A comprehensive assessment of electrochemical ocean alkalinity enhancement in seawater: kinetics, efficiency, and precipitation thresholds

[Geoengineering News]

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https://egusphere.copernicus.org/preprints/2024/egusphere-2024-108/

Authors

Mallory Ringham, Nathan Hirtle, Cody Shaw, Xi Lu, Julian Herndon, Brendan Carter, and Matthew Eisaman

Received: 12 Jan 2024 – Discussion started: 22 Jan 2024

Abstract. Ocean alkalinity enhancement (OAE) is a promising approach to marine carbon dioxide removal (mCDR) that leverages the large surface area and carbon storage capacity of the oceans to sequester atmospheric CO2 as dissolved bicarbonate (HCO3-). The SEA MATE (Safe Elevation of Alkalinity for the Mitigation of Acidification Through Electrochemistry) process uses electrochemistry to convert some of the salt (NaCl) in seawater or brine into aqueous acid (HCl), which is removed from the system, and base (NaOH), which is returned to the ocean with the remaining seawater. The resulting increase in seawater pH and alkalinity causes a shift in dissolved inorganic carbon (DIC) speciation toward carbonate and a decrease in the surface-ocean pCO2. The shift in the pCO­2 results in enhanced CO2 uptake or reduced CO2 loss by the seawater due to gas exchange. The net result of this process is the increase of surface-ocean DIC, where it is durably stored as mostly bicarbonate and some carbonate. In this study, we systematically test the efficiency of CO2 uptake in seawater treated with NaOH at beaker (1 L), aquaria (15 L), and tank (6000 L) scales to establish operational boundaries for safety and efficiency in scaling up to field experiments. Preliminary results show CO2 equilibration occurred on order of weeks to months, depending on circulation, air forcing, and air bubbling conditions within the test tanks. An increase of ~0.7–0.9 mol DIC/ mol added alkalinity (in the form of NaOH) was observed through analysis of seawater bottle samples and pH sensor data, consistent with the value expected given the values of the carbonate system equilibrium calculations for the range of salinities and temperatures tested. Mineral precipitation occurred when the bulk seawater pH exceeded 10.0 and Ωaragonite exceeded 30.0. This precipitation was dominated by Mg(OH)2 over hours to 1 day before shifting to CaCO3, aragonite precipitation. These data, combined with models of the dilution and advection of alkaline plumes, will allow for estimation of the amount of carbon dioxide removal expected from OAE pilot studies. Future experiments should better approximate field conditions including sediment interactions, biological activity, ocean circulation, air-sea gas exchange rates, and mixing-zone dynamics.

How to cite. Ringham, M., Hirtle, N., Shaw, C., Lu, X., Herndon, J., Carter, B., and Eisaman, M.: A comprehensive assessment of electrochemical ocean alkalinity enhancement in seawater: kinetics, efficiency, and precipitation thresholds, EGUsphere [preprint], https://doi.org/10.5194/egusphere-2024-108, 2024.

Source: EGU Sphere

[Tom Goreau]

Bubbling simply can’t work efficiently unless very deep, impossible to do because of the pressure gradient!

 

It’s just incredible that such claims are published in “peer” “reviewed” journals!

 

Equilibration of CO2 with H2CO3 is kinetically very slow and lags way behind equilibrium unless carbonic anhydrase (CA) enzyme is present in large amounts.

 

Without it we would not be able breathe or control the pH of our blood and tissues!

 

That is precisely why organisms evolved CA very early in the Precambrian, why it is the most abundant enzyme in the world, used for photosynthesis, respiration, and calcification, by ALL forms of life including Archaea and Bacteria.

 

This fact is almost universally ignored by CO2 modelers and CDR speculators, who assume equilibrium!

 

Good data under field conditions are needed for realistic numbers instead of made-up ones!

 

Respir Physiol

. 2000 Jun;121(1):1-12.

 doi: 10.1016/s0034-5687(00)00110-9.

