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Earth Science Technology

Graphene-Based Sieve Turns Seawater Into Drinking Water (bbc.com) 111

An anonymous reader quotes a report from BBC: A UK-based team of researchers has created a graphene-based sieve capable of removing salt from seawater. The sought-after development could aid the millions of people without ready access to clean drinking water. The promising graphene oxide sieve could be highly efficient at filtering salts, and will now be tested against existing desalination membranes. It has previously been difficult to manufacture graphene-based barriers on an industrial scale. Reporting their results in the journal Nature Nanotechnology, scientists from the University of Manchester, led by Dr Rahul Nair, shows how they solved some of the challenges by using a chemical derivative called graphene oxide. Isolated and characterized by a University of Manchester-led team in 2004, graphene comprises a single layer of carbon atoms arranged in a hexagonal lattice. Its unusual properties, such as extraordinary tensile strength and electrical conductivity, have earmarked it as one of the most promising materials for future applications. But it has been difficult to produce large quantities of single-layer graphene using existing methods, such as chemical vapor deposition (CVD). Current production routes are also quite costly. On the other hand, said Dr Nair, "graphene oxide can be produced by simple oxidation in the lab." Graphene oxide membranes have already proven their worth in sieving out small nanoparticles, organic molecules and even large salts. But until now, they couldn't be used to filter out common salts, which require even smaller sieves. Previous work had shown that graphene oxide membranes became slightly swollen when immersed in water, allowing smaller salts to flow through the pores along with water molecules. Now, Dr Nair and colleagues demonstrated that placing walls made of epoxy resin (a substance used in coatings and glues) on either side of the graphene oxide membrane was sufficient to stop the expansion.
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Graphene-Based Sieve Turns Seawater Into Drinking Water

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  • by Anonymous Coward

    The biggest problem isn't removing the salt, it is what to do with all the excess salt that remains. If you dump it back into the ocean, it wipes out all sea life in a large radius. It is pretty devastating.

    • by camperdave ( 969942 ) on Tuesday April 04, 2017 @03:12AM (#54168991) Journal
      We could use it as salt, or we could fill in the salt mines we've been digging, or we could drop it into the oceans to counteract all the freshwater melt coming off the polar ice caps from the global warming.
      • or we could drop it into the oceans to counteract all the freshwater melt coming off the polar ice caps from the global warming.

        I think this was OP's point. If you dump it back in the oceans then... unless you spread it very, very thinly over a wide area, you'll end up with pockets of highly concentrated saline ocean which is very harmful to sea life.

        • by ShanghaiBill ( 739463 ) on Tuesday April 04, 2017 @04:29AM (#54169129)

          unless you spread it very, very thinly over a wide area, you'll end up with pockets of highly concentrated saline ocean which is very harmful to sea life.

          An obvious solution would be to dilute it with fresh water before dumping it into the ocean.

          • by Dog-Cow ( 21281 )

            I really hope you were being sarcastic.

            • by namgge ( 777284 )
              Whoosh!
            • No need to be sarcastic. It's relatively cheap to transport salt to a location where fresh water is abundant, compared to moving that fresh water to where the salt is obtained as a result of desalination.
            • by DarkOx ( 621550 )

              I expect the GP was being sarcastic but that isn't perhaps so crazy. We already treat waste water heavily in most places before we dump it back into rivers or the ocean. If you are doing this on a community scale I don't see why transporting the salt over to the waste water plant and mixing it back into the that isn't entirely impractical.

              There are two problems
              1) the waste water already will contain a number of dissolved substances it may or may not be able to still dissolve enough salt to match the salin

              • How Much Salt? (Score:5, Interesting)

                by sycodon ( 149926 ) on Tuesday April 04, 2017 @11:23AM (#54170641)

                Los Angeles consumed about 17,957,000,000 in August of 2013 [scpr.org]

                A gallon of sear water contains 4.5 oz of salt

                So if LA used exclusively desalinized water, they would have 10,100,812,500 lbs of salt on their hands (17,957,000,000*4.5/8)

                This is about 126,260,156 cubic feet.

                Your average Panamax [bulkcarrierguide.com] cargo ship has about 3.6 million cubic feet of space.

                This is about 35 ships worth of salt.

