Current approaches to water desalination are tremendously expensive and energy-intensive, so the search is very much on for new technologies that can get the job done more efficiently. Scientists in Melbourne have put forward one rather promising solution, developing a new kind of system that heats up and purifies water using only the power of the Sun.
The device was developed by scientists at Australia’s Monash University, who say that water treatment accounts for around three percent of the world’s energy supply. Like other researchers around the globe, they have turned to sunlight to try and lighten the load, this time directing it toward what is known as a solar steam generator.
In simple terms, these devices concentrate sunlight onto a body of water, heating it up and causing it to evaporate. The resulting steam can then be used to drive turbines that produce electricity in concentrated solar power plants, perhaps sterilize medical equipment cheaply for the developing world, or simply to separate salt from water.
But one problem with the lattermost application is that the salt tends to gather on the surface of the material, which makes it difficult to produce pure water. The Monash University researchers worked around this problem with an intricately designed solar steam generator that prevents the salt from spoiling the broth.
It consists of a disc crafted from super-hydrophilic filter paper, a material that attracts water, which is coated with a layer of carbon nanotubes that convert sunlight into heat. Water is fed into the center of the disc via a simple cotton thread, where the heat turns it into steam that builds up on the disc while pushing the salt to the edge.
In this way, the device removes almost 100 percent of salt from the water, a level that leader of the team Professor Xiwang Zhang assures us is “high enough for practical applications.” The salts that accumulate at the edges, meanwhile, can also be harvested for use.
Zhang and his team tested out the device using salty water from a bay in South Australia, and found that it absorbed 94 percent of the light across the solar spectrum. It worked whether wet or dry, with light exposure heating up the device from 25 to 50° C (77 to 122° F) when dry and from 17.5 to 30° C (63.5 to 86° F) when wet, within just one minute.
“This device can produce six to eight liters (1.6 to 2.1 gal) of clean water per square meter (of surface area) per day,” Zhang tells New Atlas. “We are working to further improve the water production rate.”
Zhang and his colleagues hope that with further work, the device could be put to use providing clean water to remote communities that are currently without access. But its value mightn’t end there. The technology could be used in other areas where more efficient water purification methods might come in handy, such as mining and wastewater treatment.
“We hope this research can be the starting point for further research in energy-passive ways of providing clean and safe water to millions of people, illuminating environmental impact of waste and recovering resource from waste,” says Zhang.
Hydrophilic disc uses solar power to separate salt from water [New Atlas]