Biochar

Charcoal, biochar and activated carbon from wood stock are all made using the same process: pyrolysis. This is the carbonisation of wood by heating it in an oxygen depleted environment. In simple terms, charcoal for burning is made with very little oxygen present. This prevents any of the tars and oils that inhabit the pores within the structure of the wood from burning away. The charcoal is dense and has a high calorific value. If you introduce some oxygen into the process the volatiles start to burn away, creating a sponge like structure within the wood. The charcoal becomes lighter and more friable. This process is known as ‘activation’. Introducing oxygen is certainly not the best way to activate charcoal (you can’t make high quality activated carbon this way), but it is the easiest . 

So at one end of the scale you have charcoal, in the middle you have biochar (which is partially activated) and at the other end is activated carbon. The ecological value of the charcoal we produce very much depends on how activated it is; the more activated the better! 

How does biochar work

The biocharBBQ produces biochar; charcoal which has been activated. It achieves this by allowing sufficient oxygen to reach the charcoal to burn out the tiny pores within the wood, forming a sponge like structure. This structure can have a vast surface area, 300 – 2,000 m2/g.

As liquids and gases pass through biochar, some particles are attracted to its surface via a process called ‘adsorption’. These particles remain attached, forming a film. Eventually the structure will become saturated and adsorption will stop. (This short video by ‘Dr. Beckman’ illustrates the principal)

Activated charcoal adsorption has limitations. Although it will adsorb a wide range of impurities and contaminants, such as odours, pigments and chlorine, other substances, such as fluoride and sodium, will pass straight through.

Biochar benefits can roughly be divided into two categories: manufacture and storage.

Manufacture: a piece of Biochar is like a bee hive with no bees; no more than a space with lots of empty compartments, it is of no use by itself. Introduce a swarm of bees to the hive and they will, in time, make you honey. Biochar is much like a hive, but for micro-organisms. It offers them a safe, electron-rich home where they can thrive and produce chemicals beneficial to the plants around them.

Storage: Biochar is very good at retaining moisture and chemical compounds. However, the bonds that hold them within the biochar are weak and can easily be overcome by the plants who need them. This makes biochar an ideal storage structure.

The effectiveness of activated charcoal depends on the degree of activation, and the original source material. The way the biocharBBQ makes activated charcoal is not precise, so the degree of activation varies enormously. However, for our intended purpose that doesn’t matter. Commercial water filters use small amounts of highly activated charcoal. We achieve the same results by using a larger quantity of biochar, but we are making it for free!

 

Although we use the biochar we produce in Kenya for water filtration, please do not do the same with your biochar, as it is possible that the wood you use has picked up chemicals which might survive pyrolysis and still be harmful.

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