Cronulla Water Resource Recovery Facility

Treating wastewater

Cronulla is one of about 30 water resource recovery facilities in Greater Sydney. Here, we treat wastewater to a tertiary standard. We use some of the treated water for on-site reuse and return the rest to the environment.

Facts and figures

Location: Captain Cook Drive, Kurnell

Population served: 250,000 people

Area served: 145 square kilometres – including the suburbs of Cronulla, Sutherland, Helensburgh, Menai, Bundeena and Maianbar

Wastewater treated: 53 million litres each day

Treatment level: Tertiary

Recycled water applications: We reuse some water on-site for industrial purposes like washing down equipment and filter backwashes.

Environmental discharge: We release the treated wastewater to the ocean at Potter Point, Kurnell.

Biosolids produced: 19,000 tonnes each year.

Operating licence and regulation: We operate the facility under 2 sets of rules:

Technical resources
Cronulla Wastewater Treatment Plant technical data technical specifications for the facility
What's in wastewater? – common wastewater parameters
Removing nutrients in wastewater fact sheet

Flow chart

Primary treatment

Primary wastewater treatment removes large solids using physical separation processes. Most of the solids removed can be treated for beneficial reuse.


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 grit such as sand and coffee grounds to the edges. It collects in the bottom of the tank where a scraper removes it.

Large solids like wipes, food scraps, rubbish, cotton buds and plastic are caught on the screens.


Sedimentation tanks enable 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.

At Cronulla, we’ve covered the top of the sedimentation tanks with a canvas material to control odour.

We use sedimentation tanks to remove floating scum and settled solids. We’ve covered the tanks to help control odour.

Secondary treatment

Secondary treatment removes nutrients such as phosphorous and nitrogen using physical and biological processes. Learn more about Removing nutrients in wastewater.


We add a high concentration of microorganisms (activated sludge) to the wastewater. By varying the amount of air in different parts of the tank, we ensure different types of microorganisms can break down nutrients like nitrogen and phosphorous.

Microorganisms break down nutrients in the bioreactor.

Secondary clarifier

The activated sludge settles to the bottom of the clarifier where scrapers remove it. We recycle some of this sludge back into the bioreactor and treat the rest to produce biosolids.

The treated water from the top of the tank flows to tertiary treatment.

We use clarifiers to separate the activated sludge from the treated wastewater.

Tertiary treatment

Tertiary treatment uses physical processes to remove very fine solids and disinfect the treated wastewater.


Filters made of layers of sand and coal trap remove any remaining floc and fine solids.


We use ultraviolet light to kill any remaining microorganisms that can make people sick. We pass the water through a set of submerged ultraviolet lamps that destroy microorganisms by damaging their DNA.

We use layers of sand and coal to filter the treated wastewater.

Releasing the water

At our facilities, we use recycled water instead of drinking water wherever we can. Hoses, sprays and filter backwashes all use recycled water.

We release the remaining treated wastewater into the ocean at Potter Point, Kurnell.

Renewable energy generation

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


At Cronulla, we use cogeneration to produce up to 60% of the facility's total energy needs.

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


We're trialling co-digestion at Cronulla.

We collect pulped fruit and vegetable waste from local businesses to add to the digesters, which creates more biogas. We can then use the biogas to make extra renewable energy in the cogeneration engine.

Learn more about energy management and climate change.

We use cogeneration to produce renewable energy that we can use on-site.

Operations and maintenance

Running the facility

Several staff manage, operate and maintain the facility. They collect and analyse water samples, do laboratory testing, and manage special projects to keep it running safely and efficiently.

Maintaining the facility

Three types of maintenance are required to keep the facility operating: preventative, planned and reactive.

See the table below for examples.

Staff working at the facility monitor its performance.

Maintenance type




Prevents a breakdown

Oiling a motor


Replacing equipment as it reaches the end of its useful life, before a breakdown

Replacing a worn motor


Fixing equipment that has unexpectedly broken down

Repairing a motor


Cogeneration is the production of heat and energy at the same time.


Co-digestion involves adding extra organic waste to parts of the facility to increase the amount of biogas and energy generated.