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Science Forum

  1. Standard member sonhouse
    Fast and Curious
    12 Jul '11 12:43 / 4 edits
    Turning one cubic meter of water into steam requires about 10 kilowatt hours of energy (about 250 gallons). Using reverse osmosis cuts that down to about 4 kwhr.

    This new method, actually more of a refinement because I used the same concept at the cleanroom I worked at to make DI water, an ionization process that uses electric fields to separate salt from water.

    In this case, the energy required goes down to 1.5 kwhr per cubic meter of seawater.

    For that 250 million gallon number, it would need a power plant running about 175 megawatts continuously to get that much water in a year. That would generate about 700,000 gallons per day.
    http://www.physorg.com/news/2011-07-desalinating-seawater-minimal-energy.html

    So to get 250 million gallons would require about 1.5 gigawatt hours of energy as opposed to 4 gigawatt hours for reverse osmosis and 10 gigawatt hours for steam.

    That would take a powerplant of about 175 megawatts 24/7 and would generate about 600,000 gallons a day of fresh water. So if a nuclear power plant running 2 gigawatts were used you could generate over 6 million gallons a day.
  2. 12 Jul '11 12:45
    That is good news, especially considering the looming water shortages in some parts of the world.
  3. Standard member sonhouse
    Fast and Curious
    12 Jul '11 13:50
    Trying to figure if those numbers are right. It says 1.5 kilowatt hours to make 1 cubic meter. 1 cubic meter is about 250 gallons. You can get 1.5 kilowatt hours by running about 65 watts continuously. So it sounds like the power of a light bulb can give you 125 gallons per day per person.

    A wiki piece says NYC uses about 110 gallons per day per person of fresh water. So 65 watts times 10 million sounds like it needs about 650 million watts running continuously. So one nuclear power plant looks like it could make enough water for the whole city.

    Can you verify my numbers?
  4. Standard member uzless
    The So Fist
    13 Jul '11 17:31
    Originally posted by KazetNagorra
    That is good news, especially considering the looming water shortages in some parts of the world.
    Salt water is like oil today.

    Soon, we'll be taking salt water and sending it to a "refinery" to make fresh water and then pipe it across the country to "distribution centres" where it will then be piped into your home via municipal pipes.
  5. 13 Jul '11 20:18
    Originally posted by uzless
    Soon, we'll be taking salt water and sending it to a "refinery" to make fresh water and then pipe it across the country to "distribution centres" where it will then be piped into your home via municipal pipes.
    All that already happens except that we start with river water not salt water. But treatment and piping is already in place.
  6. Standard member sonhouse
    Fast and Curious
    14 Jul '11 20:13
    Originally posted by twhitehead
    All that already happens except that we start with river water not salt water. But treatment and piping is already in place.
    The river part is going away in the midwest USA, the Ogallala aquifer is fast disappearing due to over use. That aquifer is the last dregs of the last ice age when much of western Canada was a giant lake ten times bigger than the Great Lakes, it all drained out to become the Ogallala aquifer.

    It's ironic the dust bowl years would not have been a big deal if they had just known there was trillions of gallons of water for the taking right beneath their feet.

    Of course that would have just used it up that much sooner but it would have saved a lot of people their farms.

    If it takes a gw to make enough water for 10 million people then it would be something like 30 or 40 gw for the whole country.
  7. 14 Jul '11 21:01
    Originally posted by sonhouse
    If it takes a gw to make enough water for 10 million people then it would be something like 30 or 40 gw for the whole country.
    But that is presumably for personal use only. Surely the big users of water are not households?
  8. 14 Jul '11 21:05
    Originally posted by sonhouse
    The river part is going away in the midwest USA, the Ogallala aquifer is fast disappearing due to over use. That aquifer is the last dregs of the last ice age when much of western Canada was a giant lake ten times bigger than the Great Lakes, it all drained out to become the Ogallala aquifer.
    I thought the Mississippi flooded this year? Can't they find a way to put the Mississippi water into the aquifer? Surely cleaning Mississippi water is cheaper than desalinating sea water.
  9. 14 Jul '11 22:46
    Originally posted by twhitehead
    But that is presumably for personal use only. Surely the big users of water are not households?
    households are one of the biggest users of drinking grade water.
    Most industries use less purified water, some can and do happily use pure sea/river water.
    where the same source is used for both there is obviously conflict, but if you are going to the trouble of desalinating sea water you expect the results to be drunk not used in industry...

    That said, in most of the western world we use vastly more expensive purified drinking water showering, bathing, dish-washing, and flushing the lavatory than actually drinking.

