What is Direct Ocean Capture (DOC)?

Direct Ocean Capture is a set of technologies designed to remove carbon dioxide directly from seawater. It is often referred to by the acronym DOC. The ocean acts as a massive natural reservoir for carbon. It absorbs about a quarter of the carbon dioxide emitted into the atmosphere every year. As the ocean absorbs this gas, the concentration of carbon in the water increases. Direct Ocean Capture systems aim to pull that carbon out of the water so it can be stored or used in industrial processes.

For a founder, this represents a specific branch of the carbon removal industry. While most people are familiar with planting trees or pulling carbon from the air, the ocean offers a different set of physics and chemistry to work with. The goal is to strip the dissolved inorganic carbon from the water. This effectively creates more capacity for the ocean to absorb more carbon from the sky. It is an indirect way of cleaning the atmosphere by cleaning the water first.

Most Direct Ocean Capture systems rely on electrochemical processes. In a typical setup, seawater is pumped into a system where it passes through a series of membranes or cells. By applying an electrical current, the system can change the acidity or alkalinity of the water. When the water becomes more acidic, the dissolved carbon dioxide is released as a gas. This gas is then captured and compressed for sequestration or for use in making low carbon fuels and materials.

There are several ways to approach this process.

• Bipolar Membrane Electrodialysis uses electricity to split water molecules.
• Electrochemical pH swing processes move the water between acidic and basic states to trigger the release of gas.
• Liquid solvent systems use specialized chemicals that bind to the carbon in the water.

Once the carbon is removed, the treated water is returned to the ocean. This water is now carbon depleted. It is capable of absorbing a fresh batch of CO2 from the air above it. This cycle turns the surface of the ocean into a giant filter for the planet. For a startup, the engineering challenge is doing this with as little energy as possible. The less energy you use to extract a ton of carbon, the more viable your business becomes.

Direct Ocean Capture is frequently compared to Direct Air Capture or DAC. While both seek to remove CO2, they operate in very different environments. The primary difference is the concentration of the carbon. Carbon dioxide is about 150 times more concentrated in seawater by volume than it is in the air. From a purely scientific perspective, this means you do not have to move as much medium to get the same amount of carbon.

In Direct Air Capture, you need massive fans to push huge volumes of thin air through filters. In Direct Ocean Capture, the ocean has already done the work of concentrating the carbon. However, water is much heavier and more viscous than air. Moving water through a system requires significant pumping power. This is a trade off that founders must calculate carefully.

Another comparison point is the footprint of the facility. Because the concentration is higher, a DOC plant can theoretically be smaller than a DAC plant of the same capacity. This might lead to lower capital expenditures for physical hardware. On the other hand, the ocean is a harsh environment. Saltwater is corrosive. Any startup building DOC hardware must invest heavily in materials that can survive constant exposure to brine and sea life.

Founders looking to enter this space often look for ways to piggyback on existing infrastructure. Building a standalone offshore platform is incredibly expensive. Instead, startups are looking at specific scenarios where they can integrate their tech.

• Desalination plants already pump massive amounts of seawater and have existing intake and outtake pipes.
• Offshore wind farms provide a direct source of renewable energy to power the electrochemical cells.
• Shipping vessels could potentially integrate DOC units to offset their own emissions while in transit.
• Co-location with aquaculture farms could help manage local acidity levels for shellfish.

Integrating with a desalination plant is a common starting point. These plants are already moving the water and filtering it. Adding a DOC component to the tail end of the process reduces the initial infrastructure costs. This allows a startup to focus on the carbon extraction technology rather than the plumbing.

Another scenario involves the voluntary carbon market. Companies are increasingly looking to buy high quality carbon removal credits. Direct Ocean Capture is seen as a high quality credit because the removal is permanent and measurable. Unlike a forest that might burn down, carbon injected into deep geological formations or turned into rock is gone for good.

Building a DOC startup is not without significant risks and unanswered questions. One of the biggest unknowns is the long term ecological impact of returning treated water to the ocean. While the water is chemically similar to what was taken in, the local change in pH could affect micro-organisms or coral reefs. Founders need to provide transparent data on how their process alters the local marine environment.

Another challenge is Measurement, Reporting, and Verification, often called MRV. In the air, it is relatively easy to measure how much CO2 a fan is pulling. In the ocean, the currents and the chemistry are more complex. Proving exactly how much atmospheric CO2 was drawn down because of your ocean treatment is a difficult scientific hurdle. Investors and credit buyers will demand rigorous proof before they pay for the service.

Energy costs remain the primary barrier to scale. To be climate positive, the energy used must be from renewable sources. If a startup uses coal power to run a DOC plant, they might end up releasing more carbon than they capture. Finding cheap, consistent renewable energy near the coast is a logistical puzzle that requires a deep understanding of the energy grid.

The cost per ton of carbon removed via DOC is currently high. It is significantly more expensive than traditional offsets like reforestation. This is known as the green premium. Founders must find a way to drive this cost down through better membrane technology or more efficient electrochemical cycles. The goal for most in the industry is to reach a price point below one hundred dollars per ton.

At the moment, the market is supported by early adopters and tech companies willing to pay a premium for permanent removal. This provides a sandbox for startups to iterate. However, to build a business that lasts and has a global impact, the technology must eventually compete on a cost basis with other forms of sequestration.

Success in this field requires a multidisciplinary team. You need marine biologists to understand the ecology. You need electrochemists to optimize the cells. You need mechanical engineers to build for the ocean. Finally, you need a solid grasp of the regulatory landscape. The ocean is governed by a patchwork of international and local laws. Navigating these permits is often just as hard as the engineering itself. Founders who can manage these diverse threads will be the ones to build something solid in the blue economy.