Biochar is charcoal produced from biomass. It is a high-carbon, fine-grained residue which can be produced either by an ancient technique of covering burning biomass with soil and letting it smoulder or through a modern pyrolysis process.
Pyrolysis is the direct thermal decomposition of biomass in the absence of oxygen to produce solid (biochar), liquid (bio-oil) and gas (syngas) products, Pyrolosis can be combined with biofuel production in a process that is energy-positive (producing 3-9 times more energy than invested) and carbon-negative (withdrawing CO2 from the atmosphere).
The carbon captured in the biochar remains in the soil for a long time – typically about 5,000 years – depending on the feedstock material, how charred the material is, the surface:volume ratio of the particles and the conditions of the soil the biochar is placed in.
In addition to its potential for carbon sequestration, biochar has numerous other benefits when added to soil. It can prevent the leaching of nutrients out of the soil and increase the available nutrients for plant growth; it can increase water retention and reduce the amount of fertilizer required. In addition, it can decrease nitrous oxide emissions by up to 80% and reduce methane emissions from soil, further reducing greenhouse gas emissions.
Although some organic matter is necessary for agricultural soil to maintain its productivity, much of the agricultural waste can be turned directly into biochar, bio-oil and syngas.
One immediate application is in switching from “slash-and-burn” to “slash-and-char” techniques to prevent the rapid deforestation and subsequent degradation of soils in areas like the Amazon where it would invtease the amount of the carbon left in the soil from ablout 3% to up to 50%.
Bio-oil can be used, without modification, as a replacement for numerous applications where fuel oil is used, including fueling space heaters, furnaces, and boilers – or it can be upgraded to make biodiesel. Syngas can be burned directly, used as a fuel for gas engines and gas turbines or used in the production of methanol and hydrogen.