These 4 companies are removing carbon dioxide from the ocean. Here's how

As the largest carbon sink on Earth, our ocean is the unsung heroes of the fight against emissions and climate change. They absorb a quarter of all carbon dioxide emissions and 90% of the excess heat these emissions cause.

What if we could make the ocean absorb even more CO2 from our atmosphere? This is the concept behind Direct Ocean Capture (DOC).

While the world’s drive to reduce CO2 and other greenhouse gas emissions continues, mitigating new emissions alone will not take us to net zero, according to studies referenced by the Intergovernmental Panel on Climate Change (IPCC), which monitors progress towards the targets set by the Paris Agreement. In addition to decarbonizing new emissions, we must find ways to remove existing carbon from the atmosphere – generating “negative emissions”.

One method for doing this is Direct Air Capture (DAC), which draws CO2 directly out of the atmosphere. It is then either stored deeply underground or used in various industrial applications. However, DAC is costly as the concentration of CO2 in the air is relatively low.

Direct Ocean Capture (DOC) is similar to DAC in that it removes dissolved carbon directly from seawater using a range of electrochemical processes. The treated seawater is then returned to absorb more CO2 from the atmosphere. The ocean contains 150 times more carbon dioxide than the atmosphere, making DOC potentially more efficient and lower-cost than DAC.

While industrial carbon capture systems that clean the flue gases of power plants and factories have been around for many years, DOC is still in early development stages. Here are four companies pioneering the technology.

The Amsterdam-based start-up uses electrolysis – which splits water molecules into oxygen and hydrogen – as the starting point for extracting CO2 from seawater. It says its method will cost less than $100 per ton of CO2 when operating at scale – less than half of the typical cost of DAC.

The technology operates on renewable energies such as solar and wind, making it a clean energy process that could virtually be conducted anywhere. The method returns only water, no chemicals, to the sea afterwards, the company states.

Another advantage of Brineworks’ technology is that it produces hydrogen as a by-product. This could become a future revenue stream as demand for “green”, carbon-free hydrogen increases in the wake of heavy industries such as steel and cement-making decarbonizing.

TechCrunch reports that the start-up has recently secured $2.2 million in funding to develop its method.

A spin-off from the California Institute of Technology (Caltech), Captura employs electrodialysis to extract CO2 from seawater. Electrodialysis works by acidifying ocean water to release CO2 dissolved in the seawater and then capturing it with a membrane. Captura’s technology also uses renewable energy to fuel its process, without any additives or by-products. The company aims to reuse existing infrastructure such as desalination plants or decommissioned oil rigs.

Captura has gained support from the US Department of Energy and industry players like Norway’s Equinor. The two companies are currently working together on a pilot project in Hawaii that will remove 1,000 tons of CO2 annually.

Sea02 also draws on electrodialysis to separate CO2 from the seawater it is dissolved in. Once captured, CO2 is either sequestered or made available for onward use. The decarbonized water is returned to the ocean, where it can start absorbing CO2 from the atmosphere again.

SeaO2 is currently seeking storage providers in Europe as partners to secure sequestration capacity. A spin-out of Delft University, the company’s goal is to remove 250 tons of carbon this year, increasing its output to one million tons – or a gigaton – by 2045.

Ebb focuses on organizations that process water, including aquaculture farms, desalination plants, coastal industry plants and ocean research labs. As seawater flows through these facilities, Ebb’s technology separates it into acidic and alkaline solutions using low-carbon electricity.

The alkaline solution is then returned to the ocean, where it binds CO2 to form bicarbonate, which the company describes as a stable form of CO2 storage for 10,000 years. The Ebb process also helps to lower ocean acidity, which affects marine species such as fish and shellfish.