The distribution and physiological significance of carbonic anhydrase in vertebrate gas exchange organs

R P Henry ¹, E R Swenson

• PMID: 10854618 
• DOI: 10.1016/s0034-5687(00)00110-9

Abstract

The enzyme carbonic anhydrase (CA) catalyzes the reversible hydration/dehydration of CO(2) and water, maintaining a near-instantaneous equilibrium among all chemical species involved in the reaction. CA is found in association with all tissue and organ systems involved in the transport and excretion of CO(2), from the site of CO(2) production, metabolically active tissue such as muscle, to circulating red blood cells in the vasculature, to the various organs of gas exchange, the lungs and gills. The presence of the enzyme in every fluid compartment along the pathway of CO(2) transport appears necessary in order to allow the dehydration of HCO(3)(-) to keep pace with the rapid diffusion of CO(2) across biological membranes. Within the actual organ of gas exchange, CA is compartmentalized in multiple subcellular fractions, with the specific subcellular localization determining the enzyme's physiological function.

 

From: Renaud de RICHTER <renaud.d...@gmail.com>
Date: Saturday, January 27, 2024 at 2:23 PM
To: Chris Vivian <chris....@btinternet.com>, Tom Goreau <gor...@globalcoral.org>, Greg Rau <gh...@sbcglobal.net>
Subject: Re: [CDR] A comprehensive assessment of electrochemical ocean alkalinity enhancement in seawater: kinetics, efficiency, and precipitation thresholds

Dear Gentlemen,

Any answer, opinion or feeling to share with me?

Thanks!

Bw

renaud

 

Le mer. 24 janv. 2024 à 19:41, Renaud de RICHTER <renaud.d...@gmail.com> a écrit :

Dear Thomas, Chris, Greg

 

The article preprint below, finds that "Preliminary results show CO2 equilibration occurred on order of weeks to months, depending on circulation, air forcing, and air bubbling conditions within the test tanks."

What is your feeling or opinion on the system developed by some startups, removing and capturing CO2 from the first 1 to 10 meters of the ocean surface and releasing slightly more alkaline seawater to the surface (depleted of its CO2). Will this returned seawater have the opportunity or capacity to extract the same amount of CO2 from the atmosphere as was removed from the upper ocean by the startup?

 

Thanks

Bw,

Renaud

 

---------- Forwarded message ---------
De : Geoengineering News <geoengine...@gmail.com>
Date: mer. 24 janv. 2024, 11:37
Subject: [CDR] A comprehensive assessment of electrochemical ocean alkalinity enhancement in seawater: kinetics, efficiency, and precipitation thresholds
To: <CarbonDiox...@googlegroups.com>

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[Anton Alferness]

Tom - 

Matthew Eisaman is a brilliant physicist, not an oceanographer, and he has been working on this approach for quite some time, with the last 3 or so years in a partnership with NOAA. Other's on the author list (I believe more than 1) are oceanographers. I highly doubt they are making anything up. He is on this list so I assume you can simply ask him for more detail. 

When you say: Equilibration of CO2 with H2CO3 is kinetically very slow and lags way behind equilibrium

how slow? A day, a month, a year, 10 years? 

When you say: This fact is almost universally ignored by CO2 modelers

how is this ignored in the models and what do you suspect would be the general direction results if it were included in some meaningful way?

Thanks-

-Anton 

To view this discussion on the web visit https://groups.google.com/d/msgid/CarbonDioxideRemoval/BY3PR13MB4994235F025F3556E47544EBDD782%40BY3PR13MB4994.namprd13.prod.outlook.com.

[Ken Caldeira]

Richard Zeebe's book has been studied by most carbon cycle modelers that I know, and the resulting understanding has been incorporated into carbon cycle models.

https://www.sciencedirect.com/bookseries/elsevier-oceanography-series/vol/65/suppl/C


Thus, the idea that kinetics of CO2 hydration is simply ignored by carbon cycle scientists seems to be made without foundation.

In the oceans, it is often the transport of carbon from the mixed layer to the deeper ocean that is rate limiting, and explicitly modeling disequilibria in the hydration step often adds unnecessary complexity without materially affecting results.

A more accurate statement would be, "For many processes of interest to CO2 modelers, explicitly representing the hydration step would have no material effect on model results, and so the assumption of chemical equilibrium between CO2 and H2CO3  has in many circumstances proved to be a useful simplifying assumption."

That said, it is likely that some studies have made equilibrium assumptions when they should have modeled the kinetics, but I would guess that that is a tiny minority of published studies.

To view this discussion on the web visit https://groups.google.com/d/msgid/CarbonDioxideRemoval/CAHxOCYufNJWL1wuNJpasZrkG8Z%3DnOj%3D1NOObg7VDPTP1owvhLQ%40mail.gmail.com.

