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From: Biniam Tekle (biniamt@dehai.org)
Date: Tue Apr 26 2011 - 10:23:03 EDT
"The group has installed fog collectors in countries like Guatemala, Chile,
Nepal, Eritrea and Yemen. One net covers 430 square feet, and the whole
structure costs about $1,000, he said. In one mountainous village in
Guatemala, FogQuest installed 35 nets to catch fog, he said"
http://edition.cnn.com/2011/TECH/innovation/04/26/fog.harvesting.mit/index.html?section=cnn_latest
(CNN) -- Let's say you live in a really dry area and you don't have much
drinking water. Meanwhile, you wake up every morning to the sight of fog
floating by. Instead of walking miles and miles to get water from a faraway
river, what if you could just extract drinking water from those low-hanging
clouds?
That's what a researcher at MIT is trying to make possible with new work to
improve "fog harvesting," the term for the process of getting water out of
mist by using giant tarps made out of engineered materials.
The art of fog harvesting is simultaneously high- and low-tech.
To catch the fog, workers erect giant nets on stands of bamboo sticks or
metal poles. This contraption catches the fog as it floats though the meshed
material.
The nets don't catch all that much water -- about 1 liter for a net that
measures 1 meter by 1 meter -- but that's enough to make a big difference in
some parts of the developing world, said Shreerang Chhatre, a Ph.D.
candidate at MIT who is doing research on materials that could improve fog
technology.
"If you're thinking from a Western point of view, from the point of view of
a Western consumer who consumes 200 liters of water every day" then this
technology doesn't make much sense, he said. "In order to get that, we would
need a humongous, huge surface. We want to get drinking water, water that is
absolutely necessary for survival for people. That, we need in small
quantities."
Chhatre is trying to improve the materials the fog nets are made of so that
they will collect more water. The nets he's working on are made of tiny
steel rods woven together until they look somewhat like a chain-link fence.
The metal is coated with two materials, one that attracts water and one that
repels it.
The goal is to attract the fog to the net, but once it touches the surface,
Chhatre wants the liquid to roll down the contraption as fast as possible
and into a bucket. If the water remains on the net for a long time, it
evaporates, he said. A water-repelling compound, which acts somewhat like
Teflon on a frying pan, encourages the water to roll down the net for
collection.
It's unclear how well the materials Chhatre is developing will work in the
real world. So far he's only done lab tests on this engineered mesh.
He is not the first person to work on fog-harvesting technology.
A Canadian nonprofit called FogQuest has been installing moisture-catching
nets in remote desert areas for about 10 years.
Still, there are only about 15 active fog-catching projects in the world,
said Robert Schemenauer, FogQuest's executive director.
The technology has the potential to change lives in remote areas of
mountainous deserts, where fog is really the only water source, he said, but
it won't work in cities or even large towns, because fog collectors produce
such a small volume of water. That's why the idea hasn't taken off in a big
way, he said.
The group has installed fog collectors in countries like Guatemala, Chile,
Nepal, Eritrea and Yemen. One net covers 430 square feet, and the whole
structure costs about $1,000, he said. In one mountainous village in
Guatemala, FogQuest installed 35 nets to catch fog, he said.
Schemenauer is somewhat skeptical of developing new materials to improve fog
collection. FogQuest uses cheap, agricultural shade nets for its fog
collectors. There's room for that technology to be improved, he said. But
many researchers have tried to develop a material that will catch more water
at less cost.
"A thousand people have wanted to try to build a better material for
collecting fog droplets and no one has done it very well -- yet," he said.
"I have absolutely no problem if you can design a particular material that
would work better and would have other properties that are better. We'd
certainly look at it," he said. "But you also have to think about the
manufacturing side of it. We are using something that is used in vast
amounts for another purpose, so the cost is really low."
Chhatre said he believes his higher-tech material may prove to be more
efficient at collecting water from fog and will be low-cost.
"It helps tune the motion of the droplets so we can collect the maximum
amount of water," he said.
If he succeeds, the practice of fog harvesting may someday be common in
areas where water is scarce.
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