In Part 1 I talked about the history of Bio Char. In Part 2, I discussed some of the controversy surrounding this soil amendment. Here in Part 3, I’ll look at how you obtain bio char and explore ideas for its future applications in cities.
Bio char is made much differently than the charcoal we use for grilling food. The production of regular charcoal is very dirty in terms of Carbon Dioxide and other pollutants. Grilling charcoal burns “cold” (400 degrees Fahrenheit), fast, and dirty. In contrast, BioChar burns “hot” (800 to 850 degrees Fahrenheit), slow, and cleaner.
Bio char burns from the top down. The charring bit actually comes from the biomass NOT touching the flames, but being heated by the flames through a container. The firing is a self-fueling process, and the bio char absorbs CO2 while it burns.
Making it yourself seems to be one common approach to obtaining bio char. There are many how-to pages on the web, some of them excellent and thoughtful. On the commercial scale there are bio char stoves that can moved to the biomass source or the biomass brought to a central Bio Char stove.
Generally the process occurs in a container within a container. Often, although not always, they are both made of metal. The inner container is filled with the biomass (branches, plant parts, manure, lawn clippings) and has vents on the bottom. The outer container is only slightly larger than the inner container, and is filled with the fuel (often wood chips) that will char the biomass. A chimney is put over the whole contraption. The wood chips are ignited and the biomass in the inner container begins to char.
The biomass does not come in contact with the flames. The bottom vents out from below and draws in carbon dioxide while oxygen feeds the wood chip fuel in the outer container and embeds the carbon dioxide in the bio char within the inner container. The charring process lasts several hours; the chimney does not belch black smoke, it vents white smoke, and is very hot. After the burn, the char is saturated with water and mixed into soil at about a 1:10 ratio. Ultimately, bio char should comprise about 8% to 10% of soil volume.
Currently, Kelby Fite and Bryant Schoenbrock are testing bio char on street trees in Chicago. It will be very interesting to follow their results in the years ahead. The Australians and New Zealanders are also taking a great interest in bio char. I would suggest following the research of Dr. Johannes Lehmann at Cornell University, that great center of horticultural research.
Bio char can, I believe, be an extremely valuable tool in our work to ecologically revitalize urban centers through reducing stormwater runoff, reusing organic waste, and enhancing damaged city soils without importing expensive sands and aggregates to aerate compaction. Perhaps we can begin to produce bio char in and around cities from the freely available and troublesome biomass waste stream. This “terra preta” can then be treated to become activated carbon (an astonishing stormwater filter) and to amend existing damaged and compacted urban soils. Trees planted in adequate volumes of this mix would benefit tremendously.
An arrangement like this would create a self-perpetuating system of green infrastructure that costs less and exponentially increases in value as it ages. Maybe this old way is the best way to reinvigorate our fields, and forests. What we once did to revitalize our precious soil, perhaps we can do once again in our urban forests.
Bottom image: kelpiew