Monday, 9 July 2012

Whatever happened to biochar?

I have been reading 'Ten Technologies to Fix the Planet' by Chris Goodall which is a little bit out of date now (it was published in 2008) so it is interesting to see how the technologies he recommended are faring. The one which seems to be going absolutely nowhere is biochar – capturing carbon by heat treating biomass and mixing it into soil. Carbon created this way can stay in the soil for centuries and improves fertility in a number of ways, not least by improving its water holding properties and drought tolerance.

Chris says: ‘..making charcoal is easy and can be done profitably by poor farmers in the tropics,’ and he reports on a trial in Cameroon where subsistence farmers added biochar to corn plots and significantly increased yields, up to double the normal.

Soils hold enormous quantities of carbon: 1600 billion tonnes globally, according to Goodall which is twice that in plants and trees and 200 times as much as we generate from fossil fuels each year. We could add a great deal of carbon to the soil without making much overall difference to the carbon cycle. Also biochar can be made very cheaply. So – how come we still can’t invest in biochar for carbon offsetting as I suggested in my post last year Carbon offsetting - does it really work?

I am coming round to the idea that biochar, though it has huge potential benefits, also carries serious risks and in practice it may be impossible to manage. Australia seems to be closest to having a standard for using biochar and it is still some way off. Although its new Carbon Farming Initiative explicitly lists biochar as a potential activity for carbon storage it does not have an approved methodology for assessing projects using it, nor even one under consideration.

What is Biochar?

Biochar is more or less the same thing as charcoal except it is used in agriculture rather than being burnt for energy. Since biochar is supposed to remain in the soil for a long time, you need to be a bit more careful of what is in it than if you are just going to burn it.
  • You don’t want any contamination with heavy metals or other toxins.
  • You want to make sure that the carbon is properly stabilised.
  • For good water holding properties you need the right particle size and structure (which means you need a higher temperature to make it than ordinary charcoal).
  • Biochar can be strongly alkaline, which is great for neutralising acid soils but if yours isn’t then you need to be careful.
  • Biochar can contain nitrogen and other nutrients which it is useful to know about.

If you are a poor farmer you don’t want to have to measure these properties but you don’t need to. Most of them are directly related to what you make the biochar from and how you make it which you can control, more or less, depending on your equipment.

Biochar for carbon storage

If you want to invest in biochar as a carbon storage mechanism, you also need to be very careful also about what biochar is made from, how it is made and how it is used.
  • It must be made from waste material or from biomass products which have been grown sustainably. Chopping down the virgin forest to make biochar will increase carbon in the atmosphere, not reduce it.
  • It must be made using a clean efficient process which locks up the carbon in a stable form and doesn’t release greenhouse gases during the process. As I described in How Green is my Charcoal Barbecue?, heating the material to make char inevitably produces some methane which is a very powerful greenhouse gas – 70 times more powerful than CO2 in the short term. It is essential this gas is captured and used, or at least flared off. However, traditional charcoal making techniques don’t control the gases coming off.
  • Biochar needs to be mixed properly into the soil. If it just sits on the top it will either dry out and blow away or be washed away in a heavy rain. Tiny carbon particles in the air are a health hazard and will increase global warming rather than reducing it.

All these considerations and a few more are included in the current European Biochar Certificate standard published by the Biochar Science Network.

A recent paper in Brazilian Agricultural Research [1] points out that the oversight needed to prevent abuse of financial incentives is similar to that needed for sustainable forestry and says ‘although debate over the relative merit of each forestry certification scheme continues, it appears that in those countries that undertake international sustainability reporting … and have adequate governance to ensure compliance,…there is evidence that there are improved sustainability outcomes. Where there is no reporting obligation, or absence of mechanisms to ensure measurement, monitoring or compliance, the reverse is true.’

Biochar could pay for itself as a soil fertility treatment on a local scale, but local production methods are unlikely to meet all the requirements for sustainable carbon storage. You can do it at home, - this video shows how to make it in small batches or you can buy efficient retorts such as that pictured above from - and then it is up to you to make sure you are reducing climate change and not increasing it.

It looks like large scale use of biochar for carbon storage is likely to cost more in bureaucracy than in technology – if it ever does get off the ground.

[1]  Annette L. Cowie, Adriana E. Downie. Brendan H. George, Bhupinder‐Pal Singe, Lukas Van Zwieten and Deborah O’Connell (2012) Is sustainability certification for biochar the answer to environmental risks? Pesq. agropec. bras., Brasília 47(5)


  1. Hello Nicola,
    A few notes on your section headed 'What is biochar'.
    Biochar made from untreated wood will be clean and free from contamination.
    Wood produced charcoal is very stable.
    Water holding properties, amongst other things, needs investigation. Many propose that char made from straw and other materials will be suitable for biochar, but the cellular structure of these things is probably not as effective as that of wood. The cellular structure of whatever you're charring is carried over into the charcoal. Good biochar is all about surface area.
    Properly produced charcoal from any method is PH neutral. I've never seen alkaline charcoal from an untreated wood source.

