Erich Knight, who commented on my previous post in great detail, supplied some further resources to read and study so that I could better understand this phenomenon called biochar.
The first question that I had was really basic: what is biochar? Well, it isn’t terra preta (terra preta is an Amazonian soil that has high levels of carbon of anthropogenic origin). Biochar is similar to charcoal in that it is produced by burning under the same oxygen-limited conditions that professional charcoal burners (known as colliers) have used for thousands of years. Biochar is essentially the same product that the Amazonian peoples used to create what became known as terra preta soils but modern production techniques yield more than biochar from organic feedstocks. The definition of biochar according to the International Biochar Initiative (IBI) also requires that it be used as a soil amendment for agricultural and environmental gain.
The biochar that is being produced today is different from charcoal in that it is a product of modern technology and industrial processes. Originally, the term biochar was applied to the material produced by a process called “slow pyrolysis” in which oxygen is limited, heating is slow, and the temperatures are from 450 to 650 degrees Centigrade. Two byproducts of this process are the production of synthetic gas, shortened in the literature to “syngas“, and “bio-oil.” Slow pyrolysis yields about 30% bio-oil, 35% biochar, and 35% syngas. The term “biochar” has since been extended to include the matter produced by the processes of fast pyrolysis, intermediate pyrolysis, and gasification. These other processes produce less biochar and varying percentages of bio-oil and syngas. The charcoal yield from traditional processes used by colliers might be as little as 10% with no syngas or bio-oil being produced whereas industrial techniques produce as much as 35% biochar plus syngas and bio-oil.
Can biochar be produced by the methods that colliers the world over have used for centuries? Yes. But industrial methods of producing biochar yield syngas and bio-oil in addition to charcoal. Traditional methods of charcoal production allow syngas and bio-oil to be wasted.
If you would like to read more about the technical details of how biochar is produced, please download this document, produced by Australia’s Commonwealth Scientific and Industrial Research Organization (CSIRO).
There is a lot more to biochar than the definition of what it is – that information will be the subject of future posts.