Academics pour cold water on pipe dream

20 October 2004

A $680m plan to pipe water from the Shoalhaven district to boost Sydney's water supply should be an option of last resort, according to UNSW's Kensington Group of sustainability specialists.

The Group says localised methods of distribution and treatment are much more energy and cost efficient.

"It's a lot to spend to bolster supplies by only 25 percent, " said Professor Tony Fane of UNSW's UNESCO Centre for Membrane Science and Technology. "It's conceivable that existing conservation measures could reduce demand by about 15 percent. An equivalent amount could be achieved by reclamation of wastewater which could be used for industry and agriculture."

The pipeline plan includes the possibility of desalinating seawater. Professor Fane said that while desalination as a solution has some merit, it too is one of the least appealing options. On a cost basis alone, reclamation of wastewater to a high quality is far cheaper at less than 40c per 1000 litres compared with about 80 to 90c per 1000 litres for the lowest cost seawater desalination. The major difference lies in the salt content of wastewater, which is about 100 times lower than seawater.

"With today's membrane processes, one can end up with reclaimed water of similar quality to seawater desalination, in fact the technology applied is very similar," he said. "While there may be public opposition to using reclaimed water for drinking, it can produce high quality water for use in industry, irrigation and maintaining stream flow in rivers."

Water reclamation and reuse can be done on a large or small scale, and there are potential benefits for the small decentralised approach. Decentralisation means treating and reusing water at the suburb, cluster or even household level. This could involve small treatment plants, such as the compact and efficient Membrane Bioreactor. Following treatment and disinfection, water could be provided for toilet flushing, car washing and irrigation of gardens, parks and golf courses etc. For grey water recycling, even less sophisticated technology would be required.

Such a system, as Professor Waite, the Director of the University's Centre for Water and Waste Technology points out, would require the adoption of more innovative technology and a greater commitment by the community to water conservation.

Professor Nicholas Ashbolt, another member of the Kensington Group and a global expert on water, said communal rainwater capture, treatment and reuse or storage with groundwater offers a good compromise between ready implementation and water saving potential. "As existing buildings are renovated, third pipes supplying such treated rainwater can be introduced for all non-potable household uses," he said.

"Specific areas of Sydney with sewer overflow problems could be approached in a more radical way, such as with the installation of vacuum-flushed toilets and local trenchless technology to reticulate toilet flushings to localised treatment stations, ultimately producing soil amendment.

"The resulting grey water left for the sewer would cause significantly less health risk during overflow periods, and would be readily amenable to inexpensive sand filter treatment at overflow points before release."

The Kensington Group is a high-level sustainability think-tank involving academics from across the University. The group aims to facilitate debate through comment on matters of regional, state and national concern and through industry and public events.