Cheaper seawater desalination

Posted on 31 July 2013

By Neil Palmer, CEO

creek bed

Can Perth avoid harsh water restrictions in the drier years forecast as the effects of climate change escalate faster than originally thought across the south-west of Western Australia?

Households in Perth and the South-West must start drinking recycled water within three years or be prepared to pay $1 billion for a third desalination plant within a decade, according to Daniel Mercer’s article Dry climate limits water options in the West Australian on 11 July.

Mr Mercer’s article quotes Peter Moore, Chief Operating Officer of the Water Corporation, who warned Perth’s climate was drying much quicker than predicted and the Government would have to choose another major drinking water source for the city and wider South-West.

The article went on to say Mr Moore suggested a desalination plant would need to produce at least 45 billion litres a year to be efficient (about the same size as the Perth Seawater Desalination Plant at Kwinana) and Perth’s northern water network would need significant upgrades to accommodate it.

Does a new desalination plant need to cost this much?

During the Millennium drought, Australia built six large desalination plants (by world standards) and a potable water recycling system in all mainland state capitals at a cost of more than $12 billion. With the exception of the first (the Perth Seawater Desalination Plant at Kwinana where the cost is around $1.20 per kL) the water produced from Australia’s desalination plants is quite expensive at $US2 to 3 per kL. In fact, it is three to five times more expensive than water produced, for example, in Israel’s five largest desalination plants.

Is there a way we can produce water in Australia from the sea for less than say $US1 per kL? I believe there is.

Rather than just building one 45 billion litre per year desalination plant in the north of Perth, we believe construction and ongoing costs could be significantly reduced if a number of smaller plants were installed along the coast delivering desalinated water into existing water supply systems, reducing large new delivery infrastructure costs.

A number of identical plants would enable a production line approach to construction offering savings and could enable efficient local manufacture of an assembly of reverse osmosis trains, pipework, buildings and electrical controls. Smaller plants could also be staged, and built when needed, reducing the need for large land acquisition and associated environmental and landscaping costs.

There would be low visual and environmental impact with smaller plants able to be located in existing harbour, industrial or commercial areas. They may be able to use beach well intakes where seawater is filtered through natural beach sand or subsurface strata, substantially reducing the need for pre-treatment, which normally requires expensive multi-media or membrane filtration. This has been successfully implemented overseas on large desalination plants at Fukuoka, Japan; Sur, Oman and San Pedro del Pinitar in Spain.

Simple pipe outfalls for return of the concentrate could be built using a small number of diffusers based on the Kwinana operation in Cockburn Sound. This has been demonstrated to have no adverse environmental impact over six years of operation.

It may be possible to reduce the cost of post treatment remineralisation by blending desalinated seawater with the existing mains supply.

In the larger plants, more expensive two-pass reverse osmosis has been used mainly to reduce boron concentration. Although there are no health issues at the levels from seawater desalination, boron is known to adversely affect some horticultural activities, and blending could bring it to within acceptable limits.

Our current large Australian plants are all committed to purchase renewable energy through the power networks which include transmission costs. If the smaller plants had their own small gas-fired alternators, energy costs could be reduced. Indeed, in times of peak power consumption, the desalination plants could be shut down and power supplied to the grid, the higher prices during such periods offsetting normal energy costs.

Adopting all or some of these approaches would almost certainly bring the total unit cost of desalinated seawater to less than $US1 per kilolitre.

In the longer term, populated areas along the lower south-west coastline are likely to also require their own desalination plants. Water supplies for Albany, Denmark, Walpole and Bunbury are also dwindling and may one day need to be augmented by seawater desalination. Lessons learned from the cheaper, smaller scale approach could bring immense benefits.

Further improving the technology and reducing costs is an ongoing challenge for scientists and authorities alike, and “core business” for the NCEDA, but what is certain is the ongoing ability of desalination to provide clean, safe and reliable drinking water whatever the weather – climate resilience on tap.

NCEDA is funded by the Australian Government’s Water for the Future initiative. For further information visit desalination.edu.au and follow @DiscoverDesal on Twitter.

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