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Science

Sunlight Helps Turn Salty Water Fresh 58

Posted by Soulskill
from the that's-very-kind-of-the-sunlight dept.
MTorrice writes "With energy-efficient desalination techniques, water-starved communities could produce fresh water from salty sources such as seawater and industrial wastewater. But common methods like reverse osmosis require pumping the water, which uses a substantial amount of energy. So some researchers have turned to forward osmosis, because in theory it should use less energy. Now a team has demonstrated a forward osmosis system that desalinates salty water with the help of sunlight. The method uses a pair of hydrogels to absorb and squeeze out freshwater."
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Sunlight Helps Turn Salty Water Fresh

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  • by Anonymous Coward on Tuesday November 12, 2013 @08:32PM (#45407547)
    How is this distinctly more efficient than simply using sunlight to warm water, which evaporates, and collecting the fresh water that condenses? Desalination plants work like this, except they tend to use energy from some other source to boil the incoming seawater.
    • by OhANameWhatName (2688401) on Tuesday November 12, 2013 @08:42PM (#45407633)

      How is this distinctly more efficient than simply using sunlight to warm water, which evaporates, and collecting the fresh water that condenses?

      It's patentable.

    • by icebike (68054) on Tuesday November 12, 2013 @08:45PM (#45407655)

      How is this distinctly more efficient than simply using sunlight to warm water, which evaporates, and collecting the fresh water that condenses? Desalination plants work like this, except they tend to use energy from some other source to boil the incoming seawater.

      Efficiency isn't one of the claims being made here. In fact TFA indicates that at the lease an order of magnitude improvement is required to get this anywhere near competitive.

      But they do mention that the highest temperature required is 30C, with is well withing what you can collect with nothing more than greenhouse, and a heck of a lot lest than evaporator processes need.

      However, the summary jumped to conclusions about the seawater bit.

      The device also struggles with desalinating seawater, which has a salt concentration about 17 times greater than the team’s test solution, As a result, he says the current method would be most useful for purifying industrial wastewater streams that have a lower salt concentration.

      .

      So, not really practical at this time.

    • by dgatwood (11270)

      That's exactly what I was wondering. I've always thought it would be cool to build a giant floating greenhouse, with water running down the sloped ceiling sections into catch basins that slowly slope downhill towards shore and eventually become pipes flowing downhill to a fully enclosed reservoir with a pumping station—a completely passive desalinization plant. I'm not sure you'd ever get the evaporation rate up high enough to be viable, but it would look awesome. :-)

    • How is this distinctly more efficient than simply using sunlight to warm water, which evaporates, and collecting the fresh water that condenses? Desalination plants work like this, except they tend to use energy from some other source to boil the incoming seawater.

      That is generally what I was wondering. And you don't have to actually boil the water, a proper dome will allow the water to evaporate, collect on the inner surface, and drip down sides for collection. Problem there is the large size you need for it to collect enough to be useful.

      • by Anonymous Coward on Tuesday November 12, 2013 @09:03PM (#45407819)

        That is generally what I was wondering. And you don't have to actually boil the water, a proper dome will allow the water to evaporate, collect on the inner surface, and drip down sides for collection. Problem there is the large size you need for it to collect enough to be useful.

        I think you're not thinking big enough.

        Imagine a large sphere, maybe 8000+ miles across, illuminated by natural sunlight. You could put salt water on the outer surface of the sphere -- enough to cover 3/4 or so of the surface -- and it would naturally evaporate and condense above the surface of the sphere in certain regions and fall down in drops. A system of canals could be used to conveniently collect the water. All you would have to do is put devices that use water in those regions, and they'd have a steady supply of water. My calculations show that you could easily get 1000 kg per square meter per year in the right areas, without having to put in energy at all.

        Of course, there would also be parts of the sphere where almost no water would fall, but that problem is pretty easy to solve -- just don't put anything that needs water in those areas.

