Microbial risk assessment and mitigation for underground hydrogen energy storage in salt caverns: A multidisciplinary investigation

Underground hydrogen storage (UHS) in salt caverns is a promising solution for large-scale renewable energy storage, but its long-term stability may be compromised by hydrogenotrophic microorganisms such as sulphate-reducing bacteria (SRB). This study integrates global salt basin analysis, numerical modelling, and laboratory experiments to assess microbial risks associated with the hydrogen storage. We evaluated salt deposits across six continents, reviewed microbial communities in seawater sources commonly used for the leaching, and simulated SRB behaviour under varying hydrogen concentrations. Experiments using both commercial SRB strains and indigenous consortia from Western Australia revealed minimal microbial activity under hypersaline, low-carbon conditions. These findings suggest that microbial risks in salt caverns may be strongly constrained by salinity and nutrient availability under realistic cavern conditions. Consequently, this may reduce the likelihood of hydrogen loss in properly designed cavern systems. We also propose practical mitigation strategies, including thermal sterilization and site-specific biocide use. This work highlights the need to integrate microbial risk assessments into site screening and design for safe and sustainable hydrogen storage. • Global salt basin assessment identifies microbial risks for hydrogen storage. • Numerical models simulate sulphate-reducing bacteria under hydrogen. • Laboratory experiments reveal minimal microbial activity in hypersaline conditions. • Salinity and nutrient limitations strongly restrict microbial growth in caverns. • Mitigation strategies include thermal sterilization and targeted biocide treatment.