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Long-term results show water quality and ecosystem health in inland waterways and Sydney beaches continue to be maintained.

Wastewater treatment system discharges

Indicator: Total mass of phosphorus and nitrogen discharged to streams/rivers from inland sewage treatment plants

In 2009–10, Sydney Water’s inland sewage treatment plants (STPs) discharged 9.3 tonnes of phosphorus and 317 tonnes of nitrogen to streams and rivers in the lower Hawkesbury-Nepean catchment. These loads were within the limits permitted under licences issued by the Department of Environment, Climate Change and Water (DECCW).

Diffuse sources, such as agricultural runoff, contribute an estimated 352 tonnes of phosphorus and 2,229 tonnes of nitrogen to the lower Hawkesbury-Nepean each year. Studies indicate that this may comprise 70-80% of the total phosphorus and nitrogen loads in the catchment.¹ Point sources, such as inland STPs, contribute the remainder.

Sydney Water’s inland STPs provide tertiary treatment with additional nutrient removal to remove phosphorus and nitrogen to very low levels. DECCW licences specify concentration limits for phosphorus, nitrogen and other pollutants (including chlorine and metals). In 2009–10, discharges from inland STPs continued to meet DECCW licence requirements for concentrations of phosphorus and nitrogen.

For the majority of our inland STPs, the median phosphorus concentration was less than 0.1 milligram a litre (mg/L), exceeded only at Picton STP. The median nitrogen concentration was less than 10 mg/L at most inland STPs, except at Castle Hill and Winmalee.

The dry weather mass of phosphorus and nitrogen discharged to inland streams and rivers has remained low since 2002–03, when Sydney Water began a major upgrade of its STPs and also started to decommission poorly performing STPs. The slight reduction in the amount of nitrogen and phosphorus discharged during dry weather in 2009–10 is attributed to the St Marys Water Recycling Plant (Replacement Flows) Project, which began commissioning at the end of March 2010. This project connects the St Marys, Penrith and Quakers Hill STPs to a new, advanced plant at St Marys where wastewater is further treated. The highly treated recycled water is released into the Hawkesbury-Nepean River below Penrith Weir. Nutrient loads are expected to further improve next year when the plant’s full benefits are realised.

Further improvements have come from the upgrade of West Camden STP in August 2009, and the stage two amplification of Rouse Hill STP, commissioned in March 2009. Nitrogen loads discharged from these plants fell about 47% and 22% respectively and phosphorus loads fell about 76% and 21% respectively compared to 2008–09.

Overall, the largest amounts of nitrogen came from Winmalee, St Marys and Castle Hill STPs, and the largest amounts of phosphorus came from Winmalee, St Marys and Penrith STPs. The increase in wet weather phosphorus load during 2009–10 is attributed to significant inflows due to heavy rain and flooding around West Hornsby STP in February 2010.
Nutrient loads are influenced by wet weather events, population growth and the treatment capacity of STPs. In wet weather, wastewater inflows can exceed the capacity of STPs and bypass some treatment processes, which is permitted under DECCW licence conditions.

For more information on Sydney Water’s wastewater treatment system licences, please see the DECCW website and public register at www.environment.nsw.gov.au/licensing/

Total mass of phosphorus discharged to streams/rivers from inland sewage treatment plants

Note: In 2008–09, Sydney Water adopted a revised methodology to improve the accuracy of dry and wet weather load calculations and amended previously reported numbers accordingly.

Total mass of nitrogen discharged to streams/rivers from inland sewage treatment plants

Note: In 2008–09, Sydney Water adopted a revised methodology to improve the accuracy of dry and wet weather load calculations and amended previously reported numbers accordingly.

Indicator: Total mass of suspended solids and grease discharged from ocean sewage treatment plants

The total mass of suspended solids discharged from ocean STPs in 2009–10 was 59,235 tonnes. The total amount of grease discharged was 11,238 tonnes.

Approximately 75% of Sydney’s wastewater is treated at the North Head, Bondi and Malabar ocean STPs and discharged through their deepwater outfalls. These STPs contributed about 99% of the suspended solids and grease loads discharged in 2009–10. The year’s loads were well within the limits permitted under the DECCW licences, and there is no evidence of any significant environmental impacts from these discharges.

Suspended solids and oil and grease loads have remained relatively constant since the late 1990s. Works at North Head STP accounted for a slight increase in dry weather suspended solids loads in 2009–10 compared to 2008–09.

Loads are influenced by population growth and wet weather events. Over the past four years, Sydney Water has focused on maintaining the performance and reliability of STPs to continue to serve Sydney’s growing population. For more information on STP upgrades, please see Sydney Water’s website: sydneywater.com.au/MajorProjects

Total mass of suspended solids discharged from ocean sewage treatment plants

Note: In 2008–09, Sydney Water adopted a revised methodology to improve the accuracy of dry and wet weather load calculations and amended previously reported numbers accordingly.

Total mass of oil and grease discharged from ocean sewage treatment plants

Note: In 2008–09, Sydney Water adopted a revised methodology to improve the accuracy of dry and wet weather load calculations and amended previously reported numbers accordingly.

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