                There are about 16,900 bulk carrier ships operating in the world.

                • Given that the salt came from the oceans, you could just dump it back into the sea.

                  • by sycodon ( 149926 )

                    Three ships leaving port a month and dumping the salt during the trip to HI would be enough.

                    Really...given the ships plying the waters these days distributing the salt over a large area is a trivial exercise.

                • by dgatwood ( 11270 )

                  There are 16 ounces to a pound, not 8, so it's half that. Still, that's a lot of salt.

              • The real problem is:

                3) Places where freshwater flows into the ocean are brackish, and the organisms there are adapted to a low-salinity environment. Increasing the salinity there can disrupt the ecosystem just the same as it would further out in the ocean.

                There is really no good place to dump the excess salt. We can't just dump massive amounts of salt anywhere there is life. Maybe it could be prepared for human consumption---sea salt is often treated as a premium grocery item. I have no idea what volume to

          • by Anonymous Coward

            Why not sell it to the upper-class restaurants in the US as a finishing salt. I'm sure with some clever marketing a few oz could be like $30, which could be used to purchase fresh water. It's all in the marketing...maybe Salt of the Earth.

          • Nah, just make flamingo nesting grounds with it. Environmentally friendly, if you're a flamingo.

        • But it is great for SEA MONKEYS®
    • by Zocalo ( 252965 )
      Salt can work fairly well as an energy storage device in green energy systems that are prone to fluctations in flow like solar and wind. Basically, you use some excess energy to heat up a volume of salt (to around 3000C is typical) then, when the wind drops or night falls, harvest that thermal energy back to provide power as the salt cools. Reheat the salt when your power source returns, and repeat.
      • How do you contain salt at 3000 C?
        • by Lehk228 ( 705449 )
          carefully.
    • by Provocateur ( 133110 ) <[moc.liamg] [ta] [deidehs]> on Tuesday April 04, 2017 @05:39AM (#54169277) Homepage

      Scientist: Do you know what this means?

      Nick: There'd be an *awful* lot of salt.

      • Scientist: Do you know what this means?

        Nick: There'd be an *awful* lot of salt.

        And some gold too.

        • Scientist: Do you know what this means?

          Nick: There'd be an *awful* lot of salt.

          And some gold too.

          Cowboy Neal is salty too.

          • Scientist: Do you know what this means?

            Nick: There'd be an *awful* lot of salt.

            And some gold too.

            Cowboy Neal is salty too.

            Seems like the basis for a song there.

      • by Sloppy ( 14984 )

        It's "Wow! They'd have enough salt to last forever!"

    • Re: (Score:2, Interesting)

      "The biggest problem isn't removing the salt, it is what to do with all the excess salt that remains. If you dump it back into the ocean, it wipes out all sea life in a large radius. It is pretty devastating."

      This is classic enviro bullshit. You just claimed that if we suck in some seawater, separate the water from the minerals, and then return the minerals to the ocean again, that they magically turn toxic against the same species that have been spending their lives in it? Human desalination cannot change

      • Re:yes but.... (Score:5, Insightful)

        by Ol Olsoc ( 1175323 ) on Tuesday April 04, 2017 @10:33AM (#54170283)

        "The biggest problem isn't removing the salt, it is what to do with all the excess salt that remains. If you dump it back into the ocean, it wipes out all sea life in a large radius. It is pretty devastating."

        This is classic enviro bullshit.

        And your response is typical reaction to an uninfomed person, making their statement magically said by all people concerned about the environment

        You just claimed that if we suck in some seawater, separate the water from the minerals, and then return the minerals to the ocean again, that they magically turn toxic against the same species that have been spending their lives in it? Human desalination cannot change the amount of water or salt in the environment. "Excess salt" does not exist.

        Okay lads, let's sit down and talk like adults, because you are both wrong.

        One of the first things we have to look at is the amount of salt that might be returned to the ocean. So we have a desalinization plant. Until the plant is taking a significant amount of water out, extracting the salt, and returning the salt to the ocean, it is hardly going to be a blip in the percentage of salt. So that environut you're railing at is generally wrong. Because there is one hellava lot of water in the ocean.

        note: because of local conditions, you would want to have a distributed return of the salt. You do not want to just dump it on the shoreline.

