This vegetable charcoal, which she obtains by heating oxygen-deprived cocoa shells at high temperatures, has the ability to trap greenhouse gases for centuries.
Sustainable fertilizer, biogas production, "green" concrete, this technology, whose industrialization is in its infancy, could become key to the ecological transition.
According to the IPCC, biochar would make it possible to store 2.6 billion tons of CO2 on a large scale each year, out of the 40 billion emitted by humanity. But its massification remains a challenge.
Amazonia
"We are reversing the carbon cycle," Peik Stenlund, CEO of Circular Carbon, the German company with 40 employees that manages the Hamburg plant, one of the largest in Europe, told AFP.
In a white silo, the facility receives, via a network of grey pipes, cocoa hulls, production waste from a nearby factory belonging to a multinational chocolate company.
Peik Stenlund, CEO of Circular Carbon, in front of transport bags for cocoa hulls, on May 10, 2023 in Hamburg, Germany © Axel Heimken / AFP
These elements are heated to more than 600 degrees without oxygen, to prevent their combustion, in a process called pyrolysis. The biochar comes out in the form of a black powder, trapping CO2 from cocoa.
Without this process, the carbon from these residues, unused by industry, would have evaporated into the atmosphere during their decomposition, thus contributing to global warming.
Now he is sequestered "for centuries," David Houben, a researcher at the UniLaSalle institute in France, told AFP.
A ton of biochar stores on average "the equivalent of 2.5/3 tons of CO2", according to the scientist. Any plant can be used.
Biochar has long been used by pre-Columbian civilizations as fertilizer. It was rediscovered in the twentieth century by scientists studying the "terra preta", extremely fertile black soils of the Amazon.
Its sponge-shaped structure improves agricultural yields, with better absorption of water and nutrients, decreasing the need for irrigation and fertilizer.
Peik Stenlund, CEO of the company "Circular Carbon" at the biochar production plant, on May 10, 2023 in Hamburg, Germany © Axel Heimken / AFP
In Hamburg, a strong heat and a smell of chocolate emanates from the factory pipes.
The biochar is packaged in dozens of white bags, before being sold to farmers in the region.
Silvio Schmidt, 45, who looks after a potato field near Bremen, is one of them. "We have very sandy soils. We hope that this will make it possible to make quality humus to provide more nutrients and water to the soil," he told AFP.
Prohibitively expensive
Pyrolysis also releases biogas, which in turn is sold to the nearby plant. In total, 3,500 tons of biochar and "up to 20 mWh" of gas are produced each year in the plant, along with 10,000 tons of cocoa hulls.
But this circular system will be complicated to apply on a large scale to achieve the IPCC's objectives.
"To release less carbon than we store, everything has to happen locally, with little or no transport. Otherwise it makes no sense," says David Houben.
© Axel Heimken / AFP
This is not always the case. Not all soils are receptive to biochar, "more effective in tropical climates", and the raw material is "not available everywhere", according to the researcher.
Above all, the cost of biochar is prohibitive, "around a thousand euros per tonne, too much for a farmer," says David Houben.
The researcher believes that other uses, such as "construction", should be encouraged. Biochar can be used in the manufacture of "green" concrete.
To make the activity profitable, the sector relies on another growth pool: carbon credits.
The idea is to sell certificates to companies wishing to achieve carbon neutrality to offset their CO2 emissions.
With these resources, "we see strong growth in the sector in the future, with a multi-billion euro market," says Stenlund. The company plans to open three new plants in the coming months.
All over Europe, projects are multiplying. Annual production is expected to increase from 53,000 to 90,000 tonnes between the end of 2022 and the end of 2023.
© 2023 AFP