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Public Radio's Environmental News Magazine (follow us on Google News)

Filtering Seawater

Air Date: Week of

Shrinking supplies of fresh water combined with new advances in technology are making California officials take another look at seawater desalination. Erik Anderson reports from KPBS in San Diego.


CURWOOD: Southern California is looking to the ocean to help quench its thirst for fresh water. That’s because it’s becoming cheaper to get the salt out of sea water, as long as you have plenty of power. Desalination is a multi-billion dollar industry that’s already doing a brisk business in the Middle East. Now there is a proposal to build five plants along the Golden State’s southern coast. From member stations KPBS in San Diego, Erik Anderson reports.


ANDERSON: The ocean has long been a tantalizing solution to Southern California’s water woes. Filtering seawater was expensive and Colorado River water was cheap. Recently, the bottled water and pharmaceutical industry have driven technological advances in water filtration. San Diego County Water Authority spokesman Bob Yamada says new filters can treat twice as much water with half the energy, and that’s dramatically lowering the cost.

YAMADA: As we look out to the future in developing new water supplies, seawater desalination is right on the cusp of being cost competitive with those new water supplies.

ANDERSON: So Southern California water officials are proposing enough desalination capacity to provide water for 250,000 families a year. The new optimism for large-scale ocean desalination projects is based on the success of a host of small groundwater plants, like this one in Oceanside.


ANDERSON: First, says manager Casey Jaworski, they filter sediment out of the brackish water.

JAWORSKI: Then the water goes to the high pressure pumps, then the water goes to the membrane. There, the feed water is separated. Seventy-five percent of the water will be drinking water, twenty-five percent will be concentrate water, which goes out into the ocean.

ANDERSON: After the salt is removed, the water’s pH levels are balanced.


ANDERSON: Inside the plant’s lab, workers can monitor a series of faucets that are constantly running. The taps represent water at different stages of the desalination process.

JAWORSKI: Raw, no we don’t want any raw. Here is product, okay.

ANDERSON: Jaworski puts a glass under the finished product and takes a drink.

JAWORSKI: We do use sodium hypochloride as disinfection, so you won’t get a smell, and most people don’t taste it at all.

ANDERSON: But the lessons learned here only go so far when you start talking about filtering hundreds of millions of gallons of ocean water. Even with recent technological advances, it takes a lot of power to filter large volumes of water. That’s why Southern California officials are proposing to build their desalination facilities right beside the region’s power plants.


ANDERSON: County Water Authority spokesman Bob Yamada stands near the Encina Power Plant north of San Diego. The towering 900 megawatt facility sits on the coast, and Yamada says it’s natural: the salt water, and power, are already there.

YAMADA: As you can see over here behind my shoulder, they have a cooling water circulation system that takes water from the ocean. And then it’s discharged back to the ocean, and they circulate large volumes of cooling water.

ANDERSON: Poseidon Resources hopes to tap into that system, drawing off water that’s already been used to cool the turbines. Half that water would be filtered to produce 50 million gallons of fresh water, and the salty residue would be mixed back in with the rest of the coolant water and piped offshore. Company spokesman Peter MacLaggan says this solves a major environmental hurdle for desalination plants: what to do with the salt.

MACLAGGAN: That 50 million gallons a day of concentrated sea water mixes with the 800 million gallons going out of the power plant. Before we even discharge into the outfall from the power plant, we are well below the natural variability in the salinity.

ANDERSON: Biologists say the discharge shouldn’t hurt the coastal environment. But some people are concerned about something else: the heavy draw on California’s power. In the Middle East solar energy is fueling some new desalination projects, but here, MacLaggin says that’s not practical. He says it would require buying large swaths of expensive coastal land to build solar arrays.

MACLAGGAN: We’ve looked into other sources of energy to fire the power plant, renewable sources and traditional sources, and typically, what you find is while the renewable sources are becoming more cost-effective, they still haven’t gotten to the point where they’re able to compete with purchasing the power directly from the power plant itself.

ANDERSON: But the reliance on traditional energy sources makes some people leery. The director for the Center of Energy Studies at San Diego State University Alan Sweedler says the push to build power plant-based desalination facilities could leave the region with a difficult choice. If power supplies get pinched, like they did during California’s recent energy crisis, public officials may be forced to choose between water and power.

SWEEDLER: We need the power from those plants. And if we begin to rely very heavily on desalination, that means we’re going to have to import more power, we’re going to have to possibly build another power plant on the coast, or we’re going to have to generate power someplace else in the county.

ANDERSON: All of those options could be very costly for an area that already has some of the highest power prices in the country. But with the memory of the California power crisis ebbing, and the supply of Colorado River water shrinking, officials appear ready to spend billions to tap into the ocean’s potential as a drinking water source. For Living on Earth, I’m Erik Anderson in San Diego.



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