Queensland
Most effluent released directly into waterways from sewage treatment plants in Queensland comes from the more populated coastal areas in South East Queensland (SEQ), and from coastal Great Barrier Reef (GBR) catchments.
The combined volume of treated sewage released to coastal waterways has been relatively steady since 2010 at around 290 gigalitres per year, with exception in 2021 and 2022.
- Slight reductions in 2014 and 2016 are most likely due to below-average rainfall and a subsequent reduction in inflows to the sewage treatment plants.
- Larger annual volumes were observed in 2021 and 2022, due to significantly above average annual rainfall in SEQ, including the 2021-22 Southern Queensland Floods.
Nitrogen and phosphorus are present in treated sewage and can impact waterways, particularly by promoting excessive plant and algal growth.
Nitrogen
- Sewage treatment plants released about 1,200 to 1,300 tonnes of nitrogen to coastal Queensland waterways annually from 2010 to 2019.
- Nitrogen load was lower in 2014 and 2016, attributed to lower rainfall and treated sewage volumes, particularly from SEQ treatment plants.
- A significant increase to over 1,500 tonnes of nitrogen was observed from 2020 to 2023, attributed mainly to increased loads released via the ocean outfall from the Sunshine Coast treatment plants and due to increased volumes caused by high annual rainfall in 2021 and 2022.
Phosphorous
- In 2022, sewage treatment plants released 470 tonnes of phosphorous into Queensland’s coastal waterways.
- There have been significant decreases in phosphorous load since 2015, except for an increase in 2023
- The average phosphorus concentration of releases in Queensland in 2022 was 1.2 mg/L, reduced from 2.1 mg/L in 2010.
- This significant reduction in phosphorus concentration and load is attributed to improved treatment from both SEQ and GBR plants.
