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Mineral CO2 storage in basalts: when deep underground bacteria get involved

At a time when alternative geo-engineering solutions are multiplying to offset the excessive emissions of carbon dioxide into the atmosphere as a result of the massive use of fossil fuels (coal, oil, gas), the natural ability of basalts to mineralize CO2 into solid carbonates has long been seen as an attractive and promising avenue for long-term storage of this greenhouse gas and limiting environmental risks.

Mineral CO2 storage in basalts: when deep underground bacteria get involved

Publication date: 20/10/2017

General public, Press, Research

Related themes : Earth System Science

This CO2 mineralisation capacity was recently assessed in situ in deep basaltic flows as part of the CarbFix1 project carried out in Iceland at the pilot site associated with the Hellisheidi geothermal power plant, where two injections of acid gas (CO2± H2S) were carried out in 2012.

But low-temperature basalts (< 120°C) are now recognised as one of the most important microbial habitats on Earth and host abundant and diverse microbial communities, most of which are still poorly understood. They are therefore rarely taken into account in technologies that use the subsurface for geological storage.

Illustration of the CarbFix1 injection site.
Basalt field where CO2 is stored at depth, with volcanic gases released by the Hellisheidi geothermal power station in Iceland in the background. Bénédicte Ménez - IPGP

Since 2008, the geomicrobiology team at the Institut de Physique du Globe in Paris has been monitoring the reactivity of deep-sea ecosystems during acid gas injections in Iceland. These researchers have shown that deep ecosystems respond very quickly (within a few weeks) to injections of CO2. The acidified groundwater first of all led to a marked reduction in microbial richness and stimulated the growth of chemolithoautotrophic (CO2-using) ferroxidant bacteria and degraders of complex aromatic compounds probably produced by the dissolution of the rock. In particular, they show that the dissolution of the basalt was key to this biological stimulation by releasing the nutrients and energy sources required for the growth of these microorganisms. In turn, these microbial activities affected the redox state of the aquifer, the availability of the elements needed for carbonation and the fate of the injected carbon, with probable consequences for the efficiency of mineral storage.

Groundwater filtration at the head of a well drilled into the basalts to collect the micro-organisms that make up deep ecosystems. Bénédicte Ménez - IPGP

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