background image
With an optimal material choice, output can
be as high as three times that of the current
version, says Kim. Unlike any of the exist-
ing 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 oper-
ated 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 pas-
sively, Rao says, ¡°now we have demonstrat-
ed that this is indeed possible.¡±
The current version can only operate over
a single night-and-day cycle with sunlight, Kim says, but ¡°continous opera-
tion 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 scal-
ing 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 pour-
ing 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.¡±
¡°This technology is fantastic, because of the practical demonstration of
an air-cooled water harvesting system based on MOFs operating in a real
desert climate,¡± says Yang Yang, a professor of materials science and
engineering at the University of California at Los Angeles, who was not
involved in this work.
¡°This provides a new approach to solving the problem of water scarcity in
arid climates,¡± Yang says. ¡°This technology, if one can further increase its
production capacity, can have a real impact in areas where water is scarce,
such as southern California.¡±
Device Harvests Water From Desert Air
Field tested system could provide drinking water in extremely arid locations
calling all bird
watchers... Pg 10
mother¡¯s day fishing
derby... Pg 4
feeding back yard
chickens... Pg 9
local music master
David Starr... Pg 12
(March 22, David L. Chandler, MIT 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 Na-
ture Communications and includes some signifi-
cant 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,
2018 APR/MAY #9-2
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 au-
thors 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 kilo-
gram of MOF, the researchers say.
(Researchers at MIT have developed a new device that
is able to extract moisture from very dry air.
Image: Courtesy of the researchers)