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Wires turn salt water into freshwater
Phys.Org ^ | June 8, 2012 | Lisa Zyga

Posted on 06/10/2012 10:10:32 PM PDT by Kevmo










June 8, 2012 by Lisa Zyga


(Phys.org) -- As a rising global population and increasing standard of living drive demand for freshwater, many researchers are developing new techniques to desalinate salt water. Among them is a team of scientists from The Netherlands, who have shown how to transform brackish (moderately salty) water into potable freshwater using just a pair of wires and a small voltage that can be generated by a small solar cell. The simple technique has the potential to be more energy-efficient than other techniques because of the minimal amount of mixing between the treated and untreated water.



(a) Seven pairs of graphite rods/wires are dipped into brackish water. (b) An electrical voltage difference is applied between the anode and cathode wires via copper strips, causing the electrodes to adsorb salt ions. (c) Scanning electron microscopy image of the membrane-electrode assembly. Image credit: S. Porada, et al. ©2012 American Chemical Society

The researchers, led by Maarten Biesheuvel from Wageningen University in Wageningen, The Netherlands, and Wetsus, Centre of Excellence for Sustainable Water Technology in Leeuwarden, The Netherlands, have published their study on water desalination with wires in a recent issue of The Journal of Physical Chemistry Letters.

As the researchers explain in their study, there are two main ways to desalinate salt water. One way is to remove pure water molecules from the salt water, as done in distillation and reverse osmosis, particularly for water with a high salt concentration. The opposite approach is to remove the salt ions from the salt water to obtain freshwater, which is done in deionization and desalination techniques using, among other things, batteries and microbial cells.

Here, the scientists used the second approach, in which they removed positively charged sodium ions and negatively charged chlorine ions from brackish water to produce freshwater. To do this, they designed a device consisting of two thin graphite rods or wires, which are inexpensive and highly conductive. Then they coated the outer surface of the wires with a porous carbon electrode layer so that one wire could act as a cathode and one as an anode. The wires were clamped a small distance apart in a plastic holder, with each wire squeezed against a copper strip.

To activate the electrodes, the researchers dipped seven sets of wire pairs into a container of brackish water and ran electrical wires from the copper strips to an external power source. Upon applying a small voltage difference (1-2 volts) between the two graphite wires of each wire pair, one wire became the cathode and adsorbed the positively charged sodium cations, while the other wire became the anode and adsorbed the negatively charged chlorine anions from the salty water.

Enlarge
(a) Multiple pairs of porous electrode wires adsorb salt ions under an applied voltage. (b) A porous electrode temporarily stores ions as the device is carried to the brine container. (c) After short-circuiting the cells, salt is released in the brine container, and the wires are transferred back to the freshwater container. Image credit: S. Porada, et al. ©2012 American Chemical Society
The ions are temporarily stored inside the nanopores of the carbon electrode coating until the wire pair is manually lifted from the once-treated solution and dipped into another container of waste water, or brine. Then the researchers removed the voltage, which caused the electrodes to release the stored ions into the waste water, increasing its salinity. By repeating this cycle eight times, the researchers measured that the salt concentration of the original brackish water, 20 mM (millimolars), is reduced to about 7 mM. Potable water is considered to have a salinity of less than roughly 15 mM. As Biesheuvel explained, this improvement could be useful for applications involving the treatment of moderately salty water.

“The new technique is not so suitable for extremely salty waters, as it is based on removing the salt, and making the remaining water less salty,” Biesheuvel told Phys.org, explaining that distillation and reverse osmosis are still superior for desalinating seawater (500 mM salinity and higher). “The new technique is more suitable, for example, for groundwater, or for water for consumer applications that needs to be treated to remove so-called ‘hardness ions’ and make it less saline. These water streams are less saline to start with, say 100 mM or 30 mM. Or this new approach can be of use to treat water in industry to remove ions (salts) that slowly accumulate in the process. In this way there is no need anymore to take in freshwater and/or to dump used water (at high financial penalty).”
One of the biggest advantages of the technique is that it avoids inadvertently mixing the brine with the water being treated during the process, which limits the efficiency of other deionization techniques. By using a handheld wire-based device and producing freshwater in a continuous stream, the researchers could split the two types of water in separate containers to avoid mixing. Only a minimal amount of brine, about 0.26 mL per electrode, is transferred between containers, which does limit the degree of desalination but to a lesser extent than other techniques. Another advantage of the new technique is that it has the potential to be less expensive than other desalination methods.

