The principle behind biochar carbon removal project is to convert waste biomass into biochar, which possesses long-term chemical and biological stability. Its high resistance to degradation in the environment enables it to remove CO2.
A qualified biochar carbon removal project converts waste biomass into biochar through anoxic/anaerobic processes such as pyrolysis carbonization. It requires that methane emissions from pyrolysis be reduced to extremely low levels during production. The stability of the biochar material is assessed based on the molar hydrogen to organic carbon ratio. Materials with a (H/Corg) ratio less than 0.2 are classified as difficult to decompose in the environment.
Biochar feedstocks must be derived from biomass or waste biomass with sustainable sources, such as agricultural waste, biodegradable waste, and municipal wood waste.
Biochar can only be used in carbon storage scenarios, such as soil amendment and wastewater treatment. Its use as fuel or reducing agent is prohibited.
Fossil fuels can be used in biochar production, but pyrolysis gases produced during the process must be burned or recovered to avoid methane emissions. The H/Corg ratio of the biochar product must be less than 0.7.
The biochar production process should undergo a life cycle assessment (LCA) according to standards, demonstrating net negative emissions throughout the entire chain. At the same time, the production process must meet relevant international and local environmental protection and safety regulations.
Carbon Sequestration Mechanism of Biochar
Biomass waste undergoes a series of pyrolysis carbonization processes, including water loss, volatilization of active substances, structural breakage, and collapse, reconstructing its biological structure and transforming it from waste material into biochar.
As the pyrolysis and carbonization temperature increases, the molecules gradually transform from an amorphous carbon structure to a graphitic microcrystalline structure, with aromatic compounds, minerals, and other functional groups forming the "skeleton" of biochar.
Compared to biomass raw materials, biochar crystals are larger and have a more ordered overall structure. This porous structure exhibits extremely high carbon stability, enabling it to adsorb and protect organic carbon through physical processes, allowing the carbon it holds to remain in the soil for a long time.
Furthermore, the porous structure has an extremely high specific surface area, providing numerous adsorption sites for greenhouse gases. This further enhances the physical capture of greenhouse gases, achieving the goal of physical carbon reduction.
The carbon sequestration effect of biochar depends not only on its physical properties but also on the synergistic effect of its unique chemical and biological mechanisms.
Biochar achieves chemical carbon sequestration through abundant surface functional groups, charge characteristics, and high adsorption capacity. It binds with the soil, converting organic carbon (POC) into stable organic-mineral complexes (MAOC), protecting it from microbial decomposition.
Furthermore, due to its porous structure, it significantly reduces nitrous oxide (N2O) release through charge transfer effects and reactions with surface functional groups. Simultaneously, it chemically inhibits methanogenic bacteria and promotes methanogenic bacteria activity, thereby reducing methane (CH4) emissions.
In terms of biological carbon sequestration, biochar enhances microbial carbon use efficiency by regulating soil microbial communities and functions. This reduces respiration carbon loss and increases microbial biomass carbon accumulation.
It also increases soil carbon content by strengthening rhizosphere processes, improving soil fertility and structure, promoting plant root development, and enhancing root biomass and exudates.