[Tom Goreau]

CO2-bicarbonate equilibrium is reached so slowly in nature that it is useless for biological regulation of pH, that’s why we evolved Carbonic Anhydrase in the earliest stages of life on Earth!

 

There is perhaps no more urgent need than equilibrating CO2 that we can exhale away from our lungs to separate it from bicarbonate ions that buffer blood and tissue pH.

 

These fluxes are very tightly biologically regulated, they have to be, because the natural kinetic exchange of CO2 and bicarbonate is far too slow to be useful for respiration!

 

The same applies equally well to equilibration of CO2 with bicarbonate across the air-water interface!

 

See the key phrase in the abstract below:

 

The distribution and physiological significance of carbonic anhydrase in vertebrate gas exchange organs

R P Henry ¹, E R Swenson

 

The presence of the enzyme in every fluid compartment along the pathway of CO(2) transport appears necessary in order to allow the dehydration of HCO(3)(-) to keep pace with the rapid diffusion of CO(2) across biological membranes.

 

My father, Thomas F. Goreau, the first diving marine scientist, was a top authority on medical measurement of respiration with the Warburg Apparatus, pH regulation in tissues, and on diving physiology, who realized 70 years ago that these fundamental medical biology principles also explained how corals, and all organisms, regulate pH at the site of calcification.

 

They apply to any process relying on equilibration between CO2 and the pH of dissolved inorganic carbon pools.

 

Biology tells us something very fundamental about the kinetics of how the carbon system actually works in nature, which we ignore at our risk if people are investing real money in processes that do not work as they assume!

 

Thomas J. F. Goreau, PhD
President, Global Coral Reef Alliance

Chief Scientist, Blue Regeneration SL
President, Biorock Technology Inc.

Technical Advisor, Blue Guardians Programme, SIDS DOCK

37 Pleasant Street, Cambridge, MA 02139

gor...@globalcoral.org
www.globalcoral.org
Skype: tomgoreau
Tel: (1) 617-864-4226 (leave message)

 

Books:

Geotherapy: Innovative Methods of Soil Fertility Restoration, Carbon Sequestration, and Reversing CO2 Increase

http://www.crcpress.com/product/isbn/9781466595392

 

Innovative Methods of Marine Ecosystem Restoration

http://www.crcpress.com/product/isbn/9781466557734

 

Geotherapy: Regenerating ecosystem services to reverse climate change

 

No one can change the past, everybody can change the future

 

It’s much later than we think, especially if we don’t think

 

Those with their heads in the sand will see the light when global warming and sea level rise wash the beach away

 

“When you run to the rocks, the rocks will be melting, when you run to the sea, the sea will be boiling”, Peter Tosh, Jamaica’s greatest song writer

 

[Tom Goreau]

These kinetic controls do not much affect the rate liquid circulation and equilibration in the interior of the ocean, but they are crucial when there is any interface between gaseous and liquid phases.

[Anton Alferness]

Thank you both Tom and Ken for your thoughtful responses. 

Tom, you say: CO2-bicarbonate equilibrium is reached so slowly in nature that it is useless for biological regulation of pH

which makes sense for living / breathing critters like us, but doesn't give me an understanding of why you think that OAE modelers / speculators (I don't use that term because of the negative connotation, but I get what you mean with it) are wrong or that adding alkalinity to cause the ocean to absorb more atmospheric gas won't work as a CDR methodology (please correct me if I am mischaracterizing your hypothesis).  

Ken, you say: In the oceans, it is often the transport of carbon from the mixed layer to the deeper ocean that is rate limiting, and explicitly modeling disequilibria in the hydration step often adds unnecessary complexity without materially affecting results. 

which suggests that in order for OAE to be more effective, perhaps deploying it more horizontally (across more of the vastness of the ocean than a limited point source location) or in areas of more vertically mixed conditions or to artificially / mechanically mix an area while adding... may be that secondary step rather than just watching the natural ocean physics to mix it which is rate limiting. Am I being too simple with that? 

Both: thank you kindly for educating me here. 

[Tom Goreau]

Wherever you are concerned with CO2 transfer between air and water these kinetic factors are dominant.

 

There’s a clear discussion of the kinetics of hydration of CO2 on page 192-195 of the 3d Edition of Aquatic Chemistry: Chemical Equilibria and Rates in Natural Waters, the 1022 page masterpiece by Werner Stumm and my own teacher James Morgan.

