Biochar Carbon Capture

Plants remove carbon dioxide (CO2) from the atmosphere. Much of this carbon is locked into the plant until that plant decomposes or is burnt, when the carbon is released back into the atmosphere.


When biomass such as wood is turned into charcoal, the carbon in that wood becomes stabilised. Biochar is charcoal produced in order to dig it into soil. Being stable, the carbon in the biochar is then sequestered.

It can take hundreds or even thousands of years for biochar to decompose in soil. This is known from studies of soils such as terra preta (black earth) of the Amazon basin, a type of soil made by indiginous Amazonians between 450BC and 950AD. Terra preta is characterised by large amounts of charcoal and organic matter in otherwise nutritionally poor ‘oxisol’ soils. Not only has the charcoal remained relatively stable, the nutrients have also remained stable for over 2000 years in some cases. This ancient civilisation was carbon negative. We have a lot to learn from such cultures.

Burning fossil fuels releases CO2 into the atmosphere. This CO2 was otherwise stable and locked deep into the Earth. Figures from the IPCC (International Panel on Climate Change) give 1983 as the year we passed the point of irrevirsible climate change, 350ppm (parts per million) in the atmosphere. We have (June 2012) exceded 400ppm.

Biochar offers a potential alternative solution to the current dilema of needing sustainable food and energy whilst also needing to reduce atmospheric CO2 levels. It could be a tool for change to a sustainable system. Heat can be generated by burning biomass gases and biochar can be left unburnt. In other words, biochar can be produced whilst generating heat. Not only does biochar stabilise CO2, it also reduces the need to generate energy through unsustainable means such as burning fossil fuels.

Appropriate Soil Conditions.

As a market gardener, I am very aware of the effects that cultivating soil has on that soils structure. The increased bacterial activity from aerating the soil and the breaking up of soil agregates from cultivation result in the rapid depletion of organic matter. I believe that biochar is less stable when soils are cultivated compared to when permaculture or other low tillage practices are employed.

The extent to which biochar remains stable in soil has been determined in experiments which do not mimic field cultivations and from studying soils such as ‘terra preta de los Indios de Amazonia’ which have remained uncultivated.

For this reason I am in the process of re establishing my annual vegetable plots so that there are cultivated and an uncultivated beds. (See ‘Swansea Biochar, Our System).

I believe that the increased ba



Appropriate Scale Technology

being small scale, cook stoves do not support the felling of trees.

Scale is of relavence as it is one of many factors which determine whether gasification and pyrolisis technology remains truly carbon negative.

On a large scale, CHP (Combined Heat and Power) plants generate electricity whilst capturing the heat from burning biomass. It is possible for these plants to also produce biochar.

Pyrolizers, also on a large scale, are more suited to producing biochar. These plants produce bio gas or they distil the gas to produce bio oil.

The focus here is on micro gasification; domestic heat and cook stoves which produce biochar. Larger scales require a lot of embodied energy in the plants, transportation systems and packaging for the biochar and so they can be responsible for the release of more CO2 than they sequester. The carbon sequestered as biochar should not be used to justify any further burning of fossil fuels; fossil fuel carbon would otherwise remain stable for millions of years whereas biochar is only stable for thousands of years.

Tools in the hands of large companies can have the effect of centralising power. Company directors are motivated by continued growth and can easily lose sight of their ethics. Biochar production which involves deforestation, land grabbing and importing biomass for feedstock is unlikely to be environmentally beneficial.

Domestic biochar producing stoves keep feedstock and biochar local and can be used by growers to become truly CO2 negative without the need for deforestation. The dimensions of this drawing of a biochar rocket stove are deliberitely set as to maximise heat capture. Enough heat is produced from one burn to heat a domestic water cylinder and to provide overnight heat. Any larger and heat would be wasted.

One reason for advocating the cook and domestic heat stove scale is that these stoves do not require or encourage trees to be cut down. They work fine on branches, sticks chipped brush and other high carbon biomass.

In the UK, it is currently easy to get wood chip delivered by tree surgeons who otherwise have to pay to dispose of it. Alternatively the improved efficiency means that these stoves can be run simply by gathering twigs and branches from woodland floors.

People using these stoves can do so in conjunction with small scale biomass growing projects. It is possible for a family to become self sufficient in heat without the need for harvesting woodland or forestry.


Sustainable Inputs

Current agricultural practices favour the growing of low carbon high nitrogen plants such as grass. Forests and woodlands, on the other hand, are high carbon but are very slow growing. Areas of fast growing, high carbon crops could easily be grown in gardens, farms and allotments. These crops would provide fuel for heating and cooking and the carbon in these crops would be stabilised as biochar and returned to the soil to further improve fertility.

Willow and hazel are fast growing tree crops which can be coppiced every few years as part of an efficient woodland management scheme.

Japanese knotweed makes for a controversial crop because of its ability to establish and out compete other plants. It is a very fast growing perennial which should be grown in containers and should in no way be allowed to spread into fields or hedgerows.

Bamboo is another fast growing perennial more suited to tropical conditions. However certain varieties of bamboo do grow well in Europe.


Hemp is illegal to grow in many countries without a licence but, being a fast growing annual crop (producing over 4 times the amount of biomass as fast growing wood in a year), it is ideally suited as a biomass crop for small scale growers. I hope enough people start to break the laws preventing the growth of hemp in order to get a ball rolling here. In my experience, not only do the seeds need protecting but also the seedlings will be eaten by birds. Enviromesh or fleece can be used to protect the crop.

It is important to point out that hemp should not contain any of the active component of marijuana (THC) and that should people try to smoke it, nothing much will happen. I am merely advocating the growing of a fast growing, high carbon annual crop for burning in biochar stoves in order to generate heat, sequester CO2 and improve soil fertility. (The seeds can also be harvested for food.)