Water, Water, Everywhere, So Let's All Have a Drink
(Top Posts - Science - 061808)

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Water, Water Everywhere,
So Let's All Have a Drink

Offshore desalination could turn the oceans
into an inexhaustible water supply.
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The only significant seawater desalination,
or desal, facility in operation in the United
States is the Tampa Bay Seawater Desalin-
ation Plant, which after a problem-plagued
start is finally producing 25 million gallons
of water a day, or about 10 percent of the
region's water supply.

California, Texas, Massachusetts, and Geor-
gia are all cautiously considering similar
saltwater desal plants. But critics say these
plants are energy hogs that have a hugely
detrimental impact on coastal marine life.

One potential alternative that's getting a
lot of attention these days, not just in the
United States but around the world, is the
idea of offshore desalination platforms or

"There are so many obstacles and hurdles
to overcome in building and running a
desal plant onshore ... that going off-land
is kind of a no-brainer."

Offshore, the water can be extracted from
an optimal depth where sea life density is
low and where the water is cleaner, reduc-
ing the extensive pretreatment that onshore
plants must perform.

Furthermore, the concentrated saltwater
left over after processing can be more thor-
oughly diluted in the deep ocean rather than
being dumped near shore, where marine
life is plentiful.

And the cost of powering an offshore plant
is expected to be less than for land-based
plants; while land-based plants end up hav-
ing to buy third-party power, an offshore
plant could produce its own without the

The notion of offshore desal platforms is
not entirely new-India has built a test plant,
and a Spanish company wants to construct
a wind-powered one-but most such ap-
proaches are geared toward small produc-
tions of 5 million gallons or less per day.

Far more ambitious is a plan from Water
Standard Company, a Houston-based water-
treatment outfit that intends to build a Sea-
water Desalination Vessel (SDV) that could
output up to 15 times that much-up to
three times the production of the Tampa
Bay desal plant.

The SDV, moored a mile or more offshore,
would generate its own power with efficient
gas turbines, which could use biofuels if
sufficient supplies are available.

The SDV would use the same desal method
the Tampa plant uses, reverse osmosis, in
which seawater is pumped at high pressure
through dense membranes to remove the
salt. It's basically the same process that cruise
ships (80,000 gallons per day) and military
ships (aircraft carrier: 300,000 gallons per
day) have used to convert seawater to fresh-
water for decades.


Water Standard says it's well aware of the
costs and regulatory hurdles; to lessen the
regulatory burden, the company expects
the first ship will probably be built for
Israel, Australia, China, or the Middle East
-areas where there is a great demand for
water and an easier path to government


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