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Sunlight Helps Turn Salty Water Fresh

Posted by Soulskill on 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."

58 comments

  1. Amount of energy? by Anonymous Coward · · Score: 0

    Isn't there a lot of wind and sunlight on the coast? It seems the energy problem is solved. Just build the pumps.

  2. Am I missing something? by Anonymous Coward · · Score: 5, Insightful

    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.

    1. Re:Am I missing something? by OhANameWhatName · · Score: 4, Insightful

      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.

    2. Re:Am I missing something? by icebike · · Score: 4, Informative

      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.

      --
      Sig Battery depleted. Reverting to safe mode.
    3. Re:Am I missing something? by dgatwood · · Score: 1

      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. :-)

      --

      Check out my sci-fi/humor trilogy at PatriotsBooks.

    4. Re:Am I missing something? by Austrian+Anarchy · · Score: 1

      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.

      --
      Time Bomber the Book coming soon.
    5. Re:Am I missing something? by Anonymous Coward · · Score: 0

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

      Scale? Only the water on the surface can evaporate, so the efficiency of the system depends on the surface area of the pond. Using natural sunlight, and depending on the weather, this may not work out too well. Then there's the question of what to do when your ponds fill up with salt. At least with an osmosis system, you can discard the brine as soon as it's processed. Seems like this system is geared towards poorer nations with limited resources. It may be much easier to maintain a closed system like this than to rely on a large complex of covered ponds and condensers.

    6. Re:Am I missing something? by Anonymous Coward · · Score: 5, Insightful

      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.

    7. Re:Am I missing something? by Anonymous Coward · · Score: 2, Informative

      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 their fancy stuff to produce water faster.

    8. Re:Am I missing something? by Anonymous Coward · · Score: 0

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

      Anything that evaporates will be in the condensate. They are talking about industrial waste. Organic solvents, etc. could still be in the water.

    9. Re:Am I missing something? by CastrTroy · · Score: 1

      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.

      --

      Anthropic principle: We see the universe the way it is because if it were different we would not be here to see it.
    10. Re:Am I missing something? by Anonymous Coward · · Score: 0

      Restrict the water in-flow. Then have the evaporation chamber under a vacuum. (Not entirely passive though as levels would need to be maintained. But depending on how you maintain the pressure drop it may not need much energy. A solar panel with pumps could do it, or perhaps a solar heated boiler off to the side and a steam eductor.)

      Your evaporation rate will be greatly increased and you'd be surprised at how much fresh water you could make.

      By the way, a lot of industrial distillation for large scale fresh or de-ionoized water is done under vacuum. We're talking 10's of thousands of gallons per day. They typically drop the boiling point down to temperatures common to a household water heater.

      You might not achieve anything near an industrial scale given the heat input, but if done right there should be more than enough freshwater to supply a typical household with a fairly simple greenhouse-style system.

    11. Re:Am I missing something? by Anonymous Coward · · Score: 0
      You'll need a time-machine.

      "In 1870 the first US patent was granted for a solar distillation device to Norman Wheeler and Walton Evans.[4] Two years later in Las Salinas, Chile, Carlos Wilson, a Swedish engineer, began building a direct method solar powered distillation plant to supply freshwater to workers at a saltpeter and silver mine. It operated continuously for 40 years and produced an average of 22.7 m3 of distilled water a day using the effluent from mining operations as its feed water."

    12. Re:Am I missing something? by Anonymous Coward · · Score: 3, Insightful

      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.

    13. Re:Am I missing something? by Anonymous Coward · · Score: 0

      There is a test of using solar energy focused on quartz tubes carrying waste water where the H2O was steamed out and drawn off. The remainder was sanitized sludge that could be used as fertilizer. Didn't require hi-pressure pumps and all the energy is from focused mirrors and solar cell panels.
      Another method used quite well in Baja California, is to fill a tray with sea water and place a glass (or fiberglass) panel over the tray at a 45 degree angle. At the bottom of the tray is a chute that drains condensed water to a container. An 8 X 24' tray can produce up to 2 gallons a day of fresh water. On energy input is to pump (or carry) the seawater to the tray.

