OPEN FOR BUSINESS: Sand City's new desalination facility--actually a brackish water treatment plant--is expected to produce more than 370 million liters per year of potable water through reverse osmosis filtration. Energy Recovery Inc.'s PX Pressure Exchanger is a cylindrical ceramic rotor installed within the desalination system to make the process more efficient.
Image: COURTESY OF THE CITY OF SAND CITY, CALIF./CHARLES POOLER
-
The Best Science Writing Online 2012
Showcasing more than fifty of the most provocative, original, and significant online essays from 2011, The Best Science Writing Online 2012 will change the way...
Read More »
When Sand City, Calif., officially opens the spigot to the state's first full-scale seawater desalination facility Wednesday, residents throughout the city will begin tapping into the Pacific Ocean as a source of drinking water. The city's goal is to provide a seamless transition so that consumers do not recognize any difference in quality or taste compared with the reservoir water that used to provide their potable water.
Although the plant has been operating for testing purposes for more than a year, it is now fully permitted by the California Department of Public Health and can be connected directly to California-American Water Company's (Cal-Am) water grid serving much of the Monterey Peninsula. If all goes according to plan, Cal-Am's water tanks, which serve Sand City as well as other communities in the area, will be pumping more than 370 million liters of water less per year from their Carmel River and Seaside Aquifer reservoirs, says City Engineer Richard Simonitch. That is because the new desalination facility—actually a brackish water treatment plant—is expected to produce that volume of potable water instead, using reverse osmosis filtration, which forces seawater through a semipermeable membrane that separates salt from water.
West coast water woes
California's water scarcity goes back nearly a century (and even served as a major plot device in Roman Polanski's 1974 film noir Chinatown, which is set in Los Angeles in 1937). Sand City is one of several places in California and the U.S. Southwest with limited water resources.
The state awarded Sand City $2.9 million in grant funding for the desalination plant in 2007. The funding was made possible thanks to California Proposition 50, passed in November 2002 to allow the state to borrow $3.4 billion for a variety of water projects, including those to create safe drinking water. The project as a whole cost about $11.9 million, with the city covering $9 million of that through redevelopment funds and city capital improvement funds. Cal-Am will use water produced from the desalination plant to offset their current overdrafting of the Carmel and Seaside, but as Sand City grows the city will have access to more water as needed.
Whereas more potable water is incentive enough for the desalination plant, the city has other incentives, too. California has restricted Sand City from any new building until the city increases its water supply, says City Administrator Steve Matarazzo. "There's significant urban blight in Sand City, and the city wants to redevelop those areas, which it can't do without more water," he adds. The new facility should solve that problem, given that Sand City's current water needs are only about 117 million liters per year.
Sand City, which covers only about 1.5 square kilometers of land, benefits from being located near what Matarazzo refers to as a "seawater wedge" that keeps part of the city's coastal area brackish, meaning the water is saltier than freshwater but not as briny as seawater. Since the water is less salty, it requires less energy and costs less to desalinate than would regular ocean saltwater.
Turning to reverse osmosis
The desalination plant works by drawing the brackish water in through wells that are each about 30 centimeters in diameter and 18 to 27 meters deep. The plant has four wells but uses only two at any given time. "The water in these wells is free of sea life, except microbes, by virtue of the fact that they were drilled into the sand aquifer from an inland location," Simonitch says. The sand acts as a natural filter.
Sand City's desalination plant employs reverse osmosis because it is more cost-effective than other methods of removing salt from seawater, Simonitch says. There are primarily two ways to extract drinking water from saltwater—distillation and reverse osmosis, both of which require a lot of energy. Although the actual cost of desalination varies from region to region, it can cost anywhere from just under $1 to well over $2 to produce one cubic meter (1,000 liters) of potable water from the ocean (about as much as two people in the U.S. typically use in one day), Peter Gleick, president of the Pacific Institute, wrote in a July 2008 article for Scientific American.* It costs about 10 to 20 cents to get that much water from a river or aquifer, he adds. Meanwhile, the average delivery price of municipal water in the U.S. is around 60 cents a cubic meter, according to the American Water Works Association.
In distillation, seawater is boiled, evaporating the water and leaving the salt. The evaporated water is collected and condensed back into liquid, according to Gleick. Reverse osmosis is less expensive than distillation and, as a result, more commonly used. A major criticism of reverse osmosis—in addition to leaving behind highly concentrated brine that can harm aquatic life if this super-salty water is put back into the ocean—is that the process is inefficient and generally wastes a lot of energy.
See what we're tweeting about
18 Comments
Add CommentHuh? People in the US typically drink 500 liters of water a day?(1000 liters/2) That is well beyond the point of water poisoning!
Reply | Report Abuse | Link to thisPeople in the US typically use 500L a day, though not all by drinking. This is per-capita average that includes not only drinking, but showering, watering the lawn/garden, washing the car, doing dishes, etc.
Reply | Report Abuse | Link to thisthat is still alot, will have to test that in my own house,
Reply | Report Abuse | Link to thisThanks, seannelson1969, for pointing out the error. I've corrected the article to indicate what Gleick actually wrote: one cubic meter (1,000 liters) of potable water from the ocean is about as much as two people in the U.S. typically use in one day. I suppose this takes into account when you wash your car or water your lawn. --Larry
Reply | Report Abuse | Link to thisThe water will be much better quality than the chlorinated water of nearby communities.
