Page last updated at 09:20 GMT, Monday, 16 March 2009

Biochar: Is the hype justified?

By Roger Harrabin
Environment analyst, BBC News

Biochar in action
Biochar brings benefits to soils, boosting plant growth

Green guru James Lovelock claims that the only hope of mitigating catastrophic climate change is through biochar - biomass "cooked" by pyrolysis.

It produces gas for energy generation, and charcoal - a stable form of carbon.

The charcoal is then buried in the ground, making the process "carbon negative".

Researchers say biochar can also improve farm productivity and cut demand for carbon-intensive fertilisers.

There's a flurry of worldwide interest in the technology, but is the hype justified?

Fertile ground

A ripe whiff of sludge drifts across the sewage works in Bingen, Germany, as a conveyor belt feeds a stream of semi-dried effluent into a steel container.

Behind the container, the treated effluent emerges in the form of glittering black granules. In a flash of eco-alchemy, they are turning sewage into charcoal.

The charcoal is then buried to lock the carbon into the ground and prevent it entering the atmosphere.

Proponents of the technology say it is so effective at storing carbon that it should be included in the next global climate agreement.

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Engineer Helmut Gerber from the University of Applied Sciences, Bingen explains how biochar is created.

Burying the biochar can also improve soil fertility, say experts.

Field trials are about to begin at Rothamsted, south-east England, to assess the benefits to soil structure and water retention.

Experiments in Australia, US and Germany are already showing some remarkable results - especially on otherwise poor soils where the honeycomb granules of biochar act as a reservoir for moisture and fertilisers.

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Could biochar be used to make plants grow faster?

A growing worldwide movement is now bringing together the soil scientists fascinated by the benefits of biochar, which was first discovered in Pre-Columbian Amazonia, and the engineers devising new ways of making the char.

They are being backed by activists who are concerned about climate change.

At Bingen, the design engineer for the biochar plant, Helmut Gerber, originally devised the pyrolysis equipment to overcome the problem of ash from sewage waste choking conventional boilers.

Normally, sewage treatment is a significant source of greenhouse gases. The waste is usually incinerated (with more emissions) and the resulting ash is used in the building industry.

At Bingen, 10% of the sewage stream is being diverted to the prototype pyrolysis plant, where it is heated with minimum oxygen.

Carbon monoxide and methane are driven off and burned to heat the pyrolysis process.

Mr Gerber claims his process radically cuts the fuel costs and carbon emissions needed to treat the sewage.

'Carbon negative' process

Working with Professor Winfried Sehn from Bingen's University of Applied Sciences, Mr Gerber calculates that 60% of the carbon from the sewage is locked up in the char.

The buried carbon will be kept from entering the atmosphere for a projected 1,000 years or more.

And as the sewage was originally created from plants, which removed CO2 from the atmosphere, the total process is described as carbon negative.

The pyrolyser at Bingen - like others being developed elsewhere - can transform any carbon-based substance, including some plastics.

That means pyrolysis can get energy from agricultural waste, food waste and biomass. But the catch is that it creates less energy than burning biomass in a conventional way.

Research by oil giant Shell, showing a keen interest in biochar as a carbon storage mechanism, suggests that it can capture half the carbon from the biomass by foregoing a third of the potential energy.

Dr Bruno Glaser
Now there is a lot of excitement about what biochar can achieve
Dr Bruno Glaser

For all its apparent benefits, there are substantial barriers to the progress of biochar.

Perfecting and disseminating the technology at an affordable price will be an issue.

Moreover, current financial systems reward energy production from biomass and waste - not carbon storage. Biochar would need clear global incentives.

One key to its progress will be ongoing research into the soil benefits.

The porous biochar attracts worms. It also captures nutrients that would otherwise run off the land, which reduces the need for carbon-intensive fertilisers.

Research at Cornell University in New York, US, suggests that burying biochar appears to double the capacity of soils to store organic carbon (compost releases its carbon in a few years).

Research in Australia suggests that biochar also reduces emissions of the powerful greenhouse gas nitrous oxide from soil.

New studies at the University of Bayreuth, Germany, shows that biochar may almost double plant growth in poor soils.

"Research on biochar began back in 1947," says Dr Bruno Glaser, a researcher from the University of Bayreuth.

"But this has been forgotten until the 1980s. Now there is a lot of excitement about what biochar can achieve."

Dr Glaser is working on studies to see how effective it proves to be on poor soils in northern Germany.

At Newcastle University, Professor David Manning is also an enthusiast. He says with the right incentives biochar could perhaps lock up as much carbon as the amount generated by aviation.

Several biochar stoves have been developed for use in developing countries. Belize and a number of African governments are attempting to get biochar accepted as a climate change mitigation and adaptation technology for the post-2012 treaty to be negotiated in Copenhagen in December.

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