Clean energy from contaminated land

A team of Australian and Chinese scientists has pioneered a new way to make clean energy from land contaminated with toxic waste.

A collaboration between researchers from Australia’s CRC for Contamination Assessment and Remediation of the Environment (CRC CARE) and its offshore partners HLM Asia Group and Shaoguan University has delivered proof of concept for a new system for cleaning up badly polluted land that produces greenhouse-friendly energy for homes and industry at the same time.

“This is a genuine win-win solution,” says CRC CARE Managing Director Professor Ravi Naidu. “We use special plants to extract the toxins from the soil - and then we convert the plants to safe, clean energy.”

Like most industrialised countries, China has a number of sites so contaminated by heavy metals from past industrial or mineral processing that the only solution was usually to fence them off and abandon them. It has been estimated that up to one-tenth of the country’s farming land is affected by industrial pollution, which can reach consumers via the food chain.

The Australia-China team has demonstrated that a fast-growing plant called Giant Napier grass can not only be used to cleanse affected soils of contaminants, but can then be converted to ethanol for transport fuel or steam for electricity production.

Biomass harvested from an experimental plantation at Shaoguan University, Guangdong Province, China, is already being used to generate electricity for 100 households - and the team is already working to share the breakthrough internationally.

“There were several stages to the project,” says Prof Naidu. “First we had to mass produce a newly developed strain of Napier grass that is fast growing and has high energy value, which we did using plant tissue culture techniques. This plant grows well on degraded land and produces high yields.

“In field research we have been able to show it can be used for phytoremediation, which is the use of plants to extract particular minerals and metals from contaminated soils selectively, using their roots. By continually planting and harvesting these crops, over a decade say, you can lower the level of toxicity in the soil and make the land fit for human uses again, including for housing.”

This technique is equally valuable in China and Australia, Prof Naidu explains, as it can convert worthless land to high-value real estate - especially in cities, where land is very scarce.

“Then we had to devise more efficient ways for converting this grass to sustainable energy and use it to reduce greenhouse emissions from traditional coal-burning generators. We have pursued several different approaches here, including gasification and pyrolysis.

“In particular, we are working on so-called second-generation biofuel production which employs techniques such as steam explosion to extract clean energy from grasses, crop and timber waste. Worldwide there is a race on to perfect a commercial method for doing this - and our team is among the leaders.”

Prof Naidu said the CRC CARE-China partnership was also working on a project to remediate red mud - the waste product from alumina processing which is causing a major disposal headache worldwide. “Both China and Australia are big aluminium producers - so solving the problem of disposing of millions of tonnes of red mud produced each year is a national priority,” he adds.

“Australia has an estimated 160,000 contaminated sites, and Asia is thought to have several million. The CRC CARE-China partnership is an example of how the Australian cooperative research model is being used to tackle a global problem, by pooling scientific expertise and resources,” Prof Naidu says.

“Through research alliances such as this we are also exploring and creating export opportunities for Australian companies that specialise in clean-up, as well as educational export opportunities for our universities.”