Carbonscape - Charcoal

April 2008
New Zealand produces millions of tones of wood waste, which could be converted into biochar, or finely ground charcoal, and incorporated in the soil like lime for a range of benefits. Carbonscape of Picton is developing one of the first portable pyrolysis units for producing charcoal.

Carbon sequestration using biochar, or charcoal made from woody products, particularly forest wastes, is being put forward as an alternative to open burning which releases carbon dioxide (a greenhouse gas) back into the atmosphere to contribute to global warming.

Already 75% of the carbon in the world is in the soils.

Dry wood has a carbon content around 50% while biochar has a carbon content of 70-80%.

Carbonscape of Picton is a start-up company which has a pyrolysis (wood combustion in the absence of air) plant under development. Director Nick Gerritsen, a lawyer by training, is a venture capitalist and intellectual property specialist. He has founded and directs several NZ companies which are commercializing home-grown technology, mainly from the primary sector.

Pyrolysis captures about half of the original carbon in the biomass feedstock, compared with 3% from normal burning.

Charcoal making has been practiced for hundreds of years, mainly for conversion of wood to a light, cleaner-burning, high-energy fuel. But in the Amazon, people have been using charcoal deliberately to improve their soils with carbon.

A hectare of metre-deep terra preta soil contains around 250t of carbon, compared with 100t in unimproved soils from similar parent material.

Maori may also have added charcoal to soils to make them warmer and to lift fertility.

Interest in using biochar for carbon sequestration has developed over the past few years, because it has considerable associated benefits.

Agricultural productivity gains from high soil carbon levels.

Biochar incorporation in the soil will reduce nitrous oxide emissions.

Bioremediation of heavy metals and other chemical contaminants in soils.

Sequestration is achieved when the biochar is incorporated in soil, which effectively locks up the carbon for thousands of years.

The other beneficial effects are achieved differently.

Carbon is not a plant nutrient in itself, but it improves soil structure and water retention, enhances nutrient availability, lowers acidity and reduces the toxicity of aluminium to plant roots and soil microbiota.

The humus build-up also becomes a sink for nitrogen, and so a higher carbon/nitrogen ratio in soils will reduce nitrous oxide emissions (another greenhouse gas) and nitrate leaching.

Climate change scientists propose growing crops such as willow, eucalypts or poplar and then harvesting the woody material, which incorporates carbon for the production of biochar.

Agronomists propose incorporating biochar and gain considerable yield benefits for crops such as soybeans, sorghum, potatoes, maize, wheat, peas and rice.

Biochar can also be enriched with nitrogen as a replacement for nitrogen fertilizers like urea, which produce carbon dioxide in manufacture.

A slow rate of wood pyrolysis produces about 35% biochar, 30% bio-oil and 35% gas. The gas can be used to heat the whole process. The oil is low-energy and would need upgrading for use as a transport fuel. It is best used to heat greenhouses and in stationary engines for electricity generation.

The Ministry of Agriculture and Forestry has awarded $3million on biochar research to Massey University over the next four years. Two professorial positions have been created one on biochar and soil science, the other on pyrolysis.


Carbonscape aims to develop a self-contained biochar/agrichar plant which is portable and can be placed near wood harvesting or processing sites. Nick Gerritsen says that over 13 million tones of wood waste are produced annually in New Zealand, which often incurs charges for dumping.

Carbonscape would not initially be producing charcoal for biochar, but for industrial uses of charcoal, as a substitute for coal, because prices are rising internationally. Carbon credits will be earned for the treatment of wood waste into charcoal. However Carbonscape is not locked into this end-use.

The emissions from the plant will be scrubbed and clean not smoky and polluting.

The company was founded by Nick Gerritsen, former Christchurch mayor Vicky Buck and olive industry pioneer Hamish Macfarlane, and others.

It recently hired its first manager, who is overseeing the building of the pilot plant, with chemistry contracted elsewhere.