Environment & Energy
Related: About this forumDesalination out of Desperation
Even in drought-stricken California, San Diego stands out. It gets less rain than parched Los Angeles or Fresno. The region has less groundwater than many other parts of the state. And more than 80 percent of water for homes and businesses is imported from sources that are increasingly stressed. The Colorado River is so overtaxed that it rarely reaches the sea; water originating in the Sacramento River delta, more than 400 miles north, was rationed by state officials this year, cutting off some farmers in Californias Central Valley from their main source of irrigation. San Diego County, hot, dry, and increasingly populous, offers a preview of where much of the world is headed. So too does a recent decision by the county government: it is building the largest seawater desalination plant in the Western Hemisphere, at a cost of $1 billion.
The massive project, in Carlsbad, teems with nearly 500 workers in yellow hard hats. When its done next year, it will take in more than 100 million gallons of Pacific Ocean water daily and produce 54 million gallons of fresh, drinkable water. While this adds up to just 10 percent of the countys water delivery needs, it will, crucially, be reliable and drought-proofa hedge against potentially worse times ahead.
The county is betting on a combination of modern engineering and decades-old desalination technology. A pipe trench under construction leads to a nearby lagoon inlet; 18 house-size concrete tanks await loads of sand and charcoal to treat the salt water before it is ready for desalination; pressurizers lead to a stainless-steel pipe one meter in diameter. This final piece of gleaming hardware will convey water under high pressure into 2,000 fiberglass tubes, where it will be squeezed through semipermeable polymer membranes. What gets through will be fresh water, leaving brine behind.
The process is called reverse osmosis (RO), and its the mainstay of large-scale desalination facilities around the world. As water is forced through the membrane, the polymer allows the water molecules to pass while blocking the salts and other inorganic impurities. Global desalination output has tripled since 2000: 16,000 plants are up and running around the world, and the pace of construction is expected to increase while the technology continues to improve. Carlsbad, for example, has been outfitted with state-of-the art commercial membranes and advanced pressure-recovery systems. But the plants remain costly to build and operate.
http://www.technologyreview.com/featuredstory/533446/desalination-out-of-desperation/
TreasonousBastard
(43,049 posts)2naSalit
(86,628 posts)pscot
(21,024 posts)seems unlimited.
quadrature
(2,049 posts)irrigation districts (aka desert-farmers)
have first call on water from the
Colorado River, as a result of laws
passed circa 1890.
---> if people would stop trying
to water the desert,
there would be plenty of water for people
as long as farmers get water fo $50 a acre-foot,
they have NO PROBLEM with
city people 20 times as much.
must be nice to be a hereditary water-lord.
hunter
(38,313 posts)It's among the least sustainable industries we've yet devised.
Oh well, nobody asked me.
Rising seas and more violent weather extremes will eventually put an end to it.
We're setting the stage for some unimaginable refugee problems, even here within the U.S.A..