Researchers at the University of Utah have introduced a compact atmospheric water harvesting device that efficiently extracts water from the air using a fuel process, promising to address global water shortages.

Earth’s atmosphere contains an enormous amount of water, enough to fill Utah’s Great Salt Lake 800 times over. Removing some of that moisture is seen as a promising solution to providing clean drinking water to billions of people around the world who suffer from chronic water shortages.

Current Atmospheric Water Harvesting (AWH) technologies have numerous drawbacks related to size, cost, and efficiency. But a new study by engineers at the University of Utah has led to findings that could increase efficiency and bring the world one step closer to using air as a cooking water source in arid places.

The research presents a first-of-its-kind compact, fast-cycle, fuel-powered AWH device, said Sameer Rao, senior author of the study published in the journal Cell Reports Physical Science, This two-stage prototype relies on adsorbent materials that pull water molecules from non-humid air and then apply heat to convert those molecules into liquid form, said Associate Professor of Mechanical Engineering.

“Hygroscopic materials inherently have an affinity for water. They absorb water wherever you go. One of the best examples of this is the stuff inside baby diapers, said Rao, a father of a baby himself. “We work with a special type of hygroscopic material called a metal-organic framework.”

Rao likened the metal-organic frameworks to Lego bricks that can be rearranged to build all sorts of structures — in this case, they’re arranged to form a molecule ideal for gas separation.

“They can do this in a way that absorbs water vapor from the air, nothing more. They’re really selective,” Rao said. Developed with graduate student Nathan Ortiz, lead author of the study, the prototype uses aluminum fumarate shaped into panels that collect water as air passes through.

“The water molecules get trapped on the surface of our material, and it’s a reversible process. And so they sit on the walls instead of rooting into the material itself,” Ortiz said. “The thing about these absorbent materials is that they have a very large internal surface area. There are a lot of places where water molecules can get trapped.”

Just one gram of this material covers the surface area of ​​two football fields, according to Rao, meaning that only a small amount of material can hold so much water.

Technological details and military application

“This whole surface is at the molecular scale,” Rao said. “And that’s great for us because we want to trap the water vapor on that surface inside the pores of that material.”

Funding for the research came from the DEVCOM Soldier Center, a program run by the Department of Defense to promote technology transfer in support of Army modernization. The Army’s interest in the project stems from the need to hydrate soldiers operating in remote areas with few water sources.

“We thought of this specifically for defense applications, so that soldiers would have a small, compact device to produce water without having to carry a large water canteen,” Rao said. “It will literally produce water on demand.”

Rao and Ortiz have filed a preliminary patent based on the technology, which also has non-military uses.

“I think while designing the system, we also have a broader view of the water issue. It is not just a defence issue, it is largely a civil issue,” Rao said. “We are considering the daily drinking water consumption of a household. That works out to about 15-20 litres a day.”

In this proof of concept, the prototype achieved a goal of producing 5 liters of water per day per kilogram of adsorbent material. According to Ortiz, the device will outperform packaged water in the field within three days.

The second stage of the device involves heating the water into liquid form using a standard military camp stove. This works because of the exothermic nature of the water collection process.

“When it collects water, it gives off some heat. Then we add heat to change that,” Ortiz said. “We’ve got a fire going here, we’ve done everything to raise the temperature. And when we raise the temperature, we release water molecules rapidly. When we have really humid airflow, condensation is much easier at ambient temperatures.”

Atmospheric water harvesting technologies that are easier to implement when the air is humid are emerging, but none have resulted in equipment that can be used practically in arid environments. Ortiz believes his device could be the first because it runs on energy-dense fuels like the white gasoline used in camping stoves.

The team decided not to use photovoltaics.

“If you rely on solar panels, you’re limited to working during the day or you just need batteries that weigh more. You’re still doing the job. “It takes up a lot of space,” Ortiz said. “This technology is best in dry conditions, while cooling is best in high humidity conditions.”