Western Treatment Plant

Located in Werribee, the historic plant sustainably treats half of Melbourne’s sewage while providing an internationally-recognised bird habitat. Learn how it works.

Facts about the plant

  • occupies 10,500 hectares — the same size as Disney World
  • produces 40 billion litres of recycled water a year
  • is energy self-sufficient, generating all its electricity from sewage gas
  • declared an internationally-significant wetland for waterfowl in 1983, under the Ramsar Convention

Sewage treatment process

The plant treats sewage using a series of large ponds, called lagoons — the largest of which can hold 600 million litres. These are managed to suit different types of bacteria, which break down different sewage pollutants. The whole process uses very little energy and takes around 35 days.

Anaerobic lagoons

The first lagoons have large plastic covers about four times the size of the MCG, which are designed to keep out oxygen. This creates an anaerobic (no oxygen) environment where certain bacteria thrive.

As the bacteria decompose organic material in the sewage they produce odours and methane gas, which is captured under the covers. This reduces odour and greenhouse emissions and allows the gas to be used for powering engines that generate electricity.

Aerobic lagoons

Sewage then flows into uncovered aerobic ponds. Here, machines pump oxygen in the water to make it suitable for another type of bacteria, which removes nitrogen and clumps together in the process.

These solid clumps are easily separated from the wastewater once the sewage enters settling tanks, called clarifiers. The leftover solids are dried and stored in large piles, or reused as biosolids.


Once water reaches the final pond it has been thoroughly cleaned. It can then be released into Port Phillip Bay under strict conditions set by EPA Victoria to protect the environment.


Some water is further treated to produce recycled water. This is supplied to customers and used to water the plant’s pastures and wetlands.

Bird habitats

Over the decades we’ve improved the efficiency of our treatment processes and no longer use all our lagoons. These shallow ponds make great habitat for birds: leftover nutrients provide plenty of insects to eat, and there’s water all year round.

The vast site also contains a variety of natural habitats, which together support diverse plant, animal and reptile species — some that are critically endangered.

More than 280 bird species have been recorded at the plant, including migratory shorebirds that travel from Siberia each year. It is therefore recognised at as a wetland of international importance under the Ramsar Convention, and as one of Australia’s best birdwatching sites.

Improvements for the environment

Melbourne Water is working hard to improve our environmental performance in the wastewater treatment field. An Environmental Improvement Plan has been carefully drafted to describe how Melbourne Water uses various processes to provide continuous improvement in environmental management at the Eastern Treatment Plant (ETP) located in Bangholme and the Western Treatment Plant (WTP) located in Werribee.

This plan defines the key high priority actions Melbourne Water is pursuing to achieve its various environmental goals; however, it does not attempt to capture all of the initiatives in place.

If you have any queries on the plan, please contact the Customer Service Centre.

Last updated:
11 January 2018