In the News

SALT OR NO SALT?  BLENDED OR ON THE ROCKS?

By Chris J. Magyar   

Good Times Weekly, 03/26/2008

The pilot desalination plant is finally pumping out answers.

Can seawater filtration be environmental and economical? It’s a sunny day when officials decide to invite the media and the public for a tour of the up-and-running $4 million pilot desalination plant at Long Marine Lab, which is a good thing, because Santa Cruz city councilperson Mike Rotkin’s microphone is running on solar power.

Speaking of the eventual permanent plant that will result from this project sometime between 2012 and 2015—location, price and very existence to be determined—Rotkin says, “We want to make sure we’re taking in water in a way that doesn’t harm the aquatic life, and we also want to make sure we have a way of dealing with the salty water that comes out of this process in a way that’s environmentally sound.”

The pilot plant, because it uses the existing Long Marine Lab intake and reconstitutes the seawater after it’s been processed and tested, will determine nothing about those issues. Those will be dealt with in a separate Environmental Impact Review if the technology for desalinating water proves to be effective and affordable. “We also know desalination is an energy-intensive process,” Rotkin continues, “and we’re symbolizing our commitment to making the eventual plant a carbon neutral project by running this microphone off solar power.” The pilot plant, as a temporary structure, is running off the PG&E grid on the city of Santa Cruz’s bill.

So there will still be plenty of big unknowns regarding the future of desalination after the pilot plant’s one year of operation, but the process for turning ocean water into drinking water will be exhaustively studied, at least. Rotkin states several times how impressed he is by the fact that the project is a joint effort between the Santa Cruz City Water Department and Soquel Creek Water District (with a small assist from UC Santa Cruz). “You don’t often get government agencies working together like this,” he says. The goal is to produce 2.5 million gallons of water a day, enough to relieve severe droughts for Santa Cruz (which depends entirely on rainfall) and provide about 1 million gallons a day to Soquel Creek (which depends entirely upon groundwater that’s rapidly salinating due to seawater intrusion and overdraft).

Seawater will pass through four stages at the plant. Step one is a simple straining process to remove large debris like seashells and kelp. Step two is a flocculation bath, in which chemicals are added to absorb and separate out particles. The plant is also testing the ability to skip this step, in order to avoid adding chemicals if possible. Step three is normal water filtration, similar to what’s done for fresh water treatment. The plant is trying out a variety of filtration methods to discover the one that prepares the seawater most effectively: slow sand filtration (the water drains through sand and bacteria), granular media filtration (the water is pushed through coal and sand), and two varieties of ultrafiltration (the water is pushed through hollow fiber membranes that look like five-foot-long udon noodles and feel like stretched rubber bands).

Step four is the main event, in which the cleaned seawater is pressurized to 1,000 pounds per square inch and forced through reverse osmosis (RO) filters, which are cylinders that resemble extra-large paper towel rolls. The water is pushed from the surface of the rolls to the center, where a small pipe delivers the fresh water. The plant will be trying different RO filters from several manufacturers to find the best fit. About half the water that begins this process comes out fresh. The other half is a concentrated salty sludge that gets rejected by the plant and, normally, pumped back into the ocean.

Bill Kocher, head of the Santa Cruz City Water Department, says there’s a possibility that the future plant will mix this sludge with the treated wastewater stream that’s already pumped into the bay, bringing the eventual discharge to the approximate salinity of natural seawater. He’s also hoping for a harsh winter going into 2009.

“We grabbed some of the heavy red tide water from this year,” he says, “and we hope to put it through the test, but it would be good if we got a mixture of bad water scenarios to really put the process through the wringer.” The plant isn’t just a fun toy; it’s mandated by the state that any new source of water be tested, and since ocean water is not uniform from region to region, it’s necessary to run this pilot with Monterey Bay water. While the most likely scenario in the case of a red tide (or, heaven forbid, an oil spill) is just to turn the plant off, officials are curious to see what the filters can and can’t handle.

Tours are available to the public. To find out more, visit scwd2desal.org or call 420-5214.

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