North Head Wastewater Treatment Plant

The North Head Wastewater Treatment Plant is one of 30 wastewater treatment and water recycling plants in greater Sydney.

Aerial photograph of North Head

North Head Wastewater Treatment Plant is located on the coast at Manly.

Location Bluefish Road, Manly
Population served  1 million people
Area served 452 km2

Including from Seven Hills in the west, south to Bankstown and north to Ku-ring-gai and Collaroy.
Amount of wastewater treated each day 336 million litres
Treatment level Primary
Environmental discharge We release the treated wastewater to the ocean using a deepwater ocean outfall. The deepwater ocean outfall is 3.6 km from the shoreline, 82 m maximum water depth and has a diffuser zone of 720 m.
Amount of biosolids produced each year  12,000 tonnes
Operating licence and regulation We operate the plant under two sets of rules:

Primary treatment

Primary wastewater treatment removes large solids using physical separation processes.

Most of the solids removed can be treated for beneficial re-use.

North Head flow diagram

Treatment flow chart. Select the flow chart to see a larger version.


Screens trap and remove large solids as wastewater flows through.

Grit removal

We inject air into a tank, causing the water to spiral. The air flings the grit, such as sand and coffee grounds, to the edges. It collects in the bottom of the tank where a scraper removes it.


Sedimentation tanks allow solids to settle to the bottom of the tank while oil and grease float to the top. Scrapers at both the bottom and the top of the tanks remove the solids, oil and grease, which are then treated to produce biosolids.

North Head primary sedimentation tanks

We use sedimentation tanks to remove solids, oil and grease.

Ocean discharge

Aerial photograph of Manly.

Treated wastewater from North Head is discharged to the ocean.

Most of the treated wastewater is discharged to the deep ocean outfall. The treated wastewater enters a large tunnel that carries it under the sea bed about 3.6 km out to sea, where the ocean is about 60 m deep. At the deepest point, it is 82 m deep.

The wastewater is released into the ocean through diffusers. The diffusers are spread over about 720 m at the end of the tunnel into an area off the eastern seaboard that is naturally swept by currents flowing north to south.

Sunlight, saltwater and wave action work together to naturally break down and disinfect the treated wastewater.

We monitor the marine environment and test for toxicity to check for any impact. We continue to work with The NSW Environment Protection Authority to study the marine environment around the deep ocean outfalls.

Some wastewater is further treated and re-used in the plant as cooling water and to flush equipment.

We're constantly looking for ways to reduce our carbon footprint and use alternate and renewable energy sources.

At North Head, we produce up to 58% of the plant's total energy needs from renewable sources.

Learn more about energy management and climate change.


We have a hydro-electric generator at North Head Wastewater Treatment Plant.

The treated wastewater falls down a long drop shaft on its way to the deepwater ocean outfall.

The falling water has enough kinetic energy to drive a water powered generator, producing hydroelectricity.


At North Head, we use cogeneration to meet some of the plant's energy needs.

We capture methane gas (biogas) from the anaerobic digesters and use it to power a combustion engine that drives an electricity generator.

North Head cogeneration engine

The cogeneration engine turns biogas into energy and heat.

Running the plant

A team of staff manage, operate and maintain the plant. They collect and analyse water samples, do laboratory testing and manage special projects to keep the plant running safely and efficiently.

Staff member at North Head

Staff monitor the plant to make sure it's working at it's best.

Maintaining the plant

There are three types of maintenance required to keep the plant operating: preventative, planned and reactive.

Maintenance type Description Example
Preventative Prevents a break down Oiling a motor
Planned Replacing equipment as it reaches the end of its useful life, before a break down Replacing a worn motor
Reactive Fixing equipment that has unexpectedly broken down Repairing a motor