A seawater desalination method that requires less energy relative to the more commonly used processes offers an efficient route to counter global water shortages. The thermal desalination technology developed by Australian National University researchers uses heat instead of electricity in a treatment train where water remains in the liquid phase throughout the entire process. 

The scheme is driven by moderate heat — temperatures less than 100° C — generated directly from sunlight, or waste heat from machines like air conditioners or industrial processes. The temperature gradient maintained in the system propels salt ions to the colder side to encourage their removal.

The thermodiffusive desalination process described in Nature Communications was tested by sending seawater through a narrow channel heated from above to 60° C and cooled from below to 20° C. The treatment duration was reduced from days to minutes by shortening the channel height from 30 cm to 1 mm and adding multiple channels.  As the salt migrates to the cooler water, the device reprocesses the warmer, purified water through the channel while the cooler, saltier water is removed.

Salinity was reduced by 3% with each pass through the channel. The researchers report that after repeated cycles, seawater salinity can be reduced from 30,000 ppm to less than 500 ppm. Electricity consumption in this energy-conscious treatment system is also greatly lowered, and can be as low as 3 Wh/m³.