The sewage treatment process

Virtual sewage treatment plant tour

Looking for educational resources for teachers and students about the water cycle and sewage treatment? Browse through our Education program.

Sewage treatment plants (STPs) in a nutshell


Unfortunately, sewage smells. However we do our very best to minimise odour at our sewage treatment plants (STPs).

We routinely implement a number of measures to lower the impact of odour on the community. These include:

  • sealing the sewer
  • regular cleaning
  • addition of chemicals to prevent odours being emitted
  • biological and chemical treatment of odour. 

Odour emissions and intensity are affected by a number of variables such as the age of the sewage, wind direction, rain and temperature.

If you have any concerns regarding our sewage treatment plants, or if you notice any damage or faults, please contact us.


Unitywater is licensed to operate its sewage treatment plants (STPs) by the Department of Environment and Science (DES). To maintain our compliance, we must operate according to the strict conditions contained in these licences.

Unitywater has an effluent monitoring program for each treatment plant, as directed by DES. Effluent is sewage that has been treated through various stages.

You can see our STP performance reports and information about our effluent quality and licence compliance below:


Sewage Treatment Plant Performance Report 2022-23 (1.4MB)

Sewage Treatment Plant Performance Report 2021-22 (PDF 1.6MB)

Sewage Treatment Plant Performance Report 2020-21 (PDF 1.1MB)

Sewage Treatment Plant Performance Report 2019-20 (PDF 2MB)

Sewage Treatment Plant Performance Report 2018-19 (PDF 1.8MB)

Sewage Treatment Plant Performance Report 2017-18 (PDF 2.2MB)

Sewage Treatment Plant Performance Report 2016-17 (PDF 3.4MB)

Sewage Treatment Plant Performance Summary 2015-16 (PDF 8.2MB)

Annual Recycled Water Performance Reports


Sewage goes through a multi-stage process of treatment at our plants. These processes clean and filter the sewage to remove: 

  • bad bacteria
  • non-organic matter (plastics, wet wipes etc)
  • organic solid matter
  • sediment
  • pollutants.

At some sewage treatment plants, we add Magnesium Hydroxide Liquid (MHL), also known as Milk of Magnesia, to raw sewage. This is an important product that helps reduce odour and protect underground assets against corrosion.

Find out more by downloading our batching plant process diagram (PDF 1.53MB)

Take a virtual video tour of a sewage treatment plant.


We own 17 sewage treatment plants (STPs).Unitywater Sewage Treatment Plant, Murrumba Downs

They are located in the following areas:

  1. Brendale
  2. Bribie Island
  3. Burpengary East
  4. Coolum
  5. Cooroy
  6. Dayboro
  7. Kawana
  8. Kenilworth
  9. Landsborough
  10. Maleny
  11. Maroochydore
  12. Murrumba Downs
  13. Nambour
  14. Noosa
  15. Redcliffe
  16. South Caboolture
  17. Woodford

You can view STP locations on a map of our region.  

How you can help



Everything you flush down the toilet or put down a sink or drain gets treated in our sewerage network.

You can help save the environment, reduce treatment costs, defer the need for expensive upgrades to our sewer networks and keep sewerage access fees down.

Here are some tips on how you can help.

And remember: definitely do not flush wet wipes down the toilet (even if the packaging says they are flushable)! 

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