Why is it difficult to turn seawater into drinking water?

Discussion in 'General Science & Technology' started by Saint, May 31, 2012.

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  1. Saint Valued Senior Member

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    Why is it difficult to turn seawater into drinking water?
    In order to solve water shortage problem.

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  3. AlexG Like nailing Jello to a tree Valued Senior Member

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    The salt is dissolved in the water and must be removed.

    To do so on any large scale requires a large amount of machinery.

    The Island of Aruba in the Carribean makes all of it's drinking water via the worlds largest desalinization plant.
     
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  5. keith1 Guest

    A relatively new process called nano osmosis is the most energy and cost efficient way to desalinate...

    search: nano-osmosis desalination
     
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  7. Epictetus here & now Registered Senior Member

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    You can look up the various processes used to desalinate water. I suppose what Keith says is so, but up until now it's an expensive, nearly unfeasible process except when there is really no alternative. I've have read that while 20th century wars have been about oil, 21st century wars will be about water. And yet, the Iran-Iraq War of the 1980's was about water (and I don't know what the present war in Iraq is about anymore). Short answer to your question: I don't know. Sorry. :shrug:
     
  8. keith1 Guest

    There is more fresh water in the asteroids than can be found on Earth.
    And the first commercial spaceship docked this week at the space station.
    It will be an interesting century to be alive.

    (Maybe a water meteor breaks up when entering earth's atmosphere, and harmlessly rains all over the place.
    Then again, maybe not--maybe to best use it where it lies frozen).
     
  9. Saint Valued Senior Member

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    Can we use solar energy to evaporate the seawater and then condense it?
     
  10. Read-Only Valued Senior Member

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    Mmmmm... Well, just two things in passing, one is I think many people forget the TREMENDOUS amount of fresh water in the U.S./Canadian Great Lakes. The other is the billions of billions of gallons of fresh water in the rivers of the world (that aren't that polluted in every case) that simply runoff into the oceans every single day.

    The true major problem is that much of the water is simply in the wrong place to meet human needs. But there's really no need to go looking into outer space to get it - just work on better ways to divert/transport what we have and employ the latest desal process to a greater degree in the true arid regions of the world.
     
  11. Aqueous Id flat Earth skeptic Valued Senior Member

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    Sure. A solar still.
     
  12. Asguard Kiss my dark side Valued Senior Member

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    You do realise that river mouths are important too? Esteries tend to be where most ocean fish spawn and that not even looking at what would happen if there was no ware returning to the ocean. How concentrated would it end up?
     
  13. Epictetus here & now Registered Senior Member

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    Water meteors!? Way out Keith! You force me to reprint this:

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    How much of Jupiter's moon Europa is made of water? A lot, actually. Based on the Galileo probe data acquired during its exploration of the Jovian system from 1995 to 2003, Europa possesses a deep, global ocean of liquid water beneath a layer of surface ice. The subsurface ocean plus ice layer could range from 80 to 170 kilometers in average depth. Adopting an estimate of 100 kilometers depth, if all the water on Europa were gathered into a ball it would have a radius of 877 kilometers. To scale, this intriguing illustration compares that hypothetical ball of all the water on Europa to the size of Europa itself (left) - and similarly to all the water on planet Earth. With a volume 2-3 times the volume of water in Earth's oceans, the global ocean on Europa holds out a tantalizing destination in the search for extraterrestrial life in our solar system.
    http://apod.nasa.gov/apod/ap120524.html
     
  14. Epictetus here & now Registered Senior Member

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    Condensed water? What do you mean? Like canned milk? Just add...water....?

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  15. Aqueous Id flat Earth skeptic Valued Senior Member

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    Condense the vapor.
     
  16. Aqueous Id flat Earth skeptic Valued Senior Member

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    The other sad part of that is that all the discharge from the cities upstream has accumulated at the estuary. Sounds gross anyway.

    Another worry about fresh water is the depletion of glaciers that feed all the major rivers. Presumably there will always be snow melt, but imagine that becoming the new normal. Then if a dry spell were to set in, you could imagine the Nile or Yangtze going dry. It would be a disaster.

    I like this idea of deriving fresh water from sea water. I think it's forward thinking. It would be interesting to live on an island where everybody was on the same page with ideas like this and cooperated to really do something completely new and different that actually worked as as far as low-impact living is concerned.
     
