Scheduled for commissioning in September 2006, this new plant - the largest of its kind in the southern hemisphere - will ultimately supply 17% of Perth’s needs and make Western Australia the country’s first state to use desalination as a major public water source.

With an initial daily capacity of 140,000m³ and the inbuilt potential for expansion to 250,000m³/d, the plant will be the largest single contributor to the area’s integrated water supply scheme, providing an annual 45GL and serving a population of 1.5 million.

The contract was awarded by the Water Corporation of Western Australia to the Multiplex Degrémont Joint Venture in April 2005. The project is to be executed under an alliance arrangement, implemented in two phases covered by separate design / construct and operate / maintain contracts. The operational phase of the contract runs for 25 years.

In addition to the design, construction and operation of the plant itself, the project also involves the provision of a seawater intake, pre-treatment and product water facilities, a pipeline and a new pumping station.

The total project cost is AU$387 million, with annual running costs of less than AU$20 million. The anticipated water cost has been estimated at AU$1.17/kL.

BACKGROUND

Growing concern over the dwindling natural supplies of water across the region in the wake of the hotter, drier shift in the climate acted as the main driver on the project. The winter of 2001 saw the poorest inflow of water to the reservoirs serving the Perth metropolitan area since 1914 and by 2002 it was clear that the region was suffering the worst two-year drought on record. In 2005, it was confirmed that in the eight years from 1997 stream flows had dropped to an annual average of 115GL compared with the 161GL/yr over the previous 23 years (1974 to 1997).

The initial response was to implement a medium-term drought recovery plan, which included restrictions on sprinkler use, obtaining a temporary increase in groundwater allocation and the provision of $142 million to further augment supply capacity.

This led to the construction of three bores into the Yarragadee aquifer deep below Perth’s northern suburbs and a further nine into the shallower aquifer at Mirrabooka. Two new dams were also constructed in the South West, where rainfall is naturally more plentiful - at Samson Brook and Wokalup Creek.

By 2004, these combined initiatives had added nearly 40GL of water to the municipality’s integrated supply system.

To safeguard the future of supply in the longer term, the Water Corporation have adopted what they have termed a ‘security through diversity’ strategy. This approach comprises seven key platforms - water trading with irrigators, water recycling, enhanced catchment management, demand management, new groundwater, new surface water and the construction of the new desalination plant.

SEAWATER REVERSE OSMOSIS (SWRO) PLANT

The new facility uses seawater reverse osmosis (SWRO) technology and is being built in the heavy industrial centre of Kwinana, close to the recently completed Water Reclamation Plant, some 25km south of Perth.

Competitive tendering for the new plant design began in September 2004 between pre-qualified consortia and bids were received the following February. In April 2005, the contract for the plant was awarded and construction began almost immediately, with work beginning on the pumping station in May and pipeline construction in September.

The Cockburn Sound is an area of environmental sensitivity and the potential impact of the new plant on this water has been the subject of extensive consideration, with strict monitoring conditions imposed on TDS, temperature, DO and the sediment habitat in the vicinity.

The plant will operate continuously, drawing water with an input salinity of 35,000mg/L to 37,000mg/L at 16°C to 24°C via the new intake structure. This will amount to under 0.02% of the water in the sound being removed per day, which will first pass through a pre-treatment filter to protect the pores of the membranes, before being forced through the spiral wound membrane elements of the RO treatment trains.

After treatment, the product water will be treated with lime, chloride and fluoride before being stored and ultimately blended with water from other sources and entering the municipal integrated supply system. The filter backwash and concentrate stream will be returned to the Sound.

Although the concentrate flow will be about 7% salt, the discharge nozzles are designed to act as diffusers, ensuring that mixed water salinity will fall to less than 4% within 50m of the discharge point. As a result, there will be less than 1% increase in the salinity of the receiving waters.

Electricity for the desalination plant - which has an overall 24MW requirement and a production demand of 4.0kWh/kL to 6.0kWh/kL - will come from the new 80MW Emu Downs Wind Farm. The wind farm, which will consist of 48 wind turbines and be located 30km east of Cervantes, is being developed by Stanwell Corporation, a power generation corporation owned by Queensland Government and Western Australia’s Griffin Energy.

The power supply arrangement between the Water Corporation and Western Power as energy suppliers will ultimately make the desalination plant the largest facility of its kind in the world to be powered by renewable energy.

When the plant begins operation in October 2006, it will provide a third water source for Perth, parts of the South-West and towns serviced through the Goldfields Pipeline to Kalgoorlie Boulder and complement existing dams and groundwater schemes.

KEY PLAYERS

The client and plant owner is the Water Corporation of Western Australia. The main contractor is the Multiplex-Degrémont JVC and the plant operators will be Degrémont over the 25-year life of the contract.

McConnell Dowell Constructors have the subcontract for the mechanical installation works. Western Power are the energy suppliers, using renewable power from the wind farm developed by Stanwell Corporation and Griffin Energy.