Penrith Water Recycling Plant

Penrith Water Recycling Plant is one of 30 wastewater treatment and water recycling plants in greater Sydney.

Here, we treat wastewater to tertiary standard. We use the recycled water for on-site re-use and environmental flows, and to water local sporting fields.

Aerial view of the plant

Penrith Water Recycling Plant produces high quality recycled water.

Want to visit a wastewater treatment or water recycling plant?

Come behind the scenes to see firsthand how the wastewater of Penrith and the lower Blue Mountains is treated and recycled back into the Nepean River.

We offer excursions and technical tours to high schools, universities and community groups.

Find out more about Excursion requests.
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 each day  24 million litres
Treatment level  Tertiary
Recycled water applications
  • We reuse 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 each year  20,000 tonnes.
Operating license and regulation We operate the plant under three sets of rules:

Primary Treatment

Penrith flow chart

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

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.

Wipes and rubbish caught on a screen.

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).


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.

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.

Image of a clarifier tank.

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 three stages - aeration, settling and decanting - in one tank, rather than passing through separate tanks.

Aerial image of the IDAL at Penrith.

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.

Image of the filter tanks.

We use sand to filter the treated wastewater.


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.

Image of the disinfection tank.

We add chlorine to make sure the water is safe for the environment.

We use recycled water for many different things.

On-site re-use

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

Local sports fields

We supply Penrith Council with as much recycled water as they need to irrigate the local sports fields.

Penrith sportsfield

Local sports fields use recycled water from Penrith. 

Environmental flow

We release some water into the local creek to help keep the creek alive and healthy.

Advanced treatment

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.

Penrith advanced outflow

Highly treated recycled water returns to Penrith to be released for environmental flow.

Discharge at Penrith

We release high quality recycled water for environmental flow at Penrith.

Penrith wier

The recycled water is released into the Hawkesbury-Nepean river.

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.
Operators at Penrith

Plant staff check things are working well and organise maintenance. 

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