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Earth Technology

Battery Turns Saltwater Into Drinking Water 114

Posted by timothy
from the we-call-it-elon-water dept.
An anonymous reader writes "German researchers have developed a battery that can remove sodium and chloride ions from seawater. In theory, their invention could be far more energy efficient than thermal desalination or reverse osmosis. This would cut the cost of using salt water for drinking or irrigation. It could also be used to make compact desalination systems for boats and life rafts, or crops. Each battery is made with manganese oxide nanorod electrodes, which absorb sodium when an electrical current passes through them. When the current is reversed, they dump the sodium ions out into waste water."
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Battery Turns Saltwater Into Drinking Water

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  • How much energy? (Score:5, Interesting)

    by CapOblivious2010 (1731402) on Saturday February 11, 2012 @10:03AM (#39004629)
    Interesting, but how much energy does it take to run this thing? (they call it a 'battery', but I don't think it actually generates electricity). Many of the places that are short on fresh water are also short on electricity (especially "green" energy), so this may not be as helpful as it sounds.
    • Re:How much energy? (Score:5, Informative)

      by Smallpond (221300) on Saturday February 11, 2012 @10:08AM (#39004671) Homepage Journal

      They call it a battery because it is a series of electrical cells. The term "battery" means the series arrangement; it comes from a military term for a series of guns. Generating electricity is the best-known use of an electrical battery, but isn't the definition.

    • by mrmeval (662166)

      It's "an electrochemical cell that can desalinate seawater".

      You can thank Aaron Rowe for calling it a battery. I'm sure he plays with his food with his feet.

      • Re:How much energy? (Score:5, Informative)

        by MagusSlurpy (592575) on Saturday February 11, 2012 @01:11PM (#39005859) Homepage

        Actually, the authors call it a battery in their paper. [acs.org] And it is.

        Here's the salient part of the paper:

        In this work, we demonstrate a novel electrochemical cell named a “mixing entropy battery”, which extracts energy from the difference in concentration of two solutions and stores it as chemical energy inside the electrode material’s bulk crystal structure. This approach allows us to overcome the challenges of supercapacitor electrodes based on activated carbon. This device consists of a reversible electrochemical system where the salts in the electrolyte are the reactants and the electrode stores ions. We employed two different electrodes: an anionic electrode, which interacts with Cl ions selectively; and a cationic electrode, which interacts with Na+ ions selectively. These electrodes are initially submerged in a low ionic strength solution (river water) in their discharged states, when the electrode materials contain the respective ions incorporated in their structures. In this dilute solution, the battery is charged by removing the Na+ and Cl ions from the respective electrodes (Figure 1a, step 1). Successively, the dilute electrolyte is exchanged for a concentrated solution (seawater), which is accompanied by an increase in the potential difference between the electrodes (Figure 1a, step 2). At this higher potential difference, the battery is discharged, as the anions and cations are reincorporated into their respective electrodes (Figure 1a, step 3). The concentrated solution is then removed and substituted by the dilute electrolyte (river water), which results in a decrease in potential difference between the electrodes (Figure 1a, step 4). We note that the exchange of solution could also be carried out via a flow process, which could be attractive for large scale energy extraction.

        • Re: (Score:2, Funny)

          by Anonymous Coward

          Sounds like a prima facie case of A Salt and Battery...

    • Re:How much energy? (Score:5, Interesting)

      by errandum (2014454) on Saturday February 11, 2012 @10:46AM (#39004901)

      What I'd really want to know is if it is more efficient to use a solar panel to charge the battery to then separate the salt or simply to use the sun to desalinate the water using the tradition process.

      • You clearly don't live in Wales. We have neither sun nore drout...
    • Re:How much energy? (Score:5, Informative)

      by jonadab (583620) on Saturday February 11, 2012 @10:54AM (#39004937) Homepage Journal
      Batteries don't generate energy. They store it, chemically. (Well, the ones we usually think of as "batteries" work chemically.)

