Simple device could pull drinking water from dry desert air, scientists say

By Mary Elizabeth Williams-Villano

Calcium chloride and nanotubes make it work.


It may be possible to capture drinking and irrigation water from the air using a simple device, even in the most arid desert regions, according to a story posted on the EurekAlert! science news website.

Researchers from Saudi Arabia’s King Abdullah University of Science and Technology say a device that can capture its own weight in water from fresh air, and then release it when warmed by sunlight, could provide a secure new source of drinking water in remote, arid regions.

If this technology could be put to work on a large scale, it would have vast implications for the irrigation industry as well. Imagine a sprinkler system that needs no connection to a water main.

Previous trials of materials and devices intended to tap the nearly 13 trillion tons of water Earth’s atmosphere contains proved too inefficient, expensive or complex to be practical. Now, a prototype device developed by Peng Wang and his team at KAUST’s Water Desalination and Reuse Center could change that.

The device utilizes calcium chloride, a substance familiar to snow removal professionals. It’s a cheap, stable, nontoxic salt with a high affinity for water, so much so that it will absorb vapor from the surrounding air to the extent that eventually, a pool of liquid forms. "The salt can dissolve itself by absorbing moisture from air," says Renyuan Li, a Ph.D. student on Wang's team.

The fact that calcium chloride turns from a solid to a salty liquid after absorbing water has been a major hurdle for its use as a water capture device. "Systems that use liquid sorbents are very complicated," says Li.

To overcome this problem, the researchers incorporated the salt into a polymer called a hydrogel which can hold a large volume of water while remaining a solid. They also added a small amount of carbon nanotubes, 0.42 percent by weight, to ensure the captured water vapor could be released. Carbon nanotubes efficiently absorb sunlight and convert its energy into heat.

The team put 35 grams of the hydrogel into a simple prototype device. It was left outdoors overnight on a day where the relative humidity hovered at around 60 percent. The next day, after 21/2 hours of exposure to natural sunlight, most of the water was released and collected inside the device.

"The hydrogel's most notable aspects are its high performance and low cost," says Li. If the prototype could be scaled up to produce 3 liters of water per day, the minimum daily water requirement for adults, the cost of the absorbent hydrogel would drop as low as half a cent per day.

Wang says that the next step will be to fine-tune the hydrogel so that it will release harvested water continuously rather than in batches.