Teacher background information
Wastewater is a hidden part of everyday life. It is collected every day from households, commercial businesses and industries. Wastewater is directed to treatment plants and treated to an environmentally acceptable standard before being reused or safely discharged back into the environment.
Our treatment plants
In WA, Water Corporation is responsible for the treatment and disposal of wastewater. It operates more than 113 wastewater treatment facilities around the state. The three large metropolitan plants at Beenyup, Subiaco and Woodman Point treat approximately 80% of the state's wastewater.
What is wastewater?
Wastewater is the spent or used water from a community. It comes from domestic, commercial and industrial sources. The collection, treatment and disposal of wastewater are an integral part of the water cycle that maintains the balance of water in nature.
Surprisingly, wastewater is 99.97% water because by far the greatest volume comes from showers, baths and washing machines. The rest is dissolved and suspended matter. Wastewater also comes from industrial processes.
Wastewater treatment is a series of processes that remove the pollutant materials from wastewater such as solids, oil and greases, detergents, nutrients, heavy metals and bacteria. These processes are carried out at wastewater treatment plants. The treatment involves speeding up the natural processes of bacterial breakdown and removing solids by filtration and settling. The treated wastewater then:
- returns to the marine environment via ocean outfalls
- is re-used in horticulture or to irrigate recreational areas
- infiltrates back into the ground
There are 3 stages of wastewater treatment:
- Preliminary treatment
- Raw wastewater enters the plant from wastewater pipes and flows through a screening process to remove large items (called screenings).
- After screening, the wastewater flows through grit removal tanks to allow grit to settle while the organic material remains suspended.
- The grit is removed and sent to an approved landfill site together with the screenings.
- Primary treatment
- The wastewater is pumped into the primary sedimentation tanks to let the solids settle to the floor of the tanks while oil and grease floats to the top.
- Mechanical scrapers remove the settled solids and the oil and grease is removed.
- The settled solids are further treated and become bio solids.
- Secondary treatment
- In aeration tanks the wastewater is treated with a natural bacterial process and air, which breaks down the remaining organic compounds in the water.
- The water then flows into the secondary sedimentation tanks. Here the biologically active sludge settles and is removed.
- The treated wastewater is then suitable for ocean discharge.
Did you know?
In Perth around 370 million litres of wastewater, the equivalent of 185 Olympic-sized swimming pools, is collected every day.