    14. Re:Am I missing something? by M.+Baranczak · · Score: 1

      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.

    15. Re:Am I missing something? by jafac · · Score: 0

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

      --

      These are my friends, See how they glisten. See this one shine, how he smiles in the light.
    16. Re:Am I missing something? by Smauler · · Score: 1

      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.

    17. Re:Am I missing something? by Anonymous Coward · · Score: 0

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

      Anything that evaporates will be in the condensate. They are talking about industrial waste. Organic solvents, etc. could still be in the water.

      Which are significantly more less volatile than water.

    18. Re:Am I missing something? by TWiTfan · · Score: 1

      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!!"

      --
      The cow says "Moo." The dog says "Woof." The Timothy says "Thanks, valued customer. We appreciate your input."
    19. Re:Am I missing something? by dgatwood · · Score: 1

      By my math, that's only enough water for about 60 people (assuming average usage). That might be enough water for a tiny mining community, but it is an inconsequential amount of water in the context of even your average small town, much less a city of any size. Like I said, I'm not sure you'd ever get the evaporation rate up high enough to be viable.

      --

      Check out my sci-fi/humor trilogy at PatriotsBooks.

  3. Is it wrong if... by Anonymous Coward · · Score: 0

    I thought it was talking about the dishwashing liquid from Sunlight, at first?

  4. Yeah, it's called a penguin by Anonymous Coward · · Score: 1

    http://en.wikipedia.org/wiki/Supraorbital_gland

  5. Wait, I've heard this one before! by Somebody+Is+Using+My · · Score: 5, Funny

    Desalinating salty water using sunlight?

    Oh right.

    IT'S CALLED RAIN!
    (patent pending)

    1. Re:Wait, I've heard this one before! by bob_super · · Score: 5, Funny

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

    2. Re:Wait, I've heard this one before! by Em+Adespoton · · Score: 2

      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....

    3. Re:Wait, I've heard this one before! by 140Mandak262Jamuna · · Score: 1

      Patent does not good to you, if you are hawking some vaporware.

      --
      sed -e 's/Chuck Norris/Rajnikant/g' joke > fact
    4. Re:Wait, I've heard this one before! by cellocgw · · Score: 1

      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 :-)

      --
      https://app.box.com/WitthoftResume Code: https://github.com/cellocgw
    5. Re:Wait, I've heard this one before! by Em+Adespoton · · Score: 1

      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

  6. system that desalinates salty water by bob_super · · Score: 1, Funny

    Designed by the ministry of duplicate redundant adjectives.

    1. Re:system that desalinates salty water by gargleblast · · Score: 2

      ... division of redundancies division, at 16:30 PM after afternoon tea.

  7. Sunlight "helps"? by Dan+East · · Score: 1

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

    --
    Better known as 318230.
  8. What about this system? by GoodNewsJimDotCom · · Score: 2

    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.

    --
    God spoke to me
    1. Re:What about this system? by artor3 · · Score: 1

      Where does the salt go?

    2. Re:What about this system? by Anonymous Coward · · Score: 0

      Salt is a bitch. Your metal mirrors will become corroded metal mirrors very quickly.
      Concrete isn't real fond of salt either, particularly as if it gets concentrated enough to crystalize out .

      And, what's left in the pond ?, salt ?. Going to dump that on the nearby fields are you ?.

    3. Re:What about this system? by Anonymous Coward · · Score: 0

      Salt is a bitch. Your metal mirrors will become corroded metal mirrors very quickly. Concrete isn't real fond of salt either, particularly as if it gets concentrated enough to crystalize out . And, what's left in the pond ?, salt ?. Going to dump that on the nearby fields are you ?.