        But before you go patting yourself on the back, it is possible to get so much salt that it affects what if anything can live in the water. Mono Lake is one example. It has become so salty that no fish live in it. Brine shrimp and algae are it. The salinity level has varied - topping out at alomst 100 framps per liter in the early 80s. We've stopped diverting so much water, and the salinity level is lowering now, the target is 70 grams per liter. The reason we'r eallowing the lake to replenish is that it is an important migratory pathway for a lot of birds. The Great Salt Lake in Utah, which is the remnant of Lake Bonneville is another hypersaline body of water, and ecologically similar to Lake Mono. The Dead Sea is another hypersaline area, and it's named dead sea for a reason. Not much can live there. A few types of bacteria. So you are completely wrong - It is highly possible to have excess salt.

        So by spreading the return of the salt to the ocean over an area that avoids local hypersalinization, we'll not have much effect on the salinity of the oceans.

        • by PPH ( 736903 )

          So by spreading the return of the salt to the ocean over an area that avoids local hypersalinization, we'll not have much effect on the salinity of the oceans.

          Right. But who would build a desalinization plant in a location that would be susceptible to local hypersalinization? The plant efficiency would drop and fresh water production would eventually cease. Plants will be built in places with sufficient ocean currents to dilute their brine output and carry it away.

          • The plant efficiency would drop and fresh water production would eventually cease.

            The plant might see reduced efficiency, but there is a limit on how high the salinity will go since there is always some fresh water coming in. The problem is that desalination plants will remain effective in a large salinity range----a range which includes levels harmful to oceanic life.

            E.g., Israel plans to desalinate water from the Red Sea, which is one of the saltiest bodies of water on Earth. Only the Dead Sea and a few obscure lakes are saltier.

            Israel plans to address their problem by pumping the brin

          • So by spreading the return of the salt to the ocean over an area that avoids local hypersalinization, we'll not have much effect on the salinity of the oceans.

            Right. But who would build a desalinization plant in a location that would be susceptible to local hypersalinization? The plant efficiency would drop and fresh water production would eventually cease. Plants will be built in places with sufficient ocean currents to dilute their brine output and carry it away.

            My reply was in the context of the people having the disagreement. Of course, you don't want to dump in the same area you extract from.

          • Re:yes but.... (Score:4, Interesting)

            by mrchaotica ( 681592 ) * on Tuesday April 04, 2017 @01:37PM (#54171711)

            This entire thread has been idiotic, because everybody's missing the most important factor:

            The desalinized water doesn't leave the system; it gets used and returned.

            People drink the water, piss it back out, and flush it down the drain. The drain goes to the sewer. The sewer goes to the wastewater treatment plant. So re-salinize the wastewater after treating it and you can dump it back into the ocean at the same salinity you started with! (Give or take losses from outdoor watering and gains from precipitation falling into combined sewers, anyway. The net difference could be significant, but we shouldn't dismiss the idea out-of-hand by assuming so.) So just build the two treatment plants next to each other and pipe the salt across from the desalinizer to the resalinizer.

            Or better yet, just build one plant capable of treating any water (seawater or wastewater) to a drinkable standard, and make the damn thing a closed loop!

            • Problem solved... Well done everyone.

            • This was my point. Water on the Earth circulates in a closed system, with none of it being "used up" or permanently sequestered. When fresh water leaches soluble minerals out of the rocks in the places where it flows, nature dumps all of the minerals into the oceans or into land basins without an outlet.

              Man has the ability to optionally pull dissolved minerals out of the natural circulation and use them for human purposes. Now that desalination is about to vastly increase the amount of dissolved minerals th

              • This was my point. Water on the Earth circulates in a closed system, with none of it being "used up" or permanently sequestered.

                However, if you think that pushing saltwater into freshwater streams is even remotely a good idea, you might look up what saltwater does to freshwater flora and fauna.

                The return paths are not paved with salt, but freshwater. Either through evaporative processes like water to cloud to rain, or via streams, virtually all that are freshwater.

                • "However, if you think that pushing saltwater into freshwater streams is even remotely a good idea, you might look up what saltwater does to freshwater flora and fauna."

                  Nowhere did I mention dumping salt into fresh water. We have plenty of salt water where it can go.

