Melbourne
3.2 Wastewater system
Supporting information
The volume presented in the water accounting statements (29,132 ML) represents the estimated volume of wastewater stored in Melbourne Water's western and eastern treatment plants. There are a number of other smaller wastewater treatment plants operated by the urban retailers in the Melbourne region; however, their volumes were not included as they were not considered significant or material to the 2013 Account.
The breakdown of the estimated volume of wastewater storage at the western and eastern treatment plants is shown in the following table.
Treatment plant |
Component |
Volume at 30 June 2013 (ML) |
Volume at 30 June 2012 (ML) |
|
115 east lagoon |
4,373 |
4,055 |
|
55 east lagoon |
6,138 |
5,805 |
|
25 west lagoon |
6,201 |
5,935 |
|
85 west C lagoon |
973 |
931 |
|
85 west A lagoon |
483 |
459 |
|
85 west B lagoon |
845 |
736 |
Western Treatment Plant |
145 west A lagoon |
1,133 |
829 |
|
145 west B lagoon |
1,430 |
1,065 |
|
Walsh's lagoon |
1,429 |
1,140 |
|
Lake Borrie north lagoon |
1,782 |
1,139 |
|
Lake Borrie south lagoon |
1,875 |
1,153 |
|
Western lagoon |
540 |
166 |
|
T-section lagoon |
523 |
163 |
Western Treatment Plant subtotal |
|
27,725 |
23,576 |
Eastern Treatment Plant |
Volume in storage undergoing treatment |
409 |
580 |
|
Volume stored in effluent holding basins |
998 |
1046 |
Eastern Treatment Plant subtotal |
|
1,407 |
1626 |
Total |
|
29,132 |
25,202 |
Quantification approach
Data source
Provided by
Method
Wastewater system storage was calculated using the following methods:
An estimate of wastewater storage volume was based on surveys conducted by Melbourne Water between 1980 and 2000 to determine the approximate volume of each lagoon at the western treatment plant. The total storage volume at this plant was the sum of the individual lagoon volumes.
An estimate of wastewater storage volume was determined using level gauging in effluent-holding basins. Levels were interpreted as volumes using stage–storage relationships. Stage–storage relationships were determined from surveys of the effluent holding basins. Effluent-holding basins at the eastern treatment plant that held wastewater at the time of measurement were Forebay, SEHD, and EHB6.
Assumptions, limitations, caveats and approximations
- The total storage volume for the Western Treatment Plant is assumed to be the same for 1 July 2011 and 30 June 2012.
- The calculation of wastewater storage was based on surveys conducted between 1980 and 2000. Since the surveys were completed, the volume of sludge in the process has varied considerably, and there have been significant changes in the operation of the lagoons that undertake the bulk of the wastewater treatment.
- The content of liquid in aeration tanks was approximately 50% primary effluent and 50% activated sludge.
- Raw sewage, and primary and secondary effluent channel volumes have not been included as the volumes are insignificant.
Uncertainty information
The uncertainty estimate for the Melbourne Water Western Treatment Plant volumes was +/– 20%.
The uncertainty estimate for the Melbourne Water Eastern Treatment Plant volumes was not quantified.