If there’s one resource we’re running out of in the fight against global warming, it’s time. That’s why, as countries prepare for the next climate summit with decarbonization goals in focus, scientists and engineers are exploring more direct methods to reduce atmospheric carbon dioxide in the short term. One such approach gaining attention is carbon sequestration, which can accelerate the process without replacing the use of renewable energy or indirect strategies like reforestation.
This article explores five key carbon sequestration technologies:
- Carbon Capture and Storage (CCS)
- Direct Air Capture (DAC)
- Bioenergy with Carbon Capture and Storage (BECCS)
- Mineralization
- Ocean carbon sequestration
1. Carbon Capture and Storage (CCS)
The core idea behind carbon capture and storage is to trap and store carbon before it’s released from industrial facilities. This can be done in several ways, from post-combustion gas separation to oxy-combustion—where pure oxygen is used to produce nearly pure CO2.
Once captured, the carbon can either be injected into geological formations deep underground or converted into raw materials for other industrial processes.
2. Direct Air Capture (DAC)
Direct air capture (DAC) offers more flexibility, as it involves placing large machines in almost any location to suck in air and capture CO2 using liquid solvents or solid sorbents that bind to carbon. Once captured, CO2 is released via pressure or heat, after which it’s stored or repurposed as a raw material, similar to the CCS method. Although this technology is currently expensive, future cost reductions are anticipated.
3. Bioenergy with carbon capture and storage (BECCS)
Since plants naturally absorb large amounts of carbon dioxide, another strategy involves using biomass to capture carbon. Agricultural residues or plant matter with high carbon content are converted into biofuels to produce heat or electricity, or burned directly. During combustion, carbon capture techniques—similar to those used in CCS—are applied, such as underground storage or conversion into raw materials. The result is a net reduction of atmospheric carbon dioxide.
4. Mineralization
Mineralization is one of the more recent carbon sequestration techniques, relying on natural chemical reactions to turn CO2 into solid, stable carbonates. This reaction typically occurs with minerals like basalt or olivine. In industrial settings, this process is used to create calcium carbonate, which is added to cement to produce carbon-negative concrete.
5. Ocean carbon sequestration
The ocean has enormous potential for natural CO2 sequestration. In fact, along with forests and agricultural soils, oceans are among the planet’s largest carbon sinks, absorbing a quarter of global emissions. Some researchers propose artificially enhancing this capacity. Two approaches include:
- Increasing ocean alkalinity by adding powdered limestone, which reacts with CO2 in the water to form bicarbonate.
- Ocean fertilization, which involves adding nutrients like iron to stimulate phytoplankton growth. Phytoplankton are microscopic plants that absorb CO2 through photosynthesis.
Currently, the high costs and potential environmental risks of these methods make them impractical for large-scale use. However, other approaches are available to reduce CO2 emissions in industrial processes.
One example is using industrial slag to reduce the amount of CO2 needed to produce concrete. ACCIONA’s green concrete used in the Port of Cádiz, for instance, generates 27% fewer emissions.
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