            • This entire thread has been idiotic, because everybody's missing the most important factor:

              The desalinized water doesn't leave the system; it gets used and returned.

              People drink the water, piss it back out, and flush it down the drain. The drain goes to the sewer. The sewer goes to the wastewater treatment plant. So re-salinize the wastewater after treating it and you can dump it back into the ocean at the same salinity you started with!

              Well, since you called me an idiot, there is a problem with your great wisdom.

              Imagine a fellow so much smarter than others that he suggests injecting saline brine into freshwater streams. Apparently in genius world, all sewage treatment plants are along the coast.

              Who knew? Thanks for elightiening us, I better check to see if those sewage plants near me are actually CIA listening stations or something. The allegedly treated effluent they are allegedly dump into the alleged freshwater streams and can

              • Well, since you called me an idiot...

                No I didn't; I called the thread idiotic. There's a difference.

                Apparently in genius world, all sewage treatment plants are along the coast.

                ...But now I will, you blithering moron!

                In case you hadn't noticed, the topic of this thread is desalinization. That's something you only consider doing in the first place when the ocean is the least-inconvenient place to get the water supply from. Given that assumption, can you guess what the most convenient body of water to dischar

                • That's something you only consider doing in the first place when the ocean is the least-inconvenient place to get the water supply from. Given that assumption, can you guess what the most convenient body of water to discharge the wastewater into might be?

                  That's right, the ocean!

                  I admit, there are places that have water supplies other than the ocean. But in that case, they have water supplies other than the ocean and the problem of what to do with the excess salt is moot because you're not desalinizing to begin with!

                  Hold on a second. Your story has changed - a lot If I recall, and cutting and pasting seems to verify that. You wrote :

                  "People drink the water, piss it back out, and flush it down the drain. The drain goes to the sewer. The sewer goes to the wastewater treatment plant. So re-salinize the wastewater after treating it and you can dump it back into the ocean at the same salinity you started with!

                  I don't recall myself or anyone else in this subthread saying that the saline sludge shouldn't go back in t

        • Salt lakes like the big one in Utah are historically sources of salt, not places where we are going to dump more of it. Ever driven I-80 between SLC and Wendover? You see salt extraction plants lined along the highway, taking salt out of the lake. One level higher up is the Bonneville Salt Flat, which we are tryingto keep salty so we can race on it.

          We will be desalinating from the oceans, and what salt we return will be to the oceans.

    • That's not "the biggest problem". In fact, it's not really much of a problem at all. You don't end up with "salt", you end up with water that has a higher salinity than the input water. You keep enough new salty or brackish water moving through the input side to dilute the effect of pulling water out. Compared to the amount of water moving around in the tides, the desalinization plant is small potatoes. Compared to the amount of water removed from the oceans by evaporation, it is insignificant.

      Now perhaps y

      • by skids ( 119237 )

        You might even be able to recover some energy from the brackish water as you mix it back in via an osmotic power cells.

    • The biggest problem isn't removing the salt, it is what to do with all the excess salt that remains. If you dump it back into the ocean, it wipes out all sea life in a large radius. It is pretty devastating.

      I thought the biggest problem was violating the laws of thermodynamics. Salt water is at a lower entropy than separated water and salt. It takes energy to separate salt and water. We already know how to separate salt and water. Maybe this is more efficient?

  • I'm no chemistry expert, but isn't graphene oxide simply CO2?
  • Seer (Score:2, Informative)

    by dohzer ( 867770 )

    Sure, but the Water Seer [waterseer.org] can turn air into drinkable water!

    • by Anonymous Coward

      Water Seer is a sorry hoax.

      https://www.youtube.com/watch?v=LVsqIjAeeXw

  • Two questions (Score:4, Interesting)

    by malx ( 7723 ) on Tuesday April 04, 2017 @03:36AM (#54169023)

    1. What throughput / flowrate can you achieve, per unit of area?

    2. How do you clear clogging?

    • It is easy to clear the clogging. You use another graphene filter to get more freshwater to clear clog in the original filter.

      Oh, yeah, how you clear clog in the other filter? Come on, Sherlock, you just have cleared the clogs and have a fresh good clean graphene filter in your hand don't you realize that. You use the original to clear the clog of the other filter. Simple. Just. use. your. brain.

