UK Biochar Research Centre
Charchive Standard Biochars

What is biochar?

We define biochar as the porous carbonaceous solid produced by the thermochemical conversion of organic materials in an oxygen-depleted atmosphere and which has physiochemical properties suitable for the safe and long-term storage of carbon in the environment and, potentially, soil improvement. This definition is deliberately flexible and refers to both the production of biochar and its application.

We define a sustainable biochar system as one which: a) produces and deploys biochar safely and without emitting non-CO2  greenhouse gases (such as methane and nitrous oxide); b) reduces net radiative forcing; and c) does not increase inequality in access to and use of resources. Systems which meet the above criteria rarely really exist at demonstration or commercial scale at the current time, and do not include traditional charcoal production (often encompassed by other definitions) unless fugitive gas clean-up and soot removal is practised.

The structure of biochar is largely amorphous but contains some local crystalline structure of highly conjugated aromatic compounds (Downie et al., 2009). The crystalline particles are in the order of nanometers in diameter and composed of graphite-like layers arranged turbostratically (i.e. the layers are not aligned). In addition to the graphene sheets cross-linked in a random fashion, biochar also contains aromatic-aliphatic organic compounds of complex structure (including residual volatiles), and mineral compounds (inorganic ash) (ibid.). Finally, there are voids in the biochar structure formed as pores (macro, meso and micropores), cracks and morphologies of cellular biomass origin. It is the unique structure of biochar which imbues it with some unusual characteristics. The carbon atoms are strongly bound to one another, and it is this which makes them resistant to attack and decomposition by micoorganisms.

Reference:  Downie, A., Crosky, A. and Munroe, P. (2009), Physical Properties of Biochar, in Lehmann, J. and Joseph, S. (editors), Biochar for Environmental Management, Earthscan, London: 13-32.