ASR - A Global Partner for the Sustainable Management of Coastal and Marine Resources


Location: Melbourne, Australia

Type of Project: Numerical Modelling, Outfall Assessment

Client: Melbourne Water, Australia

ASR Projects- Melbourne

An aerial view of the Western Treatment Plant.

Project Overview:

The Western Treatment Plant (WTP), 35 km west of Melbourne, is the largest lagoon and land sewage treatment plant in the world. It services more than 1.6 million people, treating about 55% of the sewage generated in the Melbourne metropolitan area. About 500 ML d-1 of sewage is processed at the plant, and the discharge forms the single largest nutrient input to Port Phillip Bay. In accordance with a revised discharge licence for the Western Treatment Plant, Melbourne Water commissioned ASR Ltd and Primary Industries Research, Victoria (PIRVic) to carry out studies of the mixing zone.

Project Outcomes:

This study considered the zone of influence within Port Phillip Bay of nutrients, particulate organic carbon, contaminants, and bacteria discharged by the WTP. The study aimed to quantify the effectiveness of a range of indicators of the above threats and the compliance of current indicators with State Environmental Protection Policies (SEPP). A number of indicators of impacts of the WTP are recommended. The two highest priorities are seen as better measurement of the extent of nutrient influence in the bay, and an improved understanding of the role of particulate organic carbon (POC) in maintaining the high intertidal productivity near the WTP outfalls. The latter is of importance as POC appears to sustain the high benthic productivity near outfalls upon which internationally important waders are dependent. The study proposed that nutrient influence should be monitored using the stable isotope 15N, which is greatly enriched in the outfalls from the WTP, by monitoring its concentration in macroalgae deployed around the outfall.

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