Wastewater treatment
What is wastewater?
Wastewater is the water you've used in your homes, schools, businesses and industries. It goes down drains from sinks, baths, showers, laundries and toilets and other drains inside buildings.
Wastewater is 99% water. The remaining one per cent is made up of things you've added to water as you've used it.
Most wastewater in Sydney comes from inside people's homes.
Who makes wastewater?
You do! About 70% of greater Sydney's wastewater is made inside the home.
You're part of the urban water cycle. Your interaction with wastewater may seem small, but you're one of nearly five million people making wastewater every day.
Your interaction with wastewater connects to:
We're all connected, so what you do can make a big difference.
What kinds of things are in wastewater?
There are a lot of drains inside your home that take wastewater away. Do you know where all the drains are inside your home?What you put down the drain inside your home, school or business goes into wastewater.
Anything that goes down the drain ends up in wastewater. We need to take it back out, so we can return the treated wastewater to the environment.
Drains | Common things in wastewater |
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Kitchen
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Bathroom
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Laundry
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About 75% of all wastewater pipe blockages involve wet wipes. These blockages can cause wastewater (sewage) overflows into homes or creeks.
Flushed wet wipes are costing our community $8 million every year and this figure is growing! Find out more about the need to keep wipes out of the pipes.
What can you do to contribute to sustainable water management?
We all have a role to play in sustainable water management. Your interaction with wastewater connects you to the urban water cycle and the environment.You can help by:
- putting wet wipes and tissues in the bin
- putting only pee, poo and toilet paper in the toilet
- scraping food leftovers into the bin or compost before you wash up
- using a sink strainer to catch small pieces of food and putting them in the bin or compost
- pouring fats, oils and milk into used containers with secure lids and putting them in the bin
- using environmentally friendly detergents and cleaning products
- washing paint brushes in a bucket and pouring the water in the garden away from drains
- disposing of household chemicals using your local council's Household Chemical CleanOut services
- using the half flush on the toilet and taking shorter showers to reduce the wastewater you produce
- teaching and encouraging others to help make their interaction with and impact on the wastewater system a positive one.
One of the best things you can do is start your own plan to contribute to water management and share it with others.
Why not tell your friends and family what you're doing and explain how they can help look after the wastewater system and protect the environment?
These things have a dramatic impact on our wastewater system.
Problem substances | Effects on wastewater systems and/or environment | Pollution prevention and disposal options |
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Pesticides (including flea rinses) and chemicals |
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Food waste, oil and grease, milk or other liquid leftovers |
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Paint and paint-related products |
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Solvents and fuels |
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Solid items including plastics, rubber, fibres and organic material |
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Treating wastewater is about removing or breaking down what people have added to the water that leaves their home, school or business.
Three stages of wastewater treatment
Wastewater can go through up to three levels of treatment called primary, secondary and tertiary treatment to remove waste.
Different plants treat wastewater to different levels. We treat the wastewater so it's fit for purpose. This means we treat wastewater to suit the environment (creek, river or ocean) that will receive it, or to suit how it will be re-used.
Primary treatment
Primary treatment removes large solids from wastewater.
Screens trap and remove things such as food scraps, wet wipes, cotton tips and plastic (called screenings) as wastewater flows through. Grit tanks cause small, heavy particles like sand (grit) to sink to the bottom of a tank and a scraper removes it.
Sedimentation tanks allow solids (sludge) to settle to the bottom and oils and grease (scum) float to the top. Scrapers at the top and bottom of the tanks remove the sludge and scum, which are then treated to produce biosolids.
Primary treatment is the first stage of treatment.
Secondary treatment
We add microorganisms (activated sludge) to the wastewater. The microorganisms break down nutrients (like nitrogen and phosphorous) and small organic solids.
Next, we separate the activated sludge from the treated wastewater. The treated wastewater flows to tertiary treatment. The activated sludge is turned into biosolids.
Secondary treatment uses bacteria to break down nutrients.
Tertiary treatment
We filter the water and disinfect it with chlorine or ultraviolet light (UV). This kills any remaining microorganisms.
Tertiary treatment removes very small particles.
Treatment plants
You can learn more about some of our wastewater treatment and water recycling plants:
- St Marys Water Recycling Plant
- St Marys Advanced Water Recycling Plant
- Penrith Water Recycling Plant
- Wollongong Water Recycling Plant
- Rouse Hill Water Recycling Plant
- Cronulla Wastewater Treatment Plant
- North Head Wastewater Treatment Plant
- Wastewater treatment plant virtual tour
We offer excursions and technical tours to schools, universities and community groups. Request an excursion.
Treated water
We treat wastewater so clean water can be safely returned to the environment or re-used.
We're always finding new ways to recycle water. The treated wastewater (recycled water) can be used:
- in homes and businesses to water gardens and flush toilets
- in industry
- to fight fires
- to irrigate parks, farms and sports fields
- to maintain river flow.
Solids and sludge
The grit and screenings captured in wastewater treatment are sent to landfill. The sludge collected is turned into a fertiliser called biosolids.
Biosolids are used in agriculture, forestry and rehabilitation. 100% of our biosolids are beneficially re-used, with at least 70% used in agriculture.
Find out more about solids recycling.