The subject of biochar production has an extraordinary number of variables. The variables could be grouped as follows,
- biomass (wastes & process residues - plant/animal/human, dedicated crops/coppice, algae)
- scale: kg/day > tonnes/hr (cooking stove > gardener kiln/retort > farm/community > industrial production)
- conversion process: traditional/simple > future/complex; batch or continuous; gasification, pyrolysis, HTC, microwave; slow, fast or flash carbonization; high or low temperature
- process products: biochar, producer gas, heat, steam, CO2, electricity, bio-oil/wood vinegar, ash, refined products (charcoal, activated carbon, gas/liquid fuels/products, fertilizer)
- post-production inoculation (minerals, fertilizers, wood vinegar, compost, urine, humus, Mycorrhizae/microfauna)
- economic, environmental and social settings.
How do all these variables affect the safety and efficacy of biochar? does it matter? I keep reading that not all biochars are the same. From the list above, this is hardly surprising but I don't think safety will be an issue. The negative impacts of declining soil carbon due to industrial / contemporary farming practices seem to be well understood. The terra preta field trial has been running well for some time. The large and growing number of formal and informal soil trials around the world will be the ultimate arbiter but thats not going to produce a biochar industry any time soon.
These 'upstream' variables for biochar production are matched by 'downstream' application variables for climate, geography, soil type, land use (crop, grass, forest, plantation, organic, intensive, tillage), application rates/methods, utilisation goals/objectives (soil enhancement, remediation, fertilizer reduction/efficiency, carbon sequestration, emission/erosion control).
The decision to make/buy/use biochar may be relatively simple - optimizing the economic outcome based on the many variables will be the hard part. Having some standard assessment criteria between the upstream production and downstream application would aid the decision process. Help may soon be at hand with the development of biochar testing standards...
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