high pH of 9.0 in the higher H2 concentrations and pressures. The highest maximum consumption rate was at 100%H2 with 0.05 mmoles/day and at 90%H2 with 0.22 mmoles/day for the SRB and methanogen, respectively. For the different pressures, the maximum consumption rate for the SRB was stable at 0.04 mmoles/day, while for the methanogen was at 2 barg with 0.59 mmoles/day. In the micromodel at 35 barg, the consumption rate for the SRB was 1.23 ·10−6 mmoles/day. The lower consumption rate could be due to the pore geometry, fewer microbial cells, and unfavorable environments caused by waste and byproducts. The production of H2S by the SRB was influenced by the high pH, resulting in a dominant sulfide concentration in the form of HS–. Meanwhile, the microbial activity of the methanogen did not encounter limiting factors, leading to the highest CH4 concentration of 29.92% at 2 barg. The SRB was able to inhibit their microbial activity and poses a lower risk for H2 loss, corrosion, and clogging in UHS. However, the methanogen had effective metabolic processes and consumed the available H2 regardless and produced CH4. Therefore, more studies should be conducted to control the microbial activity in the subsurface to ensure safe and stable UHS. | |
