Sewage Treatment Process
Sewage is treated differently at the Eastern and Western Treatment Plants.
Sewage at the Western Treatment Plant goes through three stages of treatment to produce high quality recycled water (Class A).
At the Eastern Treatment Plant sewage currently goes through two treatment stages before it is disinfected to produce Class C recycled water.
By end-2012 a major upgrade of the Eastern Treatment Plant will see effluent being treated to an advanced tertiary standard.
The current sewage treatment process follows two stages:
Primary treatment
Primary treatment includes:
- filtering out large objects (such as cotton buds, rags and other rubbish) using fine screens;
- aerating the sewage to remove finer particles like grit and sand; and
- sedimentation, where heavy items sink to the bottom forming a layer called sludge. The settled sludge and floating debris is then pumped to larger tanks, known as digesters, where it is later broken down by bacteria.
Secondary treatment
In secondary treatment, different types of bacteria exist side by side in aerobic (with oxygen) and anaerobic (without oxygen) environments, breaking down organic material and removing nutrients in the plant's aeration tanks. TThe water then passes through sedimentation tanks where more sludge settles to the bottom to finally produce clear treated water, also known as effluent.
The treated effluent flows to large holding ponds before it flows through microscreens for a final screening process. Just before the treated effluent flows out of the plant to be recycled or released to the environment, it is disinfected with chlorine. The treated effluent must meet EPA Victoria licence requirements before it is returned to the environment.
Upgrading to a tertiary treatment process
By end-2012 a major upgrade of the Eastern Treatment Plant will see effluent being treated to an advanced tertiary standard.
The main benefits of the upgrade are:
- reduced impact on marine environment where treated water is discharged at Boags Rocks
- more options to use treated water for non-drinking purposes because of its higher quality
Treating sewage to an advanced tertiary standard adds several additional steps to the secondary treatment process including ozone and UV disinfection, biological filtration to reduce ammonia, oil and grease, foam, litter and solids, and chlorination.
View the process in more detail
Learn more about the Eastern Treatment Plant Tertiary Upgrade Project and tertiary sewage treatment.