From Vapor to Liquid

June 28, 2018

We’re surrounded by water molecules in the air. Even in the driest environments, it swirls around us as airborne vapors. For decades researchers have worked to develop ways to extract and collect water from the air but these concepts have typically required large amounts of energy and have often proven unwieldy.

However, two new projects, outlined in papers published this month in Science Advances, have refined water extraction technologies and built upon their efficiencies, demonstrating remarkable innovation and promise.

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The first development is a water production device designed by a team of scientists at UC Berkley that works by using a metal-organic framework—a powdery combination of zirconium and carbon atoms—that acts as a sponge, absorbing water molecules from the air. When the device is heated by the sun, the material releases the water molecules, which condense on the walls. The liquid flows into a collection vessel.

“If you expose this material to humid air, the framework will get saturated with water molecules,” says chemist Eugene Kapustin, coauthor on the paper. “And then, because the water molecules don’t stick too tightly to the interior of the framework, we can release this water by heating the powder.”

Kapustin and his fellow researchers are currently improving upon the system by testing a higher-efficiency aluminum-based collection medium. They report that the material can complete at least 150 cycles of filling and drying without experiencing any degradation.

The second innovative water production project builds on fog catching devices. As Janice Kaspersen, editor of Erosion Control, recently explained, communities in Chile’s Coquimbo region are successfully harvesting fog with nets that capture moisture and pipe it to a storage container.

The efficiency of these passive fog devices is relatively low, however, yielding only 1–2%. By using electric fields and charging air atoms, a team of researchers led by Maher Damak and Kripa K. Varanasi, recently found that they could ionize water droplets and make them attracted to the mesh collector. The ionization is so effective, in fact, that droplets that aren’t captured in the mesh collector turn back around and come through it, resulting in 99% efficiency.

Operating at 60 watts per square meter of mesh, the device is surprisingly efficient, especially in comparison with other conventional air-water generators that chill air and allow it to condense.

The team is considering a wide range of applications including cooling towers at power plants. These units consume massive amounts of water and release it to the atmosphere as they reject waste heat in vapor plumes. Those water molecules, researchers explain, could be captured and collected for on-site reuse.

What other applications would you suggest for these water production technologies? 
About the Author

Laura Sanchez

Laura Sanchez is the editor of Distributed Energy and Water Efficiency magazines.