    A good blog. If any readers use charcoal, buy British. It's not been flown halfway around the world, it's not been doused in petrochemical to make it burn and it's all made from sustainable woodland practices.

    1. I totally agree that it is important to make biochar from untreated wood and buy locally made charcoal. I am not convinced about charcoal being pH neutral. It isn't the carbon that is the problem, it is the ash. Char from hardwood is relatively low in ash but still has some. This page explains more: I believe you can remove ash by washing the biochar.

  2. Hi Nicola,

    The IBI (International Biochar Iniative) has developed standards to certify the quality of biochar. We hope this will provide confidence when purchasing biochar and the impetus to the establishment of a viable biochar industry.

  3. As Anonymous says, the IBI standard ( is for the quality of the biochar itself. It does not guarantee the sustainability of the biomass source, the production process or handling. It is certainly a step forward but not enough. The European standard is much more rigorous - and much harder to get certification.

  4. Ah, I see your point about ash making the biochar alkaline. However, all of ours is made in the retort shown at the head of the blog and this method means no ash at all. The wood you turn to charcoal is never exposed to flame and kept in a low oxygen environment and so does not burn, therefore no ash. This will apply to all charcoal made using a total retort.
    As a point of interest most of our biochar is sourced from short rotation willow grown as part of a waste processing system at The Donkey Sanctuary here in Devon. The remainder comes from normal woodland management.
    You are certainly right to say the source of the biomass needs to be qualified. Biochar can be helpful in easing the world's problems but should be viewed as a long term aid, not a short term panacea. It is far from that.

  5. "Chopping down the virgin forest to make biochar will increase carbon in the atmosphere, not reduce it." Not if you then regrow biomass on top of the biochar, and then again, and again, etc. The ancient Amazon civilisation did this leaving deposits up to 2 m deep. See 'Terra Preta' on Wikipedia.

    I was recently in touch with the UK Rep of Pyreg GmbH. He says you can now buy their rector. See

    I found a BBC report with videos:

    The paper I produced with H2-Patent includes biochar as an optional part of a hydrogen economy based on biomass. The object of H2-Patent is to produce hydrogen from biomass at lower cost than natural gas. A pressurised reactor operating at 9.6 ton/hour or more (dry) should achieve this.

  6. Modern Thermal conversion of biomass burns only the hydrocarbons in that biomass, conserving the carbon for the soil. At the large farm or village scale modern pyrolysis reactors can relieve energy poverty, food insecurity and decreased dependency on chemical fertilizers.
    Please take a look at this YouTube video by the CEO of CoolPlanet Biofuels, guided by Google's Ethos (and funding along with GE, BP and Conoco) they are now building the reactors that convert 1 ton of biomass to 120 gallons of bio – gasoline and Biochar for soil carbon sequestration.

    Black Swan of Biochar

    Short a nano material PV / thermoelectrical / ultracapasitating Black swan,
    What we can do now with "off the shelf" technology, what I proposed at the Commission for Environmental Cooperation, to the EPA chiefs of North America.
    The most cited soil scientist in the world, Dr. Rattan Lal at OSU, was impressed with this talk, commending me on conceptualizing & articulating the concept.

    Bellow the opening & closing text. A Report on my talk at CEC, and complete text & links are here:

    The Establishment of Soil Carbon as the Universal Measure of Sustainability

    The Paleoclimate Record shows agricultural-geo-engineering is responsible for 2/3rds of our excess greenhouse gases. The unintended consequence, the flowering of our civilization. Our science has now realized these consequences and has developed a more encompassing wisdom. Wise land management, afforestation and the thermal conversion of biomass can build back our soil carbon. Pyrolysis, Gasification and Hydro-Thermal Carbonization are known biofuel technologies, What is new are the concomitant benefits of biochars for Soil Carbon Sequestration; building soil biodiversity & nitrogen efficiency, for in situ remediation of toxic agents, and, as a feed supplement cutting the carbon foot print of livestock. Modern systems are closed-loop with no significant emissions. The general life cycle analysis is: every 1 ton of biomass yields 1/3 ton Biochar equal to 1 ton CO2e, plus biofuels equal to 1MWh exported electricity, so each energy cycle is 1/3 carbon negative.

    Beyond Rectifying the Carbon Cycle;
    Biochar systems Integrate nutrient management, serving the same healing function for the Nitrogen and Phosphorous Cycles.
    The Agricultural Soil Carbon Sequestration Standards are the royal road for the GHG Mitigation;

  7. Lots of materials could be decomposed with this procedure, including products such as rubber tires, which could be broken down and also changed into important byproducts using thermal decomposition rather than merely being landfilled.

    Pyrolysis Reactor