Underground storage of hydrogen could be an alternative way to store large amounts of energy. However, microbial consumption of H2 is still a major uncertainty factor. Since microbial life is widespread in the crust of the earth an underground storage site needs to be seen as a habitat for microorganisms. Microbial activity at the H2 storage site might affect the stored H2 as well as the integrity of the storage site itself.
There is great need for more information about microbial H2 transformation activity at conditions relevant for underground H2 storage i.e. elevated pressure, high temperature and about potential geochemical interactions with surrounding fluid and rock material.
In this study, different fluids from potential subsurface storage sites representing storage in salt caverns or porous rock reservoirs were investigated. While some fluids were inactive, long lasting hydrogen consumption was observed by a porous rock reservoir fluid. Microbial H2 oxidation tolerated high pressure as well as pressure and temperature fluctuations reflecting cycles of H2 storage. In this fluid microbial H2 consumption was shown to be sulfate dependent and led to the formation of sulfide. Furthermore, an increase of sulfate reducing bacteria during microbial H2 consumption was identified by high-throughput sequencing of 16S rDNA. These results indicated the oxidation of H2 by sulfat reducing bacteria to be the presumed process in this porous rock reservoir fluid. Due to the heterogeneity of the investigated fluids, microbial H2 oxidation activity at different H2 underground storage sites cannot be generalized but requires site specific investigations.