“This technique can be made very inexpensive, just carbon rods or wires to conduct the electrons, onto which you can simply ‘paint’ the activated carbon slurry, which becomes the porous carbon electrode,” Biesheuvel said. “Because of its simplicity and low cost, it might out-compete state-of-the-art technologies for certain applications, and may also have advantages over the technology called capacitive deionization (CDI or cap-DI), which is beyond the development stage and commercially available. Also, the voltage required is low, just 1.2 V for instance, and DC, perfectly compatible with solar panels. Thus it can be used at off-grid or remote locations.”
In addition, Biesheuvel explained that the wire pairs can be used repeatedly without degradation, which could give the device a long lifetime.

“In capacitive techniques where the porous carbon electrodes are used to capture ions and release them again (in the so-called ‘electrical double layers,’ or EDLs, formed in the very small pores inside the carbon), it is well-known that the cycle can be used for thousands or tens of thousands of times (until the experimenter gets tired) without any appreciable decay,” he said. “For the wires we only went up to six times repeat and found, as expected, no changes. This is in contrast to battery-style techniques, either for energy storage or desalination, where one would expect to lose performance (like rechargeable batteries, which can only be charged, say, 100 times successfully). That is because in those techniques there is real chemistry going on, phase changes, change of the micromorphology of the anode/cathode materials. Here, in the wire desalination technology, nothing of that kind, the EDL is a purely physical phenomenon where ions are stored close to the charged carbon in the nanopores under the action of the applied voltage, and later released again.”
The researchers also found that the efficiency could be improved by adding a second membrane coating to the electrodes. For instance, a cationic membrane on the cathode wire has a high selectivity toward sodium cations while blocking the desorption of chlorine anions from within the electrode region. As a result, cationic (and, on the anode wire, anionic) membranes could enable the electrodes to adsorb and remove more ions than before.

In the future, the researchers plan to perform additional experiments using the cationic and anionic membranes. They predict that these improvements could increase the desalination factor from 3 to 4 after eight cycles, with 80% of the water being recovered (i.e., 20% of the original water becomes brine). The researchers also want to use the technique to treat large volumes of water, which they say could be done by using many wire pairs in parallel to accelerate the desalination process.
“This research continues by scaling up the technology (testing larger arrays of wires), packing them more closely, and trying our hand on automation to have the rods lifted automatically from one water stream into another,” Biesheuvel said. “We also want to test ‘real’ ground/surface waters, not only artificial simple salt mixtures as tested now.”
More information: S. Porada, et al. “Water Desalination with Wires.” The Journal of Physical Chemistry Letters. DOI: 10.1021/jz3005514
Journal reference:Journal of Physical Chemistry Letters












TOPICS: Business/Economy; Culture/Society; News/Current Events; Technical
KEYWORDS: desalination; physics; science

1 posted on 06/10/2012 10:10:51 PM PDT by Kevmo
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To: Kevmo

Yeah, but I can make an electric pickle.

http://www.youtube.com/watch?v=mh7VHcuaPCg&feature=fvwrel


2 posted on 06/10/2012 10:17:52 PM PDT by mylife (The Roar Of The Masses Could Be Farts)
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To: Kevmo

Yes, but what about the fish? The enviros want to know!


3 posted on 06/10/2012 10:19:34 PM PDT by MichaelCorleone (The GOPe has played us like a violin for the last time; high time to build the Constitution Party.)
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To: Kevmo
Keep a-movin', Dan.

4 posted on 06/10/2012 10:19:34 PM PDT by I see my hands (It's time to.. KICK OUT THE JAMS, MOTHER FREEPERS!)
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To: Kevmo

I wonder how they will tax and control this? I am sure the NY Slimes will have an article soon saying that we are going to run out of saltwater soon. /s


5 posted on 06/10/2012 10:35:04 PM PDT by volunbeer (Don't worry America, our kids will pay for it!)
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To: AdmSmith; AnonymousConservative; Berosus; bigheadfred; Bockscar; ColdOne; Convert from ECUSA; ...

Thanks Kevmo .
As a rising global population and increasing standard of living drive demand for freshwater...
...the only reason anyone reports about global thirst is to push the AGW agenda, rather than to actually save lives.


