Researchers have built a device that can harvest drinkable water out of thin air with nothing but the power of sunlight.
Drawing Water From Air
Researchers at the University of California Berkeley have developed a solar-powered water harvester that can extract water from air at low costs even in arid environments.
The new invention could potentially become useful in communities that live in parched conditions, where water supplies run dangerously low.
The device works on a day/night cycle and operates at ambient temperatures and sunlight levels. It does not require an external energy source aside from the sun.
Lab-To-Desert Field Tests
In October 2017, the team took their water harvester and set it up in the Arizona desert in Scottsdale, Arizona, where humidity levels can fluctuate between 40 percent during the night and 8 percent during the day.
They found that the device can harvest up to 200 milliliters of water, or up to 7 ounces, for every kilogram of porous material that absorbs water from the air.
"This laboratory-to-desert journey allowed us to really turn water harvesting from an interesting phenomenon into a science," says Omar Yaghi, water harvesting pioneer and James and Neetlje Tretter chair in chemistry at UC Berkeley.
Details of the study are published in the journal Science Advances.
How It Works
The water harvester is essentially a box within a box. The inner box is made up of 2 square feet of highly absorbent material called a metal-organic framework (MOF). It is housed in a second box with a transparent top and sides.
At night, the top lid is left open to let the MOF absorb moisture from the air. It is then closed during the day to trap heat inside and allow the MOF to release water. Water condenses outside of the box and pools at the bottom, allowing the researchers to collect it with a pipette.
An MOF is a highly porous solid material that can easily absorb liquids and gases. Inside the material are internal channels so many that an MOF the size of a sugar cube can spread out to occupy six football fields.
For this study, Yaghi and his team used MOF-801, a material made from zirconium. Before trooping to the desert, the researchers tested MOF-801 in a proof-of-concept water harvester in a lab setting. Using less than 2 grams of MOF, the researchers proved their hypothesis when they saw the walls of the device fogging up.
Less Expensive Options
Although effective as an MOF, zirconium is an expensive metal, and the costs of it could potentially thwart the possibility of making water harvesters commercially viable.
Aluminum, which is 150 times cheaper than zirconium, is a promising alternative. It can also collect twice as much water for every kilogram of MOF. A water harvester with an aluminum MOF, called MOF-303, can create 400 milliliters of water. This is about the equivalent of three cups of water.
Field tests also show that the water harvester can be configured to suit different conditions, even in places with very low humidity, where the device can collect water even at dew points below zero.
"The key development here is that it operates at low humidity," Yaghi says, "because that is what it is in arid regions of the world."
The team hopes to set up the next field test using MOF-303 at Death Valley in late summer. One of the hottest places in the world, Death Valley's temperatures can go as high up to 110 degrees Fahrenheit during the day.
