What is ocean alkalinity enhancement and why is it important?

5 August 2024

The PML team provided independent monitoring and analysis of a pilot trial by Planetary Technologies in 2022 in St Ives Bay (UK), which involved the addition of magnesium hydroxide to wastewater.

In this video and Q&A Dr Vassilis Kitidis, Marine Biogeochemist at PML and scientific lead on the study's monitoring and analysis, delves into the findings – recently published in the peer-reviewed journal ‘Communications Earth & Environment’ (“Magnesium hydroxide addition reduces aqueous carbon dioxide in wastewater discharged to the ocean”), the significance of the trial, and the next steps for advancing this promising technology.



Can you explain how Ocean Alkalinity Enhancement (OAE) works?
Under natural conditions, rocks weather over millions of years, increasing the alkalinity of seawater and allowing the oceans to absorb more CO₂ from the atmosphere. By replicating and accelerating this process, we can enhance the ocean's ability to remove CO₂. This involves grinding up rocks rich in alkaline materials and adding them to seawater. This, in turn, increases the water's capacity to absorb CO₂ from the atmosphere, thereby reducing atmospheric CO₂ levels.
 
What specific materials were used in the pilot trial to enhance ocean alkalinity?
In the trial carried out by Planetary in St Ives Bay, magnesium hydroxide was used. It’s a naturally occurring mineral used in many household products. The magnesium hydroxide was added to wastewater as a slurry, which dissolves in the water and reduces its CO₂ concentration. The treated wastewater, now containing the magnesium hydroxide slurry, is then discharged into the sea. This process not only reduces the carbon footprint of the wastewater but also has the potential to draw down CO₂ from the atmosphere.
 
What role could it have in terms of helping tackle climate change?
To achieve net zero emissions, we must first significantly reduce our current emissions. However, reducing emissions alone is not enough; we also need to actively remove CO₂ from the atmosphere. This approach addresses both the historical burden of emissions and the residual emissions from industries that are challenging to decarbonize.

There are various methods for CO₂ removal, including land-based and ocean-based techniques. Each method has its own set of advantages and challenges, such as scalability and cost. To effectively combat climate change, we need a wide portfolio of solutions. Ocean alkalinity enhancement (OAE) is one such solution.

What were the key findings of your study regarding the use of magnesium hydroxide in wastewater treatment?
Our study demonstrated that adding magnesium hydroxide to wastewater significantly increases its alkalinity and reduces dissolved CO₂. This reduction was substantial enough to suggest that with a sustained and scaled-up application, we could achieve net atmospheric CO₂ removal. Near the offshore discharge site, lower CO₂ and higher pH levels were detected up to a few meters away, confirming the alkalinization was successful.

The study was the first-of-its-kind to show such results outside of laboratory conditions. The results align with our laboratory and computer model predictions, providing a proof of concept that OAE can work in real-world conditions. The peer-reviewed publication of our study validates these results and sets the stage for further research and larger-scale trials.

Can you describe the field trial process and the results that led to the publication of your study?
The field trial took place in September 2022. We added magnesium hydroxide to treated wastewater at the wastewater treatment plan in St Erth which was then discharged as it normally would be via the offshore outfall outside St Ives Bay. We monitored the changes in CO₂ concentration and pH levels at each stage. The trial demonstrated that increasing the alkalinity of wastewater is a viable OAE method.

Can you elaborate on your approach to testing new technologies like ocean alkalinity enhancement?
Our approach to testing new technologies is both phased and gated. We begin by testing the technology in a controlled environment, such as a lab bottle, where it is safe and manageable. Next, we use computer models to simulate the process. Afterward, we scale up to an aquarium setting to observe the impacts more broadly. Finally, we move on to small-scale field trials. At each stage, we thoroughly examine the evidence to ensure it is safe to proceed to the next phase. This methodical approach helps us minimize risks and maximize our understanding of the technology’s impacts.

What are the potential environmental impacts of adding magnesium hydroxide to seawater, and how do you address these concerns?
Our studies show that the concentrations of magnesium hydroxide we use are well below toxic levels for marine life. We plan to continue rigorous testing in any subsequent trials we might be involved in to further understand and mitigate any ecological effects. Our goal is to continue to ensure that the approach is safe and environmentally sustainable.

How significant is this publication for the future of ocean alkalinity enhancement and other similar technologies?
This publication is a major milestone. It provides the first field-based evidence that ocean alkalinity enhancement can effectively reduce CO₂ levels. This finding is crucial for proving the concept and advancing the development of OAE and similar technologies. By demonstrating that OAE can work outside of laboratory conditions, we take a significant step towards making this, and other carbon removal methods, viable parts of climate change mitigation.

What are the key challenges and opportunities for implementing ocean alkalinity enhancement on a larger scale?
The key challenges for implementing ocean alkalinity enhancement on a larger scale include logistical and economic considerations, such as the production and distribution of alkaline materials. Ensuring that the technology is environmentally sustainable and socially acceptable is also crucial. However, there are significant opportunities as well. OAE has the potential to be a cost-effective and scalable solution for CO₂ removal. It can be integrated with existing wastewater treatment infrastructure, reducing implementation costs. Furthermore, OAE offers a way to address both historical and residual emissions, making it a valuable tool in the broader effort to combat climate change.

How does this research contribute to the goal of achieving net zero emissions and reversing climate change?
Ocean alkalinity enhancement is part of a portfolio of solutions needed to achieve net zero emissions and reverse climate change. By providing a viable method for actively removing CO₂ from the atmosphere, OAE complements other strategies such as emission reductions and controls. Our research demonstrates that OAE can be an effective tool in mitigating climate change, helping to restore the balance of CO₂ in the atmosphere and move towards a more sustainable future.

How do you feel about the outcomes of this research and its potential impact?
I am extremely pleased with the outcomes of the research. It is exciting to see our work transition from theoretical and lab-based stages to successful field trials. The potential impact of this research on reducing atmospheric CO₂ and combating climate change is highly significant. It provides a tangible pathway towards achieving net zero emissions and beyond, which is deeply satisfying both personally and professionally.
 
 

Related information

Full paper: Magnesium hydroxide addition reduces aqueous carbon dioxide in wastewater discharged to the ocean >>
 

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