MORE INFORMATION- Water

Desalination

Desalination refers to the process that removes excess salt and other minerals from water in order to obtain fresh water suitable for animal consumption or irrigation, or, if almost all of the salt is removed, for human consumption.  Sometimes table salt is produced as a by-product of this process.  Desalination of ocean water is practiced in many countries that have little to no natural freshwater supplies such as the Middle East, the Caribbean, parts of the United States, North Africa, Singapore, Spain, Australia and China.  It is also used on many ships and submarines that cannot store large amounts of fresh water.

A desalination plant separates salt water into two parts.  One part has a low concentration of dissolved salts (the fresh water) and the other contains the remaining dissolved salts (the brine).  The plant requires energy to operate and can use a number of different technologies for the separation process.  The amount of water discharged as brine waste varies from 20 to 70 percent depending on the technology used and the initial salt content of the water.

The desalination process is quite expensive and it uses a lot of energy.  It also produces a very concentrated waste stream of brine (salty water) which has to be disposed of responsibly.  Desalination is generally a last resource only implemented when all other options have failed or are not available.  The most common, modern methods of desalination are thermal processes and reverse osmosis (RO) although there is an increased trend to RO due to the advances in this technology in the last 10 years.

As Australia has been severely affected by both drought conditions and changes in rainfall patterns, a great deal of attention is now focused on new sources of water to supplement traditional supplies.  One of the alternative sources is desalination and it has been advocated, and seriously considered, for many applications and can provide drought proofing for water short areas.



Figure 1:  The RO Desalination Process  (Source:  http://www.awa.asn.au/)