        • by CastrTroy (595695)
          This.

          I wonder why people choose to live in such inhospitable places. We aren't at the point where people are taking up every square meter of land, yet people still choose to live in ridiculous places.
          • Re: (Score:3, Insightful)

            by Anonymous Coward

            I wonder why people choose to live in such inhospitable places.

            At least in the US, it's because the people who live there don't realize that the area they have chosen to live cannot sustain them. They think of it as paradise, since they have "perfect weather year-round". It's up to Someone Else to worry about pumping fresh water over the Tehachapi Mountains, and about where that water is coming from.

          • by jafac (1449)

            because all the hospitable places are too overcrowded with other people?

          • by TWiTfan (2887093)

            I wonder why people choose to live in such inhospitable places.

            The Sam Kinison principle: "You see this, fucker? It's sand. You know what it's going to be in a thousand years? SAND!!"

        • Imagine a large sphere, maybe 8000+ miles across, illuminated by natural sunlight. You could put salt water on the outer surface of the sphere -- enough to cover 3/4 or so of the surface -- and it would naturally evaporate and condense above the surface of the sphere in certain regions and fall down in drops. A system of canals could be used to conveniently collect the water.

          Yeah, that was first place we looked. Most of those are too polluted to drink, or they're owned by someone else, or both.

    • Re: (Score:2, Informative)

      by Anonymous Coward

      Evaporation takes a great deal of energy: about 2 MJ/kg.

      If the solar flux is 500 W/m^2 and the system is otherwise perfectly efficient, that would permit evaporating at most 0.9 L/m^2-hr.

      The system in the article can produce 10 L/m^2-hr with unconcentrated sunlight of that intensity, or 25 L/m^2-hr if concentrated to 2 kW/m^2. So it's at least 10 times more efficient than evaporation, and in practice quite a lot more than that.

      Concentrating the sunlight is less energy-efficent, but allows a given area of th

    • by Smauler (915644)

      There are a whole load of problems with large scale desalination. It's been done, and is done on a wide scale currently.

      There's a reason why cities most on the coast don't use seawater... they use the water from their rivers. It's cheaper, and better generally.

    • I got to know Stella when she was working on an improved way to distill salt water into fresh using solar energy (or other forms of heat). Engineer Charlie Parker has built the prototype for her. In essence, her approach involved having a rotating cylinder with a carpet-like surface which rotated into salt water at the bottom and had heat applied near the top. Her idea was that the wicking action of the material would make it easier for the fresh water to evaporate. Back then, there were not any detailed e

  • by Somebody Is Using My (985418) on Tuesday November 12, 2013 @08:45PM (#45407651) Homepage

    Desalinating salty water using sunlight?

    Oh right.

    IT'S CALLED RAIN!
    (patent pending)

    • by bob_super (3391281) on Tuesday November 12, 2013 @08:54PM (#45407733)

      Your patent is useless, your technology is just a stream served by my Cloud.

    • Cloud-based desalination will be the next big thing, I'm sure of it! People will be providing DsaaS solutions globally!

      I use three different modules: roof, gutter and barrel, which together take advantage of the synergistic features enabled by cloud-based desalination.

      The patent applications should start flooding in any day now....

      • by cellocgw (617879)

        I use three different modules: roof, gutter and barrel, which together take advantage of the synergistic features enabled by cloud-based desalination.

        Sadly, there are parts of the US where collecting rainwater off your roof is illegal. Something about maintaining the water table to support farming, or whatever. Just warning you before you spend all that money on your patents :-)

        • I use three different modules: roof, gutter and barrel, which together take advantage of the synergistic features enabled by cloud-based desalination.

          Sadly, there are parts of the US where collecting rainwater off your roof is illegal. Something about maintaining the water table to support farming, or whatever. Just warning you before you spend all that money on your patents :-)

          My patents will be full of marketspeak, but never once mention collecting rainwater. They'll apply to collecting any sort of runoff from any surface, as long as it comes from "the cloud" :D

    • Patent does not good to you, if you are hawking some vaporware.
  • Designed by the ministry of duplicate redundant adjectives.

