Western Treatment Plant cover replacement project


We are partially removing and replacing the western section of a lagoon cover at the Western Treatment Plant, as part of regular maintenance to ensure the plant continues operating efficiently.

View of large lagoons with white plastic covers
The 55 East lagoon, showing the covers to be partially removed during these works.

Why this is important

The Western Treatment Plant is a place of historic and cultural significance. It sustainably treats half of Melbourne’s sewage using a series of large ponds, called lagoons.

The first sections of each lagoon have large plastic covers measuring 450 metres by 220 metres. These are designed to contain odour and keep out oxygen, creating an anaerobic (no oxygen) environment where certain bacteria thrive.

As the bacteria decompose the organic material in 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.

However, the decomposed organic material gradually builds up under the cover in the form of scum and sludge, and must be periodically removed to maintain efficiency.

What’s happening and when

The lagoon will be exposed while we:

  • remove scum that sits at the top of the lagoon
  • pump sludge from the bottom of the lagoon
  • build and install new replacement cover segments.

Trial cover removal

The covers replacement project is complex. To minimise the impact on the community and ensure the project’s success, from June to July 2020 we trialled removing a cover on the Western Treatment Plant’s 25 West lagoon.

This successful trial helped to inform the design of the new covers, allowing us to incorporate renewable design techniques which are more sustainable and save resources by reducing waste.

The use of the recycled covers will also help reduce the time taken to retune the covers on future projects.


Scum and sludge removal

We have finished removing scum and sludge from the 55 East lagoon, and installation of the new covers has begun.

As we complete the process of pulling the covers across the lagoon, a small amount of new scum may need to be removed but we expect this to be minimal.

Not Started

Cover installation and resealing

The final stage of the project involves resealing the covers, which we anticipate will be completed soon after.

We thank the community for their patience as we undertake these important works.

More information

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Bulletins and newsletters

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Last updated:
9 May 2021