      Nonetheless, I don't know how they propose to be more energy efficient than a mirror-based distillation rig. Besides keeping the parabola aimed at the sun, which requires negligible energy, the main costs of running such a rig are keeping it supplied with water to distill and flushing it out with solvent once in a while to prevent salt buildup. (You can even use filtered seawater for the solvent.) The latter costs seem unavoidable for electrical-cell-based desalination, and the former is, as I said, negligible.

      Of course, it only works in parts of the world that get a lot of sunshine, so for example it would be a non-starter in northern Ohio. (Not that we need desalination in Ohio. Most of our water management issues involve finding ways to get the water to drain away more efficiently so it doesn't flood our basements; that seems likely to be common in places that don't get enough sunshine to boil water with a parabolic mirror... but I suppose there could be exceptions.)
      • by brusewitz (1510021) on Saturday February 11, 2012 @11:34AM (#39005177)

        Of course, it only works in parts of the world that get a lot of sunshine, so for example it would be a non-starter in northern Ohio.

        I think the fact that Ohio is not near any source of saltwater would be the real non-starter.

        • Of course, it only works in parts of the world that get a lot of sunshine, so for example it would be a non-starter in northern Ohio.

          I think the fact that Ohio is not near any source of saltwater would be the real non-starter.

          Love how you excised the OP's context-clarifying statement that said, "Not that we need desalination in Ohio"

          Still pretty darn funny, though

        • by jonadab (583620)
          > I think the fact that Ohio is not near any source of saltwater would be the real non-starter.

          Granted.
      • by mcgrew (92797) *

        That depends on your definition of "generate". Generators don't create energy either, they just convert it from kinetic energy. Batteries (except rechargeable batteries) just convert chemical energy to electricity.

      • by FunkDup (995643)
        the dude said generate electricity, not energy
      • by Anonymous Coward

        Batteries don't generate energy.

        Well, thermodynamics preaches that nothing generates energy.

    • Re:How much energy? (Score:5, Informative)

      by tqk (413719) <s.keeling@mail.com> on Saturday February 11, 2012 @10:59AM (#39004961)

      Interesting, but how much energy does it take to run this thing? (they call it a 'battery', but I don't think it actually generates electricity).

      Re-read TFA. They came up with this desalination gizmo by reversing another gizmo that does create electrical energy.

      I think this's brilliant thinking. They didn't just read the paper. They read it, understood its implications, and extrapolated them in the opposite direction. That's what I expect from scientists. I wish I saw that kind of thinking more often.

      As for this gizmo, I'd like to see it built as a group of looping boxes, progressively yielding purer product as it goes through them in sequence. Add other boxes in the chain to filter out other stuff that this gizmo doesn't filter, and you end up with an office water-cooler machine that produces pure water and recyclable sludge. I'd definitely buy one!

    • Re:How much energy? (Score:5, Informative)

      by Jack Malmostoso (899729) on Saturday February 11, 2012 @11:06AM (#39005005)

      Interesting, but how much energy does it take to run this thing?

      From the abstract: "Here, we demonstrate an energy consumption of 0.29 Wh lâ"1 for the removal of 25% salt using this novel desalination battery, which is promising when compared to reverse osmosis ( 0.2 Wh lâ"1), the most efficient technique presently available."

      • by TheLink (130905)
        RO water is much purer though. However efficient it gets I doubt this method will remove the other crap from the water, including crap...

        Isn't this similar to electrodeionization?
        • by mosb1000 (710161)

          Isn't this similar to electrode ionization?

          Yes, though the closest analogue is probably electrodialysis reversal [wikipedia.org]. The difference is that no existing technology has been able to economically remove salt in concentrations as high as seawater (though they have been used for brackish water).

        • Re: (Score:2, Informative)

          by waimate (147056)

          Very pure water is bad for you, as it leeches good minerals out of your cells (reverse reverse osmosis, if I'm not mistaken aka osmosis). If your desalination does too good a job, you have to "cut" that water with impure water.

