Beenyup Wastewater Treatment Plant
The Beenyup Wastewater Treatment Plant serves Perth's rapidly developing northern suburbs from Quinns Rock through to Scarborough and inland through Dianella and Bayswater to the foothills east of Midland.
It is an advanced secondary treatment plant. Its current sapacity is 120 megalitres per day, but ultimately it will be developed to treat 150 megalitres per day, servicing a population of up to 750,000 people.
Odour control upgrade
In 2008-10, the Beenyup WWTP capacity was expanded from 120 ML/day to 135 ML/day (the flows from about 660,000 people), with a further expansion of the odour control facilities.
The odour control objective was to expand the capacity of the plant with no net increase in odour emissions and no increase in odour impact. Objective odour consultants Consulting Environment Engineers prepared a report on the outcomes of the odour control upgrade.
 | Download the latest odour performance verification report |
Treatment process
Raw wastewater entering the plant passes through bar screens that remove materials such as paper, rags and other large objects from the flow and mechanically rake the material into a screw conveyor.
This material is then pressed and disposed to secure landfill.
After screening, the wastewater flows into circular grit removal tanks, aerated to allow the inorganic material (grit) to settle and the organic material to pass through.
Following removal of screenings and grit the wastewater passes very slowly through large, rectangular primary sedimentation tanks allowing about 50 per cent of the suspended solids to settle out as sludge.
The sludge is collected by a scraper mechanism and pumped to the solids handling area for thickening and digestion.
The treated liquid leaving the tanks is called "primary treated wastewater" and it passes to secondary treatment.
Secondary treatment is achieved in aeration tanks by the "activated sludge" process where ideal conditions are provided for microbiological life to grow rapidly and consume the organic material in the wastewater.
Microorganisms require oxygen to survive and this is provided by blowers which inject air through fine bubble dome diffusers on the floors of the tanks.
Following aeration, the treated wastewater passes slowly through circular clarifiers in which the activated sludge settles leaving a high quality secondary effluent.
The settled sludge containing active micro-organisms is rapidly removed using scrapers and is returned to the aeration tanks.
Solids removed from the primary sedimentation tanks and excess solids produced by the activated sludge process are thickened and fed to the anaerobic digesters.
Following digestion, the sludge is mechanically dewatered to produce a biosolid, suitable for use as a soil conditioner.
Secondary wastewater flows by gravity to the Indian Ocean in the vicinity of the Marmion Marine Park and is discharged into 10 metres of water via two outlets, one 1850 metres and the other 1650 metres offshore where it is rapidly diluted and dispersed.
Regular monitoring of ocean water quality is carried out to confirm that environmental and health standards are met.
Numerous analyses are regularly carried out to monitor the performance of the plant.
Regular tests are carried out to check compliance with the Department of Environment licence.
History
Early subdivisions in the northern suburbs were served by small local wastewater treatment plants. These were gradually closed down when a temporary plant was established at Beenyup in 1970.
In 1972 the first stage of the permanent plant was commissioned which catered for a flow of 3.6 megalitres per day. This plant utilised the extended aeration process and provided for wastewater to be disposed of on-site by soakage.
By 1978 the plant had been expanded to treat 27 megalitres per day using the conventional activated sludge process. At this time a gravity outfall was commissioned which enabled the treated wastewater to be discharged into the Indian Ocean off Ocean Reef.
Further facilities were commissioned in 1984 to enable the plant to treat 54 megalitres of wastewater per day. The sludge digestion facilities were commissioned in 1990, replacing the sludge incineration process.
New secondary treatment facilities were opened in 1996.
Monitoring for impacts on marine environment
Every day, about 100 million litres of wastewater is discharged about 2 kilometres offshore, via an underwater outlet at Ocean Reef. Ocean Reef is part of the Marmion Marine Park, and comprises an area of rocky limestone reef and sand habitats. Some seagrass meadows grow to the south of the outlet.
The impacts of the wastewater discharge on the marine environment are monitored by the Perth Long Term Ocean Outlet Monitoring Program
Marine plants
Increased nutrient levels in the water column have the potential to impact on a range of marine plants, including microscopic phytoplankton, macroalgae and seagrasses.
At Ocean Reef, slightly increased phytoplankton populations can occur directly above the wastewater outlet at any time of the year due to the elevated nutrient levels from the wastewater. The increase in phytoplankton is still within levels typically found in other coastal waters around Perth.
To date, no changes in the types of phytoplankton associated with the Ocean Reef outlet have occurred. This indicates that this phytoplankton population is healthy, and that the impact of wastewater discharge on the phytoplankton is low.
In some situations, nutrients from wastewater can cause the growth of nuisance algae, which may out-compete the natural seaweed habitats on the sea floor. Studies of seaweed at Ocean Reef to date indicate that no such impacts have occurred. The low proportion of nuisance algae in the naturally occurring kelp and other seaweeds shows this area near the outlet 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 Ocean Reef, no changes in the numbers and types of animals living in the sand and rocky reefs due to the ocean outfall have been detected.
More information
| | Download the Beenyup Wastewater Treatment Plant brochure |
For more information about the Beenyup Wastewater Treatment Plant please call 08 9306 7615. For information about metropolitan wastewater treatment plants please email wastewater@watercorporation.com.au
