-
-
Search
-
Contact us
-
Log in
Treating wastewater
The North Head Wastewater Treatment Plant is one of 30 wastewater treatment and water recycling plants in greater Sydney. Here we treat water to a primary standard before releasing it to the ocean via a deep-water ocean outfall.
Facts and figures
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: 336 million litres each day.
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: 12,000 tonnes each year.
Operating licence and regulation: We operate the plant under two sets of rules:
- Environmental protection licence issued by NSW Environmental Protection Authority (EPA). View the licence limits.
- Biosolids produced by the plant must meet the EPA's biosolids Environmental guidelines: Use and disposal of biosolids products.
Flow chart
Primary treatment
Primary wastewater treatment removes large solids using physical separation processes.
Most of the solids removed can be treated for beneficial re-use.
Screening
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
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.
We use sedimentation tanks to remove solids, oil and grease.
Releasing the water
Most of the treated wastewater is discharged to a deep ocean outfall. It 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.
Treated wastewater from North Head is discharged to the ocean.
Renewable energy generation
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.
Hydroelectricity
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.
Cogeneration
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.
The cogeneration engine turns biogas into energy and heat.
Operations and maintenance
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.
Maintaining the plant
There are three types of maintenance required to keep the plant operating: preventative, planned and reactive.
See the table below for examples.
Staff monitor the plant to make sure it's working at it's best.
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 |
Come behind the scenes
Want to visit one of our sites? We offer free excursions and technical tours to schools, universities and community groups.