Definition of a Desalination Plant
Desalination refers to a process that removes excess salt from water. Desalination may be utilized for irrigation of arable land, but the primary focus is on making seawater fit for human consumption. Desalination plants are the buildings within which large-scale desalination takes place. Desalination plants are found in many countries, particularly nations with comparatively little precipitation.
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Production
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It is estimated that desalination plants produce upwards of 12 billion gallons of water a day across the world. However, given that the average American citizen consumes 159 gallons of water a day, this is a very small percentage of consumable water. In drier nations, the extent of desalination provision is much higher. For instance, it provides 60 percent of the drinking water in the Gulf States.
Evaporation and Distillation
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The most common way that industrial plants extract salt from water is by large-scale evaporation and distillation. The water is heated in one container. This makes the water evaporate, leaving the solidified salt behind. The vapor is then cooled and condensed back into a liquid in another container.
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Reverse Osmosis
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The second most common form of desalination process is called reverse osmosis. In this method the salty water is forced under pressure through a filter that is fine enough only to allow pure water through. This separates the salt from the water, but also extracts all other minerals as well, such as calcium and magnesium, which may have to be added after the filtration stage.
Oher Processes
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Less common processes used for desalination include electrodialysis, which filters out the salt using membranes and the naturally occurring electrical charges of salt ions, and freezing, because when water crystallizes, it excludes salt.
Drawbacks
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For all of these processes, the biggest drawback is the amount of energy required to perform them. One estimate for a desalination plant proposed for the river Thames in London (completed in 2010 but not yet operational) was that, using reverse osmosis, it would create more than 25,000 tons of carbon dioxide each year. The second major drawback is the effect on marine life, as the intake of ocean water affects plankton levels, the basis of the food chain for all life in the oceans.
Largest
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The largest desalination plant in the world is the Jebel Ali Power and Desalination Plant located on the coast of Dubai in the United Arab Emirates. It produces 140 million gallons of water per day. The desertlike conditions of much of the Arab Emirates has meant great investment in this form of drinking water production. Compare it to the largest in America, where precipitation levels are higher and the need for desalination lower: the Tampa Bay desalination plant produces 25 million gallons a day.
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References
- Photo Credit salt cellar image by Edsweb from Fotolia.com