 

They suggest that 10-20 seconds are needed for equilibration, which is much too slow for biology, or for rapid exchange across gas-water interfaces, but might work in large well mixed volumes in the ocean interior. A large bubble can rise as 30-40 centimeters per second, so can travel tens of meters before equilibrating, smaller ones have velocities around 28-30 cm per second, which is independent of velocity, so the equilibration distance is not much shorter. Not sure about very small bubbles, cc’ing Russell Seitz who knows much more about it.

 

Bubbles are ellipsoidal in shape, motion is irregular, and velocity is independent of bubble diameter (U is approx. 28 - 30 cm/sec) for bubbles having radii up to 0.75 cm. For larger bubbles their velocity tends to increase to 35 - 40 cm/sec, but they are not stable and tend to subdivide into smaller bubbles.Feb 22, 2006

Bubble

UCLA Samueli School of Engineering

http://www.seas.ucla.edu › stenstro › Bubble

 

PDF

 

 

Thomas J. F. Goreau, PhD
President, Global Coral Reef Alliance

Chief Scientist, Blue Regeneration SL
President, Biorock Technology Inc.

Technical Advisor, Blue Guardians Programme, SIDS DOCK

37 Pleasant Street, Cambridge, MA 02139

gor...@globalcoral.org
www.globalcoral.org
Skype: tomgoreau
Tel: (1) 617-864-4226 (leave message)

 

Books:

Geotherapy: Innovative Methods of Soil Fertility Restoration, Carbon Sequestration, and Reversing CO2 Increase

http://www.crcpress.com/product/isbn/9781466595392

 

Innovative Methods of Marine Ecosystem Restoration

http://www.crcpress.com/product/isbn/9781466557734

 

Geotherapy: Regenerating ecosystem services to reverse climate change

 

No one can change the past, everybody can change the future

 

It’s much later than we think, especially if we don’t think

 

Those with their heads in the sand will see the light when global warming and sea level rise wash the beach away

 

“When you run to the rocks, the rocks will be melting, when you run to the sea, the sea will be boiling”, Peter Tosh, Jamaica’s greatest song writer

 

 

 

 

[Greg Rau]

Guys,

The CO2 equilibration time in the surface ocean relative the residence time of non-air-equillibrated surface water (via marine biological or chemical CO2 removal) is (now) well appreciated:

https://bg.copernicus.org/articles/20/27/2023/

https://aslopubs.onlinelibrary.wiley.com/doi/10.1002/lol2.10330

Actually measuring/modeling this effect is the hard/uncertain part, and I don't think direct measurement is possible due to signal dilution in the air/sea equilibration time frame. I think tracers could be important in validating ocean models at specific locations and hence reasonable CDR efficiencies estimated, but there will always be uncertainty. mCDR is not alone here, however.

Other ideas? 

Greg 

Abstract. Ocean alkalinity enhancement (OAE) is a promising approach to marine carbon dioxide removal (mCDR) that leverages the large surface area and carbon storage capacity of the oceans to sequester atmospheric CO2 as dissolved bicarbonate (HCO3-). The SEA MATE (Safe Elevation of Alkalinity for the Mitigation of Acidification Through Electrochemistry) process uses electrochemistry to convert some of the salt (NaCl) in seawater or brine into aqueous acid (HCl), which is removed from the system, and base (NaOH), which is returned to the ocean with the remaining seawater. The resulting increase in seawater pH and alkalinity causes a shift in dissolved inorganic carbon (DIC) speciation toward carbonate and a decrease in the surface-ocean pCO2. The shift in the pCO­2 results in enhanced CO2 uptake or reduced CO2 loss by the seawater due to gas exchange. The net result of this process is the increase of surface-ocean DIC, where it is durably stored as mostly bicarbonate and some carbonate. In this study, we systematically test the efficiency of CO2 uptake in seawater treated with NaOH at beaker (1 L), aquaria (15 L), and tank (6000 L) scales to establish operational boundaries for safety and efficiency in scaling up to field experiments. Preliminary results show CO2 equilibration occurred on order of weeks to months, depending on circulation, air forcing, and air bubbling conditions within the test tanks. An increase of ~0.7–0.9 mol DIC/ mol added alkalinity (in the form of NaOH) was observed through analysis of seawater bottle samples and pH sensor data, consistent with the value expected given the values of the carbonate system equilibrium calculations for the range of salinities and temperatures tested. Mineral precipitation occurred when the bulk seawater pH exceeded 10.0 and Ωaragonite exceeded 30.0. This precipitation was dominated by Mg(OH)2 over hours to 1 day before shifting to CaCO3, aragonite precipitation. These data, combined with models of the dilution and advection of alkaline plumes, will allow for estimation of the amount of carbon dioxide removal expected from OAE pilot studies. Future experiments should better approximate field conditions including sediment interactions, biological activity, ocean circulation, air-sea gas exchange rates, and mixing-zone dynamics.