6 posted on 06/10/2012 10:39:28 PM PDT by SunkenCiv (https://secure.freerepublic.com/donate/)
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To: Kevmo

Why is electricity needed to get the activated carbon to absorb the Na+ and Cl- ions? Why can’t the carbon do that of its lonesome? Also how quick does the carbon load up and can it be electrically purged of the same ions into salt water?


7 posted on 06/10/2012 11:09:07 PM PDT by HiTech RedNeck (Let me ABOs run loose Lou!)
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To: HiTech RedNeck

Why is it when a lib discovers a freshman year chemistry experiment it is hyped as the discovery of the century?

It seems to me that you could use some highly reflective material developed by people smarter than me to push water from a liquid to a global warming gas and then just pipe it into a drinking well when it condenses.

The salt could be used for McDonald’s fries.

If there is a coast line or a source of gravity and water, you could use that energy to generate the power necessary to run the entire thing.

You might even be able to grow algae while you are at it.

Am I stupid or is this a simple process?


8 posted on 06/10/2012 11:36:48 PM PDT by willyd
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To: SunkenCiv

The sentence you quoted was talking about increasing population and standard of living. Neither of those mentions global warming. If large quantities of the oceans were to be converted to fresh water, we’d have deserts blooming, many more plants & food growing, converting CO2. Basically global warming would be a quirky thing of the past, like our ancestors worrying about not getting enough calories to survive winter.


9 posted on 06/10/2012 11:55:34 PM PDT by Kevmo (SUCINOFRAGOPWIASS: Shut Up, CINOs; Free Republic Aint a GOP Website. It's A Socon Site.)
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To: HiTech RedNeck

On the same thoughts....how expensive are the electrodes to replace.....eventually they will need to be.


10 posted on 06/11/2012 12:06:05 AM PDT by Puckster
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To: Puckster

Bookmark


11 posted on 06/11/2012 1:13:17 AM PDT by publius911 (Formerly Publius 6961, formerly jennsdad)
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To: I see my hands

Don’t listen to the man
cause he’s filled the burning sand
with water.
Cool
clear
water.

I loved that as a kid and it was on a blue 45 rpm. too.

Drove my poor mother nuts.


12 posted on 06/11/2012 1:46:44 AM PDT by tet68 ( " We would not die in that man's company, that fears his fellowship to die with us...." Henry V.)
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To: Kevmo

The only problem with all that is there may be some
reason for all that salt water, we go messing with
the balance and who knows what would happen.

Just sayin.


13 posted on 06/11/2012 1:49:23 AM PDT by tet68 ( " We would not die in that man's company, that fears his fellowship to die with us...." Henry V.)
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To: tet68

I was thinking the same thing.


14 posted on 06/11/2012 2:20:02 AM PDT by cableguymn (If your policies are pushing the economy in to headwinds.. TURN YOUR POLICY AROUND!)
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To: Kevmo

Well done!!!


15 posted on 06/11/2012 3:07:21 AM PDT by SueRae (The Tower of Sauron falls on 11.06.2012)
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To: volunbeer

Salt’s already banned in NYC, so it’s a cakewalk from there on in.


16 posted on 06/11/2012 3:20:55 AM PDT by carriage_hill (All libs & most dems think that life is just a sponge bath, with a happy ending.)
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To: Kevmo

I find the carbon nanotube filtration more intriguing. The pores are literally too small for anything larger than water molecules to pass through. So it can remove salt from water, but it can also filter out microorganisms, poisons, metals, etc. Water flows through it 10,000 times more easily than through existing reverse osmosis membranes which require a lot of energy to force water through them.


17 posted on 06/11/2012 3:30:10 AM PDT by Kellis91789 (The ultimate result of shielding men from the effects of folly is to fill the world with fools.)
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To: Kevmo

They’ve been using membranes to convert salt water into fresh water for several decades. All these guys did was make the membrane into a tube. for convenience.
I hope the patent office wasn’t stupid enough to give them a patent on stuff that’s been around for decades.


18 posted on 06/11/2012 4:22:34 AM PDT by BuffaloJack (End the racist, anti-capitalist Obama War On Freedom.)
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To: willyd
"when a lib discovers a freshman year chemistry experiment it is hyped as the discovery of the century"

I think you're giving the discovery too much credit. Middle School seems more likely to me. The article uses the word "could" 19 times. A REAL scientific article would use the word "did". The article also talks of electricity only using the word "volt". The critical word is "power". Voltage is irrelevant, if it takes too much power to run the operation.

