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Recycling water
St Marys Water Recycling Plant is one of 30 wastewater treatment and water recycling plants in greater Sydney. It treats wastewater to tertiary standard. We use the recycled water for onsite re-use, irrigating a local golf course and environmental flows.
Facts and figures
Location: Links Road, St Marys
Population served: 160,000 people.
Area served: 84 km2, including the suburbs of Cambridge Park, Werrington Downs, Blackett, Mt Druitt, Minchinbury and St Clair.
Amount of wastewater treated: 33.5 million litres each day.
Treatment level: Tertiary.
Recycled water applications: We re-use some water on site for industrial purposes like washing down equipment and filter backwashes. Dunheved Golf Course uses our recycled water. They use up to 2 million litres a day to water the greens.
Environmental discharge: We release 4–8 million litres a day to a tributary of South Creek. We send the remainder to the St Marys Advanced Water Recycling Plant for advanced treatment before we release it to the Nepean River.
Amount of biosolids produced: 20,000 tonnes each year.
Operating licence and regulation: We operate the plant under 3 sets of rules:
- Environmental protection license issued by NSW Environmental Protection Authority (EPA). View the licence limits.
- Recycled water produced by the plant must meet the Australian guidelines for water recycling.
- Biosolids produced by the plant must meet the EPA's biosolids Environmental guidelines: Use and disposal of biosolids products.
Technical resources
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.
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 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 scrapers on the sedimentation tank to remove floating scum and settled solids.
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
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).
The bioreactor has different aeration zones.
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 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.
Large paddles stir chemicals into the water to help remove tiny particles.
Tertiary clarifier
When the flocs become large enough they settle to the bottom of the clarifier and are removed.
The treated water flows from the top of the tank to the filters.
Filtration
Filters made of layers of sand and coal trap and remove any remaining floc and fine solids.
Disinfection
We add chlorine to kill any micro-organisms. We remove any residual chlorine before discharging the treated wastewater to the environment or recycling it.
Flocs settle to the bottom of the tertiary clarifier.
Re-using the water
On our plants, we use recycled water instead of drinking water where ever we can. Hoses, sprays and filter backwashes all use recycled water. We use the remaining recycled water in a few ways.
Local golf course
We supply the local golf course with as much recycled water as they need to irrigate the greens and fairways.
Environmental flow
We release some water into the local creek, a tributary of South 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.
Dunheved Golf Course uses recycled water instead of drinking water to irrigate the greens.
We release high quality recycled water for environmental flow at Penrith.
Operations and maintenance
Running the plant
Eight 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 below for examples.
Staff monitor the plant to make sure it's working at its 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.