Opinion: Nature-Based DAC Technologies Should Become The Main Force For Extracting CO2 From Air

Opinion: Nature-Based DAC Technologies Should Become The Main Force For Extracting CO2 From Air - Carbon Herald

By Natalia Golovkina, Director of Innovation Multiplier

This opinion is a continuation of a previous one that introduced readers to an alternative point of view on existing DAC technologies. This op-ed aims to inform people about natural technologies for removing CO2 from sea water and air (nature-based DAC technologies) using only sunlight and discusses the positive effects of them on biodiversity and the ecosystem. It also searches for supporters and partners (criticism and discussion are welcome).

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Nature-Based DAC technologies

Understanding of the approaching climate catastrophe forces society to reassess the traditional energy resources used and devote huge amounts of money to the accelerated development of solutions to restore the climate and the entire ecosystem. 

Nature-based DAC technologies should become the main force for extracting CO2 from atmospheric air, but unfortunately traditional views and approaches prevent the use of this natural potential.

Nature has incredible physical, mechanical, chemical, biological and thermal potential that is practically not used by humanity. That includes gravity, solar energy, wind, rain, lightning, tides, convective currents, gas exchange between the atmosphere and the ocean, and finally photosynthesis. 

What better way to seize these opportunities and restore climate change? 

Let’s consider several practical solutions that use nature’s potential to remove anthropogenic CO2 from the biosphere and call this natural DAC technology. CO2 is the only atmospheric gas that enters into a chemical reaction with water and due to this, the earth’s hydrosphere contains 100 times more CO2 than atmospheric air.

Consequently, it can be extracted in larger quantities from water than from air, but DAC technologies involve the movement of large masses of liquid and high energy costs.

Of course, you can use rivers or hydroelectric power stations that move huge flows of water and extract dissolved CO2 from there, but let’s talk about the other two and most important climate regulators on the planet, the sun and the ocean. They ensure the balance of atmospheric gases and can be an example of nature-based DAC technologies.

Let’s consider the use of the main chemical process responsible for the balance of important water parameters – the carbonate buffer system. This buffer system regulates the content of dissolved and chemically bound CO2 in seawater and creates optimal conditions for the life of all biological organisms.

A natural physico-chemical method for extracting CO2 and carbonates from sea water.

The temperature of air and water on the planet is constantly changing and this significantly affects the CO2 content both in the atmosphere and in the ocean. This natural phenomenon can be used to create natural DAC technology. 

When seawater is heated to a temperature of 60-70 degrees Celsius, almost all CO2 dissolved in water evaporates and, to maintain the chemical balance, carbonic acid (H2CO3) decomposes into CO2 and H2O, and with further evaporation of CO2, calcium and magnesium carbonates precipitate. Here is a real example we use to remove and capture CO2 from seawater. 

A film of selective material is placed on the surface of sea water and absorbs solar energy. Converting radiant energy into heat, the water heats up and CO2 dissolved in it rises to the surface. It accumulates between the film and the surface of the water. Only a small vacuum pump is required for the CO2 extraction. 

Why isn’t this simple solution used everywhere?

The misconception is to consider only one physical process and ignore the other chemical components. From physics, we know that to heat 1 liter of water by 1 degree, it is necessary to expend 4200 Joules of energy. Sunlight can only offer us 800-2000 watts per square meter – this is partly due to the high heat capacity of water.

But how does nature use solar heat and maintain the balance of water system parameters? The answer is very simple – you don’t need to heat the entire ocean, but it is enough to heat only a thin surface layer. When CO2 evaporates from a thin heated layer of the water surface, the carbonate buffer system instantly reacts and extracts a new portion of CO2 from the water, which also evaporates. 

To maintain a certain balance of parameters, with significant evaporation of CO2, precipitation occurs in the form of MgCO3 and CaCO3. But do not forget that sea water is a chemical solution and if in one place it has a low concentration of substances and in another place a high concentration, diffusion and mixing of the solutions occurs until their concentrations equalize. 

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The mixing process is also influenced by waves and currents. Of course, this is a somewhat simplified presentation of much more complex processes and relationships, but our goal was to show how complex natural mechanisms can be used to remove CO2. 

To evaluate this method, laboratory tests were carried out in the university laboratory of our partners. They didn’t aim to prove that CO2 evaporates when heated, but rather prove that only the surface layer of water is heated, and the lower layers are cooled (no matter how paradoxical this may sound). There are proven scientific explanations for this.

Now let’s discuss the largest and most important method of biological CO2 sequestration.

This is a mechanism created by nature to saturate the atmosphere with oxygen and remove carbon dioxide from the atmosphere – sunlight, ocean, microalgae and photosynthesis. 

Microalgae and other photosynthetic organisms use CO2, nutrients and sunlight to grow and produce oxygen. Microalgae are the base of the food chain. They are key players in restoring biodiversity and the health of the marine ecosystem.

The growth rate of microalgae is impressive, as they can double every day, and one kilogram of microalgae biomass absorbs 1.8 kg of CO2. Sometimes the rapid growth of microalgae (bloom) causes unpleasant consequences. 

With a high biomass density and lack of sufficient light, microalgae stops growing and dies. The biomass is decomposed by microbes that absorb oxygen and produce toxins. It is inappropriate to blame only cyanobacteria for toxicity.

Has anyone ever wondered why microalgae bloom on the surface of the water?

I will put forward one very interesting hypothesis. When water is heated (as we discussed earlier), CO2 evaporates. On the surface, the concentration of CO2 is higher than in the water column – this is the factor that is necessary for the rapid growth of microalgae – lots of CO2, light and nutrients.

Microalgae have been cultivated for hundreds of years, but how can it be used in the marine environment? 

We have created an underwater photobioreactor that uses only sunlight, dissolved CO2 and nutrients to control the growth of microalgae in large volumes of seawater. To control the parameters and growth of biomass in such a large volume of water, a unique methodology was created that allows, by measuring only one parameter, to assess the effectiveness of the entire process; of course, this would not be possible without AI.

Perhaps this is the world’s first underwater DAC technology using microalgae, which allows biological sequestration of CO2 and at the same time a positive effect on the marine ecosystem – restoring biodiversity, purifying water from dissolved organic substances, eliminating hypoxia in sea water and much more. 

Truly alarming are some scientific studies that claim that the microalgae population decreases by 1% annually and it’s scary to think what this could lead to.

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