    • Re:Two questions (Score:4, Informative)

      by swb ( 14022 ) on Tuesday April 04, 2017 @08:17AM (#54169655)

      From what I've read in the marine world, there's no cure for clogging, just ways to minimize it. Multi-stage sea strainers cheaply and/or easily replaced and cleaned to get the water as de-gunked as possible before it hits the really good membrane. And enough water storage that you don't have to run your water maker in poor quality harbor or shallows water.

    • by jafiwam ( 310805 )

      2. How do you clear clogging?

      Review a diagram of a current desalination plant.

      Two things can declog. First, you can run the filter backwards for a short time, water in motion can dislodge built up material far in excess of the water that flowed forward gathering that material. Second, for salts themselves clogging, you let natural entropy take care of it for you.

      These filters are often tubes through which high pressure water is added, cleaned water enters the outer jacket area and falls off. Higher salinity water continues down t

    • Serious answers: 1. It sounds like they don't have numbers yet; and there's more to it than flow-rate. Massively more important than flow-rate is the theoretical watts per Liter needed to force the water through under pressure. ("Theoretical" because you don't worry about pump-efficiency when comparing filter performance.)

      2. "Clearing" the filter isn't exactly a thing because the salt never crystallizes. It remains in the water that's on the intake side of the filter. You "clear" the filter by not allowin

    • Since this is a filter, I am going to guess it will probably be like a replaceable filter system.  This is huge for not needing energy to work.
  • by Anonymous Coward on Tuesday April 04, 2017 @04:17AM (#54169105)

    Desalination of seawater by reverse osmosis [wikipedia.org] is an old hat. The main challenge from an energy POV is the high pressure [wikipedia.org] differential (and the flow, of course) needed. This won't change much with a new membrane.

    Of course, a new membrane might have other desirable properties (cost, robustness, whatever), so every new option is a Good Thing, but the abstract suggests that graphene is something new here. It isn't. Just one more tool in an old chest.

    • by Chrisq ( 894406 )

      Desalination of seawater by reverse osmosis [wikipedia.org] is an old hat. The main challenge from an energy POV is the high pressure [wikipedia.org] differential (and the flow, of course) needed. This won't change much with a new membrane.

      Of course, a new membrane might have other desirable properties (cost, robustness, whatever), so every new option is a Good Thing, but the abstract suggests that graphene is something new here. It isn't. Just one more tool in an old chest.

      That's what they're hoping from TFA:

      "When the capillary size is around one nanometre, which is very close to the size of the water molecule, those molecules form a nice interconnected arrangement like a train," Dr Nair explained.
      "That makes the movement of water faster: if you push harder on one side, the molecules all move on the other side because of the hydrogen bonds between them. You can only get that situation if the channel size is very small."

      ...

      "This is our first demonstration that we can control the spacing [of pores in the membrane] and that we can do desalination, which was not possible before. The next step is to compare this with the state-of-the-art material available on the market," said Dr Nair.

    • I've never heard a good explanation why we don't use tidal energy to create the requisite pressure. Open gates at mean sea level, wait for high tide to flood reservoir, close gates, open much smaller exit path past filters during tide retreat, rinse, repeat. The massive water reserve attempting to push through the narrow exit path raises the pressure of the water.

      There must be a good physics or economics explanation as to why this doesn't work (not enough pressure, the amount of energy required to build the

  • Another graphene-is-the-material-of-the-future spectacular application that will come to absolutely nothing because or something or another. In a few months time, nobody will even remember about it.
  • by Merk42 ( 1906718 ) on Tuesday April 04, 2017 @09:04AM (#54169801)
    Yes.
    Come to market.
  • by Anonymous Coward

    The natural process of osmosis will persist. This is the tendency for water to flow through the filter in the wrong direction (the fresh water flows into the salt water). Sea water has (I looked it up) an osmotic pressure of 28 atmospheres (411 pounds per square inch)...one must supply a pressure of this amount to stop the exfiltration. To make a substantial amount of water go through in the right direction, you'll need double this...at least 800 psi. To maintain this pressure requires a lot of energy. Usua

  • Graphene is finally worth its salt?

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