Recent research published in ‘Environmental Research Letters’ explores an innovative approach to marine carbon dioxide removal (CDR) through enhanced alkalinity in seawater. Conducted by Tarang Khangaonkar from the Energy and Environment Directorate at the Pacific Northwest National Laboratory and the University of Washington, the study focuses on the Salish Sea in Washington State, where high-alkalinity seawater is generated using bipolar membrane electrodialysis technology. This method effectively removes acid from seawater, allowing the alkaline stream to be returned to the ocean.
The research utilized a shoreline-resolving hydrodynamic model that incorporated biogeochemistry and carbonate chemistry to simulate the response of estuarine waters to the discharge of alkalinity-enhanced seawater. Two deployment scales were tested, with a significant increase in total alkalinity (TA) of 2997 mmol m^−3 and a pH of 9. The findings revealed that a large-scale deployment in a small embayment, Sequim Bay, could remove approximately 2066 tons of CO2 per year, which constitutes 45% of the total simulated removal. This rate of 3756 mmol m^−2 per year is notably higher than the global requirement of 63 mmol m^−2 per year to achieve a target of 1.0 gigaton of CO2 removal annually.
One of the key insights from the study is the impact of mixing and dilution of the added alkalinity as it moves away from the discharge source. The research indicated that while the near-field area experienced significant CO2 removal, the effectiveness diminished over larger areas, with a total of 2176 tons of CO2 removed across a much broader region. Khangaonkar noted, “With shallow depths limiting vertical mixing, nearshore estuarine waters may provide a more rapid removal of CO2 using alkalinity enhancement relative to deeper oceanic sites.”
The implications of this research extend to various commercial sectors, particularly in marine conservation, carbon trading, and environmental technology development. Companies focused on carbon capture and storage may find opportunities in deploying alkalinity enhancement technologies, potentially leading to new revenue streams through carbon credits. Additionally, the findings could influence policies aimed at mitigating ocean acidification, which poses threats to marine ecosystems and fisheries.
Overall, this research not only advances our understanding of marine CDR techniques but also highlights a promising avenue for commercial applications that could contribute to global climate goals. As the need for effective carbon management strategies grows, innovations like those explored by Khangaonkar and his team could play a crucial role in shaping sustainable practices in ocean management and climate change mitigation.
