How a Desalination Plant Works

Ocean water is too salty to drink--unless the salt is removed first.

Desalination is the process of removing salt from saltwater. According to The Economist, desalination requires a great deal of electricity and is often expensive. Nonetheless, interest in desalination has grown in recent years as cities and governments in arid regions seek new sources of water.

Types

Desalination can be accomplished by one of two processes: distillation or reverse osmosis. Both processes achieve the same end result but work differently. Other processes have been proposed but remain experimental at this time.

Function

In the distillation process, seawater is evaporated or turned into water vapor, leaving the salt behind. The water vapor is then condensed to form pure water. Typically this process takes place at reduced pressure in order to decrease the boiling point of the water. The reverse osmosis approach involves forcing seawater at high pressure through semipermeable membranes, typically made from thin film composites. The pore size in the membranes is such that only water molecules can pass through, so the substances dissolved in the seawater are left behind. Reverse osmosis often involves a pre-treatment step like microfiltration.

Impacts

Desalination enables us to tap into an inexhaustible supply of water--the ocean. It can also act as a potential source for cities in desert regions that lack access to rivers or lakes. On the other hand, desalination can have local environmental impacts, especially if the salty brine created as a byproduct of the process is not handled properly. Desalination can also be expensive and energy-intensive, so whether or not it's the best solution may depend on local priorities and resources.

References

• Organization of American States: Desalination by Reverse Osmosis
• The Economist: Cheaper Desalination