In field tests, device harvests water from desert air

March 22, 2018 by David L. Chandler, Massachusetts Institute of Technology
Credit: CC0 Public Domain

It seems like getting something for nothing, but you really can get drinkable water right out of the driest of desert air.

Even in the most arid places on Earth, there is some moisture in the air, and a practical way to extract that moisture could be a key to survival in such bone-dry locations. Now, researchers at MIT have proved that such an extraction system can work.

The new device, based on a concept the team first proposed last year, has now been field-tested in the very dry air of Tempe, Arizona, confirming the potential of the new method, though much work remains to scale up the process, the researchers say.

The new work is reported today in the journal Nature Communications and includes some significant improvements over the initial concept that was described last year in a paper in Science, says Evelyn Wang, the Gail E. Kendall Professor in the Department of Mechanical Engineering, who was the senior author of both papers. MIT postdoc Sameer Rao and former graduate student Hyunho Kim SM '14, PhD '18 were the lead authors of the latest paper, along with four others at MIT and the University of California at Berkeley.

Last year's paper drew a great deal of attention, Wang says. "It got a lot of hype, and some criticism," she says. Now, "all of the questions that were raised from last time were explicitly demonstrated in this paper. We've validated those points."

The system, based on relatively new high-surface-area materials called metal-organic frameworks (MOFs), can extract potable from even the driest of , the researchers say, with relative humidities as low as 10 percent. Current methods for extracting water from air require much higher levels - 100 percent humidity for fog-harvesting methods, and above 50 percent for dew-harvesting refrigeration-based systems, which also require large amounts of energy for cooling. So the new system could potentially fill an unmet need for water even in the world's driest regions.

By running a test device on a rooftop at Arizona State University in Tempe, Wang says, the team "was field-testing in a place that's representative of these arid areas, and showed that we can actually harvest the water, even in subzero dewpoints."

Researchers at MIT have developed a new device that is able to extract moisture from very dry air. Credit: Massachusetts Institute of Technology

The test device was powered solely by sunlight, and although it was a small proof-of-concept device, if scaled up its output would be equivalent to more than a quarter-liter of water per day per kilogram of MOF, the researchers say. With an optimal material choice, output can be as high as three times that of the current version, says Kim. Unlike any of the existing methods for extracting water from air at very low humidities, "with this approach, you actually can do it, even under these extreme conditions," Wang says.

Not only does this system work at lower humidities than dew harvesting does, says Rao, but those systems require pumps and compressors that can wear out, whereas "this has no moving parts. It can be operated in a completely passive manner, in places with low humidity but large amounts of sunlight."

Whereas the team had previously described the possibility of running the system passively, Rao says, "now we have demonstrated that this is indeed possible." The current version can only operate over a single night-and-day cycle with sunlight, Kim says, but "continous operation is also possible by utilizing abundant low-grade heat sources such as biomass and waste heat."

The next step, Wang says, is to work on scaling up the system and boosting its efficiency. "We hope to have a system that's able to produce liters of water." These small, initial test systems were only designed to produce a few milliliters, to prove the concept worked in real-world conditions, but she says "we want to see water pouring out!" The idea would be to produce units sufficient to supply water for individual households.

The team tested the water produced by the system and found no traces of impurities. Mass-spectrometer testing showed "there's nothing from the MOF that leaches into the water," Wang says. "It shows the material is indeed very stable, and we can get high-quality water."

Explore further: Device pulls water from dry air, powered only by the sun

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antialias_physorg
5 / 5 (1) Mar 22, 2018
Somehow I can't get the image of Dune-style windtraps out of my mind. This seems like it could be a heaven-sent for a lot of arid regions or where water is a basis for conflicts (Israel/Palestine?). I hope they get this ready for prime time ASAP.
AlohaMilton
5 / 5 (2) Mar 22, 2018
I do wonder, what is the effect on the neighbors if an area upwind is extracting every last bit of already scarce moisture? Is this going to increase the size of an arid region as it tries to support too many living within it already?
SCVGoodToGo
5 / 5 (1) Mar 22, 2018
My first job was programming binary load-lifters, very similar to your moisture vaporators in most respects.
antialias_physorg
5 / 5 (1) Mar 22, 2018
I do wonder, what is the effect on the neighbors if an area upwind is extracting every last bit of already scarce moisture?