  17. Fraggle Rocker Staff Member

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    It's been calculated that these (plastic) devices could easily be manufactured in the poorer nations where the cost of living is low, and therefore where fair salaries are also low. This would boost those nations' economies while producing a device that could be sold at a profit for five dollars. A practical-size solar still will produce one liter of clean fresh water per day in a sunny, warm climate--which happens to be where most of the people live who desperately need clean fresh water. One liter isn't a lot but if used wisely it will make the difference between dysentery (still the leading cause of child mortality in many countries) and health for hundreds of millions of adults and children.

    A wealthy philanthropist like Bill Gates or Warren Buffett could provide one of these to every person on earth who needs one within ten years (politics and logistics would surely make it impossible to distribute them any faster than that anyway, considering the kinds of governments most of those countries have), without using up his entire annual charity budget.

    They can use just about any kind of water as input, including polluted rivers, industrial effluent, or even plain old sewage.
    But don't forget that as the average temperature rises, so will the relative humidity. Ice ages always bring drought and warm spells always bring rain. This will feed the rivers as well as delivering rainwater directly to many places that now have to pipe it in. The Sahara may once again be a breadbasket.

    It was an epochal drought and famine in Africa during the depths of an ice age 60KYA that encouraged a band of the San people (or "Bushmen") in desperation to walk out of Africa into Asia in search of better weather. They got all the way to Australia before they found what, to them, (due to the vagaries of weather patterns) was paradise. Remember that during an ice age more of the earth's water is locked in permanent icecaps and glaciers, so sea level is lower. The distance between all those islands was narrower, making the voyage practical in Stone Age-technology boats.

    The San people still exist (although they now live much farther south due to the desertification of North Africa as the ice age ends--the increase in rainfall is not uniform across the entire planet) and DNA analysis proves that they are, indeed, the ancestors of all non-African people. (I've oversimplified the story, there was a second San emigration 10K years later which populated the other continents.)
    Average rainfall will increase on islands just as it will on the continents. The biggest problem islanders will face as this ice age comes to its ultimate termination is the rise in sea level. Most of the smaller islands like Manhattan and the Maldives will simply be under 50m or more of water, as will Florida, Bangladesh, Holland, and a majority of the world's cities.
     
  18. billvon Valued Senior Member

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    Dean Kamen developed a very similar device. It uses anything combustible (cow dung, coal, anything) and any sort of water to produce 250 gallons of drinking water a day and 200 watts of electric power. Its cost (if mass produced) would be around $1000 each.
     
  19. Trippy ALEA IACTA EST Staff Member

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    It's not. It happens naturally all over the world every day. All it requires is - get this... Sunlight!
     
  20. KilljoyKlown Whatever Valued Senior Member

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    It's not that it's difficult, it's just expensive when scaled up to the needs of a growing city. So it's not the first choice of a way to supply anyone's water needs. But it is an option that can be used if your back is up against the wall. As water becomes more scarce driving up it's price, the option to desalinate will become more attractive and common.
     
  21. AlexG Like nailing Jello to a tree Valued Senior Member

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    On Aruba, which is a desert island and has no fresh water sources, world's first land based large size desalination plant based on plate evaporator module


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  22. Aqueous Id flat Earth skeptic Valued Senior Member

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    Cheeeee---yeck!

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    It would be great to see this come to fruition. Availability of clean water ought to be considered a basic human right.

    Excellent. I'll look into that. I have played around with this wondering how it might be done using mostly natural material available to the locals. For example, suppose all they needed to import were rolls of aluminized plastic reflectors and maybe a few basic machine parts. In other words make it as dirt cheap as possible, so it's readily available to as many people as possible.

    The thing I had in mind was a solar collector that uses a gutter made of clay that accepts the reflective sheets and forms a parabolic focus on a pipe -- now it gets dicey -- made of clay also? Maybe glazed? Something that can boil water for starters, without requiring fuel. Once that's worked out, the desalination comes into the reach of just about anyone. I'm not sure how easy it is to find clay in areas that would benefit from this but it was a idea that interested me nonetheless.
     
    Last edited: May 31, 2012
  23. Trippy ALEA IACTA EST Staff Member

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    You can do it even simpler than that with Black polyethylene, clear polyethylene, a large-ish shallow container, a bucket (or similar) and a bunch of rocks.

    Addendum: Here's a slightly more advanced example: http://www.clearwatersolutions.ch/desalination.html
     
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