Microbial Community Structure and Microbial Activities Related to CO2 Storage Capacities of a Salt Cavern

Salt caverns are cavities that form in salt deposits and can be used for hydrocarbon or gas storage as well as waste disposal. Despite high salt concentrations in those environments, microbial life still occurs and affects the storage or disposal capacities of the cavern. In order to predict what may occur over time it is important to understand the types of microorganisms present in salt caverns and the environmental impact of their activities. For example if salt caverns were to be used for CO2 storage, the fate of CO2 will be impacted by microbial activities. In the presence of H2 microorganisms can convert CO2 to acetic acid and water or to methane and water. Samples from a salt cavern plant used to store oily sand were obtained andused to determine microbial community composition by pyrosequencing. Community analyses showed a halophilic, thermophilic community including the genera Methanohalophilus, Methanolobus and others capable of producing methane. Oil-degrading genera (Halanaerobium and Marinobacter), sulfate-reducing genera (Desulfovermiculus and Desulfovibrio) as well as the genus Acetohalobium capable of producing acetic acid in high salt environments were also prevalent. Determination of microbial activities related to CO2 fixation or transformation (homoacetogenic activity and hydrogenoclastic methanogenic activity) indicated that the salt caverns have homoacetogenic activity at both high and low salt concentration. Methanogenic activity was observed with low salt concentration only. Thus if salt caverns were to be used for CO2 storage production of acetic acid, but not of methane, is expected if H2 is present.

盐穴（salt caverns）是赋存于盐矿床中的空腔，可用于碳氢化合物或气体储存，亦可用作废弃物处置场所。尽管此类环境盐浓度极高，仍有微生物群落存活，并会对盐穴的储存与处置能力造成影响。为预测长期演变过程中可能发生的变化，明确盐穴内存在的微生物种类及其活动对环境的影响至关重要。例如，若将盐穴用于二氧化碳（CO₂）储存，二氧化碳的归趋将受到微生物活动的调控与影响。在氢气（H₂）存在时，微生物可将二氧化碳转化为乙酸与水，或转化为甲烷与水。研究人员采集了一座用于储存含油砂的盐穴设施的样本，并通过焦磷酸测序（pyrosequencing）解析微生物群落组成。群落分析结果显示，该群落为嗜盐嗜热型群落，包含产甲烷的甲烷嗜盐菌属（Methanohalophilus）、甲烷嗜甲基菌属（Methanolobus）等菌属；降解油类的菌属（嗜盐厌氧菌属Halanaerobium、海杆菌属Marinobacter）、硫酸盐还原菌属（脱硫蠕虫菌属Desulfovermiculus、脱硫弧菌属Desulfovibrio），以及在高盐环境中可产乙酸的嗜盐乙酸菌属（Acetohalobium）同样在群落中占据优势地位。针对与二氧化碳固定或转化相关的微生物活动（同型产乙酸活性（homoacetogenic activity）及氢营养型产甲烷活性（hydrogenoclastic methanogenic activity））开展测定后发现，盐穴在高盐与低盐浓度条件下均具备同型产乙酸活性；仅在低盐浓度条件下检测到产甲烷活性。因此，若将盐穴用于二氧化碳储存且存在氢气的情况下，预计将生成乙酸而非甲烷。