19 posted on 06/11/2012 5:00:35 AM PDT by norwaypinesavage (Galileo: In science, the authority of a thousand is not worth the humble reasoning of one individual)
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To: Kevmo

Can someone help me with a half-remembered factoid?
It was many years ago and I was speed reading, and it may have been just speculative alternative history trash. But I seem to recall that there was a very low-tech way of desalinizing at sea. It had to do with dragging a small container of water alongside the ship, and the item was either made of a certain material or was designed in a certain way, and the action of passing through the sea in a moving ship was a factor.
Never could find it again but I’m positive I read it somewhere.


20 posted on 06/11/2012 5:01:51 AM PDT by Lady Lucky (God-issued, not govt-issued.)
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To: norwaypinesavage
I think you're giving the discovery too much credit. Middle School seems more likely to me. The article uses the word "could" 19 times. A REAL scientific article would use the word "did".

You noticed that, too. Even if this device works great, it removes very little salt. Kevmo has a tendency to copy and paste low quality science articles on to FR.

21 posted on 06/11/2012 5:39:49 AM PDT by Moonman62 (The US has become a government with a country, rather than a country with a government.)
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To: Kevmo

When they find a way to change water into wine, call me first?


22 posted on 06/11/2012 5:55:19 AM PDT by Old Sarge (RIP FReeper Skyraider (1930-2011) - You Are Missed)
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To: Kevmo

A solar still can make freshwater from saltwater too and with no moving parts and no energy input except the sun. They are cheap too. http://www.solaqua.com/solstils1.html


23 posted on 06/11/2012 6:06:01 AM PDT by 762X51
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To: 762X51
A solar still...no moving parts...cheap too.

Lemme guess:

A sheet of plastic, a tin can and a rock?

24 posted on 06/11/2012 6:37:04 AM PDT by ROCKLOBSTER (Celebrate Republicans Freed the Slaves Month.)
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To: willyd

The concept is simple, the execution is not. Consider the volume of water involved.


25 posted on 06/11/2012 7:11:41 AM PDT by RobbyS (Christus rex.)
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To: HiTech RedNeck
"Why is electricity needed to get the activated carbon to absorb the Na+ and Cl- ions? Why can’t the carbon do that of its lonesome? Also how quick does the carbon load up and can it be electrically purged of the same ions into salt water?"

If dipping the carbon rods in a concentrated salt solution removes the collected ions, obviously the carbon needs the help of the current to collect the ions from a more dilute solution. In any case, the charge would get the ions to the carbon more rapdly

I also wonder how many cycles they can get out of the carbon?

26 posted on 06/11/2012 7:27:57 AM PDT by HangThemHigh (Entropy's not what it used to be.)
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To: tet68

Yeah, if we start pumping all of the ocean levels down, think of all those islands that will be vulnerable to tumping over. >s


27 posted on 06/11/2012 7:27:57 AM PDT by Clay Moore (The heart of the wise inclines to the right, but the heart of a fool to the left. Ecclesiastes 10:2)
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To: Kevmo

This is stupid. Every time I’ve been at sea, I drink deeply of the ocean water. The salt is GOOD for you!


28 posted on 06/11/2012 7:32:04 AM PDT by Lazamataz (People who resort to Godwin's Law are just like Hitler.)
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To: tet68

Sons of the Pioneers or Marty Robbins.


29 posted on 06/11/2012 7:33:37 AM PDT by Ruy Dias de Bivar (I LIKE ART! Click my name. See my web page.)
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To: Kellis91789

That’s what I assumed the article would discuss - not a standard high school chemistry experiment.


30 posted on 06/11/2012 7:42:15 AM PDT by ctdonath2 ($1 meals: http://abuckaplate.blogspot.com)
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To: tet68

I think the practical use for this technology would be for making drinking water available along with some small scale drip irrigation.


31 posted on 06/11/2012 7:49:10 AM PDT by cornfedcowboy (Trust in God, but empty the clip.)
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To: mylife
"The Electric Pickle"

Sounds like a dance move. Or maybe a discotheque.

32 posted on 06/11/2012 8:10:40 AM PDT by wbill
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To: Moonman62

Kevmo has a tendency to copy and paste low quality science articles on to FR.
***You give too much credit to anyone who expresses disdain. You’re not only anti-LENR, you’re anti-science, and among the most egregious of FReepers in your tactics. We’d all be better off if you simply stopped posting on FR.