Reply | Report Abuse | Link to thisAnother good reason not to live in California. These people are completely stupid. People living in Sand City could easily move to any of tens of thousands of US cities or towns that are adequately watered by nature. Instead, they decided on an expensive, complicated water supply that is dependent on a whole lot of things beyond their control, not the least of which being energy. And what do they think is going to happen to their brackish but less salty than the ocean water table when they start pumping millions of gallons of water out of it, less than a mile from the ocean? This is a classic case of overpopulating a place that where the land is screaming, there are too many people here , and will eventually collapse regardless of human efforts (the one exception would be making the effort to move out before literally sucking all of the life out of the environment). And theyre doing it all because the state of California will not let them build anything new until they get more water! On the other hand, I am very happy that they are staying where they are, which is 2,500 miles away from me. There are enough non-sentient humans living in my neighborhood already.
Reply | Report Abuse | Link to thisWhat's with the metric calculations? We typically do the math with cubic feet or gallons per day in mind, so if you convert the liters to gallons, 1 liter = .264 gallons, you get 132 GPD per person and with 370 million liters per year, you get 98 million gallons per year or 268,ooo GPD respectively. This would only produce enough water for a little over 2,000 people, a small scale plant but still a good start. I'd like to see more of these plants here in CA!
Reply | Report Abuse | Link to thisI agree with the initiatives here, and am a bit surprised that CA doesn't have more of these plants going into coastal communities.
Reply | Report Abuse | Link to thisI think Mr. Collins should stay 2500 miles away, his views don't fit the mentality on the West Coast anyway.
Whatever the math that has or has not gone into this article, the article certainly shows that there is hope for alternate ways of getting things done. People forget that California is mostly reclaimed desert and forward thinking is necessary to provide water to it's residents.
@RCollins
Reply | Report Abuse | Link to thisWhat you say rings a bell with me. It's the only worthwhile comment so far.
@physicstech
Reply | Report Abuse | Link to this"Forward thinking" - yes. But stop just short of problems which you might not be able to solve. A complex water supply relying on the continuos availability of energy seems about as good an idea as cardboard wings. Not that I am at all familiar with California, but they do go - or have gone-in - for "windfarms. They are not alone here, to be fair, but these two are another daydream come true. Returning only a fraction of 1% of their cost annually, they are incapable of surviving without other energy sources !! And that in CAliofornia, where even I know that they have bigtime SUN - and desert, as you say. Maybe Solar pv will supply the de-salting plant. There still remains the question of how long can you upset the groundwater in this way, and what to do with the extremely salt residue. Forward thinking ? how about making a start !
Yes that is absolutely true, there is an abundance of ocean water out there that will meet California's needs well into the future....Other alternatives like OCSD & OCWD's (GWR) Groundwater Replenishment System that produces recycled water for OC.
Reply | Report Abuse | Link to thishttp://www.ocsd.com/about/featured_videos/groundwater_replenishment_system.asp
Sometimes these articles draw out the best and worst of the 'audience'. I like the articles that talk about the progress and the science - the political and sensationalist articles make me tired.
Reply | Report Abuse | Link to thisWith global fresh and drinkable water fast diminishing, reverse-osmosis desalination has slowly become the norm, especially in the water scarce regions. For the moment, the main drawback is the high energy consumption and cost.
Reply | Report Abuse | Link to thisSome scientists are working on a cheaper way to get clean and fresh water via carbon naotube technology with less input of energy. If this works satisfactorily, it could be in the market within several years.
Here's an idea that only requires the pumping of the seawater to greenhouses where the sun does the rest.
Reply | Report Abuse | Link to thishttp://www.seawatergreenhouse.com/
It's great for drier, desert regions, and can supply local fresh veggies as well... and the pumping can be run on Solar CSP!
As to the comments above about wind supply only paying back 1% of the energy it cost to build them each year? Woah... totally ignores the Life Cycle Analysis of wind studies which say wind repays the energy it took to make it in about 3 to 6 months.
(And as peak oil hits and transport, construction, and mining systems move to electricity, society will become far more energy efficient and wind will have an even *quicker* payback mainly because the 'energy in' part of the equation will be so much lower!)
With global fresh and drinkable water fast diminishing, reverse-osmosis desalination has slowly become the norm, especially in the water scarce regions. For the moment, the main drawback is the high energy consumption and cost.
Reply | Report Abuse | Link to thisSome scientists are working on a cheaper way to get clean and fresh water via carbon nanotube technology with less input of energy. If this works satisfactorily, it could be in the market
soon.
(btt1943@yahoo.com)
Something wrong with the units. A cubic meter of water weighs a ton (2,240 lbs.) but does not have the dimensions of 1,000 liters, but of a million liters! (A liter is 1,000 c.c. or a cube only a tenth of a meter square!)
Reply | Report Abuse | Link to thisMacrocompassion...a cubic meter of water weighs 1000kg(metric ton)...a liter of water weighs 1kg....10cm x 10 cm x 10cm does equal a liter. there are 100cm per meter/10cm = 10x10x10 or a thousand;-)
Reply | Report Abuse | Link to thisps.. all coastal cities should be planning on putting in desal plants...relying on rivers gets you the worst of what someone up stream throws into it and ground pumping in many cases far out strips natures ability to replenish it....hopefully yours works right the first time(or second...)...not like us in tampa fl...i think it took four times to get it right....
In sand city, the sand underneath the city filters the plankton from the seawater so the brackish water in the wells contains little organic material. Thus, the filters last much longer before becoming clogged with plankton. Reverse osmosis has been possible for 80 years. Keeping plankton from clogging the filter has always been the problem in using reverse osmosis.
Reply | Report Abuse | Link to this