          • Re: (Score:3, Insightful)

            by TheLink (130905)
            Any scientific study to back that up? e.g. proof that total amount of "good minerals" excreted in urine per day is more when you drink pure water. AFAIK if I drink RO water, I pee more often, but the pee is clearer in colour and if I'm losing more sodium that's a plus not a minus - since I'm a sedentary person who probably consumes more sodium than the RDA, and I'm not an athlete.

            Passing pure water through plumbing is a bad idea since it would dissolve all sorts of bad stuff (some places still have lead pip
          • No, no, no. No. What comes out of you is a function of your kidneys. Drinking distilled water as your only source of water is absolutely harmless. There are limits, of course, to how much your kidneys can concentrate or dilute your urine, but unless you are trying to kill yourself with water intoxication or have a disease, you'll be fine. You do need a certain electrolyte intake, but it's actually quite small. People who have electrolyte disturbances almost always have them because they have no kidney funct
      • by blackicye (760472)

        Interesting, but how much energy does it take to run this thing?

        From the abstract: "Here, we demonstrate an energy consumption of 0.29 Wh lâ"1 for the removal of 25% salt using this novel desalination battery, which is promising when compared to reverse osmosis ( 0.2 Wh lâ"1), the most efficient technique presently available."

        My first impression was that this is was largely just an academic project / exercise, there are other way more interesting applications for these nanorods. 15 times the energy to remove only 25% of the salt? geez, I guess it works, but not to make potable water in any quantity.

        Reverse osmosis is already deployed at a comparatively low cost, and scales very well, I don't see this or anything else displacing that as a desalination process any time in the near (or even somewhat further) future.

    • Interesting, but how much energy does it take to run this thing? (they call it a 'battery', but I don't think it actually generates electricity). Many of the places that are short on fresh water are also short on electricity (especially "green" energy), so this may not be as helpful as it sounds.

      True, but there are many countries that would be all agog if it would work more efficiently than reverse osmosis, places where salt water is abundant but drinking water is scarce, and energy is (relatively) abundant; think Persian Gulf states, north africa coastal states etc.

  • Almost there! (Score:5, Informative)

    by cashman73 (855518) on Saturday February 11, 2012 @10:04AM (#39004637) Journal
    The desalinated water that comes from the battery still contains too much salt for drinking, La Mantia says: “We removed up to 50% of the original salt, but we need to arrive at 98%.”

    Not sure what math they're using when 50% removal of ions is considered "de-salinated". I guess they're getting there, so by publishing this article, maybe they'll be able to snag some venture capital?

  • Maganese oxide? I thought Maganese was used for Galvanizing metal. Doesn't that mean it doesn't "oxidate"? :P

    • by tqk (413719)

      Maganese oxide? I thought [Manganese] was used for Galvanizing metal.

      Don't you mean zinc?

      • by sgt scrub (869860)

        Yeah. One of Maganese's uses is to control rust in steel. I used Galvanizing as a generalized term. I should have know better on /.

        • by tqk (413719)

          Maganese oxide? I thought [Manganese] was used for Galvanizing metal.

          Don't you mean zinc?

          Yeah. One of [Manganese's] uses is to control rust in steel. I used Galvanizing as a generalized term. I should have [known] better on /.

          It averages out. I didn't know that about manganese. Now we're both richer. :-)

          Some of us (well, I am anyway) are a veritable bottomless pit full of useless information. Put me in a room with iron ore, coal, and zinc, and I doubt I'd be coming out with any galvanized steel any time soon.

    • by jo_ham (604554)

      Manganese is a transition metal, and it certainly oxidises very readily - down to +7 in fact. I'm sure most people who have done high school chemistry remember the dark purple KMnO4 solution.

      Zinc is also a transition metal, and is what is used in the galvanising process.

  • by Hentes (2461350) on Saturday February 11, 2012 @10:11AM (#39004701)

    Isn't this called electrolysis?

    • by Anonymous Coward

      Isn't this called electrolysis?

