Desalinisation
From Simple English Wikipedia, the free encyclopedia
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[citation needed] 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]
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[edit] 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.
[edit] Considerations
[edit] 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.
[edit] Economics
The cost of building and running desalination plants depends on many factors, such as how big a facility one wants to build, and where the facility is. It is less expensive to run a desalinization plant right beside the ocean than in a town that is 1000 km inland, because the inland plant would have to pump the seawater to the plant.
For a very large desalinization plant, it might be economical to use Nuclear-powered desalination. There is a pilot plant in the former USSR.[3]
Desalination technologies are very expensive, especially for poor third world countries. It is also expensive to transport massive amounts of desalinated seawater throughout the interiors of large countries.
As well, desalinization plants produce toxic waste. The saline brine produced by desalinization plants causes marine pollution.[4]. Desalinated water is also expensive in places that are far from the sea and somewhat high.
[edit] Environmental
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.
[edit] 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.
[edit] References
- ↑ [1]
- ↑ Source: 2004 IDA Worldwide Desalting Plants Inventory Report No 18; published by Wangnick Consulting
- ↑ [2]
[edit] External links
- 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