"Drinking from the sea", explore how and why sea water is desalinated
From CNN
It's been a cruel irony for ancient mariners and any thirsty person who has ever gazed upon a sparkling blue ocean:
Water, water everywhere, and not a drop to drink.
But imagine a coastal
city of the future, say in 2035.
Along with basic infrastructure such as
a port, roads, sewer lines and an electrical grid, it's increasingly
likely this city by the sea will contain a newer feature.
A desalination plant.
Thanks to improved
technology, turning ocean water into freshwater is becoming more
economically feasible.
And a looming global water crisis may make it
crucial to the planet's future.
The United Nations predicts that
by 2025, two-thirds of the world's population will suffer water shortages,
especially in the developing world and the parched Middle East.
Scientists say climate change is making the problem worse.
Even in the
United States, demand for water in drought-ravaged California and the
desert Southwest is outpacing supply.
San Diego's billion-dollar water bet
When completed in 2016, it will be
the largest such facility in the Western Hemisphere and create 50
million gallons of freshwater a day.
"Whenever a drought
exacerbates freshwater supplies in California, people tend to look
toward the ocean for an answer," said Jennifer Bowles, executive
director of the California-based Water Education Foundation.
"It is,
after all, a seemingly inexhaustible supply."
A growing trend
Most desalination
technology follows one of two methods: distillation through thermal
energy or the use of membranes to filter salt from water.
In the distillation
process, saltwater is heated to produce water vapor, which is then
condensed and collected as freshwater.
The other method employs reverse
osmosis to pump seawater through semi-permeable membranes -- paper-like
filters with microscopic holes -- that trap the salt while allowing
freshwater molecules to pass through.
The remaining salty water is then
pumped back into the ocean.
An Introduction to the Carlsbad Desalination Plant Project :
The Carlsbad Desalination Project will provide San Diego County with a locally-controlled, drought-proof supply of high-quality water that meets or exceeds all state and federal drinking water standards.
After ten years of planning and six years in the state's permitting process, the Carlsbad Desalination pipeline has now received final approvals from every required regulatory and permitting agency in the state, including the California Coastal Commission, State Lands Commission and Regional Water Quality Control Board.
A 30 year Water Purchase Agreement is in place between the San Diego County Water Authority and Poseidon for the entire output from the plant.
Construction has already started and is expected to be complete in mid-2016.
Officials at the
Carlsbad plant say they can covert two gallons of seawater into one
gallon of freshwater by filtering out 99.9% of the salt.
There are some 16,000
desalination plants on the planet, and their numbers are rising.
The
amount of desalted water produced around the world has more than tripled
since 2000, according to the
Center for Inland Desalination Systems at
the University of Texas at El Paso.
"Desalination is growing
in arid regions," said Tom Davis, director of the center.
"We are
making progress in the USA, but the countries around the Persian Gulf
are way ahead in the use of desalination, primarily because they have no
alternative supplies of freshwater."
Israel, in an arid region with a coastline on the Mediterranean,
meets half its freshwater needs
through desalination.
Australia, Algeria, Oman, Saudi Arabia and the
United Arab Emirates also rely heavily on the ocean for their municipal
water.
In the United States, desalination projects are concentrated in coastal states such as California, Florida and Texas.
Some environmentalists
are wary of desalination, which consumes large amounts of energy,
produces greenhouse gases and kills vital marine organisms that are
sucked into intake pipes.
But proponents believe
the technology offers a long-term, sustainable solution to the globe's
water shortages.
One entrepreneur has even built
an experimental solar desalination plant in California's San Joaquin Valley.
"When other freshwater sources are depleted, desalination will be our best choice," said Davis, a UTEP professor of engineering.
California dreaming
Within the United
States, the water crisis is especially severe in California, which has
been stricken by drought over the last three years.
California's biggest
source of freshwater is the snow that falls in the Sierras and other
mountains, where it slowly melts into creeks and makes its way into
aquifers and reservoirs.
But if the planet continues to grow warmer,
snow will increasingly fall as rain and will be harder to collect
because it will swell creeks faster and create more flooding, said
Bowles of the Water Education Foundation.
Seventeen desalination
plants are being built or planned along the state's 840-mile coastline.
City officials in Santa Barbara recently
voted to reactivate their desalination plant, which was built in 1991 but shut after heavy rains filled nearby reservoirs in the early 1990s.
Another
$200 million facility has been proposed for the Bay Area, although construction won't likely begin for several years.
"The key question with
ocean desalination is how much are you willing to pay for it? The amount
of energy required to desalt ocean water can be daunting," said Bowles,
adding that operating costs at the Santa Barbara plant alone are
estimated at $5 million per year.
But advocates believe
the price of desalination will continue to decrease as the process
improves. This will be true of the massive Carlsbad plant, said Bob
Yamada, water resources manager with the San Diego County Water
Authority.
"The cost for this water
will be about double what it costs us to import water into San Diego,"
Yamada said.
"However, over time we expect that the cost of desalinated
water will equal, and be less than, the cost of imported water. That may
take 15 or 20 years, but we expect that to occur."
Ultimately, experts say,
municipalities will need to balance desalination projects with
conservation and water from more traditional sources, such as rivers,
reservoirs and recycled wastewater.
"You can't get all your
water from one source and have that source be hundreds of miles away,"
said Peter MacLaggan, senior vice president at Poseidon Resources
Corporation, which is leading development of the Carlsbad plant.
"When and if the drought
does come, and you don't have enough snowpack in the Sierras -- after
12 dry years the Rockies are seeing the impact of that today -- you've
got (water) sources here within the boundaries of San Diego County," he
said.
"We have a $190 billion
economy in this region. It's dependent on water to sustain that economy.
So the question you need to consider, is 'What's the cost of not having
enough water?'"
