Western Australia is a dry state and getting drier by the year: its dams and groundwater can no longer be expected to supply the increasing population of its fast-growing capital, Perth, so the Water Corporation is turning to other climate independent sources. John O’Hanlon speaks to project manager Nick Churchill.
Climate change has seen a dramatic reduction in the stream-flows into Perth’s dams by up to 50 per cent, as a result of a 12 per cent decline in rainfall over the last decade. A severe lack of winter rainfall during 2001/2002 required additional investment in new sources—supply capacity was doubled during this period but looking ahead 50 years, the Water Corporation and the community has a huge challenge. This it defines as “to provide water for all in an even drier climate, with twice as many people and with minimal environmental impact.” One of the key ways it intends to do this, in common with other arid areas of the planet such as California, southern Spain, India and the Middle East, is to give desalination a central role.
The government of Western Australia announced in May 2007 that its next major water source would be a new desalination plant, the Southern Seawater Desalination Plant (SSDP) on the Indian Ocean coast to the south of Perth. Water from the plant will be fed into the Integrated Water Supply Scheme near Harvey, approximately 30 kilometres inland. It’s a large resource, producing 50 billion litres (50 gigalitres) of drinking water annually, designed with the capacity to expand to 100 gigalitres per year at a future date.
At the completion of the project in late 2011, more than 30 per cent of Western Australia’s water supply will come from climate independent sources. The city has already built the $370 million Perth Seawater Desalination Plant at Kwinana, completed in 2006; and the SSDP project learned many lessons from the construction of that plant. “The design for our first desalination plant was initiated back in 2002 before large-scale reverse osmosis plants were adopted across Australia.Between then and now there has been a lot more research into energy recovery and energy efficiency,” explains project manager Nick Churchill.
The energy requirement for seawater reverse osmosis (SWRO) can now be as low as that required by many traditional freshwater supply sources, according to Energy Recovery Inc (ERI), one of the Water Corporation’s major technology partners in both plants. Improved membranes, increased pump efficiencies and the implementation of isobaric energy recovery devices have dramatically increased the energy efficiency of the process. “We are also getting much more efficient and targeted water quality in the new plant through a new and improved membrane technology process called split hybrid membrane design,” says Churchill.
The other big advance for this plant is the use of membrane filtration as a pre-treatment; before the water comes through to the reverse osmosis, it goes through a series of filters so that when it hits the membrane it doesn’t clog it. “This is a coarser membrane than the reverse osmosis membranes and it ensures a consistent quality of water going through, with better membrane life and more efficient transfer of the water.”
The Water Corporation wanted to retain ownership and control of the plant while bringing in the best practice and most advanced thinking on desalination available in the world. Accordingly, it set up an alliance that operates like a joint venture but with some significant differences. “It is effectively governed by an Alliance Lead Team which operates like a company board with participation from the Water Corporation and its non-owner partners (NOPs). The joint venture for the delivery of the project is made up of these NOPs—Spanish companies Tecnicas Reunidas and Valoriza Agua, working with Australian contractors WorleyParsons and AJ Lucas.”
Australian working practices and union laws being somewhat different from those in Europe, this was seen as an effective way of ensuring the project met Australian standards. “That is one benefit of being in the alliance,” says Churchill. “The Water Corporation will own this asset and the alliance will operate it for 25 years after it is commissioned in 2011. We were keen not to just hand over all that expertise and knowledge to the commercial companies but to capture it within our own organisation. We did the same thing on the first desalination plant, and some of the people involved in that are now taking a lead role in the second one.” Knowledge transfer has been designed into the entire 25 year project, he adds.
The project is advancing on schedule. Marine construction, dredging and offshore operations will be completed by the end of June, says Churchill: “We need to be out of the ocean by the winter.” Onshore, the microfiltration structure and the main reverse osmosis building are well into construction. From July the electrical and mechanical teams will move onto the site, building up to a complement of around 650 people. “The target date for completion of the 50 gigalitre plant is November 2011, including six months’ commissioning. All the integrating projects are on schedule too—we won’t have a desalination plant without power or pipelines!”
The announcement of the desalination plant, like others around Australia, was tied to renewable energy. The Water Corporation is sourcing a suitable renewable energy supplier. The impact on the environment of the SSDP is being monitored closely—the Water Corporation implemented the most intensive ocean monitoring programme of any desalination plant in the world at its Kwinana plant and the new one will mirror that; though its design means the impact should be even lower. The earlier plant discharges brine into Cockburn Sound, a 100 square kilometrebayenclosed by a string of islands and with a very sensitive marine ecosystem including rare sea grasses. “There was concern that the heavier saline water would sit at the bottom, and the oxygen levels drop and affect marine life. The extensive monitoring regime strongly suggests that this has not been the case.”
The SSDP is on an open coast. “We are lucky to be in a very active part of the ocean—you don’t want reefs or critical habitats and there were no show stoppers there!” Churchill continues. “The impacts will be well managed. We have done extensive modelling to show that within 50 metres of our diffuser pipe we can achieve levels within one per cent of background salinity.” The main environmental issues on land are associated with wetlands, clearing of vegetation, and protecting fauna, such as an endangered species of possum supported by that vegetation. Impacts have been avoided by routing pipes around wetlands and using already cleared areas wherever practical.
The biggest headaches are already over—marine blasting was kept to a minimum to avoid disturbing dolphins and whales. “We are in a whale migration area, so we could only blast between December and the end of April, and had to stop if whales or dolphins were seen nearby. During the dredging, when dolphins were seen in the area we stopped until they had passed by!” relates Churchill.
In the 25 year life of this plant, there can be little doubt that the sustainable water supply that the Water Corporation is creating in Western Australia today will certainly be replicated in other parts of the world that are not presently thought of as arid. www.watercorporation.com.au
