Climate Tech

Biochar has been used in agriculture for thousands of years. Now startups are deploying it as a carbon-removal method.

The method developed by indigenous farmers to improve soil is now being used for long-term CO2 storage
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Illustration: Francis Scialabba, Photo: Victor de Schwangberg/Science Photo Library/Getty Images

· 4 min read

Stems, leaves, trunks, roots, flowers, and fruits are the original carbon-removal tech.

Plants pull CO2 out of the atmosphere through photosynthesis, converting it to carbohydrates that allow them to grow. When plants die and decompose, carbon is released.

Turning that biomass into a more stable form of carbon can interrupt this cycle, removing CO2 from the atmosphere and storing it for much, much longer. And it’s not a new idea.

“Biochar is a technology that was developed actually thousands of years ago by indigenous farmers. The core idea is converting biomass into a stable form of carbon, a mineral form of carbon—a charcoal—and incorporating it into the soil,” Jason Aramburu, CEO of biochar startup Climate Robotics, said during an April event. “And farmers do it because it increases the pH of their soil and boosts their crop yield.”

How it works

Biochar is created by taking biomass—such as organic materials like trees or other plants—and heating it up in a low-oxygen environment. This process is called pyrolysis, or gasification, and produces a very stable form of high-carbon charcoal as well as bio-gas and vapor.

While biochar has long been used in agriculture, startups are now working to deploy it as a carbon-removal method.

Climate Robotics uses robots and AI to automate and accelerate the process. Finnish startup Carbo Culture has raised more than $7 million to scale its “ultra-rapid conversion” method that turns waste wood from forests and farming into stable biochar. Charm Industrial is also focused on carbon removal through biomass. The company uses agricultural waste and a gasification process that produces both biochar, which is returned to crop fields, and bio-oils, which are stored underground.

Shopify, Stripe, and Microsoft are among the 40 companies that have purchased carbon removal credits from Charm so far, which cost ~$600 per tonne of CO2. Microsoft also plans to buy 1,000 tonnes of CO2 removal from Climate Robotics this year.

Opportunities: Biochar serves dual purposes—sequestering CO2 and improving soil health. The other advantage of this carbon-removal method is its durability.

While reforestation or afforestation (aka, planting new forests) may provide about a century of increased carbon sequestration, that CO2 will eventually re-enter the atmosphere as trees die off, whether from natural causes or in the event of a forest fire.

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Turning that biomass into biochar means the carbon can be trapped in mineral form for a millenium, Aramburu said.

“The way that we measure the permanence of biochar is using an adapted soil test. So we take a sample of char, we actually measure how much oxygen and how much carbon is in the char, and that ratio determines the permanence of the char in the soil, how long it will last,” Aramburu said. “Most biochar that you would buy in the open market is going to have a permanence that’s between 100 and 1,000 years.”

Climate Robotics had Texas A&M Agrilife Extension conduct third-party testing of its biochar and the results indicated “it can sequester carbon for 1,000 years or more in commercial agricultural soils” and reduce the amount of chemicals farmers need to add to the soil, according to the company. Independent research has also found that it takes hundreds to thousands of years for biochar to break down and return carbon to the atmosphere.

Challenges: Biochar seems promising as a carbon-removal method, but experts are concerned with how it will scale.

Sourcing enough biomass to sequester carbon in biochar at the million-tonne scale that direct air capture companies are aiming for could prove difficult. Today most biochar producers rely on wood as a feedstock, which is expensive and in high demand, Aramburu told Emerging Tech Brew.

Transporting large quantities of these biochar feedstocks is also costly and inefficient, he said.

There are competing uses for agricultural waste as well, such as creating biofuels and feeding livestock. Some have suggested dedicated biochar crops, but that raises questions about cost and effective land use.

Ultimately, experts say more research is necessary to fully understand the storage potential of biochar and its influence on soils in different regions of the world.

The general consensus in the CDR space is that the industry will need to pursue many different approaches to quickly determine which techniques for drawdown will work best.

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