Increasing carbon dioxide levels in the ocean due to human activity and climate change have detrimental effects on coral reefs and marine life. To counteract this, researchers have developed a new technology.
The new technology removes CO2 directly from the ocean by using aqueous sodium hydroxide and sodium carbonate. This process helps reverse acidification and contributes to the reduction of global warming.
The development of this technology took several years of experimental work, according to Inside Climate News. The results aligned with the initial models created by the researchers.
The idea for this technology was conceived by Katherine Hornbostel, an assistant professor of mechanical engineering and materials science at the University of Pittsburgh’s Swanson School of Engineering. At the time of its development, there was limited research and funding available for carbon dioxide capture from the ocean.
The technology consists of two models that function similarly but have different geometries. One uses microencapsulated solvents containing sodium carbonate. The other employs hollow fiber membrane contactors with sodium hydroxide.
The first model
In the first model, Hornbostel and Assistant Professor Tagbo Niepa created capsules that carry a sodium carbonate-based solvent. Originally designed for body scanning purposes, these capsules were repurposed to facilitate carbon dioxide removal from the ocean.
The capsules can be described as small caviar beads that contain the sodium carbonate liquid needed for the carbon dioxide to react with. These beads are packed into capillary tubes, allowing for a significant number of contact points. The diffusion of carbon dioxide occurs as it moves from one capsule to another, reacting with the liquid inside.
The sodium capsules can be regenerated by subjecting them to steaming temperatures ranging from 100 to 120 degrees Celsius. This process removes the captured carbon dioxide, which can then be stored. Regeneration enables the reuse of the capsules to capture more carbon dioxide in future cycles.
The second model
The second model uses a hollow fiber membrane that enables seawater to enter and react with the sodium hydroxide solvents present in the cylindrical capsules. This membrane facilitates the mass transfer of seawater, allowing it to react with the solvent effectively.
The hollow fiber membrane consists of a flexible polymer similar to polypropylene, allowing gas to pass through while preventing liquids or ions. According to the research team’s paper, they are the first to demonstrate CO2 removal from seawater using a membrane contactor with a CO2 solvent.
Horbostel emphasized the importance of a high surface area in seawater, as it facilitates the faster removal of diluted carbon dioxide from the water.
The paper suggests that direct ocean capture technology can potentially access the high concentrations of bound CO2 in seawater. Furthermore, it proposes the possibility of performing offshore direct ocean capture on abandoned oil platforms, co-located with offshore wind and/or storage of captured CO2 gas.
Image Sources: Rick Henkel and Paul Horn, https://shorturl.at/bEV19
The potential of ocean carbon capture
Hornbostel acknowledges the challenges of scaling up the technology in the ocean while keeping it affordable. Increasing the pH of ocean water, which enables the release of more carbon dioxide, is one area the team will examine. The model can potentially be placed offshore in regions with high concentrations of oceanic carbon dioxide.
David Koweek, chief scientist at nonprofit OceanVisions and an expert on Hornbostel’s work, highlights the ocean’s enormous potential to contribute to gigaton-scale carbon dioxide removal. However, this potential remains largely untapped due to limited research and development in ocean-based CO2 removal technologies.
According to Hornbostel’s paper, removing 10 gigatons of carbon dioxide annually by 2050 is crucial to keeping global temperature rise below 1.5 degrees Celsius, the most ambitious goal of the 2050 Paris climate agreement.
Research indicates that more than 70 percent of Earth’s surface is covered by the ocean, which has absorbed about a quarter of the carbon dioxide resulting from human activities. The ocean and atmosphere continuously exchange carbon dioxide and other gases in their efforts to achieve equilibrium.
Carbon capture technology, according to Hornbostel, can be effective in both the ocean and the atmosphere. The ocean will remove more carbon dioxide from the air above it to compensate for the carbon dioxide being removed by the technology.
When carbon dioxide enters the ocean, it combines with water to form carbonic acid, causing the ocean’s pH level to decrease and become more acidic. This acidification poses a threat to marine life by making the ocean less habitable.
Professor Peter Petraitis from the University of Pennsylvania has observed a link between increased dissolved carbon dioxide in the ocean and a decline in mussels and gastropods in the Gulf of Maine over the past two decades. Petraitis and his team have noticed that the more ocean temperatures rise, the more gastropod populations decline.
The Gulf of Maine is experiencing lower pH levels and faster warming compared to most other global oceans. Over time, it will have limited capacity to mitigate the effects of ocean acidification.
The global ocean’s current pH level stands at approximately 8.1, exhibiting a decrease of 0.1 since the beginning of the Industrial Revolution. This minor change in pH is concerning, as a one-unit decrease in pH represents a tenfold increase in acidity.
The carbon dioxide dissolution in water leads to the formation of a mild acid, which neutralizes essential compounds like calcium carbonate and bicarbonate. This, in turn, hinders the ability of corals and other invertebrates to build their protective shells and skeletons.
Hornbostel’s research shows promising potential. However, it necessitates exploration of how the technology can be integrated with existing infrastructure, such as desalination facilities.
The study emphasizes the need for further investigation into seawater carbon dioxide capture technology. This technology is crucial in light of the accelerated warming and acidification of the world’s oceans.