3 carbon capture technologies you’ve probably never heard of

All of us will face the consequences of runaway climate change — unless, maybe, you’re living in one of Elon Musk’s new homes on Mars. But for the rest of us poor souls, tackling global heating is pretty much the top priority. 

The bad news is we are not on track to limit global temperatures rising to 1.5°C  to prevent the most catastrophic impacts of climate change. A new report has also revealed that temperatures in Europe are rising twice as fast as the rest of the world. 

Drastic cuts in emissions are required. We also need to pull out some of the carbon we’ve already put in. While this may conjure up visions of giant, air con-like machines sucking carbon out of the air, carbon removal comes in many forms.  

Remove, an Amsterdam-based accelerator programme for carbon removal startups, recently unveiled its latest cohort. It consists of 20 early-stage companies championing everything from microalgae biorefineries to biochar-based concrete. 

Some of them are simply weird — and many, wonderfully simple.    

Burying trees underground

A Dutch startup is plotting an obscure but rather straightforward way to ensure that the carbon trees pull out of the atmosphere stays locked away: burying them underground.

Trees are great at absorbing huge quantities of CO2, but they release the carbon again when they die and rot. Burying them could fix this problem.

Underground Forest plans to cut down old spruce trees, dig holes in peat or wetlands, and drive the poles directly into the soil. New trees will be planted in their place.  

“We can permanently remove up to a gigaton [of CO2] per year,” Kees de Gruiter, founder of Underground Forest, told TNW. He sees biomass burial working alongside other carbon removal technologies like Direct Air Capture (DAC).

De Gruiter says the wooden piles can act as a foundation for houses, much like Venice, Italy, which was built on over 10 million wooden piles over a thousand years ago.

While biomass burial is largely unproven, it’s nevertheless attracting attention from climate tech investors. One of them, US-based Kodama Systems has raised over $6mn from Bill Gates’ Breakthrough Energy to scale its biomass burial system.

Another budding company, Switzerland-based RECOAL, has developed a way to turn waste biomass into “negative emission coal” for storage in permanent underground deposits. 

“With the available waste biomass worldwide and the possibility to store the coal as a filling material in abandoned mines and gravel pits, the process is highly scalable,” explains the company. 

While the likes of Underground Forest and RECOAL are looking underground, others have their sights set on the ocean.   

Sealife, bro

The ocean is great at sequestering carbon. It has already absorbed 30% of the CO2 —  and 90% of excess heat — emitted by human activities. Organisms living in the sea itself do most of that work. 

For instance, seagrass — a type of seaweed — can remove carbon 30 times faster than a rainforest. The UN once called it a “secret weapon in the fight against global heating.” 

Several projects have attempted to grow seagrass with varying degrees of success. One problem is that farming by hand on the seafloor isn’t that easy. 

That’s why Ulysses Ecosystem Engineering is working on a way to plant and manage seagrass fields using “cutting-edge robotics.”

Details are scant at this point. “[We are] currently in stealth,” the startup says on its Instagram.  

Another innovative approach has emerged in the UK. London-based startup Blusink is trying to kill two birds with one stone — perhaps literally. The company has developed apple-sized “carbon-sinking” pebbles it calls “blusinkies”. 

Piles of blusinkies are spread on the seafloor where they create habitats for marine organisms like coralline algae, which absorb carbon. Over time the pebbles form so-called “rhodolith beds” that act as a carbon sink, locking in carbon for centuries. 

But the little pebbles have another trick up their sleeve: they’re composed primarily of calcium oxide, the main ingredient in lime. When in contact with this chemical compound, which the company sources as waste from the construction industry, carbon dioxide mineralises into solid carbon.    

“Our production and operation costs are extremely low compared to DAC and other technologies,” the company’s founder, Lorena Neira Ramírez, told TNW. She estimates Blusink can remove carbon at a cost of €180 per ton. To put that into perspective, DAC unicorn Climeworks currently removes carbon at a cost of €1000-1300 per ton. 

Unlike seagrass carbon capture projects, Blusink says its pebbles foster the growth of entire ecosystems, not just monocultures. “It creates environmental benefits well beyond carbon capture,” said Ramírez.

Other startups like Italy’s Limenet or the Netherlands’ Brineworks plan to throw lime dust into the ocean to absorb carbon dioxide and reduce acidity at the same time. (Ocean acidification contributes to coral bleaching.)

Key to these efforts is calcium oxide’s natural ability to solidify CO2.

Turning buildings into carbon sinks

UK-headquartered startup Calcin8 is tackling the problem the other way around. Rather than capturing CO2 from the atmosphere, it is developing a low-carbon lime to prevent more emissions in the first place.

Lime is used for a variety of industrial processes, including making cement. However, it is made by superheating limestone, which releases vast quantities of CO2. Current methods for producing 1 ton of lime emit approximately 1 ton of CO2.  

Founded in 2021, Calcin8 heats limestone in a kiln powered by renewable energy. When the limestone transforms into lime, the startup’s system captures the released CO2 for sequestration.   

“We have rejigged the production process entirely, turning lime into a carbon sponge,” the company’s founder, Behn Mapus-Smith, told TNW. 

When Calcin8’s lime is used in construction, for example, it will react with CO2 in the air and absorb it — turning buildings into carbon sinks. 

“Carbon dioxide removal will only have a meaningful impact if it scales to the gigaton level, which is a huge challenge for everyone involved in the industry,” said Mapus-Smith. 

While the International Energy Agency (IEA) vehemently supports carbon removal technologies as a part of efforts to curb global heating, most of the technologies listed here remain untested on a large scale. 

“The startups emerging in the carbon removal space will play a crucial role in assisting businesses and governments in achieving their goals of reaching net zero emissions,” said Hans Westerhof, co-founder and managing director of Remove.

With almost 40 billion tons of CO2 emitted in 2023 alone, the budding industry has a huge task on its hands. 

“All hands on deck are needed to achieve the removal scale required to address the climate crisis,” said Westerhof.