Cronulla Wastewater Treatment Plant

Treating wastewater

Cronulla Wastewater Treatment Plant is one of 30 wastewater treatment and water recycling plants 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.

Amount of 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.

Amount of biosolids produced: 19,000 tonnes each year.

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

Technical resources

 

Cronulla Wastewater Treatment Plant technical data (332KB) – Read technical specifications for the plant.

 

What's in wastewater? (279 KB) – Learn about common wastewater parameters.

 

Removing nutrients in wastewater  (192KB) – 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.

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.

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

Sedimentation

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 (192KB).

Bioreactor

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

Micro-organisms 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.

Filtration

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

 

Disinfection

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

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


Releasing the water

At our plants, 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.

Cogeneration

At Cronulla, we use cogeneration to produce up to 60% of the plant'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.

Co-digestion

We're currently trialing 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.

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


Operations and maintenance

Running the plant

Several 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 3 types of maintenance required to keep the plant operating: preventative, planned and reactive.

See the table below for examples.

Staff working at the plant monitor its performance.

Maintenance type

Description

Example

Preventative

Prevents a breakdown

Oiling a motor

Planned

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

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.


Cogeneration

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

Co-digestion

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