Biochar is charcoal type created by the pyrolysis of biomass, and differs from ordinary charcoal only in the sense that its primary use is not for fuel, but for biosequestration or atmospheric carbon capture and storage. As much as 12 percent of the world’s human caused greenhouse gas emissions could be sustainably offset by producing biochar. That’s more than what could be offset if the same plants and materials were burned to generate energy, concludes a recent study published in the journal Nature Communications. Biochar could sequester carbon in the soil for hundreds to thousands of years.
Biochar is a high carbon, fine grained residue which today is produced through modern pyrolysis processes. Pyrolysis is the direct thermal decomposition of biomass in the absence of oxygen to obtain an array of solid (biochar), liquid (bio-oil) and gas (syngas) products.
For their study, the researchers looked to the world’s sources of biomass that are not already being used by humans as food. For example, they considered the world’s supply of corn leaves and stalks, rice husks, livestock manure and yard trimmings, to name a few. The researchers then calculated the carbon content of that biomass and how much of each source could be used for biochar production.
With this information, a mathematical model was developed that could account for three possible scenarios. In one, the maximum possible amount of biochar was made by using all sustainably available biomass. Another scenario involved a minimal amount of biomass being converted into biochar, while the third offered a middle course. The maximum scenario required significant changes to the way the entire planet manages biomass, while the minimal scenario limited biochar production to using biomass residues and wastes that are readily available with few changes to current practices.
The study found that the maximum scenario could offset up to the equivalent of 1.8 billion metric tons of carbon emissions annually and a total of 130 billion metric tons in the first 100 years. Avoided emissions include the greenhouse gases carbon dioxide, methane and nitrous oxide. The estimated annual maximum offset is 12 percent of the 15.4 billion metric tons of greenhouse gas emissions that human activity currently adds to the atmosphere each year. Researchers also calculated that the minimal scenario could sequester just under 1 billion metric tons annually and 65 billion metric tons during the same period.
Instead of making biochar, biomass can also be burned to produce bioenergy from heat. Researchers found that burning the same amount of biomass used in their maximum biochar scenario would offset 107 billion metric tons of carbon emissions during the first century. The bioenergy offset, while substantial, was 23 metric tons less than the offset from biochar.
However, the team also added that a flexible approach including the production of biochar in some areas and bioenergy in others would create optimal greenhouse gas offsets. Their study showed that biochar would be most beneficial if it were tilled into the planet’s poorest soils, such as those in the tropics and the Southeastern United States.
Those soils, which have lost their ability to hold onto nutrients during thousands of years of weathering, would become more fertile with the extra water and nutrients the biochar would help retain. Richer soils would increase the crop and biomass growth — and future biochar sources — in those areas.
This is all new technology. Biochar has been found or used in the Amazonian soils. Pre-Columbian Amazonian natives are believed to have used biochar to enhance soil productivity and made it by smoldering agricultural waste. European settlers called it Terra Preta de Indio.
Biochar can be used to hypothetically sequester carbon. In the natural carbon cycle, plant matter decomposes rapidly after the plant dies, which emits CO2; the overall natural cycle is carbon neutral. Instead of allowing the plant matter to decompose, pyrolysis can be used to sequester some of the carbon in a much more stable form. Biochar thus removes circulating CO2 from the atmosphere and stores it in a stable soil form, making it a carbon-negative process.
There is still much to learn about this process which shows so much potential.
For further information: http://www.eurekalert.org/pub_releases/2010-08/dnnl-cts080510.php