Desalination
Potable water can be made from sea water, through a process known as desalinationThe removal of salt from water. This is an energy-intensive process. Also known as desalinisation.. It is preferable to make potable water from fresh water reserves rather than from sea water. This is because removing the large amount of salt (35 grams in every kilogram of sea water) requires a lot of energyThe capacity of a system to do work or the quantity required for mechanical work to take place. Measured in joules (J). For example, a man transfers 100 J of energy when moving a wheelbarrow..
Desalination can be done by distillationA separation technique which involves a solution being heated so that the solvent evaporates before being cooled to form a pure liquid. and by reverse osmosisA method of purifying water by forcing it under pressure through a membrane which has tiny holes in it. The molecules of water pass through the holes but most ions and molecules of dissolved substances do not pass through..
Distillation
Sea water is heated until it boils. The salt remains in the liquid, and the steam is pure water. The steam is cooled and condensed to make potable water.
Distillation requires a lot of energy to boil the water, and also to cool the steam down to condense it. The waste water is very salty and can be difficult to dispose of in a sustainableAn activity which does not consume or destroy resources or the environment. way which does not harm marineThings that are associated with the sea. ecosystemA community of animals, plants and microorganisms, together with the habitat where they live..
Reverse osmosis
Water is put under high pressure and passed through a membraneA very thin layer of tissue. which has tiny pores (holes) in it. The pores allow water moleculeA collection of two or more atoms held together by chemical bonds. through, but prevent most ionElectrically charged particle, formed when an atom or molecule gains or loses electrons. and molecules from passing through. Reverse osmosisThe movement of water molecules across a selectively permeable membrane from a region of higher water concentration to a region of lower water concentration. requires expensive membranes and also produces a large volume of waste water, so its efficiencyThe fraction of the energy supplied to a device which is transferred in a useful form. is often quite low.
Question
Which method of water purification would be best suited to a country in the Middle East which has a large amount of fossil fuel reserves?
Distillation would be the most appropriate method of desalination because the country would be able to use fossil fuels to provide the energy needed to boil and condense the water at a relatively low cost.