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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
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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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