    This is both easy and highly beneficial to fix.

    Also bear in mind desalination is usually there to make up the difference between consumption and supply, rather than being the sole supply. Few if any countries would want or need to produce all there water via desalination.
  10. Subscriber AThousandYoung
    Do ya think?
    14 Jul '11 23:50
    Irrigation is the big one I thought.
  11. 15 Jul '11 07:31
    Originally posted by googlefudge
    but if you are going to the trouble of desalinating sea water you expect the results to be drunk not used in industry....
    I do not see why that should be the case.
    If more fresh water is required than is available you use desalination. I see no reason why the resulting water should be used for drinking only.

    That said, in most of the western world we use vastly more expensive purified drinking water showering, bathing, dish-washing, and flushing the lavatory than actually drinking.

    This is both easy and highly beneficial to fix.

    Now that, I agree with.

    Where I come from (Livingstone) almost half the water that is purified is actually lost in pipe leaks before it even gets to the houses. Its so bad that they turn the water off at night to reduce the waste.
    Here in Cape town our garden is watered using non-purified water.
  12. Standard member sonhouse
    Fast and Curious
    15 Jul '11 17:20
    Originally posted by twhitehead
    I thought the Mississippi flooded this year? Can't they find a way to put the Mississippi water into the aquifer? Surely cleaning Mississippi water is cheaper than desalinating sea water.
    The aquifer is a LOT bigger than anything the Mississippi river could refill. It came from thousands of years of ice age glacier melt. Like I said, at the end of the last ice age and ones before that, much of central Canada became a huge system of fresh water lakes that slowly drained away underground to fill the aquifer. Even if we diverted 100 percent of the Mississippi, it would only be a stop gap measure. The Mississippi is due to rainwater collecting in the midwest, not the vast melting of continent sized mile deep ice caps.
  13. Subscriber AThousandYoung
    Do ya think?
    15 Jul '11 20:25
    Originally posted by sonhouse
    The aquifer is a LOT bigger than anything the Mississippi river could refill. It came from thousands of years of ice age glacier melt. Like I said, at the end of the last ice age and ones before that, much of central Canada became a huge system of fresh water lakes that slowly drained away underground to fill the aquifer. Even if we diverted 100 percent of ...[text shortened]... rainwater collecting in the midwest, not the vast melting of continent sized mile deep ice caps.
    Maybe global warming will help.
  14. 16 Jul '11 10:07
    Originally posted by sonhouse
    The aquifer is a LOT bigger than anything the Mississippi river could refill. It came from thousands of years of ice age glacier melt. Like I said, at the end of the last ice age and ones before that, much of central Canada became a huge system of fresh water lakes that slowly drained away underground to fill the aquifer. Even if we diverted 100 percent of ...[text shortened]... rainwater collecting in the midwest, not the vast melting of continent sized mile deep ice caps.
    But the problem is that we are using water from the aquifer, whilst allowing fresh water to flow into the sea in the Mississippi. What we need is better farming practices that reduce runoff or other ideas to store the Mississippi water rather than wasting it.
    On reading up on the aquifer I see farmers are already being less wasteful of aquifer water because they realize it is a non-renewable resource.
  15. Standard member sonhouse
    Fast and Curious
    16 Jul '11 20:26 / 2 edits
    Originally posted by twhitehead
    But the problem is that we are using water from the aquifer, whilst allowing fresh water to flow into the sea in the Mississippi. What we need is better farming practices that reduce runoff or other ideas to store the Mississippi water rather than wasting it.
    On reading up on the aquifer I see farmers are already being less wasteful of aquifer water because they realize it is a non-renewable resource.
    Damming up the Ms river could help but it is also very silty, not sure how well it could do for farming irrigation. Maybe it would be a good thing but it for sure would never replace the Ogallala, it just covers too much territory.

    I think it is too little too late for any real help in terms of conservation.

    If the climate warmed up enough to melt ice caps we would be in deep shyte doo doo much more than any help from replacing the water in the aquifer. The whole midwest would turn into another dust bowl which would not just recover in ten years like last time.

    To say nothing of the loss of coastal cities, Manhattan, Miami, Los Angeles, at least Santa Monic/Venice beach (My stomping grounds) Anchorage, where I went to high school, Japan, a lot of Islands like the Bahama's, Burmuda, etc.

    BTW, a recent study of the last major heating cycle, besides losing all the polar ice, caused deserts in half the world and lasted 200,000 years before some kind of reset occurred that brought things back to what we would call normal. That was 55 million years ago, 10 million years AFTER the dinosaurs got whacked.