Tackling the global water crisis


– [Narrator] Today, 39%
of all the fresh water taken from rivers, lakes,
and reservoirs in the United States is earmarked
for the cooling needs of power plants, that use fossil fuels, or nuclear power. The problem? A large portion of that
water ends up floating away in clouds of vapor. In other words, hundreds
of billions of gallons of clean, otherwise usable
water, are lost each year. But now, a new system, devised
by a team of MIT engineers could provide an efficient, low-cost way to capture a substantial
amount of that lost water, ultimately making power
plants less wasteful and more self sustaining, and the water collected
could become a source of potable water for parched
cities around the world. The motivation to develop this new system stems directly from the inefficiencies of current natural fog harvesting systems. Existing systems, which
generally consist of a plastic or wire mesh,
hung vertically in the path of fog banks, only capture
about one to three percent of the water droplets
that pass through them. The reason for such a tiny
percentage is the result of aerodynamics. As a stream of air passes an obstacle, such as the wires in these
mesh fog catching screens, the air flow naturally
deviates around the obstacle. Thus, carrying droplets that
were heading toward the wire off to the side. The researchers found
that once they zap the fog with a beam of electrically
charged particles know as ions, the opposite effect happens. Not only do all the droplets
that are in the path of the wires land on
them, but even droplets that were aiming for the holes in the mesh get pulled toward the
wires, due to the charge. The droplets then collect on that mesh, drain down into a collecting pan, and can be reused in the power plant or sent to a city’s water supply system. The team is currently
building a full scale test version of their system, to be placed on the cooling tower of MIT’s central utility plant. A natural gas, co-generation power plant, that provides most of
the campus’s electricity, heating and cooling. In a series of experiments,
the researchers demonstrated the concept, by building
a small lab version of a stack emitting a
plume of water droplets. They then place their ion
beam and mesh screen on it. When the condenser is off, a
thick plume of fog droplets rise form the device. Once the condenser is turned on, the plume almost instantly disappears
and liquid can be seen condensing on the wire dome. The equipment is simple,
and the amount of power required is minimal. And the result is something priceless. Access to free, clean water. The researchers say this
could be a great solution to the global water crisis, by offsetting the need
for about 70% of new desalination plant installations,
in the next decade. For example, a typical
600 megawatt power plant could capture 150 million
gallons of water a year, representing a value
of millions of dollars. The researchers aim to test the system at MIT’s central utility
plant in the fall. The campus’s power plant
tests will not only de risk the technology, but will also help the MIT campus improve
it’s water footprint. (upbeat music)

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