Surprise: less oxygen could be just the trick

It was used by the people of the Amazon for thousands of years. Now Australian researchers say biochar could reduce atmospheric carbon dioxide – while providing a new source of energy, and boosting farm productivity.

For almost 7000 years Amazonian farmers kept their soils fertile by setting organic waste alight and letting it smoulder under mud or earth, reducing it to a black carbon-rich material.

“Biochar is not unlike charcoal,” says Lukas Van Zwieten, a senior research scientist with NSW’s Department of Primary Industries.

When organic material is burnt with air it is often reduced to white ash. Trapped carbon goes up into the air as carbon dioxide, hence the greenhouse emission problem at coal-fired power stations.

But if heated while starved of oxygen “it just goes black, like a pizza left too long in the oven”, says Van Zwieten. Called pyrolysis, the process leaves up to half the carbon trapped in the char.

At Somersby, on the Central Coast, BEST Energies Australia, a company researching clean energy technology, has built a demonstration pyrolysis plant with the capacity to process 300 kilograms of dry green waste, wood waste, rice hulls, cow and poultry manure or paper mill waste every hour.

The material, says Adriana Downie, the company’s technical manager, is heated at up to 550 degrees for 40 minutes.

During processing gases are released from the material which are cleaned and burned to produce energy. This gaseous biofuel is called syngas. “Syngas can be used as a replacement for natural gas or LPG in gas-fired boilers or dryers, or to produce electricity,” says Downie.

The remaining black carbon-rich biochar can be used on farms.

Sydney Morning Herald