Direct Air Capture (DAC)
Direct Air Capture (DAC) extracts CO₂ directly from the ambient air through chemical or physical processes. The technology addresses historical CO₂ emissions already present in the atmosphere. DAC facilities operate through a three-stage process: first, large fans pull atmospheric air into the system; second, the air contacts specialized chemicals (either liquid solvents or solid sorbents) that selectively bind with CO₂; and finally, the captured CO₂ is separated and concentrated while the capture medium is regenerated for reuse.
DAC facilities can be built on non-arable land and powered by renewable energy, making them a versatile solution for carbon dioxide removal. The captured CO₂ can either be permanently stored underground or utilized for various industrial applications, though current costs range from $100 to $600 per ton of CO₂ captured.
Biomass Carbon Removal and Storage (BCRS)
Biomass Carbon Removal and Storage (BCRS) technology leverages natural photosynthesis processes. The system begins with plants absorbing CO₂, water, and sunlight to grow biomass through photosynthesis. This biomass is then harvested and processed through a thermal decomposition process that occurs in the absence of oxygen. The final product is biochar, a stable carbon-rich material that can effectively store carbon for long periods.
This process creates a negative emissions cycle, as the carbon captured by plants is transformed into a stable form rather than being released back into the atmosphere through natural decomposition.
Direct Ocean Capture (DOC)
Direct Ocean Capture (DOC) technology is particularly promising because oceans contain about 150 times more CO₂ than the atmosphere, making them an efficient medium for carbon capture.
The system works by pumping seawater through an electrochemical system, such as an electrodialysis, which generates an acid and a base solution. The acid solution is mixed with seawater to enable the conversion of bicarbonate ions (HCO₃⁻) in seawater into gaseous CO₂, which is then captured and stored or reused. The base solution with controlled safe pH is returned to seawater, increasing its local alkalinity. This enables the conversion of dissolved CO₂ into HCO₃⁻, effectively removing CO₂ from the atmosphere through the ocean’s natural carbon cycle.
DOC can be deployed on floating platforms or coastal installations. It not only helps with carbon removal but also has the added benefit of counteracting ocean acidification.
Enhanced Weathering
Enhanced weathering accelerates the natural process of rock weathering to capture and store atmospheric CO₂. This method involves mining and grinding specific types of rocks, such as basalt or olivine, into fine particles and spreading them over large areas, typically agricultural lands or coastal regions. When these rock particles interact with water and CO₂ from the air, a series of chemical reactions occur, converting the CO₂ into stable carbonate minerals, such as MgCO₃ and CaCO₃.
This process not only effectively locks away the carbon for long periods but also has potential co-benefits for soil health and crop productivity.
Carbon Farming
Carbon farming is a set of agricultural practices to capture atmospheric CO₂ and store it in soils and biomass. It transforms traditional farming into a process that not only produces food but also acts as a carbon sink, helping mitigate climate change.
Soil carbon sequestration through enhanced weathering and microbial processing is an efficient approach for capturing atmospheric CO₂. When crushed rock particles rich in calcium and magnesium silicates are applied to soil, they release essential nutrients like calcium, magnesium, and silica into the soil, improving soil fertility and potentially increasing plant biomass, which in turn contributes to carbon sequestration. They also undergo weathering reactions with carbonic acid (H₂CO₃), ultimately forming stable carbonate minerals like CaCO₃ and MgCO₃, which store carbon for millennia.
Simultaneously, plants absorb CO₂ from the atmosphere through photosynthesis, converting it into organic compounds. As plants grow and die, their roots contribute organic matter to the soil. Soil microorganisms transform organic carbon into stable soil organic matter.
The microbial activity is particularly effective when combined with enhanced weathering, as microbes can accelerate mineral weathering through the production of organic acids while also contributing to carbon storage through their biomass and metabolic products. This synergistic interaction between mineral weathering and microbial processes can significantly enhance the soil’s carbon sequestration potential.
CO₂ capture from flue gas
CO₂ capture from flue gas, also known as post-combustion carbon capture, is a critical technology for reducing greenhouse gas emissions from industrial and power generation processes. Flue gas typically contains CO₂ concentrations ranging from 3–20%.
This system uses techniques such as chemical absorption with amine-based solvents to bind CO₂, which is then released through heating and can be compressed for storage or utilization. Other methods include adsorption, membrane separation, and cryogenic processes. Captured CO₂ can be stored underground or converted into valuable products like biofuels or chemicals, supporting a circular economy and enabling carbon-neutral or even carbon-negative operations.