Melbourne's sewage oasis

A series of vast ponds and lagoons make up the Western Treatment Plant's system that treats sewage to either a Class A or Class C recycled water standard.

Sewage flows slowly through these ponds, gradually becoming cleaner as bacteria break down the organic material in the water. This process usually takes around 30 to 35 days.

How the modern lagoon systems work


Types of ponds and bacteria

Each type of pond produces different bacteria, which we need to break down the sewage.

Anaerobic Ponds

The first stage of lagoon treatment is anaerobic. This pond has no oxygen, as it's been consumed by the bacteria which break down the pollutants in the sewage. Under anaerobic conditions, bacteria produce strong odours and release dangerous greenhouse gases. These are captured under plastic covers placed over the ponds, and used to generate electricity.

Aerobic Ponds

More oxygen becomes available in the water as the sewage is treated. However, the first pond in the lagoon system needs aerators to pump oxygen into the water. This reduces odours caused by the bacteria. In remaining ponds oxygen is naturally available. By the final pond, sewage is known as treated effluent, and is ready for recycling or discharge into Port Phillip Bay.

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.