      How about back into the ocean? That is where the salt collects during natural evaporation after all.

    4. Re:What about this system? by GoodNewsJimDotCom · · Score: 1

      There's a few engineering ways to handle that, but the final answer is back to the ocean.

      --
      God spoke to me
    5. Re:What about this system? by artor3 · · Score: 1

      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.

    6. Re:What about this system? by GoodNewsJimDotCom · · Score: 1

      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 dudes. They say if I catch up with all my tasks at work that they'll let me work on some stepper motors. So there's an off chance I can get around with making mirrors that track the sun and aim it at a focal point manually. So someday I might get around to creating this system, but I'm in no rush to get it done.

      --
      God spoke to me
    7. Re:What about this system? by Smauler · · Score: 1

      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.

    8. Re:What about this system? by Anonymous Coward · · Score: 0

      You sell it to western countries who will use the sea salt in their food because it is more pure and therefor more healthy, *sigh*.

      Use sea salt because you like the taste of the contaminations, not because it is more healthy then refined salt, in fact it is probably the reverse.
      It is like audiphiles calling tube amplifiers more pure while in fact they are distorting heavy which sounds nice.

    9. Re:What about this system? by Anonymous Coward · · Score: 1

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

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

    10. Re:What about this system? by Em+Adespoton · · Score: 1

      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.

    11. Re:What about this system? by Anonymous Coward · · Score: 0

      Sell it. People go ape shit over sea salt.

  9. "turn salty water fresh" by kfsone · · Score: 1

    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"

    --
    -- A change is as good as a reboot.
  10. here come the patent trolls by ihtoit · · Score: 1

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

    --
    Political debates have me rolling my eyes so much I think I got optical whiplash. I should sue. - Foamy The Squirrel
  11. I beat you. BY several years. by Anonymous Coward · · Score: 0

    Now where is my fucking patent for replicating nature in 5 minutes?

    Design Documents

  12. The story so nice, Slashdot posted it twice! by 93+Escort+Wagon · · Score: 1

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

    --
    #DeleteChrome
    1. Re:The story so nice, Slashdot posted it twice! by Anonymous Coward · · Score: 0

      Link? Provide the link or you obviously don't know what you are talking about.

  13. Use sunlight to pump water... by viperidaenz · · Score: 3, Interesting

    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?

    1. Re:Use sunlight to pump water... by Smauler · · Score: 2

      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.

    2. Re:Use sunlight to pump water... by viperidaenz · · Score: 1

      Oops, half a billion years.

    3. Re:Use sunlight to pump water... by Anonymous Coward · · Score: 0

      The tree doesn't push, it sucks. You kind of said it yourself.

      http://www.youtube.com/watch?v=BickMFHAZR0

    4. Re:Use sunlight to pump water... by Anonymous Coward · · Score: 0

      Check wikipedia, there was multicellular life a billion years ago.

  14. Top Secret! by Alotau · · Score: 1

    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

  15. breaking down the molecules? by Anonymous Coward · · Score: 0

    can salt not be destroyed in molecules in some way or taken apart until the salt is no longer really salt in water but just some molecules therefore not killing us when drinking it?
    or is that a stupid idea :)

  16. Stella Andrassy's approach from a 25 years ago by Paul+Fernhout · · Score: 1

    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 enough measurements of energy use and water produced to know how effective that particular process was. While different overall, some aspects of the current article seem to validate her intuition on that idea of using an intermediate material to help with the distillation process...

    She was about 85 then, which goes to show people can make contributions to science, technology, and culture at any age. She lived through a lot, and through all the ups and downs seemed genuinely concerned about helping people everywhere. The motto she had on her small refrigerator door at the time was "Life must be made worth living". That from someone who had lived the life of a Countess at one time (marrying a Count at 17, when she was not from royalty), and who lost most of that from WWII. A complex life.

    --
    A 21st century issue: the irony of technologies of abundance in the hands of those still thinking in terms of scarcity.