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Technical Details
Learn more detail about Sydney’s Desalination Process
Seawater Intake
- Seawater is drawn from the ocean under gravity, via four intakes that are approximately 300 metres offshore
- The intakes are 5.2 metres high and 8.5 metres wide. They sit on the seabed about 25-30 metres below the surface and can deliver around 600 million litres of seawater per day via a 2 .5 kilometre long pipeline
- The inflow rate is less than the prevailing current (about 0.1 metres per second) so that marine life can easily swim around the intake without being caught
- Artificial reefs have been created around the structures
- Click here to see video of the seawater intake in operation
Screening
- A Penstock or gate valve is used to permit flow into the plant
- Drums screens then filter out material to 3 millimetres in diameter, such as kelp from the seawater
- Sacrificial anodes prevent corrosion of the metal screening
- Usually less than one cubic metre of material is collected per week
Pre-treatment filtration
- 12 Dual Media filters are used as an added refining process to remove more solids
- Seawater has a flocculant added to encourage particles to bind together to improve filtration
- Seawater is filtered by gravity through a layer of filter charcoal and sand
- Filtration rate, filter bed depth and size of filtering media are carefully selected to give the optimum compromise between filtered water quality and run times
- In normal operation all filters will be operating with one being taken offline for backwashing or planned maintenance
- Cartridge filters are used to refine the filtered seawater to prepare it for the reverse osmosis process
- Centrifugal booster pumps are used to elevate water pressure to about 5 bar
Waste treatment
- From overall production only 0.05% becomes solid waste
- Lime waste is thickened and dewatered and sent for beneficial reuse in agriculture
- Solids from the Dual Media filters are thickened by gravity and then dewatered in a centrifuge prior to disposal in landfill
Reverse osmosis
- High pressure centrifugal pumps increase the water pressure to 50 – 60 bar
- Filtered seawater is pushed through the reverse osmosis membranes under high pressure
- The presure required is seasonal as salinity and temperature change
- Each pressure vessel contains 8 membranes
- There are around 36,000 membranes
- There is a 2 pass reverse osmosis system, with 13 first pass trains and 7 second pass trains
- Automatic Clean In Place (CIP) system
Dual Work Exchange Energy Recovery (DWEER)
- Dual Work Exchange Energy Recovery (DWEER) devices are placed at the end of each first pass train
- 90% of energy is recovered from the seawater concentrate and is used to pressurise the incoming seawater
- This reduces the plant’s energy needs by up to 60%
- This reduces the required size of pumps and improves efficiency
Re-mineralisation
- Fluoride and minerals are added to the fresh water to meet Australian Drinking Water Guidelines and NSW Health requirements
- There is continuous online water quality monitoring throughout the entire plant process
- Water quality test are also conducted after remineralisation to ensure standards are met
Drinking Water Holding Tank and pump station
- Drinking Water Holding Tank holds 40 million litres water which is four hours of water production
- Two large variable speed pumps are used to transfer the water to the pipeline
- Four large shock absorbers reduce the effects of water hammer during start up and shut down of the pumps
Water supply – pipeline
- Drinking water is discharged to the Sydney Water network along an 18 kilometre pipeline that runs from the plant to the main water supply at Erskineville
Seawater Concentrate Outlet
- Specially designed outlet nozzles ensure that water returns to normal seawater salinity and temperature within 50 – 75 metres of the oultet
- Approximately 58% of intake water is returned to the ocean
- Seawater concentrate is twice the salinity and about 1 degree warmer
- Click here to see video of the seawater outlet in operation