Box designed to harvest water in desert dry air
WASHINGTON, June 9 (Xinhua) -- Engineers from University of California (UC), Berkeley have developed a water harvester that can extract drinkable water at very low humidity and at low cost, making it ideal for people living in arid, water-starved areas of the world.
In a study newly published in the journal Science Advances, they reported the results of the first field test in Arizona desert where the relative humidity drops from a high of 40 percent at night to as low as 8 percent during the day.
The researchers used a highly porous material called metal-organic framework (MOF) with many internal channels and holes. A sugar-cube-sized MOF might have an internal surface area the size of six football fields.
This surface area can easily absorb gases or liquids and quickly releases them when heated.
In the field test, they used MOF-801, which is made from expensive metal zirconium. The material could harvest about 200 milliliters of water per kilogram of MOF.
Also, Omar Yaghi, chemistry professor at UC Berkeley, reported that he has created a new MOF based on aluminum, called MOF-303, which is at least 150 times cheaper and captures twice as much water in lab tests.
This will enable a new generation of harvesters producing more than 400 milliliters (3 cups) of water per day from one kilogram of MOF.
The harvester is essentially a box within a box, according to the engineers. The inner box holds a 2-square-foot bed of MOF grains open to the air to absorb moisture and it is encased in a two-foot plastic cube with transparent top and sides.
The top was left open at night to let air flow in and contact the MOF, but was closed during the day so the box could heat up like a greenhouse to drive water back out of the MOF.
The released water condensed on the inside of the outer box and fell to the bottom, where the researchers collected it with a pipette.
"The key development here is that it operates at low humidity, because that is what it is in arid regions of the world," said Yaghi, who is eagerly awaiting the next field test, which will test the aluminum-based MOF.[ Editor: WPY ]