High CO2 concentrations inactivate planktonic microorganisms in a simulation of carbon capture and storage
The Endurance aquifer is a UK-based example of a hypersaline storage formation targeted for carbon capture and storage, a technology crucial for the global transition towards net zero carbon emissions. However, the potential for microorganisms to interfere with the successful implementation of long-term CO2 storage in the Endurance aquifer is so far unknown. It is also unclear if, and how, the hypersaline brine microbiome will respond after CO2 injection and whether microbial carbon uptake will take place. Therefore, this study aimed to simulate CO2-flooding in an artificial Endurance aquifer inoculated with microorganisms from hypersaline brines from the deep subsurface consisting of halophilic bacteria and archaea. It was found that flushing the artificial system with CO2 inactivated the previously viable microbiome and there was no evidence for recovery within six months. Furthermore, the rapid dissolution of calcium carbonate minerals buffered a pH drop after CO2-flushing, meaning that the inhibitory effect on microbial life is independent of pH. Contrarily, in the undisturbed controls, over the course of several months, we observed growing haloarchaea of the genus Haloplanus which shows signs that that it may be involved in carbonate precipitation, which may be useful for applied microbiology and biological enhanced CO2 sequestration. Growth occurred despite there being no intentionally added nutrients, indicating that members of this genus may be adapted to grow slowly under nutrient-deprived conditions, as is assumed to be the case in large, deep-subsurface waterbodies such as saline aquifers.