ANU desalination breakthrough to bolster global water security as planet warms

05 Jun 2024

A鈥痵impler and more鈥痗ost-efficient method for removing salt from seawater using heat,  from The Australian 精东传媒app University (ANU), could address unprecedented global water shortages.   
By 2025, 1.8 billion people will likely face what the Food and Agriculture Organization (FAO) calls 鈥.鈥浓赌&苍产蝉辫;
To help combat the water crisis, ANU researchers have developed the world鈥檚 first thermal desalination method, where water remains in the liquid phase throughout the entire process.鈥  

The research, published in , demonstrates how the power-saving method is triggered not by electricity, but by moderate heat generated directly from sunlight, or waste heat from machines like air conditioners or industrial processes. 

Lead Chief Investigator, Dr Juan Felipe Torres, a world-leading mechanical and aerospace engineer who first proposed the concept of thermodiffusive desalination, said the phenomenon behind this technology, called 鈥榯hermodiffusion鈥 or 鈥榯he Soret effect鈥, was discovered in the 19th鈥痗entury yet has remained underutilised. 
鈥淲e鈥檙e 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,鈥 he said. 
鈥淭hermodiffusion鈥痺as a phenomenon鈥痜irst reported in detail in the 1850s by Swiss scientist Charles Soret, who experimented with a 30-centimeter water tube where one part of the water was colder and the other hotter. 
鈥淗e discovered that the salt ions move slowly to the cold side.鈥 

To test whether鈥痶his effect can be used鈥痜or water desalination, the researchers pushed seawater through a narrow channel heated from above to 60 degrees and cooled from below to 20 degrees. 
鈥淒iffusion was taking 53 days to reach a steady state with a 30-centimeter tube which is鈥痬uch鈥痶oo long for our purposes and isn鈥檛 scalable,鈥 Dr Torres said. 
鈥淥ur mission became to find a way to fast-track the diffusion process.鈥 

The ANU researchers found that adjusting the conditions for separation could significantly increase the speed of the diffusion process to just a couple of minutes.鈥 
鈥淭he key was reducing the channel height from 30 centimetres to one millimetre and adding multiple channels,鈥 Dr Torres said.鈥 
ANU PhD student and first鈥痑uthor,鈥 Shuqi鈥疿u,鈥痵aid once the salt had migrated to the cooler water, the device reprocessed the warmer, purified water through the channel鈥痺hile鈥痶he cooler,鈥痵altier water was removed. 
鈥淓ach time the water passed through the channel,鈥痠ts salinity was reduced鈥痓y three per cent,鈥 Ms鈥疿u said. 
鈥淥ur research shows that after repeated cycles, seawater salinity can be reduced from 30,000 parts per million to less than 500.鈥 
According to the ANU researchers, current desalination technologies 鈥 where salt is filtered through a membrane 鈥 require large amounts of electric power and expensive materials鈥痶hat need鈥痶o be serviced and maintained.鈥 
鈥淓ighty鈥痯er cent鈥痮f the world鈥檚 desalination methods use reverse osmosis, which adds complexity and is costly to run,鈥 Dr Torres said.鈥 
鈥淚f we continue fine-tuning the current technology without changing the fundamentals, it might not be enough.  
鈥淎 paradigm shift is essential to sustain human life over the next century.鈥 
With further testing, the researchers hope to produce the first commercial unit within eight years.鈥 
The research has received funding from the Department of Foreign Affairs and Trade and Australia鈥檚 Science and Technology for Climate Partnership (SciTech4Climate) program. The project also received support from the ANU Institute for Climate, Energy and Disaster Solutions (ICEDS).
鈥淭he project has deployed a commercial state-of-the-art solar-driven desalination unit to Tonga, to pilot its application for agriculture and drought mitigation strategies,鈥 Dr Mona Mahani, from ICEDS, said.