Biochar Carbon Removal (BCR) creates carbon sinks (general term for natural or artificial reservoirs or processes that remove carbon dioxide from the atmosphere and store it for an extended period of time) by incorporating biochar into a stable matrix, such as soil or durable construction materials, thereby creating a durable carbon removal.
The CO2 capturing process:
Biochar is made by heating biomass, such as residual wood or crop waste (which has removed CO2 from the atmosphere during plant growth), at high temperatures (500-700°C), and in an oxygen-limited environment through a process called pyrolysis. Unlike in a „standard“ burning process, i.e. combustion, a portion of the carbon of the parent material remains as biochar after the pyrolysis process and is not emitted as CO2. Hereby, the chemical and structural composition of the parent material is transformed, creating highly aromatic structures (a term in chemistry for when compounds form rings with each other to create strong structures) that are very stable and persistent in ecosystems over time.
Biochar production can range from low-tech methods, such as KonTiki open kilns, to high-tech systems. In advanced setups, the heat generated during biochar production can also serve additional purposes, like drying the feedstock or generating electricity. Biochar production can therefore be realized in a wide range of contexts: from decentralized applications to replace open burning of crop residues, a practice that is commonly used in the Global South, to industrial applications where the heat generated in the pyrolysis process is directly used in district heating systems or to generate electricity.
The CO2 sequestration process:
After biochar is created, it's commonly applied to soil to enhance its properties. This is also the main focus of most BCR projects. The highly porous core structure of biochar grant it specific soil improvement properties. Biochar has been proven to increase crop yields between 10% - 42% by improving soil structure increasing water retention and nutrient retention in soils, boosting microbial activity, and enhancing soil organic carbon buildup.
Nevertheless, there is a growing range of other potential uses for biochar, each with varying levels of durability. For instance, biochar can be incorporated into long-lasting products such as construction materials. Other possibilities include its utilization in wastewater treatment, as an additive for the production of plastics, paper, and textiles or as fossil fuel replacement in metallurgic industries.
Biochar can have very different properties depending on the feedstock material and the processing conditions used to make it. Biochar made from hardwoods for instance tends to have a higher carbon content, higher surface area, and is more resistant to degradation in soil whereas biochar made from chicken manure will have higher proportions of phosphorus and ash.
The properties of biochar and its stability depend both on their parent material and the pyrolysis conditions used to produce it. The degree of aromatic condensation of biochar (i.e. concentration of complex and strong chemical structures) is directly related to its persistence in soil: the more complex and condensed the aromatic structures are in biochar, the more stable it is in soil.
Potential and scalability:
The international scientific community identified biochar as a promising net negative emissions technology (NET) for the first time in the 2018 IPCC report. In recent years, biochar has become more well known because of its climate change mitigation potential: since about half of the carbon in the original biomass remains when it is turned into biochar and resists degradation for centuries or even millennia, putting biochar into soil means locking carbon away and removing CO2 from the atmosphere long term. It is durable, verifiable, and one of the only shovel-ready and scalable negative emission technologies (NETs) available today, delivering immediate climate impact.
It is estimated that biochar can contribute to removing between 0.5 to 2 gigatonnes of CO2 per year globally (Fuss et al., 2018). In fact, nearly all of the carbon dioxide that has been removed from the atmosphere to date has been sequestered using BCR. As of mid-year 2023, biochar carbon removal accounts for 92% of all durable CDR deliveries.