High pressure for pure water

Sunday Times
20/05/2007 Page: 69

THE desalination plant planned for Binningup will operate on the same principles as the Kwinana plant. The Kwinana plant is powered by a wind farm 200km north of Perth, near Cervantes, but a renewable energy source has yet to be identified for the new plant.

Desalination uses reverse-osmosis to remove salt from water under high pressure. Sea water is collected in an onshore wet-well below sea level. It is then pumped to a reverse-osmosis system via a pre-treatment system that adds chlorine to remove biological matter. The chlorine is then neutralised so that it does not hinder the reverse-osmosis process. High-pressure pumps pressurise the sea water so that its molecules diffuse through a fine membrane that removes the salts and impurities.

Finally, the water is treated with lime and carbon dioxide to make it suitable for drinking and stored in a giant 12 megalitre tank that holds two hours of production. From there, it is pumped to the integrated water-supply system. A total of 144 megalitres of water a day can be pumped into Perth's water system.

The highly salty seawater concentrate produced as a byproduct of the process is pumped back into the sea via diffusers to minimise environmental impact. Critics of the first desalination plant were particularly sceptical of the final process, fearing that the concentrated salt water would prove hazardous to marine life. Their fears have so far proved unfounded, however, with investigations showing marine life in Cockburn Sound largely unaffected by the desalination plant.