Desalination refers to any of several processes that remove the excess salt and minerals from water in order to obtain fresh water suitable for animal consumption or for irrigation, sometimes producing table salt as a by-product.

One way to remove brine from the water is putting water under pressure and pumping ethane through it. Almost immediately crystals appear at the top made of pure water and ethane. These crystals can be melted and then the water allowed to go into a container. Because of the structure of the molecules of this substance it only picks up water and ethane, leaving the salt behind.

Desalination for brackish water is already commonplace in the U.S., where it is used to meet treaty obligations for river water entering Mexico. Indeed, desalination has spread into use in over a hundred countries, with Saudi Arabia accounting for about 24% of total world capacity.

Methods of Desalination are:

1. Distillation
   1. Multi-Stage Flash
   2. Multiple-Effect
   3. Vapor Compression
2. Electrodialysis
3. Reverse osmosis
4. Freezing
5. Membrane Distillation
6. Solar Humidification

As of 1998, the two leading methods were Multi-Stage Flash Distillation (44%) and Reverse Osmosis (42%).

Distillation of ocean water is common in the Middle East, on ships, submarines and islands. The process used in these operations is essentially the boiling of water at less than atmospheric pressure, and thus a much lower temperature than normal. Due to the reduced temperature, energy is saved, however, bacteria are not killed therefore additional water processing is necessary before the water can be used by the public.

Kuwait built the world's first large-scale desalination plant in the 1960s. Kuwait's energy reserves are so great, that Kuwait is alone of desalination using countries in using desalinated water for agriculture.

The price of desalination is rapidly declining. A modern, large, efficient plant is within 20% of the cost of developing a new, local source of fresh water. Desalination stills now control pressure, temperature and brine concentrations to optimize the water extraction efficiency. Nuclear-powered desalination could be very economical on a large scale.

From an environmental point of view, desalination is preferable to using fossil groundwater or surface water for human needs. However, desalination is not without all environmental drawbacks. Most desalination plants produce hypersaline brine that must be disposed of. The hypersaline brine has the potential to harm marine ecosystems.

See also: Soil salination

References

The ABCs of Desalting