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. KilljoyKlown Whatever Valued Senior Member

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    I won't vote for it because I don't want to pay for it, even if it was possible.
     
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  3. Saint Valued Senior Member

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    In China, some places got too much rainfall and caused flood, while other place were hit by draught,
    how can we channel the flood water to the draught area for irrigation and processing it into drinking water?
     
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  5. Billy T Use Sugar Cane Alcohol car Fuel Valued Senior Member

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    China is well aware of this fact and is building large ID pipeline (and needed pumps) to move vast amounts of fresh water from the wet south to the dry north.
     
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  7. Trippy ALEA IACTA EST Staff Member

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    In fact they have been aware of it since at least 256 BCE.

    Dujiangyan Irrigation System
     
  8. Billy T Use Sugar Cane Alcohol car Fuel Valued Senior Member

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    That is a very local irrigation project, smaller than one being built in Brazil (or existing in other countries) but China´s South-North Water Transfer Project is unique in the world – Far larger than any other.

    It will remove nearly 36 billion cubic metres of water every year from the Yangtze River Basin – which drains much of the nation’s central and western regions – and ship it to the arid North some 3,000-kilometres (1,900 miles) away!

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    Those pipes are 8.5 meters in ID – 18 wheeler trucks can easily drive thru while they are dry!

    If scheduling and operations projections are accurate, in 2014 some 13 billion cubic metres (3.4 trillion gallons) of water per year will pour through the tunnels of the central line, under construction in Henan Province, and will be sent north to help curb water shortages in more than a dozen cities, including Beijing. The eastern line, a second transfer project, should already be operating by then, transporting 14.8 billion cubic metres of water annually from the lower Yangtze River to Tianjin.

    PS it is no all pipes and tunnels - where they can they use large canals. Perhaps that is why "remove nearly 36 billion cubic metres of water every year " ends up as only 28 billion m^3 delivered to N. China?
     
    Last edited by a moderator: Jun 10, 2012
  9. Trippy ALEA IACTA EST Staff Member

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    I know.

    But it's 2200 years old, and it still manages to do what Saint was talking about, even if only on a local scale.
     
  10. Billy T Use Sugar Cane Alcohol car Fuel Valued Senior Member

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    Chinese irrigation is less than half as old as that practiced in Egypt:

    “… The Egyptians practiced a form of water management called basin irrigation, a productive adaptation of the natural rise and fall of the river. They constructed a network of earthen banks, some parallel to the river and some perpendicular to it that formed basins of various sizes. Regulated sluices would direct floodwater into a basin, where it would sit for a month or so until the soil was saturated. Then the remaining water would be drained off to a basin down-gradient or to a nearby canal, and the farmers of the drained plot would plant their crops.

    The earliest evidence of water control in ancient Egypt is the famous historical relief of the mace head of Scorpion King which dates to around 3,100 BC. It depicts one of the last predynastic kings, holding a hoe and ceremoniously cutting a ditch in a grid network. Besides attesting to the importance of these waterworks and the great ceremony attached to them, this picture confirms that Egyptians began practicing some form of water management for agriculture about 5,000 years ago.
    Overall, Egypt's system of basin irrigation proved inherently more stable from an ecological, political, social, and institutional perspective* than that of any other irrigation-based society in human history. …”

    From: http://www.waterhistory.org/histories/nile/t1.html

    But you are correct, China was redirecting water locally a long time ago, just not the first to do so.

    * It was locally managed by the farmers using it, not by a distant government. There is little accumulation of salts as they are transported deeper into the earth by the fresh water standing on the dirt for many weeks.
     
    Last edited by a moderator: Jun 10, 2012
  11. Saturnine Pariah Hell is other people Valued Senior Member

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    A: All that is a process of creating ground water and most aquifers are threatened by pollution or are being overused. Aquifers are fossil water reservoirs.
    B:The Glaciers are already melting at an alarming rate...why take more away from that?
    C: The amount of energy need to perform this task would be counter-productive to the already exisiting energy crisis. Then you would have to develope wells, filtration and(if owned by a private company) would be distrubed via plastic bottles at fixed prices.
     
  12. Trippy ALEA IACTA EST Staff Member

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    I don't recall even suggesting that they were, although I'm not convinced of which is older at this point. Yes, the egyptian examples predate the cited example, but the cited example isn't neccessarily the oldest in China.

    The point I was addressing was specific to the chinese diverting floodwaters to irrigate dry areas. I was addressing this specific point, by pointing out that the idea is not new in China, and that it has been done on a large scale in the past.
     
  13. iceaura Valued Senior Member

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    There are remains of a very old aqueduct system that tapped mountain melt floodwaters for coastal agriculture, in Peru (3-5 kBP). They are so old and were so successful for so long they (and their dependent civilizations) fell victim to geological uplift.

    There are archeological sites more than 3000 years old showing irrigation systems for moving captured rainwater and aquifer water from wells many miles ("50 km") in Iran and other places in that general area http://www.google.com.au/url?sa=t&r....org/English/GetFilePublication.aspx?FilePrm%

    Getting dissolved salt out of water means pushing against the 2nd Law in one of its most thorough applications. That's going to cost somebody, or something, a lot of energy.
     
    Last edited: Jun 11, 2012
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