      Most electrolysis cells deposit the metal on the elctrode; you can't do that with sodium, because it reacts with the water. The trick here seems to be that the sodium gets absorbed into the electrode, and so is actually removed from the water. Neat, but no coconut - yet.

  • Hmm (Score:5, Informative)

    by RenHoek (101570) on Saturday February 11, 2012 @10:13AM (#39004715) Homepage

    Of course, (good) reverse osmosis cleans out a LOT more out of the water then just salt, e.g. bacteria, viruses.

    • I'm pretty sure there is room for both techniques. For irrigation you don't need the same quality as for drinking.
    • by Anonymous Coward

      For things like those, it's easy to go through a filtration system. Salt on the other hand tends to clog up filters relatively fast making filtration on a mass scale difficult (as in costly which is why you don't see much desalination plants for water).

    • Re:Hmm (Score:5, Informative)

      by Colonel Korn (1258968) on Saturday February 11, 2012 @11:39AM (#39005207)

      Of course, (good) reverse osmosis cleans out a LOT more out of the water then just salt, e.g. bacteria, viruses.

      Do you have a sense of how dramatically expensive RO is and how much cheaper it would be if 50% of the salt in seawater could be removed in a relatively low cost preliminary separation? Somehow most of the comments on this story, both positive and negative, seem to assume its main use needs to be as a desalinization gadget where you put the saltwater in one side and delicious drinking water comes out the other. That would be amusing but not particularly useful or realistic. The value of a separation technique is going to come in the form of energy and labor savings. If I talked about this tech at work I'd hear comments like, "imagine the RO fouling reduction!"

      • Re:Hmm (Score:4, Interesting)

        by MattskEE (925706) on Saturday February 11, 2012 @01:57PM (#39006255)

        You might be right that the place for this tech is a pre-treatment for an RO process, but it isn't mentioned in the article and the researchers appear to be looking for a gadget "where you put saltwater in one side and delicious drinking water comes out the other":

        The desalinated water that comes from the battery still contains too much salt for drinking, La Mantia says: “We removed up to 50% of the original salt, but we need to arrive at 98%.”

        Doing several cycles of ion removal with the battery would further desalinate the water, but those extra cycles cost energy, so La Mantia hopes to improve the efficiency enough so that the battery can remove the salt in a single pass.

        I'd be dubious about the efficiency of doing this electrochemical desalinization to remove so much of the salt, I would think that the resistance of the water is going to rise substantially as salt leaves so it seems like more and more electrical energy will be required per mole of salt ions as the concentration drops.

        So by pre-treating water to remove much of the salt before sending it to RO the membranes will last longer before replacement? How much of the operating cost of an RO plant is determined by this? Would there be an impact on the RO process energy consumption?

    • by idji (984038)
      And don't forget Boron removal [abc.net.au].
  • by Animats (122034) on Saturday February 11, 2012 @01:33PM (#39006043) Homepage

    No, you don't put in salt water and get energy and fresh water out. You put in salt water and energy and get somewhat less salty water out.

    As with most desalinization systems, getting rid of the salt and other crud is a big problem. They haven't solved that yet. "Researchers need to find ways to remove sulfates from seawater, lower the cost of the electrodes, and protect the system from deposits of biofilm and scale that could cripple the device." It took a long time (from 1748 to 1965) before reverse osmosis membranes were developed that could handle that problem. Reverse osmosis systems require an occasional freshwater flush, but this takes far less water than the system produces. It's not clear how the numbers work out on this new approach.

  • by WaffleMonster (969671) on Saturday February 11, 2012 @09:51PM (#39009043)

    Just the other day it was discovered water magically evaporates thru sheets of graphene about as fast as you can pour.

    Kind of makes it difficult to see the point of experiments involving basic chemistry with lousy effeciency falling off a cliff as concentration of salt is reduced.

  • >When the current is reversed, they dump the sodium ions out into waste water.
    Why not just keep the salt, and make it into a packaged sea salt so as to use all of the elements and save money by making even more money from the process.

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