How to cite. Ringham, M., Hirtle, N., Shaw, C., Lu, X., Herndon, J., Carter, B., and Eisaman, M.: A comprehensive assessment of electrochemical ocean alkalinity enhancement in seawater: kinetics, efficiency, and precipitation thresholds, EGUsphere [preprint], https://doi.org/10.5194/egusphere-2024-108, 2024.

Source: EGU Sphere

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Greg H. Rau, Ph.D.

Senior Research Scientist
Institute of Marine Sciences
Univer. California, Santa Cruz
https://www.researchgate.net/profile/Greg_Rau
Co-founder and manager, the Carbon Dioxide Removal Google group
Co-founder and CTO, Planetary Technologies, Inc.
510 582 5578

510 363 1519 c

[Tom Goreau]

The time constant for CO2 equilibration with alkalinity in these papers is “months to years” and “3-4 to 8-10 years”. These must reflect the time constants for vertical mixing within the upper ocean volume, and not that of equilibration across the boundary layer itself, the focus of my comments.

[Michael Hayes]

Another Idea: Using a Supportive System of Systems Engineering Approach

A high through put confined flow infrastructure would likely allow for reasonable control of the variables found in the method being discussed, as well as be supportive of a rather wide range of other mCDR methods. The hull technology needed to do so can itself act as a C sink if mCDR derived bio oil-based high density polyethylene hulls are used. Thick walled HDPE hulls have a service life of 1200+ years, are highly recyclable, and such an infrastructure can eventually become largely self-replicating at the basic materials level.

The longterm value would likely justify the added startup costs and longer scale up time as many current... and future... CDR methods could be supported using roughly the same marine architecture and materials.

Using mCDR SoS infrastructures has never been modeled as such an mCDR system of systems engineering approach has never been published. However, the actual basket of technologies needed to deploy a largely self-replicating high through put mCDR SoS infrastructure is currently available at the marine-grade industrial level. 

To view this discussion on the web visit https://groups.google.com/d/msgid/CarbonDioxideRemoval/BY3PR13MB49949DF4E93EA7DEC311D6ECDD7F2%40BY3PR13MB4994.namprd13.prod.outlook.com.

[gattuso]

It’s just incredible that such claims are published in “peer” “reviewed” journals!

Tom Goreau: This paper is not peer-reviewed. It is a discussion paper as part of an open-review process. Anyone from the community is welcome to comment on the paper web page ("Discussion" tab"):
https://egusphere.copernicus.org/preprints/2024/egusphere-2024-108/ 

[Mallory Ringham]

Hi folks, 

I'm glad to see community discussion of this preprint and welcome comments throughout-- you can find the discussion tab at https://egusphere.copernicus.org/preprints/2024/egusphere-2024-108/ . I'd like to make a quick clarification on the methods of this paper in light of this thread: we set up a series of experiments to investigate carbon capture in well-monitored laboratory tanks designed to capture the uptake of atmospheric CO2 in response to the addition of alkalinity into seawater. This is a stepping stone towards larger in-situ experiments and field trials in which it will be very challenging to monitor seawater carbon chemistry changes against the background of dynamic, natural coastal variability. Bubbling air into these tanks is not meant to represent a pathway for OAE at scale, and I agree it is not easy to compare bubbled tanks to natural systems. However, it does allow us to investigate the potential upper bounds of CO2 capture on faster and more reasonable timescales for laboratory work than if we were to wait months for each experiment to equilibrate. Extrapolation of these results to field trials will require simulation of alkalinity releases over longer time and space scales relevant to air-sea equilibration that will in turn depend on a variety of site-specific factors.

Cheers,

Mallory

_________________

Mallory Ringham

Research Adjunct, Stony Brook University

Lead Oceanographer, Head of MRV, Ebb Carbon, Inc

mallory.rin...@stonybrook.edu