In field tests, device harvests water from desert air

Posted: March 23, 2018 by oldbrew in innovation, research
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Image credit: BBC


They say ‘the next step is to work on scaling up the system and boosting its efficiency’.

MIT-developed system could provide drinking water even in extremely arid locations, says MIT’s News Office.

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 water from even the driest of desert air, 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.”

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.”

Continued here.

Comments
  1. A C Osborn says:

    The only problem that I foresee is that it will make the area even more Arid.
    I would prefer to see some means of actually getting water there.

  2. JB says:

    Ahh, but in most instances, the captured water returns to the environment in 1-3 days. Herbert’s still suits are coming.

  3. Curious George says:

    This harvests the power of wind (bringing moisture from oceans).

  4. oldbrew says:

    No oceans in Arizona :/

  5. Richard111 says:

    Might not be a good idea to use this system in a valley. As I understand it removing water molecules from air makes it more dense.

  6. ivan says:

    OK, they had the test unit on the roof of a building in a populated area.

    Now what were the results out in the bare landscape, no buildings, no people just clear ground? Those are the results that matter.

  7. Bloke down the pub says:

    How long before the MOF gets clogged up with dust?

  8. michael hart says:

    It’s not the first from MIT to go down this silly road. Their previous attempts were given a well deserved rubbishing by Thunderfoot on youtube.

    Ultimately, the numbers will almost certainly just never add up. The slowness, low efficiency, low capacity, capital costs and energy costs will always make it cheaper to ship water from elsewhere.

  9. konradwp1 says:

    When it comes to harvesting water from desert air, there have been simpler and more practical proposals involving radiatively cooled panels which condense water on their non radiating side. In the desert environment, due to little humidity and cloud, the sky background temperature can be -50C during the day and lower again at night.

    If such a panel is sun shielded and correctly insulated, temperatures below freezing can be achieved even during the day. Some quite astounding results have been achieved with selective surfaces that radiate primarily in the wavelengths of the atmospheric window (8-14 microns). Such a material is therefore radiating not to sky background temperatures ~223K but to space background of ~3K.

    This link is to a study achieving -25C during the day:
    https://www.nature.com/articles/ncomms13729
    Of course temperatures would not be so low if external air were being introduced to the rear of the sample to condense water out, but -25C is still pretty impressive.

    The advantage to a radiatively cooled water condenser built around this technology is that besides the fan controlling air flow to the condensation side of the radiator panel, the system is entirely passive.

  10. dp says:

    How many people are lining up to tap the wealth of free water in roof-top HVAC installations? With all the biology ever present in the air is it possible to extract filthier water? Then there is that Legionaire’s Disease thing… Swamp water not quite ready to drink, I think. Might be best used for drip irrigation.

  11. Doonhamer says:

    An array of millions of Darkling beetles all with rses in the air and their backs to the oncoming breeze.

  12. oldbrew says:

    ‘Fog harp’ increases collection capacity for clean water
    March 28, 2018

    A passive, durable, and effective method of water collection, fog harvesting consists of catching the microscopic droplets of water suspended in the wind that make up fog. Fog harvesting is possible – and has gained traction over the last several decades – in areas of Africa, South America, Asia, the Middle East, and even California. As illustrated by recent headlines of South Africa’s countdown to “Day Zero,” or the day the water taps are expected to run dry, water scarcity continues to be a growing problem across the globe. Leading researchers now estimate that two-thirds of the world’s population already live under conditions of severe water scarcity at least one month of the year.

    Fog harvesting could help alleviate that shortage, and now an interdisciplinary research team at Virginia Tech has improved the traditional design of fog nets to increase their collection capacity by threefold.

    Read more at: http://phys.org/news/2018-03-fog-harp-capacity.html

  13. choey says:

    A working model can be seen on Tatooine.

  14. oldbrew says:

    Liquid-repellent surface maximizes water harvest and transport
    March 30, 2018, University of Texas at Dallas

    “Existing processes for creating fresh water, such as desalination, rely on the transition from vapor to water,” said Dr. Simon Dai, assistant professor of mechanical engineering in the Erik Jonsson School of Engineering and Computer Science. “We wanted to create a surface that can both capture and direct water droplets efficiently.”
    . . .
    The researchers have filed a patent on the technology.

    Read more at: http://phys.org/news/2018-03-liquid-repellent-surface-maximizes-harvest.html