Subiaco Wastewater Treatment Plant
The Subiaco Wastewater Treatment Plant, located on the corner of Brockway Road and Lemnos Street in Subiaco, services the Perth central area.
The plant operates under stringent guidelines, meeting Department of Environment and Conservation standards.
It will continue to serve the needs of the central metropolitan area and will continue to do so well beyond 2040.
Odour improvement project
A major odour improvement project was undertaken in early 2000. The scope of the work was to cover and treat the areas producing the highest odours – inlet channels, primary sedimentation and secondary treatment areas.
The Water Corporation continues to investigate sustainable land use options appropriate to the buffer zone around the plant to ensure future odour issues are minimised.
History
The Subiaco Wastewater Treatment Plant was first used as a treatment works in 1927 as part of the Subiaco Sewerage Scheme.
The plant then consisted of two septic tanks, with the treated wastewater from these tanks being carried in a tunnel to the ocean and discharged out to sea through a 100-metre ocean outlet.
In 1961 the plant was upgraded to include secondary treatment, heated sludge digestion and a 110-metre ocean outlet.
In 1981 the plant was again redeveloped to provide a modern treatment process capable of serving more than 300,000 people.
New features include automatic chlorination for increased odour control, modern screens and grit removal units, and an upgraded primary treatment area with automatic de-sludging.
The new fine bubble aeration system enables the plant to produce a high quality treated wastewater.
Continuous upgrading ensures that the Subiaco Wastewater Treatment Plant will be able to serve the Perth metropolitan area well beyond 2040.
Treatment process
Flows from the Perth Main Sewer, Subiaco Main Sewer, Swanbourne Pressure Main and Scarborough Main Sewer combine at the upstream end of the inlet channel.
These incoming main sewers can be injected with chlorine for septicity and odour control.
Further upstream oxygen is injected into the Perth Main Sewer, which receives the largest flow (80%), at two locations, Perth Central and Claisebrook.
Raw wastewater entering the plant flows through bar screens which collect materials such as wood and rags and mechanically rake the material into a screw conveyor.
After screening, the wastewater flows into the grit tanks to allow the inorganic material (grit) to settle and the organic material to remain in suspension.
The settled grit is periodically conveyed to a dewatering screw and, together with the screenings, is taken and disposed of as landfill.
The Primary Treatment Process consists of four circular primary sedimentation tanks, and the raw sludge pumping station.
The flow from the Preliminary Treatment Process enters the centre of the primary sedimentation tanks.
Scrapers on the floor of the tanks collect the settled draw sludge into a central hopper and pumped directly to the sludge blending tanks for further processing.
The Secondary Treatment process consists of activated sludge and sedimentation sub-processes.
The activated sludge sub-process takes place in nine reinforced concrete aeration tanks.
Compressed air is blown into the tanks from mechanical blowers housed in a building adjacent to the aeration tanks, providing the oxygen requirements for the microbiological action needed to break down the organic compounds.
The secondary sedimentation process occurs within twelve circular reinforced concrete sedimentation tanks.
The mixed liquor from the aeration tanks flows through into the sedimentation tanks through a central feed and sludge that settles in these tanks is continuously removed.
A portion of this is returned to the aeration tanks to provide the biomass to breakdown the incoming organic waste.
Excess activated sludge from the secondary process flows to the Sludge Handling Building where it is thickened in the Dissolved Air Flotation Thickeners (DAFT).
The secondary wastewater separated from the mixed liquor flows to the final wastewater pumping station and is pumped via the ocean outfall to Swanbourne Beach where it is discharged 1100 metres out and 10 metres below the surface of the ocean.
Monitoring for impacts on the marine environment
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Every day, about 55 million litres of wastewater is discharged 1 kilometre offshore from an underwater outlet at Swanbourne. The water at the outlet is about 10 metres deep.
The marine environment at Swanbourne comprises of mainly rocky limestone reef and sand habitats. Some seagrass meadows grow to the south of the outlet. The impacts of this wastewater discharge on the marine environment are monitored by the PLOOM program.
Wastewater discharged at Swanbourne contains higher levels of nutrients (mainly nitrogen and phosphorus) than the surrounding coastal waters. A nutrient plume extends between 500 metres and 2.5 kilometres from the wastewater outlet. The concentrations of nutrients in this plume are generally lower than at Ocean Reef.
Marine Plants
Phytoplankton, tiny marine plants that live in the water column, are an important part of the marine ecosystem.
There are many different types of phytoplankton in Perth’s coastal waters, including at Swanbourne. The phytoplankton population is healthy.
The naturally occurring seaweeds and seagrasses living nearby are being studied this year to see if there are any impacts from the wastewater discharge.
Marine Animals
The number and types of marine animals living in the nearby limestone reef and sand have not been affected by the wastewater discharge.
Human health
Monitoring at Swanbourne and surrounding beaches has shown that these are not affected by the wastewater outlet, and are safe for swimming (ANZECC guidelines, 2001).
More information
 | Subiaco Wastewater Treatment plant brochure |
For more information on our Subiaco operation please call 08 9380 7442
For more monitoring information please call 08 9420 3710
For further information on metropolitan wastewater treatment plants, email.