33 posted on 06/11/2012 8:14:28 AM PDT by Kevmo (SUCINOFRAGOPWIASS: Shut Up, CINOs; Free Republic Aint a GOP Website. It's A Socon Site.)
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To: Kevmo
***You give too much credit to anyone who expresses disdain. You’re not only anti-LENR, you’re anti-science, and among the most egregious of FReepers in your tactics. We’d all be better off if you simply stopped posting on FR.

I'm very much pro science and conservative. That's why I challenge the garbage you copy and paste on to FR. This article on removing a small amount of salt from slightly salty water is lacking in impressiveness. There's no attempt to estimate economic viability, is very early stage research at best, and most likely an academic waste of time and resources that will never be a practical device.

If what I have to say hurts your feelings, then challenge it rather than going ad hominem.

34 posted on 06/11/2012 8:36:43 AM PDT by Moonman62 (The US has become a government with a country, rather than a country with a government.)
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To: Lazamataz

AH! That explains a lot... ‘-)


35 posted on 06/11/2012 8:48:13 AM PDT by TXnMA ("Allah": Satan's current alias...)
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To: Kevmo
“Because of its simplicity and low cost, it might out-compete state-of-the-art technologies for certain applications, and may also have advantages over the technology called capacitive deionization (CDI or cap-DI), which is beyond the development stage and commercially available. Also, the voltage required is low, just 1.2 V for instance, and DC, perfectly compatible with solar panels. Thus it can be used at off-grid or remote locations.”

The voltage requirement for capacitive deionization is also very low, so there is no potential advantage there.

36 posted on 06/11/2012 8:54:05 AM PDT by Moonman62 (The US has become a government with a country, rather than a country with a government.)
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To: Ruy Dias de Bivar

I think Sons of the Pioneers but it was a long
time ago so am not sure.


37 posted on 06/11/2012 10:17:28 AM PDT by tet68 ( " We would not die in that man's company, that fears his fellowship to die with us...." Henry V.)
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To: Moonman62

Calling out your behavior and tactics as egregious is not ad hominem. It is truth.

But you wouldn’t know that, just like all the other things you don’t know but pretend to know. You’re as useless as a 2 storey outhouse.

I see you stopped posting to me. The next step is to stop posting about me. Just STFU.


38 posted on 06/11/2012 10:32:45 AM PDT by Kevmo (SUCINOFRAGOPWIASS: Shut Up, CINOs; Free Republic Aint a GOP Website. It's A Socon Site.)
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To: Kellis91789

I find it intriguing as well. It’s going to be expensive for a long time, whereas using a couple of carbon wires and 1.2Volts is already cheap.

Desalination: Energy Hog No More?

http://www.forbes.com/sites/ericagies/2012/05/31/desalination-energy-hog-no-more-part-1/

Copyright Burj Khalifa.

Porifera Inc. – Innovation: Carbon Nanotubes

Desalination has long been the domain of arid, energy-rich states like those in the Persian Gulf thanks to its high-energy footprint. But as populations have boomed, as climate change makes water supplies more uncertain, and as clean water regulations are tightening on industry, more governments and businesses have been looking to desalination.

Efficiency and reallocation are much cheaper and sustainable options for obtaining new water supplies for municipalities. Water reuse in cities is also up and coming, as I will discuss in a future column. But the market to clean industrial wastewater of all kinds is booming.

For all these reasons, innovation in desalination has been continuing apace. At the Blue Tech Forum in San Francisco yesterday, Tyler Algeo, a research analyst at BlueTech Research, said that patents for desalination technologies in 2010 were double the number filed in 2005. Desalination energy inputs have been reduced more than 50 percent in the past decade.

Many entities are interested in these technology breakthroughs, said Algeo: large water technology corporations, venture capital firms, Fortune 500 companies, research groups, consulting engineering practices, and government agencies.

In addition to the Middle East, Australia, Algeria, and Spain now have major desalination programs, he said.

The Forum selected three companies with various approaches to desalination: carbon nanotubes, radial deionization, and biomimetic aquaporin membranes. Today I report highlights from the company that is innovating with carbon nanotubes. Look for the other two technologies in subsequent days.

Porifera Inc. is a two-year-old company based in Hayward, Calif. Vice president of business development, Jeffrey Mendelssohn, said it has achieved a breakthrough in forward osmosis membranes by using carbon nanotubes.

