Woodman Point Wastewater Treatment Plant
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Protecting our environment - this is the main purpose of the Water Corporation’s biggest wastewater treatment plant – Woodman Point.
Every day up to 100 million litres of treated wastewater is pumped into the ocean four kilometres offshore into the Sepia Depression - west of Garden Island.
As the treated wastewater mixes and disperses in the ocean it again becomes part of the water cycle.
As well as the treated wastewater, the plant also has valuable by-products.
These products include biogas (mainly methane), and the resultant electricity generated from the biogas that makes the plant energy self sufficient for most of the day.
There are tonnes of treated residue produced to enrich market gardens and farms around WA - Woodman Point also produces water suitable for industrial reuse.
History
In 1910 the first treatment works south of Perth was built in South Fremantle.
It served the immediate Fremantle area with three large septic tanks that discharged into the ocean from Robbs Jetty.
Fremantle grew fast after World War II and by 1962 a wastewater treatment upgrade was planned.
A new plant at Woodman Point opened in 1966, another move, further south to the present location, came in 1984.
In May 2002 WA’s Premier Geoff Gallop announced that the biggest wastewater recycling plant of its type in Australia is to be built at Kwinana. The plant was to be initially capable of processing five gigalitres (five million kilolitres) of treated wastewater each year to a quality suitable for use by major Kwinana industrial customers.
The trigger for the $20 million project was the decision by Rio Tinto to establish its HIsmelt pig iron plant at Kwinana.
BP, Edison Mission, CSBP and TiWest also indicated their support.
The plant was built, and is owned and operated by the Water Corporation. It is the biggest wastewater recycling project of its kind yet undertaken in Australia.
Treatment Process
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Through continual upgrading Woodman Point has retained a low profile. Few motorists on the adjacent Cockburn Road would even be aware of the 82-hectare site.
The management and operations team work hard to ensure the operation remains as unobtrusive as possible, working for maximum throughput with minimum local disturbance.
99.97% of the wastewater arriving at Woodman Point is just water, from household kitchens, bathrooms and laundries, as well as toilets.
It’s drawn from an area bounded by Midland/Kalamunda in the east, down to Dandalup in the south, and across to the coast.
Treatment of the wastewater is now a computer-controlled process, strictly monitored by a small team of expert managers and technicians on-site to avoid atmospheric and ground contamination.
First the wastewater is screened to remove any large objects (paper, rags etc) before passing through settling tanks to remove grit (sand etc).
Next, the wastewater spends several hours in large sedimentation tanks to remove settleable solids.
Sludge from these tanks receives further treatment.
Sludge is stabilised using Woodman Point’s newest equipment, two 38-metre high anaerobic sludge digesters.
Egg-shaped for efficiency, they are the biggest of their type in the southern hemisphere.
Bacterial action at 35 degrees celsius in the digesters converts sludge into a residue that is an excellent soil conditioner for landscaping or agricultural use.
The stabilised sludge – known as biosolids – is trucked off-site daily.
Biogas is a by-product of this digestion process, used to power the plant’s on-site generators.
It is this that makes Woodman Point energy self-sufficient, with spare electricity available to the Western Power grid.
Treated wastewater travels 23 kilometres by underground pipeline to Cape Peron.
Along the way the wastewater is oxygenated prior to reaching a tower at Cape Peron and from there it flows another four kilometres into the ocean and is discharged into the 20m deep Sepia Depression.
The water is quickly dispersed and Water Corporation divers make regular checks on the pipeline in the Depression.
Under Perth's Long Term Ocean Outlet Monitoring (PLOOM) program, extensive ocean water sampling is undertaken to monitor trends in water quality and help identify any necessary improvements.
Monitoring for impacts on the marine environment
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Every day, about 110 million litres of wastewater is discharged about 4 kilometres offshore from an underwater outlet into the Sepia Depression west of Point Perron. The Sepia Depression is a 20 metre deep channel that is very well flushed with offshore ocean waters. Limestone rocky reefs, sand and seagrass meadows occur between the deep water Sepia Depression and the nearby coast.
The impacts of this wastewater discharge on the marine environment are monitored by the PLOOM program.
Wastewater entering Sepia Depression contains higher levels of nutrients (mainly nitrogen and phosphorus) than the surrounding oceanic waters.
A nutrient plume extends between 2 kilometres from the wastewater outlet at Sepia Depression. This is the largest plume of all the ocean outfalls around Perth. Nutrient levels are generally highest in winter and lowest in summer.
Marine plants
Phytoplankton - tiny microscopic marine plants - are an important component of the marine ecosystem. A significant proportion of nutrients in the wastewater discharged into the Sepia Depression is taken up and used for growth by phytoplankton in this area.
Nutrient inputs from the wastewater cause a slight increase in the amount of phytoplankton to the north of the Sepia Depression outlet, particularly in summer. The phytoplankton population in this area is healthy.
To date, no changes have occurred in the phytoplankton types occurring at the Sepia Depression outlet. These are similar to other phytoplankton populations in Perth’s coastal waters.
In some situations, nutrients from wastewater can cause the growth of 'nuisance seaweeds', which may out-compete the natural seaweed habitats. Studies on seaweed and communities near Sepia Depression have shown no such impacts have occurred. The low proportion of nuisance seaweed in the naturally occurring kelp and seaweed shows this area is healthy.
Marine animals
Metals, pesticides and other pollutants can be contained in treated wastewater at elevated concentrations, and have the potential to harm the marine environment.
At Sepia Depression, no changes in the numbers and types of animals living in the sand and rocky reefs due to the ocean outfall have been detected by monitoring.
Monitoring of shellfish near the Sepia Depression between 1995 to 1998 showed there were no detectable impacts of contaminants and that these animals were suitable for eating (ANZFA 1996).
Community Engagement
 | About the plant |
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PLOOM Program |
Woodman Point Works Approval Document
Application for works approval - to Department of Environment and Conservation December 2006.
| | Application for works document - main body |
| | Appendix 1 - Locality map, cleared area required and Certificate of Title |
| | Appendix 2 - Current DEC Licence |
| | Appendix 3 - Plant Odour Emissions: before and after works |
| | Appendix 4 - Proposed works capital cost estimate |
| | Appendix 5 - Minutes of Community Reference Group meetings |
| | Appendix 6 - Community presentations |
| | Appendices 7 and 8 - Aboriginal Heritage Letter and Public Notice Advertisement |
Odour Improvement Plan
| | Odour Improvement Plan |
| | Appendix A - Odour Contours |
| | Appendix B - Project Plan |
| | Appendix C - Community Reference Group Draft Terms of Reference |
| | Appendix D - Community Reference Group Comments |
Contact Us
For more information on our Woodman Point operation call 08 9437 8721.
For more monitoring information please call 08 9420 3710.
For further information on metropolitan wastewater treatment plants, email.