Salty and Getting Fresh: The World Cradle of Desalination Know-How Wants to Start Using It
March 31, 2012
IF CALIFORNIA were not already so famous for Silicon Valley and Hollywood, it might be renowned for the cluster of water-technology firms in its San Diego County. The reverse-osmosis (RO) spiral module, the trick that underpins turning sea- and waste-water into potable stuff, was patented in San Diego in 1964. Today dozens of firms in the area supply many of the world's roughly 13,000 RO plants in places from the Persian Gulf and Israel to Australia, China, Singapore and Spain.
Southern California itself, however, has not so far been a big user of its own technology. This is surprising, given that the whole American south-west confronts a water problem. But there is at least now a growing consensus that the existing infrastructure, consisting of vast aqueducts that carry water from the Sacramento Delta in the north and the Colorado River in the east, will not suffice as the climate gets warmer and the population increases. In places such as San Diego, which has measly and brackish groundwater and currently imports 90% of its water, the answer must be greater conservation, as much reuse as possible, with most of the rest coming from the sea.
The first part, conservation, is hardly controversial any more. San Diego today uses less water with a larger population than it did in 1989, the year water consumption peaked. The second part, water recycling, has been a harder sell, because of what the industry calls the yuck factor. It doesn't help that Americans still use the term “toilet-to-tap” for recycling, even though properly treated sewage is nowadays completely clean. Singapore made its programme acceptable in part by rebranding it as NEWater. But even the Singaporeans cannot recycle all their waste-water.
This is where desalination comes in. A firm appropriately called Poseidon Resources is now close to building the biggest desalination plant in America behind a power station by the beach in Carlsbad. The power plant sucks in 304m gallons of seawater a day for cooling in any case, so Poseidon plans to divert 104m gallons a day through its osmotic membranes.
Fondling a pipe of membranes (they are rolled like toilet paper but the size of a cannon), Poseidon's Peter MacLaggan explains the scale: if water molecules were blown up to the size of tennis balls, salt molecules would be softballs (roughly 50% bigger in diameter), viruses would be trucks, and bacteria would be the size of power plants. From the 104m daily gallons, 50m gallons of pure H2O will come out at one end and brine at the other, to be fed back into the power station's discharge, and then into the ocean.
Lots of people like the idea. Once fully running in 2015 the plant could produce 10% of the region's water. And there are plans for more desalination plants. Inland Californians, Arizonans, Nevadans and others would need to take much less water from the endangered Colorado River.
But a few people hate it a lot. Environmentalists are suing Poseidon every step of the way. Joe Geever of the Surfrider Foundation says desalination uses too much energy and that Poseidon's plant would kill too much marine life, including fish such as the goby and the garibaldi, which unfortunately happens to be California's state marine fish. He understands that there is a role for desalination, he says, but would rather not have it right there, right now, and on this scale.
Correction: The original version of this article claimed that a softball is four times the diameter of a tennis ball. In fact, it is only 50% bigger. Time we got out of our armchairs.