Monday, June 04, 2007

Desalination Studied for California

Those of us who look at the clouds for water don't give a lot of thought to places where groundwater and rivers are the main supply. When dry spells come we figure sooner or later rain will bring relief. I've come across references to desalination before and paid little attention, but this year's drought has raised my awareness of the water supply.

California is looking at desalination. Here is a short primer for people like me who know nothing about the subject.

Northern California just endured its driest winter in 20 years. The state's population is growing by half a million people a year. New dams are controversial. And this week, a two-inch endangered fish shut down the pumps at California's largest drinking water source, San Francisco Bay's delta.
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Although 10 years ago there were none, today 20 desalination projects are on the drawing board in California's coastal areas from San Diego to Marin County, including one of the largest desalination plants in the world proposed for the Bay Area.
Filtering salty ocean water into drinkable fresh water is expensive. And environmental challenges loom. But groundbreaking on several facilities may start within two years.

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New technology has cut the cost of filtering ocean water in half since 1990. Still, the process, which uses large amounts of electricity, can cost at least three times as much as other ways.
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California currently has about a dozen working desalination plants. But all are tiny, compared with the ones being proposed, producing a combined 6 million gallons of water a day. Many run on offshore oil platforms and refineries.

If all 20 of the proposed plants across the state were built, California would be producing about 300 million gallons of fresh water a day from the Pacific Ocean - a fiftyfold increase from today, according to data from the Pacific Institute, a think tank in Oakland.
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In two years, Karajeh's department has handed out $50 million in grants to fund studies and pilot plants at two dozen California desalination projects.

Still, big hurdles remain.

Fish, shrimp, even marine mammals can be crushed against intake pipes if desalination facilities aren't well built. The plants also put large amounts of brine back into oceans and bays, though usually diluted with treated waste water or cooling water from power plants at as much as 100-1 ratios.

Environmentalists also are worried that because desalination would provide more water, it could encourage more people to move to rural and pristine areas.

"Desalination is a false promise," said Mark Massara, coastal advocate for the Sierra Club. "It isn't good for California communities. No matter how little it rains, it never makes the cost, financial or environmental, worthwhile."
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How would they work?

In most modern plants, salt water is pumped through fine filters at as much as 1,000 pounds per square inch - as much as a pressure washer uses to clean sidewalks - in a process known as reverse osmosis.

The Bay Area water agencies now studying desalination began examining sites in 2003. They chose three finalists: Ocean Beach in San Francisco, where they estimate filtering salty ocean water would cost $2,700 an acre foot; the Bay Bridge, near Oakland, where less salty water would cost $2,500 an acre foot to produce; or Pittsburg, where fresher delta water would cost $500 to $1,200 an acre foot. An acre foot is enough water for a family of five for a year.

By comparison, it now costs the Santa Clara Valley Water District $300 to $400 an acre-foot to buy and treat water from state and federal agencies.

More at the link for those interested.
Terms like "acre foot" are new to my vocabulary but in coming years they are apt to become common.
This link was found at Crossroads Arabia.

1 comment:

chrisellyn said...

One of the biggest drawbacks to desalination, besides the environmental damage it can cause, is that it takes an enormous amount of electrical energy to run these plants.

For example, if the City of Santa Barbara's desal plant were operational, it would provide water for about 15,000 homes, and consume the same amount of energy as a small steel mill. It would take six of these to supply Santa Barbara's water consumption needs.

In a state already concerned with global warming and electrical capacity, I don't think this is the answer.

I recently wrote extensively on this subject. You can read it by clicking here: Aquafornia Desalination article.

My blog is Aquafornia, the Southern California water blog. You can visit my blog here: http://aqaufornia.com