Removing salt from water

　　Desalination is often seen as an expensive and energy-intensive way to remove salt from water. In Australia - the world’s driest inhabited continent where rainfall has become increasingly erratic - desalination plants treat seawater that can produce almost half of the supplies needed by the major cities.

　　“There is a significant increase in the trend for the desalination market," explained

　　Professor Vigi Vigneswaran from the University of Technology in Sydney. He says the science has growing international value.

　　"Whether we like it or not, with the global warming problems, the desalination will become a very important technology - one of the important technologies - other than the water reuse and storm water harvesting," Vigneswaran said.

　　New techniques

　　One of the projects that researchers in Sydney are pursuing is improving the membranes used in pre-treatment systems in desalination plants.

　　These thin films often become clogged, reducing their efficiency and increasing the amount of energy used to take the salt out of seawater.

　　The team in Sydney is developing new biological filters that do not become so congested and will not need chemicals that absorb contaminants.

　　Researcher Christian Kazner says more effective filtration will cut energy usage.

　　“Membranes are very sensitive to everything which is contained in the water," noted Kazner. "It will be stopped by the membrane and grow on the surface of the membrane, whether it is salts, you have scaling, it is blocked. Or whether it is organic contaminants they really collect on the surface and if you have microbes they can grow on that organic material. As much as you remove those contaminants before you filter it you improve the performance of the membrane, you reduce the energy demand and finally you can extend the lifetime of the membrane.”

　　Forward osmosis

　　While conventional desalination systems rely on a process called reverse osmosis that uses pressure to force water through membranes, work is also being done on an alternative process. Forward osmosis needs far less energy and allows water to effectively be sucked through the filters.

　　Scientists in Sydney believe this method could reduce energy consumption in the desalination process by up to 90 percent.

　　Other projects being developed include mobile salt-removal systems for remote Aboriginal communities where supplies from groundwater wells are contaminated by high concentrations of saline and nitrates.

　　The aim is to export ideas and innovation overseas, especially smaller desalination units for use in developing countries, where safe and sustainable water supplies remain a distant dream for many.