Biochar - a type of charcoal produced by burning biological material under low-oxygen conditions, stores carbon for decades, thus keeping it out of the atmosphere.

Credit: BEST Energies

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BRISBANE: Who thought a little charcoal could be a solution to climate change?

For one, climate activist and 2007 Australian of the Year Tim Flannery who has been singing its praises for a while.

According to Flannery, a type of charcoal called Biochar not only sequesters carbon, but it also provides energy and improves the agricultural output of poor soils.

Too good to be true? Not according to Evelyn Krull, a biogeochemist at CSIRO in Adelaide, Australia, who is looking into the environmental and agricultural benefits of this simple carbon sink.

"Biochar can be produced in a carbon negative way, which means it has a carbon sequestration potential," says Krull. "Applied to soil, it can result in enhanced nutrient retention, and due to its high absorptive capacity, [it] can also decrease the uptake of soil toxins."

Biochar is the solid remains of biomass (biological material) burned in an enclosed space under low-oxygen conditions, a process called pyrolysis. By keeping the oxygen levels low, more carbon remains in the char, which lasts at least 100 years.

"It has a chemical structure that makes it very difficult to break down by any physical, biological or chemical processes," says Krull.

That stability is the secret to biochar's carbon-sequestration potential. While the biomass feedstock would quickly break down, releasing its carbon back to the atmosphere, converting them into biochar locks much of their carbon into a solid form.

The rest of the biomass's carbon becomes a gas, which can be collected and used as a fuel for heat or electricity, replacing fossil fuels such as coal.

The feedstock for biochar production can be any kind of biomass, Krull says - manure collected from a feedlot, cane trash left over from sugar cane production, woodchips from a sawmill, or a dedicated biofuel crop.

Preventing the decay of the feedstock and sequestering its carbon is the main climate mitigation action of biochar, but its benefits don't stop there, says Annette Cowie, a forest scientist for New South Wales's Department of Primary Industries in Sydney, Australia.

Applying the biochar to soil improves the soil's structure, Cowie says, helping it to retain water and nutrients and reducing the amount of nitrogen fertiliser required, especially for fertiliser-intensive crops like vegetables.

Biochar also reduces emissions of nitrous oxide, a greenhouse gas produced by soil microbes that's 300 times more potent than carbon dioxide, by up to 80 per cent, according to the International Biochar Initiative. The reduction isn't just the effect of applying less fertiliser, says Cowie.

"It seems that when you apply the biochar, that nitrogen transformation process is inhibited," she says.

Plans for large-scale use

These promising observations have prompted scientists to look closely at how biochar could be used in Australia. Both Krull and Cowie say that there's still much research to be done to get the most out of biochar, with the activity of biochar made from different feedstocks and the response of different crops and soil types a particular concern.

However, some growers are already importing biochar from the Philippines, Cowie says, and some Australian government agencies are also showing interest.

Government agencies in New South Wales have already been scouting out suitable sites for commercial-scale pyrolysis plants, Cowie says, and have identified "half a dozen locations" where a plant could be supplied with 50,000 tonnes of biomass a year, the amount of feedstock a commercial plant could burn.

Locating pyrolysis plants close to the biomass supply is important, Cowie says, because transporting the feedstock too far could release more emissions than the biochar sequesters.

"We've determined that a transport distance of maybe a couple of hundred kilometres to such a plant would be reasonable," Cowie said.

Just using material already available, like urban green waste, sawmill residues and crop waste, biochar could cut Australia's greenhouse gas emissions by two per cent, or 11.5 million tonnes of carbon dioxide, Cowie says.

That's equivalent to the annual greenhouse gas emissions generated by 400,000 Australians.

"[Even] using conservative assumptions…biochar does have a substantial greenhouse mitigation benefit," Cowie says.

However, Cowie points out that while two per cent is an important contribution to climate mitigation, biochar can't offset the emissions caused by our current standard of living.

"It's certainly not going to stop us needing to reduce our fossil fuel emissions," she warns.