Methods for Desalination

Methods for Desalination
••• Tom Arthur, gil278, R. Penny, Will Etling, Matt Reinbold, and John Trainor available at Flickr.com

Primary methods of desalination, or removing salt from water, include thermal processes, such as distillation, and membrane processes, such as reverse osmosis and electrodialysis.

Function of Desalination

Desalination drilling rig

Desalination is the process of removing salts from seawater to provide purified water for industry, irrigation and drinking.

Significance of Desalination

Only 1 percent of the earth's water is liquid freshwater; 97 percent of available water resources are contaminated by salt. This makes desalination an essential component of efforts to address water shortages, especially in densely populated coastal regions.

Types of Thermal Desalination

Vapor distillation uses low air pressure to reduce desalination costs

Thermal desalination methods include vapor distillation, multistage distillation and multiple-effect distillation. Thermal methods of desalination boil water and collect purified water vapor.

Types of Membrane Desalination

Diagram of reverse osmosis method of desalination

Membrane methods of desalination include reverse osmosis and electrodialysis. Membrane processes use selective permeability to separate salts and water.

Other Types of Desalination

Freezing is an alternate desalination method

Other methods of desalination include freezing, solar dehumidification and membrane distillation (a combination of thermal and membrane methods).

Considerations When Choosing a Method of Desalination

Windmills providing green energy for desalination plant

Thermal methods require a large input of energy to heat the water. Membrane methods of desalination require energy for mechanical processes. Reverse osmosis is the most cost effective in many applications. Other considerations include the degree of purity required, scale of production and cost of chemical pretreatments.

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