Since those upwind aren't doing anything with the moisture currently (and since wind directions aren't constant)...what kind of change would you expect?

Also notice that the air column is rather high - and this will potentially drag the moisture out of one small patch up to a height of a few meters. The overall moisture content (by percentage) is not hugely affected by this.

It's a bit like "will land behind windfarms get less wind"..yes, but so what?
Eikka
5 / 5 (2) Mar 22, 2018
.what kind of change would you expect?


Increased evaporation, parching up already dry places kiling your neighbor's garden.

It's a bit like "will land behind windfarms get less wind"..yes, but so what?


Increased UHI effect by disrupting the boundary system, higher temperatures downwind from wind farms. Again, same problem.

Also notice that the air column is rather high


Yes, but moisture "up there" doesn't help when it's dry down here. It's a bit like saying "Why are you complaining about the heat wave, it's -57 degrees up there in the stratosphere."
Eikka
5 / 5 (1) Mar 22, 2018
The solace is that pulling a couple liters of drinkable water out of the air isn't going to change the ambient humidity -that- much.

But if you're pulling down cubic meters of it to run a small farm in an arid region, that's going to affect your surroundings.

A cubic meter of air at 10% humidity contains on the order of 1 grams of water. Suppose you need 1000 m^3 to extract a liter, and a million m^3 to get 1000 L of water. If you take an air column 1 meters high and remove 1000 L of water - enough for a small group of households for a day - you'll dry out a square kilometer.

Obviously, trying to extract large quantities of water for many people in desert conditions will result in environmental impacts.
mackita
not rated yet Mar 22, 2018
Guy_Underbridge
not rated yet Mar 22, 2018
Eikka: ...you'll dry out a square kilometer.
Wind.
Eikka
4 / 5 (4) Mar 22, 2018
Eikka: ...you'll dry out a square kilometer.
Wind.


If you're continuously extracting water, the areas downwind of you will experience lower moisture, all the way until the air column gets mixed up again and the difference dilutes down.

Of course the wind direction changes, but most locations have a dominant wind direction, which results in drier local climate down that way.

It's the same thing as if you build a smokestack and puff up some air pollution. It ends up going somewhere, and the areas down the dominant wind direction are getting more of your pollution than elsewhere. In this case, the areas downwind get drier more often, and that affects vegetation and animal life, like the types of plants that can grow due to overall water availability in the soil which is affected by evaporation.
betterexists
1 / 5 (4) Mar 22, 2018
The Problem is that the Underground is hot Too!
So, only way to solve the issue is by using an U-OR O_TUBE_LOOP . I used the last part of the previous sentence to simplify. I just mean ....Run a pipe underground...ALL THE WAY to Sea Bottom (Not necessary to go all the way that down) and Back to the Required Area....Hopefully, it won't burst the pipes ! Tesla should help with use of the Solar Battery issues. So, We do get ESSENTIAL FRESH WATER, but by spending Dollars for Batteries, as long as they do NOT EXPLODE in the Deserts.....So, Place Batteries at the Sea to suck Hot Air from the Desert ! Just as we drilled for oil for our cars, WE DO NEED TO CONVERT DESERTS Back to Normalcy, if NOT IMMEDIATELY, at least in decades/centuries/millennia ! ARIZONA IS ONLY 50 MILES AWAY FROM SEA !
betterexists
1 / 5 (1) Mar 22, 2018
The Problem is that the Underground is hot Too!
So, only way to solve the issue is by using an U-OR O_TUBE_LOOP . I used the last part of the previous sentence to simplify. I just mean ....Run a pipe underground...ALL THE WAY to Sea Bottom (Not necessary to go all the way that down) and Back to the Required Area....Hopefully, it won't burst the pipes ! Tesla should help with use of the Solar Battery issues. So, We do get ESSENTIAL FRESH WATER, but by spending Dollars for Batteries, as long as they do NOT EXPLODE in the Deserts.....So, Place Batteries at the Sea to suck Hot Air from the Desert ! Just as we drilled for oil for our cars, WE DO NEED TO CONVERT DESERTS Back to Normalcy, if NOT IMMEDIATELY, at least in decades/centuries/millennia ! ARIZONA IS ONLY 50 MILES AWAY FROM SEA !
Sonoran Desert Covers Large parts of S.E of U.S in Arizona and California and of N.W Mexico in Sonora, Baja California, and Baja California Sur. https://en.wikipe...ts_of_Ar
betterexists
not rated yet Mar 22, 2018
Sonoran Desert Covers Large parts of S.E of U.S in Arizona and California and of N.W Mexico in Sonora, Baja California, and Baja California Sur. https://en.wikipe...Deserts_
Sonoran Desert is the hottest desert, particularly in Mexico. It has an area of 100,000 sq mi
betterexists
not rated yet Mar 22, 2018
Large arid region of 190,000 sq mi includes deserts, such as the Great Basin Desert and Sonoran Desert; and the non-desert arid region areas (with greater than 10 inches (250 mm) annual precipitation) in the Great Basin arid region, Colorado Plateau, Mexican Plateau, and others. This arid region extends from the top of the North American Desert in Washington and Idaho southward into Mexico in the Trans-Mexican Volcanic Belt. The 'western arid region' is east of and (except for Mojave sky islands) discontiguous from the Mojave Desert, unlike the southwestern Great Basin deserts adjacent with ecotones to the northern Mojave Desert.
https://en.wikipe..._listing
TheGhostofOtto1923
5 / 5 (2) Mar 22, 2018
Hmmm like a heat pump only with water... I think we'll call it a water pump. Or something.
RealityCheck
3.3 / 5 (7) Mar 22, 2018
@AlohaMilton and @Eikka.

