Penrith Water Recycling Plant

Recycling water

Penrith Water Recycling Plant is one of 30 wastewater treatment and water recycling plants in Greater Sydney. We treat wastewater to tertiary standard and use the recycled water for on-site re-use and environmental flows, and to water local sporting fields.

Facts and figures

Location: Castlereagh Road, Penrith.

Population served: 100,000 people.

Area serviced: 63 km2, including the suburbs of Castlereagh, Cranebrook, Mt Pleasant, Penrith, Glenmore Park, Glenbrook, Blaxland, Warrimoo and Mt Riverview.

Amount of wastewater treated: 24 million litres each day.

Treatment level: Tertiary.

Recycled water: We re-use some water on site for industrial purposes like washing down equipment and filter backwashes. Penrith Council uses up to 18 million litres of our recycled water a year to water nearby sports fields.

Environmental discharge: We send the remainder to the St Marys Advanced Water Recycling Plant for advanced treatment. The water is returned to Penrith and released into Boundary Creek. It flows to the Nepean River.

Amount of biosolids produced: 20,000 tonnes each day.

Operating licence and regulation: We operate the plant under 3 sets of rules:

Technical resources

Penrith Water Recycling Plant technical data (332KB) – read technical specifications for the plant.

What's in wastewater? (279KB) – 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 re-use.


Screens trap and remove large solids as wastewater flows through.

Grit removal

We stir the wastewater rapidly, forcing the water to spiral and create a vortex. The vortex causes grit, like sand and gravel to spiral to the centre of the tank, separating it from the water.

We split the wastewater into two streams. One stream flows to the sedimentation tank and bioreactor and the other flows to the Intermittently Decanted Aerated Lagoons (IDAL).

Screens trap and remove large solids as wastewater flows through.


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.

Secondary treatment

Secondary treatment removes nutrients such as phosphorous and nitrogen using physical, biological and chemical processes. Learn more about Removing nutrients in wastewater (192KB).

Bioreactor and clarifier

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 able to break down nutrients (like nitrogen and phosphorous).

We pump the wastewater to a 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.

Clarifiers settle out activated sludge.


We add a high concentration of micro-organisms (activated sludge) to the wastewater.

Like in the bioreactor, varying the amount of air ensures different types of microorganisms can break down nutrients (like nitrogen and phosphorous). In the IDAL, wastewater goes through 3 stages – aeration, settling and decanting  – in one tank, rather than passing through separate tanks.

The IDAL goes through aeration, settling and decanting in the one tank.

Tertiary treatment

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

Chemical mixing

We add chemicals that make the smallest particles ‘stick’ together forming larger ‘flocs’. This process is called flocculation.


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


For disinfection we add chlorine to kill any microorganisms that can make us sick. We remove any residual chlorine before discharging the treated wastewater to the environment or recycling it.

Re-using the water

We use the recycled water in a few different ways.

  • On our plants, we use recycled water instead of drinking water wherever we can. Hoses, sprays and filter backwashes all use recycled water.
  • We supply Penrith Council with as much recycled water as they need to irrigate the local sports fields.
  • We release some water into the Boundary Creek to help keep the creek alive and healthy.
  • The rest of the water is sent to the St Marys Advanced Water Recycling Plant for further treatment using membrane technology. This water is released into the Hawkesbury–Nepean River for environmental flow.

Local sports fields use the recycled water.

Some water is sent for advanced treatment.

Recycled water is released into the river.

Operations and maintenance

Running the plant

A small team 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.

Plant staff check things are working well and organise maintenance.

Maintenance type




Prevents a break down

Oiling a motor


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

Replacing a worn motor


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.


The used water that goes down toilets, sinks and drains and into the sewerage system. Also known as sewage. About 99% of it is water.


Sedimentation is a physical wastewater treatment process used to settle out suspended solids in water under the influence of gravity.

Intermittently Decanted Aerated Lagoons (IDAL)

A pond or tank where wastewater undergoes several treatment processes in rotation including sedimentation, biological treatment and clarification.


Organisms that are too small to be seen without a microscope.


Solid matter that is removed during wastewater treatment. It can be processed into a material called biosolids.


The process of drawing off the liquid without disturbing the sediment


A process where air is mixed through or dissolved in a liquid or substance.


The larger particles formed when smaller particles stick together with the aid of a coagulant during the process of flocculation.


Process of small suspended particles coming together with the help of an added chemical.


A chemical process that kills microorganisms capable of causing infectious disease.


To clean a filter by reversing the flow of water and air through it.

Environmental flow

Water released from dams and reservoirs to maintain the environmental flow of rivers, and the plants and animals that rely on this water.