Wednesday, August 31, 2016

Photo Essay: Drinking Water from the Sea

It's just plain logic.

If California's reservoir and lake levels are receding because of the drought, and the sea levels are rising because of the melting polar ice caps, then we need to figure out how to put ocean water into our taps.

At least, until our rainfall and snowpack are repleted.



But the problem is that ocean water is too salty for general use and consumption, so before it even goes into the tap—or down our throats—the salt has got to be taken out.



Hence, the Carlsbad Desalination Plant at the Encina Generating Station, the largest desal plant in the Western Hemisphere.



At its most basic level, their process isn't terribly different from that of a wastewater treatment facility.



As it stands now, water from the Pacific Ocean is currently pumped in by the neighboring natural gas-fueled power plant...



...which is soon to be decommissioned, demolished, and replaced with a far smaller and more energy-efficient facility.



Every day, a hundred million gallons of water is drawn into the pump station and transferred to the desal plant.



But only half of it is actually used. The other half contains all of the salt, minerals, and other impurities that were removed by the treatment process and is discharged back into the ocean in the form of "brine."



The half of the seawater that will be converted into drinkable water supply goes through two rounds of pretreatment.



The primary pretreatment removes the solids, which include sand, gravel, and anthracite (a type of coal).



The secondary pretreatment, called microfiltration, removes even more material—but this time, it's more of the microscopic variety.



According to our guide, when the white cylindrical filters are lined up inside the filtration machine, they look like a row of cigarettes.



After the pretreatment is completed, the water still isn't desalinated, because some salts and minerals had actually dissolved in it...



...and they weren't removed along with the solid stuff.



That's where reverse osmosis comes in.



This is the most dangerous part of the tour, when you've really got to keep your hands to yourself.



It's also the "heart" of the desalination process.



The building is full of "pressure vessels" that house semi-permeable membranes.



Water is forced through the membranes to remove all of the final remaining impurities.



But the water isn't exactly drinkable yet—because it's so pure that if you put it into the water supply, it would leach metals from the pipes. So, they treat it with limestone to get some of the natural minerality back into it.



That's also when it receives its final disinfection with the addition of chlorine, and its fluoridation (which some might say actually contaminates the water).



And maybe it's just the power of suggestion, but the desalinated water does taste a little funny when you know you're drinking it.



But clearly, they're doing something right—because unlike the rest of the State of California, they have a surplus of water.



They're constantly pumping it out to regions in San Diego County—so, if the power were to go out, there would be a tide of water coming back into the plant.



That's what the blue "surge" tanks are for.

But let's hope nothing causes that to happen. Because the polar ice caps don't stop melting during a blackout.

Related Posts:
Photo Essay: West Basin Water Recycling Facility
Photo Essay: Wastewater in the Time of Drought
History in the Making