  • I'm pretty sure sunlight is responsible for 99.9% of the rest of the fresh water on the planet too.

  • by GoodNewsJimDotCom (2244874) on Tuesday November 12, 2013 @08:48PM (#45407679)
    Design a robotic software to keep mirrors aimed at a focal point.

    At the focal point, have sea water pumped into a concrete basin.

    Have a steam engine that takes sea water input, and makes electricity and desalinated water output

    Mirrors or silvery material is relatively inexpensive. Once you developed robotic sun tracking/aiming software, that isn't too expensive either. The electricity generated by the system can go towards pumping sea water into it.
    • by artor3 (1344997)

      Where does the salt go?

      • There's a few engineering ways to handle that, but the final answer is back to the ocean.
        • by artor3 (1344997)

          You're handwaving the only challenging part of the design. Are you just joking around or something? If so, your humor is way to subtle.

          • The salt will build up in the evaporation chamber. So if you use your saltwater input to flush it out each loading cycle, some would come out.

            I'm not familiar with how salt changes with temperature and if it'd cake on to the inside in such a manner that flushing it would be insufficient. Even if this is the case, what is the rate of crusting up? Could it be solved by a human coming on site once a day or once a week and scrubbing it?

            I'm an ace software guy who just got together with some hardware d
            • by Smauler (915644)

              Desalination is not easy or quick... the reason it's not caught on is because it's difficult, and energy intensive. If you're rich enough, they work... You need lots of power to run then though.

              Desalination plants are common in the middle east. There is loads of power there, and not much water.

              • by Anonymous Coward

                Desalination is quick, easy, and cheap. You just bought the lies.

                http://www.theregister.co.uk/2012/05/02/water_vs_energy_analysis/

      • Where does the salt go?

        2 places:
        1) salt cellars
        2) superheated to provide an energy sink; then used to generate electricity. This will, of course, require some sort of a gate to dump the salt from the basin at a predefined salinity level, for use in the turbine's basin. Definitely doable.

  • Not "makes salt-water safe for drinking" or "desalinates sea water", but 'turns salty water fresh'.

    Ok, so.

    Me: "Hey, Brian, did you turn this salty water fresh?"
    Brian: "Sure did"
    Me:
    Brian to ghost me: "for some value of fresh"

  • thanks, I'll stick with my hothouse desalination process. No hydrogel required. Just a big glass building and a few lengths of halfpipe.

  • Stop me if you've read this before... but this one's a dupe.

  • by viperidaenz (2515578) on Tuesday November 12, 2013 @10:51PM (#45408561)

    Already done. Over a billion years ago too.
    It's one of the methods plants use to extract nutrients from the soil.
    Osmosis does some of the work, but it is also assisted by the fact the water travels up sealed tubes in the plant to the leaves, which when the water evaporates, creates a negative pressure in that tube, sucking more up.

    How else do you think a 50m tall tree can push water to the top, overcoming 70psi of pressure?

    • by Smauler (915644)

      Already done. Over a billion years ago too.

      If only the... wait, over a billion years ago? There was basically nothing on the earth a billion years ago. No plants, no nothing. There was stuff in the sea.

      Also... yes, people have thought to look at plants techniques. It is one of the starting points.

  • Doctor Flamond: You see, a year ago, I was close to perfecting the first magnetic desalinization process so revolutionary, it was capable of removing the salt from over 500 million gallons of seawater a day. Do you realize what that could mean to the starving nations of the earth?

    Nick Rivers: Wow. They'd have enough salt to last forever.

    http://www.imdb.com/title/tt0088286/quotes?item=qt0358683 [imdb.com]

Nothing is impossible for the man who doesn't have to do it himself. -- A.H. Weiler

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