Some Bacillus bacteria can convert CO2 to rock in extreme environments
David Marchal/Getty Images
Bacteria found deep in a mine shaft in South Dakota may be able to accelerate the mineralisation of carbon dioxide under extreme conditions. Injecting such microbes underground along with captured CO2 could enable more durable storage of the greenhouse gas.
Gokce Ustunisik at the South Dakota School of Mines and Technology and her colleagues isolated different species of Bacillus bacteria found more than a kilometre beneath the surface in a former mine shaft in South Dakota’s Black Hills. They…
Some Bacillus bacteria can convert CO2 to rock in extreme environments
David Marchal/Getty Images
Bacteria may be able to accelerate the mineralisation of carbon dioxide under extreme conditions. Injecting such microbes underground along with captured CO2 could enable more durable storage of the greenhouse gas.
Gokce Ustunisik at the South Dakota School of Mines and Technology and her colleagues isolated Geobacillus bacteria species from a compost pile in Washington state that were known to tolerate high temperatures and pressures.
In laboratory tests, the researchers compared the rate at which CO2 mineralised when dissolved in…
Article amended on 14 February 2024
We clarified which bacteria were tested for mineralisation activity
This direct air capture system can pull carbon dioxide from the air for later reuse – but it requires a lot of energy
Orjan Ellingvag / Alamy
Light-sensitive molecules called photoacids could make the process of removing carbon dioxide from the atmosphere more energy efficient. Researchers are now devising ways to make photoacids more practical to use.
This could be especially valuable for direct air capture (DAC) systems, which blow air over carbon-capturing materials called sorbents. Existing systems require a large amount of energy to separate pure CO2 from sorbents in order to store or use it elsewhere. This poses a major barrier to using DAC to remove billions of tonnes of CO2 from the atmosphere each year. “That step is hitting a wall,” says Anna de Vries at ETH Zurich in Switzerland. “Every single direct air capture company is struggling and trying to make the most efficient process.”
Adding photoacids to the sorbents could help. When illuminated, each photoacid molecule changes shape and releases a proton, making the solution more acidic. This “pH swing” frees CO2 from the sorbent-photoacid mixture. When the lights go out again, the photoacids – and the solution’s pH – revert, allowing the sorbent to absorb CO2 once more. Then the cycle can be repeated.
Usually heat or pressure is used to release the CO2, but using sunlight or lamps could slash the energy needed for this step, says de Vries, who aims to halve DAC’s energy requirements. However, photoacids tend to be unstable and not very soluble in water, which limits the efficiency with which they can release CO2.
De Vries and her colleagues added various solvents to a photoacid solution and found a mix that makes photoacids more soluble and extends their lifespan from just a few hours to nearly a month.
In another approach, Uvinduni Premadasa at Oak Ridge National Laboratory in Tennessee and her colleagues found a different photoacid that can maintain its response to light longer and produce more acid, enabling it to release CO2 from a solution more efficiently.
Greg Mutch at Newcastle University in the UK says these are “elegant and innovative” solutions. However, he says a scaled-up system could face challenges – for example, losing solvent to evaporation in the air.
While these researchers focused on capturing CO2 from the atmosphere, the first larger-scale test for photoacids may happen in water. A start-up called Banyu Carbon in Washington state is using photoacids to separate CO2 from seawater, with plans to install a system that can remove one tonne of CO2 per year in 2024.
In this system, photoacids are exposed to light and the resulting acidity is temporarily transferred to seawater, causing the water to release CO2 absorbed from the atmosphere. Alex Gagnon, the company’s co-founder, says this cuts the energy needed to separate out CO2 and eliminates the need to power fans.
