Researchers at the University of California, Berkeley say they have successfully tested a new type of water harvester in the desert that can produce fresh water from thin air.
Describing their results in the journal Science Advances, the team said the harvester can collect drinkable water every day and night cycle, at both low humidity and low cost. It could therefore be employed in arid parts of the world that are devoid of water.
“There is nothing like this,” said Omar Yaghi from UC Berkeley, who invented the technology behind the harvester, in a statement. “This laboratory-to-desert journey allowed us to really turn water harvesting from an interesting phenomenon into a science.”
The device operates at ambient temperatures and in sunlight. It requires no additional energy input, nor any source of power. The key breakthrough is a powder that’s spread over the top of the box-shaped device, called metal-organic framework (MOF), something that's been tested elsewhere before.
MOF is a crystal powder of organic and metal atoms, which absorbs water like a sponge during the night when temperatures are lower but humidity is higher. Then, when temperatures warm up in the morning, water molecules are pushed out of the crystals, producing a small cup of water.
The harvester is a “box within a box”, notes UC Berkeley, with an inner box holding a bed of MOF grains that’s about 0.2 square meters (2 square feet). Surrounding this is a plastic cube of a similar size that has a transparent top and sides. The top is left open at night to let air in, but is covered during the day to heat up the interior like a greenhouse.
A trial of the device took place in Scottsdale, Arizona, in October 2017. Here, humidity reaches 40 percent at night but drops to 8 percent during the day. And the test proved to be hugely successful. Using a kilogram (2.2 pounds) of MOF, the team said they can produce about 200 milliliters (7 ounces) of water, which is admittedly not a huge amount, but enough to pique interest as it should be scalable.
“The key development here is that it operates at low humidity, because that is what it is in arid regions of the world,” Yaghi said in the statement.
And there are already plans to improve the design, with a new MOF that’s made from aluminum. This is 150 times cheaper and can capture about twice as much water. The team are planning to conduct a field test with this MOF in Death Valley later this year.