Sydney, Australia desalination plant
A longstanding dream of water users in arid areas close to the ocean and other salt water bodies has been the easy and cheap desalination of salty water. Desalination is possible by the ancient process of distillation and capture of the salt free steam for condensation, but that process is energy intensive and thus only useful when small amounts of water are needed or energy is really cheap. A technology called flash distillation has allowed energy requirements to be lessened somewhat. A quite different technique called reverse osmosis uses special filters and pressure differentials to desalinate water, a common technique for small plants but also used in large ones. It is claimed to use less energy than flash distillation. Both flash distillation and reverse osmosis require expensive facilities. The Sydney plant shown above cost A$1.7 billion (Puroserve).
Saudi Arabia is the largest user of desalinized water, and nearly 3/4 of the water consumed in Saudi Arabia is desalinated, using a little of its ample supplies of petroleum and natural gas to power flash distillation facilities. Some of the distilled water is also used for agricultural irrigation in the extremely arid portions of the theocratic kingdom. Even oil rich Saudi Arabia is now looking for other energy sources to desalinate water and has contracted for a solar powered plant, sunshine being abundant in the Saudi desert. Most Saudi plants are close to the coast, but a few also operate in the interior using salty ground water.
The city of Sydney in Australia recently brought a large desalinization plant online, a reverse osmosis facility capable of meeting about 15 per cent of the city's water demand. The plant was built and is operated by the Paris based Veolia corporation (formerly Vivendi Environnement, having been spun off from Vivendi. Prior to 1998 Vivendi was known as Compagnie Générale des Eaux (Wikipedia)). Veolia sells water supply and management services to a number of cities around the world. Growing populations, climate change, and inadequacies of current supplies have prompted several coastal cities in various countries, including Santa Barbara, California, to use one or another type of desalination to meet part of local demand.
A crucial issue in desalination is the disposal of the brine resulting from the process. Much saltier than sea water, the brine can be toxic to marine life when dumped undiluted into the ocean.
The same processes used to desalinate sea water can also be used to purify sewage and other contaminated water, but the problems of energy demand and waste disposal remain. For the next few decades desalination is likely to remain a small source for human water supplies, limited to energy rich regions and to places where the price of water is high enough to justify the costs per liter supplied.
