Impact of elevated CO2 concentrations on carbonate mineral precipitation ability of sulfate-reducing bacteria and implications for CO2 sequestration

Interest in anthropogenic CO2 release and associated global climatic change has prompted numerous laboratory-scale and commercial efforts focused on capturing, sequestering or utilizing CO2 in the subsurface. Known carbonate mineral precipitating microorganisms, such as the anaerobic sulfate-reducing bacteria (SRB), could enhance the rate of conversion of CO2 into solid minerals and thereby improve long-term storage of captured gasses. The ability of SRB to induce carbonate mineral precipitation, when exposed to atmospheric and elevated pCO2, was investigated in laboratory scale tests with bacteria from organic-rich sediments collected from hypersaline Lake Estancia, New Mexico. The enriched SRB culture was inoculated in continuous gas flow and batch reactors under variable headspace pCO2 (0.0059 psi to 20 psi). Solution pH, redox conditions, sulfide, calcium and magnesium concentrations were monitored in the reactors. Those reactors containing SRB that were exposed to pCO2 of 14.7 psi or less showed Mg-calcite precipitation. Reactors exposed to 20 psi pCO2 did not exhibit any carbonate mineralization, likely due to the inhibition of bacterial metabolism caused by the high levels of CO2. Hydrogen, lactate and formate served as suitable electron donors for the SRB metabolism and related carbonate mineralization. Carbon isotopic studies confirmed that ∼53% of carbon in the precipitated carbonate minerals was derived from the CO2 headspace, with the remaining carbon being derived from the organic electron donors, and the bicarbonate ions available in the liquid medium. The ability of halotolerant SRB to induce the precipitation of carbonate minerals can potentially be applied to the long-term storage of anthropogenic CO2 in saline aquifers and other ideal subsurface rock units by converting the gas into solid immobile phases.