Adding efficiency
Sand City says its plant addresses the brine issue by producing a solution left over from the reverse osmosis process that matches the salinity of Monterey Bay, where the solution is sent.
One way desalination facilities, including Sand City's, have tried to address the inefficiency issue is by adding energy-recovery devices into their desalination systems that boost output and cut energy consumption and costs.
The city chose PX energy recovery devices made by Energy Recovery, Inc., (ERI) in San Leandro, Calif. ERI's PX Pressure Exchanger is a cylindrical ceramic rotor installed within the desalination system. (See a video of how it works). Some of the seawater entering the system goes directly to the desalination membrane while the rest is diverted to enter one end of the cylinder. At the same time, salt-heavy concentrate (like brine, but not as strong) unable to pass through the membrane flows into the other end of the cylinder. The flow of these opposing forces entering the rotor from opposite ends spins it like a carousel, rotating 1,200 times per minute. As the rotor spins, it creates pressure that pushes the seawater toward the membrane and the concentrate out of the system. The PX Pressure Exchanger is designed to recover up to 98 percent of the energy from the stream of concentrate and feed it back to pump seawater through the membrane. Mixing between the concentrate and the seawater is minimal because the exposure time is so short, according to the company.
Sand City's desalination has two PX devices running at any given time, with two more installed as backup to provide full redundancy if the first two stop working, Simonitch says.
The pressure to find new sources of potable water has been building worldwide for years, leading some countries—Algeria, Australia, China and India, to name a few—to turn to desalination. Some areas of the U.S. have turned to desalination, including Tampa Bay, Fla., and El Paso, Tex., where local plants produce about 94 million and 104 million liters, respectively, of water per day. The world's largest desalination plant is the Jebel Ali M Station Desalination Plant in the United Arab Emirates, which is expected to be capable of producing 530 million liters of water per day when completed later this year.
The need for such facilities will only increase over time. Today, one out of six people on Earth, more than a billion, suffer inadequate access to safe freshwater, according to Peter Rogers's article "Facing the Freshwater Crisis" in the August 2008 issue of Scientific American. The article further states that by 2025 the freshwater resources of more than half the countries across the globe will undergo either stress or outright shortages, and that by mid-century as much as three quarters of Earth's population could face scarcities of freshwater.
*Correction (4/08/10): This article originally stated that one cubic meter (1,000 liters) of potable water from the ocean is about as much as two people in the U.S. typically drink in one day.
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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.
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