ANU scientists have developed a novel, cost-effective method for desalinating seawater using heat. 

This breakthrough could significantly address global water shortages anticipated to affect 1.8 billion people by 2025, a crisis labelled as “absolute water scarcity” by the Food and Agriculture Organization (FAO).

The thermal desalination method keeps water in its liquid state throughout the process, harnessing moderate heat from sunlight or waste heat from industrial machinery.

The principle behind the technology is known as thermodiffusion or the Soret effect. Discovered in the 19th century by Swiss scientist Charles Soret, this effect causes salt ions to migrate to cooler regions of a heated water column. 

“We’re going back to the thermal desalination method but applying a principle that has never been used before, where the driving force and energy behind the process is heat,” said Dr Juan Felipe Torres.

In their experiments, ANU researchers passed seawater through a narrow channel heated to 60 degrees Celsius from above and cooled to 20 degrees from below. 

Initially, the diffusion process took 53 days to reach a steady state in a 30-centimetre tube, which was impractical for scalable applications. 

The team, however, managed to expedite the process by reducing the channel height to one millimetre and incorporating multiple channels, reducing the diffusion time to just minutes.

“Once the salt had migrated to the cooler water, the device reprocessed the warmer, purified water through the channel while the cooler, saltier water was removed,” said Shuqi Xu, a PhD student and the first author of the study.

“Each time the water passed through the channel, its salinity was reduced by three per cent. “Our research shows that after repeated cycles, seawater salinity can be reduced from 30,000 parts per million to less than 500.”

Current desalination technologies predominantly use reverse osmosis, which demands high electric power and costly materials that require regular maintenance. 

“Eighty per cent of the world’s desalination methods use reverse osmosis, which adds complexity and is costly to run,” Dr Torres says. 

The ANU team, with funding from the Department of Foreign Affairs and Trade and the SciTech4Climate program, as well as support from the ANU Institute for Climate, Energy and Disaster Solutions (ICEDS), is optimistic about the commercial potential of this technology. 

Dr Mona Mahani from ICEDS highlighted the project's deployment of a solar-driven desalination unit in Tonga to test its effectiveness in agriculture and drought mitigation.

The researchers aim to develop a commercial unit within eight years, potentially revolutionising how communities across the globe secure fresh water amid escalating environmental challenges.

More details are accessible here.