Reverse osmosis is a common filtration technology that uses a pump to push water through a filter. It can be energy intensive, which is why a lot of innovation is happening in forward osmosis.

Forward osmosis uses the thermodynamic law of entropy to separate solids from a fluid. Using a vessel separated into two compartments by a membrane filter, you put a dirty liquid on one side and clean water on the other. The water passes through the membrane until the percentage of solids on both sides is the same.

“Forward osmosis works better in high fouling environments [severely contaminated water] much better than pressure-driven membrane processes [reverse osmosis] because particulate matter in high fouling environments will scrunch up against the membrane under pressure and cause membrane performance to fail,” said Mendelssohn.

Porifera’s membrane isn’t just for desal, although Mendelssohn claims that it can perform salt rejection 10 times better than existing forward-osmosis processes. The company claims it has superior permeability, durability, and selectivity for water purification to other membranes. This innovation was reported in Science magazine in 2006 and was discovered at the Lawrence Livermore National Laboratory by a group of scientists led by Porifera’s principal R&D team.

From its website:

Carbon nanotubes are seamless, atomically smooth carbon “straws” whose diameters range from less than a nanometer to tens of nanometers (a water molecule is ~0.3nm). Water flows through these unique pores 1,000 times faster than through any other pore of similar diameter. Moreover, gases also flow through the nanotubes pores more than 100 times faster than through any other nanometer scale pore. This reduction in flow resistance manifests itself in large enhancements of the membrane permeability and in drastic reduction of viscous losses.

Other applications include dewatering and water treatment of all kinds.

Markets include the Department of Defense, said Mendelssohn, which needs portable on-site desalination to reduce the number of water and fuel resupply convoys in Afghanistan.

The developing world is also a potent marketplace. Dubai’s famous Burj Khalifa skyscraper has no wastewater service, said Mendelssohn, like many newly developed areas of the city. Instead, tanker trucks remove sewage regularly. By installing an on-site water treatment and reuse facility, Porifera could reduce those truck trips by 90 percent, said Mendelssohn.

On the domestic market, the company could clean water from oil and gas hydrofracking at half the cost of current forward osmosis systems and also recycle the water for reuse onsite, said Mendelssohn.

Commercial elements will begin shipping in July, he said.


39 posted on 06/11/2012 10:57:18 AM PDT by Kevmo (SUCINOFRAGOPWIASS: Shut Up, CINOs; Free Republic Aint a GOP Website. It's A Socon Site.)
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To: Kevmo
Calling out your behavior and tactics as egregious is not ad hominem. It is truth.

Even the truth can be ad hominem. Of course, in this case it isn't.

I see you stopped posting to me.

That's what you asked me to do.

The next step is to stop posting about me. Just STFU.

I won't do that, but you're free to challenge what I say.

40 posted on 06/11/2012 11:03:51 AM PDT by Moonman62 (The US has become a government with a country, rather than a country with a government.)
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To: Kevmo
You’re as useless as a 2 story outhouse.

You might outlive having to clean it out with good venting.

41 posted on 06/11/2012 11:29:28 AM PDT by listenhillary (Courts, law enforcement, roads and national defense should be the extent of government)
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To: Kevmo
Forward osmosis uses the thermodynamic law of entropy to separate solids from a fluid. Using a vessel separated into two compartments by a membrane filter, you put a dirty liquid on one side and clean water on the other. The water passes through the membrane until the percentage of solids on both sides is the same.

Doesn't sound very useful, diluting the dirty liquid. Why use a filter at all, just add clean water to the dirty. Diluting isn't separating anything.

42 posted on 06/11/2012 1:31:12 PM PDT by Toddsterpatriot (Math is hard. Harder if you're stupid.)
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To: listenhillary

Doesn’t ‘brackish water’ = Marine estuary? No more shrimp? No more sharks?


43 posted on 06/11/2012 1:44:06 PM PDT by txhurl (Scott Walker is my President.)
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To: carriage_hill

>>> Salt’s already banned in NYC, so it’s a cakewalk from there on in. <<<

Cakes are next on the ban list.


44 posted on 06/11/2012 1:46:04 PM PDT by AFreeBird
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To: AFreeBird

for later


45 posted on 06/12/2012 8:34:54 AM PDT by politicianslie (Obama: Our first Muslim PRESIDENT,destroying America $1 Trillion at a time! And America sleeps)
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To: txhurl

There are aquifers that contain brackish water.


