Magnesium hydroxide addition reduces aqueous carbon dioxide in wastewater discharged to the ocean
Open accessAbstract
Ocean alkalinity enhancement (OAE) reduces the concentration of dissolved carbon dioxide (CO 2 ) in seawater, leading to atmospheric carbon dioxide removal (CDR). Here we report laboratory experiments and a field-trial of alkalinity enhancement through addition of magnesium hydroxide to wastewater and its subsequent discharge to the coastal ocean. In wastewater, a 10% increase of average alkalinity (+0.56 mmol/kg) led to a 74% reduction in aqueous CO 2 (−0.41 mmol/kg) and pH increase of 0.4 units to 7.78 (efficiency 0.73 molCO 2 /mol alkalinity). The alkalinization signal was limited to within a few metres of the ocean discharge, evident as 27.2 μatm reduction in CO 2 partial pressure and 0.017 unit pH increase, and was consistent with rapid dilution of the alkali-treated wastewater. While this proof of concept field trial did not achieve CDR due to its small scale, it demonstrated the potential of magnesium hydroxide addition to wastewater as a CDR solution.
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Settling rate is also an important consideration for near-shore applications, as particles may sink to the seabed.
“Settling rate is also an important consideration for near-shore applications, as particles may sink to the seabed. 29”
From A framework for understanding efficiency losses of Ocean Alkalinity Enhancement (2026) · cites this paper as [29]
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A framework for understanding efficiency losses of Ocean Alkalinity Enhancement
Lunstrum, A., Keller, D., Hartmann, J., & Moras, C. (2026) · CDRxiv · doi:10.70212/cdrxiv.2026517.v1 · Cited by 1 · see citing works
Quantified Carbon Dioxide Removal from an Alkalinity Addition Field Trial in the Kvina River, Norway
Bahler, I., Trueman, B., Vogt, R., Tucker, J., Brenan, C., & Sterling, S. (2026) · CDRxiv · doi:10.70212/cdrxiv.2026557.v1
- Authors
- Kitidis, V., Rackley, S. A., Burt, W. J., Rau, G. H., Fawcett, S., Taylor, M., Tarran, G., Woodward, E. M. S., Harris, C., & Fileman, T.
- Affiliations
- Plymouth Marine Laboratory (GB)
- PML Applications (United Kingdom) (GB)
- Corresponding author
- Kitidis, Vassilis
- ORCID
- Venue
- Communications Earth & Environment
- Published
- 2024-06-28
- Volume
- 5
- Issue
- 1
- ISSN
- 2662-4435 (ISSN-L)
- OpenAlex
- W4400399728
- Cited by
- 35
- References
- 2
- Citations by year
- 2026: 19 · 2025: 13 · 2024: 3
- FWCI
- 6.88
- Type
- journal article
- Language
- en
- Open access
- gold
- doi.org
- Locations
- Communications Earth & Environment (publishedVersion, cc-by)
- Marine Biological Association (acceptedVersion)
- DOAJ (DOAJ: Directory of Open Access Journals) (submittedVersion)
- Funders
- RCUK | Natural Environment Research Council (CLASS)
- Topics
- Physical Sciences › Earth and Planetary Sciences › Oceanography › Marine and coastal ecosystems
- Physical Sciences › Environmental Science › Environmental Engineering › CO2 Sequestration and Geologic Interactions
- Physical Sciences › Engineering › Mechanical Engineering › Carbon Dioxide Capture Technologies
- Keywords
- ocean alkalinity enhancement, magnesium hydroxide, carbon dioxide removal, wastewater discharge, seawater alkalinity, dissolved CO2, seawater pH, coastal waters, field trials
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