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Biochar feedstocks

Posts: 17
Location: Pacific Northwest
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I have been making biochar at home for about a year, using a two barrel “tin man” kiln. I have had good luck using primarily yardwaste for my feedstock. (dried blackberry canes and bamboo)
Recently, in an effort to spread the word on biochar, I held a free demo at a local community garden. The yard waste they had was primarily Scotch Broom. I was surprised at the amount of black smoke that came out of the vent stack. (Usually, my biochar burns produce very little smoke.) I have also read since the demo that Scotch Broom contains alkaloids and other toxins.
My questions are:

a. does combustion or pyrolysis from toxic or sappy plants release any harmful toxins into the atmosphere?
c. Do any toxins in plants survive pyrolysis or combustion and persist, thus spoiling the resulting biochar?


T. Vincent
Langley, WA
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Location: Cincinnati, Ohio,Price Hill 45205
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I would think that elemental toxins like lead or mercury could persist.
Complex compounds seem doomed.
Was all the feedstock dry?
Any sprays used on it?
A wet or oily feedstock  might produce  smoke.
Turns out, scotch broom flowers  are used for essential oil, and the plant is a narcotic.
A kid from Oregon won bronze in an international competition forb getting oil from the plant.
I think you had  an oily plant on your hands.
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Location: Arkansas - Zone 7B/8A stoney, sandy loam soil pH 6.5
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Very good questions Thomas,

The heat requirements for complete combustion to break down toxic materials is usually in the 1500 f range.
Unless you have a TLUD or similarly working kiln (wood is heated, released gasses are expelled and burned at high temp away from the wood being carbonized) you would not get temperatures high enough to destroy many of the known toxic materials we can find in wood.

It is these toxins that are the reason most people making biochar or other carbonized wood products (charcoal for a grill for example) first dry the wood down to fairly low moisture levels.
Toxins become airborne rather easily when wet (green) wood is heated or burned, this is why the TLUD was developed in the first place, to remove toxic materials completely from charcoal to be used in a forge and later for use in soil building.

As William brought up, scotch broom is a medicinal plant with several uses for humans.

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