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The Magic Of Water Desalination

What do Perth, Saudi Arabia and cruise ships have in common? They all rely on desalination for fresh water. And the Gold Coast, Sydney and Adelaide are about to join the club!

by Geoff Graham

Turning salty water into fresh, drinkable water is not new. In the early Australian gold rush days large areas of woodlands were stripped to feed “condensers” that boiled salty water and trapped the condensation for sale to thirsty miners.

Click for larger image
Fig.1: the layout of a typical desalination plant. It looks simple - salt water is filtered and passed through the reverse osmosis process. However, as with most things, the reality is more complex with the magic happening in the reverse osmosis section. (courtesy Sydney Water)

These days a large cruise ship will generate over a million litres of water a day from the sea using either flash evaporators or reverse osmosis, while Middle East countries such as Saudi Arabia produce over 70% of their drinking water using various forms of desalination.

Australia is not left out. The advent of a drying climate has triggered a flurry of desalination plants either planned or under construction with the first in Perth, Western Australia, running since 2006.

There are a number of technologies used for desalination but most modern large scale plants are based on reverse osmosis.

These plants are expensive to build but, in the longer term, cheaper to run. This technology is quite recent – it only got its start in the 1970s and 1980s when efficient reverse osmosis membranes were first manufactured in quantity.

In Australia

Small desalination plants have been operating across Australia for many years, providing drinking water for towns such as Penneshaw, Coober Pedy and Marion Bay in South Australia.

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