46 posted on 06/13/2012 7:47:52 PM PDT by Moonman62 (The US has become a government with a country, rather than a country with a government.)
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To: Kellis91789

Nanoporous graphene could outperform best commercial water desalination techniques
June 22, 2012 by Lisa Zyga

(Top left) Hydrogenated and (top right) hydroxylated graphene pores. (Bottom) Side view of the simulated nanoporous graphene filtering salt ions and producing potable water. Image credit: Cohen-Tanugi and Grossman. ©2012 American Chemical Society
(Phys.org) -- Although oceans and seas contain about 97% of Earth’s water, currently only a fraction of a percent of the world’s potable water supply comes from desalinated salt water. In order to increase our use of salt water, desalination techniques must become more energy-efficient and less expensive to be sustainable. In a new study, two materials scientists from MIT have shown in simulations that nanoporous graphene can filter salt from water at a rate that is 2-3 orders of magnitude faster than today’s best commercial desalination technology, reverse osmosis (RO). The researchers predict that graphene’s superior water permeability could lead to desalination techniques that require less energy and use smaller modules than RO technology, at a cost that will depend on future improvements in graphene fabrication methods.

Water permeability of various desalination techniques. The graphene nanopores can reject salt ions with a water permeability 2-3 orders of magnitude higher than commercial reverse osmosis (RO) techniques. Image credit: Cohen-Tanugi and Grossman. ©2012 American Chemical Society
“Because those carbon atoms at the pore edge would be quite reactive without passivation, in one way or another under realistic experimental conditions they will likely have some form of chemical functionalization,” Grossman said. “This can be controlled to some extent, so we wanted to explore the two limits of hydrophobic vs. hydrophilic edge chemistries. If we had no functional groups (just bare carbon) then within a short time water molecules would dissociate at the pore edge and likely either hydrogenate or hydroxylate those carbons.”

The scientists compared the two chemistries, along with different pore sizes, of nanoporous graphene in their simulations by running saltwater with a salinity of 72 g/L over the membranes, which is about twice the salinity of average seawater (about 35 g/L).
They found that, although the largest nanopores could filter water at the highest rate, large nanopores allowed some salt ions to pass through. The simulations identified an intermediate range of nanopore diameters where the nanopores were large enough to allow the passage of water molecules but small enough to restrict salt ions.
The simulations also showed that the hydroxylated graphene significantly enhances the water permeability, which the scientists attribute to the hydrophilic nature of the hydroxyl groups. Since, in contrast, the hydrogenated pores are hydrophobic, water molecules can flow through only when in a limited number of highly ordered configurations. But hydrophilic groups allow water molecules to have a greater number of hydrogen-bonding configurations inside the pores, and this lack of restrictions increases the water flux.
Overall, the results show that nanoporous graphene can theoretically outperform RO membranes in terms of water permeability, which is expressed in liters of output per square centimeter of membrane per day and per unit of applied pressure. Whereas high-flux RO has a water permeability of a few tenths, the simulations showed that nanoporous graphene’s water permeability ranged from 39 to 66 for pore configurations that exhibited full salt rejection (23.1 Å2 hydrogenated pores and 16.3 Å2 hydroxylated pores). Graphene with the largest hydroxylated pores reached 129, but allowed some passage of salt ions.
The scientists explain that there are two main challenges facing the use of nanoporous graphene for desalination purposes. One is achieving a narrow pore size distribution, although rapid experimental progress in synthesizing highly ordered porous graphene suggests that this may soon be feasible. The other challenge is mechanical stability under applied pressure, which could be achieved using a thin-film support layer such as that used in RO materials.
“Computationally, we're looking at a range of other potentially new ways to engineer membranes for desalination and decontamination,” Grossman said. “Experimentally, we are currently fabricating nanoporous membranes and hope to test their desalination performance in the coming months.”
More information: David Cohen-Tanugi and Jeffrey C. Grossman. “Water Desalination across Nanoporous Graphene.” Nano Letters. DOI: 10.1021/nl3012853
Journal reference:Nano Letters
Copyright 2012 Phys.org




47 posted on 06/22/2012 6:00:03 PM PDT by Kevmo (SUCINOFRAGOPWIASS: Shut Up, CINOs; Free Republic Aint a GOP Website. It's A Socon Site.)
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