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Gold Coast Desalination Alliance
| Project Start Date: |
2006
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| Project Finish Date: |
2008
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| Total Project Value: |
$AUD1.1 Billion |
| Client: |
Queensland State Government
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| Project Overview: |
The South East Queensland (SEQ) Desalination plant will be the first large-scale desalination facility on Australia's eastern seaboard. When completed it will provide 45GL/y of drinking water each day to South East Queensland or approximately 15% of its current water needs.
The project is being delivered by the Gold Coast Desalination Alliance (GCDA) which comprises Veolia Water, John Holland and SKM in an Alliance contract with SureSmart Water, the Queensland Government's vehicle for the delivery of the project. Veolia Water, John Holland and SKM are working closely together to design, construct and commission the plant by November 2008. The project comprises a desalination plant, marine intake and outlet tunnels and a 35km pipeline, built in urban zones, to connect the plant to the SEQ Water grid.
Desalination Plant
The desalination plant consists of pre-treatment, sea water reverse osmosis (SWRO), re-mineralisation and residuals treatment. The sea water is first pumped from the intake shaft into 3mm drum screens, where larger suspended solids from the sea such as seaweed are removed.
The SWRO treatment consists of two passes. The first pass SWRO is fed by HP pumps using a pressure centre arrangement. 97% of energy is recovered from the first pass SWRO brine and transferred to the SWRO feed by Calder DWEER energy recovery units. The first pass SWRO has a recovery of around 45%. The second pass Brackish Water Reverse Osmosis (BWRO) unit is primarily used to achieve the Boron and Bromide specifications of the final water quality. Second pass alkalisation, where the pH of the water is raised to 10 by caustic addition, is used for Boron removal. The second pass has two stages and a recovery of around 85%.
The most suitable site option for the location of the SEQ Desalination plant's construction happened to be on landfill. As a legacy to the local community the GCDA rehabilitated the site to build the plant. GCDA also relocated a soccer field so that the Tugun soccer team could continue playing soccer whilst the plant was under construction.
Tunnelling and Marine Works
Extensive tunnel and marine works were required for this project. They included the design and construction of twin 9m diameter, 40m deep intake/outlet shafts; twin 2,800mm ID, segmentally lined tunnels (2.2km inlet, 2.0 km outlet); intake and outfall risers and the connection to risers and tunnels at 65m depth under the sea.
Excavations were undertaken using two full face slurry tunnel boring machines, which met challenges posed by adverse hydro-geological conditions. Marine risers are being installed to depths of 65m below sea level by driving a sleeve through 20m of sand, then drilling through rock before inserting a liner and making-good the riser connections to the deep tunnels under the sea.
The intake is located in about 20m of water and will collect the seawater by gravity. The outlet uses a diffuser, designed to disperse the brine using the energy of the ocean. The diffuser is a 1m diameter pipeline some 180m long, with 8 dispersion outlets spaced evenly to distribute the brine within a very small mixing zone. Within an area of 120m by 225m from the outlet, the water will be dispersed to normal background salinity levels.
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