Desalinisation

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Desalinisation is a name used for various processes. These processes take most of the salt or minerals out of seawater. They are used to make fresh water which is either good for irrigation (watering crops), or as drinking water for animals, and humans.

Desalinisation of ocean water is common in the Middle East, where there are very few natural springs. It is also common in the People's Republic of China^{[needs proving]} It is used also on ships, submarines and islands in the sea.

The United States desalinized the brackish water (salty water) in rivers that flow into Mexico. The United States has signed treaties with Mexico that oblige the United States to desalinize the water.

Several Middle Eastern countries have so much energy that they use desalinated water for agriculture (farming). Saudi Arabia's desalination plants account for about 24% of total world capacity. The world's largest desalination plant is the Jebel Ali Desalination Plant (Phase 2) in Saudi Arabia. It can produce 300 million cubic meters of water per year.^[1]

Contents 1 Methods 2 Considerations 2.1 Cogeneration 2.2 Economics 2.3 Environmental 3 Experimental techniques and other developments 4 References 5 Other websites

[change] Methods

There are three basic ways to treat the water so it contains less salt and minerals:

• Distillation - Heat the water until it boils and evaporates, which leaves the salts and minerals behind.
• Filtering with membranes. The membrane acts like a sieve.
• Freezing the water
• Use geothermal energy (energy from the ground) to treat the water.

In 2004, the two leading methods for desalinization were Reverse Osmosis (47% of installed capacity world-wide) and Multi Stage Flash (36%).^[2]

The traditional process used in these operations is vacuum distillation, which means boiling of water at less than atmospheric pressure, and thus a much lower temperature than normal. Due to the reduced temperature, energy is saved.

In the last decade, many desalization plants have begun using membrane processes. Reverse Osmosis (R.O.) has taken nearly half the world's installed capacity. Membrane processes use semi-permeable membranes to filter out dissolved material or fine solids from the water. The systems are usually driven by high-pressure pumps.

Forward Osmosis (F.O.) uses a membrane filter. Water is driven across the membrane by osmotic pressure. Forward osmosis systems require no energy inputs. They are used for emergency desalination purposes in seawater and floodwater settings.

[change] Considerations

[change] Cogeneration

Some desalization plants use the same energy more than once. With In the Middle East and North Africa, some facilities to produce both electricity and fresh water. The combined facility consumes less fuel than would be needed by two separate facilities.

[change] Economics

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The building and operation costs of a desalination plant depend on many factors, such as the desalinization method employed, size of the facility and its location relative to an ocean or other salt water source. The characteristics of the particular market in which its product is consumed will also influence its costs and profitability. Desalination technologies are expensive and energy intensive, making the cost of energy another factor in the costs of desalinization.

For this reason, very large desalination plants may employ Nuclear-powered desalinization. There is currently a pilot plant in the former USSR.[3]

Another cost of desalinization is the management of wastes produced by a desalination plant. Marine pollution may result if the saline brine produced is discharged into an ocean or other body of water.[4].

[change] Environmental

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All desalinization methods produce a toxic waste product that the US Environmental Protection Agency has classified as industrial wastes. This toxic waste can harm ecosystems and marine animals.

[change] Experimental techniques and other developments

In the past many new desalination techniques have tried. The U.S. Government trying to invent a method for solar desalination. SDSU CITI International Consortium for Advanced Technologies and Security.^[3] is trying to develop geothermal desalination methods.

[change] References

1. ↑ [1]
2. ↑ Source: 2004 IDA Worldwide Desalting Plants Inventory Report No 18; published by Wangnick Consulting
3. ↑ [2]

[change] Other websites

• Middle East Desalination Research Centre
• Encyclopedia of Desalination and water and Water Resources
• Global Water Intelligence - monthly newsletter featuring 'Desal Project Tracker'
• Water Desalination Report - weekly newsletter on international desal
• International Desalination Association
• Desalination & Water Reuse - Official magazine of the International Desalination Association
• European Desalination Society