Africa Water, Sanitation & Hygiene December 2018 Vol.13 No.6 | Page 15

Water Supply
“The problem is that, increasingly, people are suffering
from drought, or their water is contaminated with items
that are dangerous but expensive to remove from the
water, such as the high fluoride contamination in parts
of Kenya. This means there are large water-stressed
swathes of the country where organizations will not drill
boreholes because the water does not meet World Health
Organization standards,” she said.
“It’s in these more niche drought and contamination
situations where water-from-air is really useful and makes
economic sense,” she says. “As the cost of producing
water from air drops—which is what we are seeking to do
with our own technology prototype—this will increase the
situations where it makes economic sense.”
Sewell and co-founders Beth Koigi and Anastasia
Kaschenko, a 2018 finalist in UN Environment’s Young
Champions of the Earth, met while doing a course on
climate change at Singularity University at the United
States’ National Aeronautics and Space Administration
(NASA) Ames Research Center in California.
Sewell says Koigi was already involved in a water filtration
business in Nairobi, but when the main dam ran out of
water, she realized access to water was a bigger issue than
cleaning dirty water. This inspired the new project.
Hertz places WeDew firmly among efforts being made
to repair the damage we have already done to the natural
world.
“We need to move beyond sustainability to a regenerative
and restorative future that comes from abundance rather
than a scarcity model… In particular, we need additional
decarbonization strategies if we are to save the planet from
ecological genocide,” he says.
Sewell believes climate volatility will continue to drive
research into water-from-air technologies.
“On a medium- to long-term basis, we absolutely believe
that climate change will cause increasing water stress across
the globe … So we believe that innovation and investment
in this space will grow.”
Saudi Researchers Produce Drinking Water from Dusty Desert Air
A simple device that can capture its own weight in water
from fresh air and then release that water when warmed
by sunlight could provide a secure new source of drinking
water in remote arid regions, new research from KAUST
suggests.
Globally, Earth’s air contains almost 13 trillion tons of
water, a vast renewable reservoir of clean drinking water.
Trials of many materials and devices developed to tap this
water source have shown each to be either too inefficient,
expensive or complex for practical use. A prototype device
developed by Peng Wang from the Water Desalination and
Reuse Center and his team could finally change that.
At the heart of the device is the cheap, stable, nontoxic
salt, calcium chloride. This deliquescent salt has such a
high affinity for water that it will absorb so much vapor
from the surrounding air that eventually a pool of liquid
forms, says Renyuan Li, a Ph.D. student in Wang’s team.
“The deliquescent salt can dissolve itself by absorbing
moisture from air,” he says.
Calcium chloride has great water-harvesting potential,
but the fact it turns from a solid to a salty liquid after
absorbing water has been a major hurdle for its use as
a water capture device, says Li. “Systems that use liquid
sorbents are very complicated,” he says. To overcome
the problem, the researchers incorporated the salt into a
polymer called a hydrogel, which can hold a large volume
of water while remaining a solid. They also added a small
amount of carbon nanotubes, 0.42 percent by weight, to
ensure the captured water vapor could be released. Carbon
nanotubes very efficiently absorb sunlight and convert the
captured energy into heat.
Renyuan Li pours the hydrogel into a petri dish and allows it to
form to the mold. © 2018 KAUST
The team incorporated 35 grams of this material into a
simple prototype device. Left outside overnight, it captured
37 grams of water on a night when the relative humidity
was around 60 percent. The following day, after 2.5 hours
of natural sunlight irradiation, most of the sorbed water
was released and collected inside the device.
“The hydrogel’s most notable aspects are its high
performance and low cost,” says Li. If the prototype
were scaled up to produce 3 liters of water per day--the
minimum water requirement for an adult--the material cost
of the adsorbent hydrogel would be as low as half a cent
per day.
The next step will be to fine tune the absorbent hydrogel
so that it releases harvested water continuously rather than
in batches, Wang says.
Source: Water & Wastewater International
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