Your worry that downwind areas will be deprived of that upwind-collected moisture is unfounded, since that water will only be 'relayed' through plant/animal/human use and 'lost' to the air once again. So it's merely temporarily cycled through before again returning to the air from whence it was extracted. So no 'net dehydration' of that air unless that extracted water 'disappears' by 'sequestering' in storage for months; or by 'transporting' it to distant locations/users (especially those 'not upwind' of those areas which would normally have receive that 'temporarily extracted/relayed water' through immediate/timely return to the local air flows).

But it's good to see that you WERE concerned on behalf of those downwind; it shows your humanity and willingness to consider others' welfare. Kudos for that. Cheers. :)
adave
not rated yet Mar 22, 2018
For such a small device the extractor is efficient. Back in the stone age, ponds were built that stayed full of water. Even today, people don't know how they work. Experts think that rain fills them up. Dorset england had a dew pond you can see on youtube. The ponds here in the US were built about 1760 only in Kentucky. One that I have visited for 15 years was in use during the civil war. There is part of a juniper carved fence nearby that uses no nails. It has no algae and never dries up. Atmospheric water fills this pond that has I estimate 25,000 gal. They are found at the top of hills at 200 feet. The ponds here are lost in the forest untended near 260 years. They have preserved species for all that time. "Jack and Jill went up the hill to fetch a pail of water". They were visiting a dew pond. The farm pond in the valley was at 84 degrees same as the dew pond. In North America no one knows they are here. Except in winter, free water no moving parts except the water.
EnricM
not rated yet Mar 23, 2018
Somehow I can't get the image of Dune-style windtraps out of my mind.


Kull Wahad!

Porgie
not rated yet Mar 23, 2018
Drying out the air for others is a non existent issue there are 3.974 billion cubic miles of air around the Earth. What disturbs me is when they started talking about using biomass and waste heat to fuel it? There is a lot they are not saying about his. Many dry deserts don't have lot of biomass to use, and how much waste heat is needed? How much CO2 will it take to get a quart of water. Workers in the hot deserts can use as much as 7 gallons of water per day. Lots ot be answered here.
Eikka
not rated yet Mar 29, 2018
Your worry that downwind areas will be deprived of that upwind-collected moisture is unfounded, since that water will only be 'relayed' through plant/animal/human use and 'lost' to the air once again.


That depends on where exactly the water ends up. In concentrated form as liquid, it tends to run off and not get evaporated back up again to follow the same route as it did before.

in other words, the water can end up thousands of miles away down the river instead of being instantly evaporated to condense downwind again.

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