Desalination: The Natural Water Cycle Of Water Distillation

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Desalination as a natural phenomenon has occurred on earth for millions of years. The natural distillation cycle of water evaporating from the sea and then condensing to form pure rain water is probably the most obvious example of this phenomenon. Aristotle describes the natural water cycle as follows (Hanbury, 1993):
The sun, moving, as it does, sets up processes of change and by its agency, the finest and sweetest water is every day carried up and is dissolved into vapor and rises to the upper region, where it is condensed again by cold and so water is formed, which falls down again to earth. Salt water evaporated forms fresh, and the vapor does not when it condenses, condense into seawater again.

The other desalination phenomenon that occurs in nature is the freezing of seawater near the polar region. The ice crystals formed are pure water, the salt being excluded from participation in the crystal growth. Desalination has been practiced in the form of distillation for over 2000 years. It is not until the eighteen century A.D, for people to recognize that the distillation process could be enhanced by cooling the condensing surface. In the eighteen century A.D., Jaber Ibn Hayyan, an Arabic scientist, wrote a major treatise on distillation (in the context of perfumery) which contained the first reference to water-cooled condensation. However, there appears no evidence of the idea being applied to seawater distillation for another thousand years (Hanbury, 1993).

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