Aquaculture for all

Researchers pioneer ocean carbon removal technique

Climate change Water quality Sustainability +6 more

Researchers have completed a successful pilot study for a novel ocean carbon dioxide removal (oCDR) method in which they altered the pH of seawater to increase its capacity for carbon dioxide absorption.

Cornwall coast.
The trial took place off the coast of Cornwall, England

Scientists from Plymouth Marine Laboratory and its commercial subsidiary PML Applications, have confirmed the viability, and potential scalability, of a novel ocean carbon dioxide removal technique designed to remove CO2 from the atmosphere by enhancing the alkalinity of treated wastewater before it is discharged out at sea.

Seawater naturally draws carbon dioxide from the atmosphere, but by increasing the pH of seawater, the capacity of the ocean for accepting CO2 can be increased. In terms of tackling global warming and mitigating climate change, emission reductions remain paramount, but ocean alkalinity enhancement and other carbon removal solutions are widely accepted as having a key part to play. Carbon dioxide removal is, for example, explicitly included in the UNFCCC Paris Agreement.

In a first-of-its-kind study, the PML team was commissioned to provide independent and impartial monitoring and analysis of a field trial carried out off St Ives Bay, Cornwall, in September 2022 by Canada-based carbon removal specialists Planetary Technologies. The trial - which followed a series of lab-based tests and modelling - involved adding a diluted form of the alkaline mineral magnesium hydroxide to the wastewater flow at the nearby wastewater treatment plant in St Erth. The treated water was then released four miles offshore through the existing outflow.

The study found that the addition of magnesium hydroxide to the wastewater flow successfully decreased the dissolved CO2 levels of the seawater by up to 74 percent, significantly increasing its potential for carbon dioxide removal. Importantly, the study also found that, after the addition of magnesium hydroxide was halted, the water alkalinity quickly returned to normal levels, showing that the process can be reversed if necessary.

“While this study demonstrates the carbon dioxide removal potential of alkalinity enhancement using magnesium hydroxide, it is imperative to consider potential ecosystem impacts, especially in terms of the scaling up of any such process. During the pilot, the alkalinity was only added for a few hours per day and we were very confident there would be no adverse environmental effects, based on our investigations,” said Dr Vassilis Kitidis, lead author of the study, in a press release.

“Magnesium hydroxide is a well understood mineral which is used in many household products and the levels at which it was being used in the trial were nowhere near anything that might have had a negative effect on marine life. We carried out monitoring throughout the trial and confirmed that Planetary Technologies adhered to all of its environmental permits,” he added.

Sam Fawcett, a PML Applications ocean carbon removal expert, highlighted the significance of this milestone, but also noted the need for transparency and trust with the public for this type of technology to be accepted.

“From initial modelling to chemistry analysis and environmental impact assessment we use our expertise to ensure that projects such as this are underpinned by high quality science. This is essential in order to accurately confirm effectiveness, understand any potential knock-on consequences, optimise techniques and ultimately to build trust,” they said.

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