Melbourne

                                                                                                   

5.2 Urban wastewater system

                             

Supporting information   


The volume recognised in the water accounting statements (24,709 ML) represents the volume of wastewater held in Melbourne Water’s Western Treatment Plant and Eastern Treatment Plant.

There are a number of other smaller wastewater treatment plants that operate in the Melbourne region, and their volumes have not been included as they are not considered significant.

The breakdown of the volume of wastewater storage at the Western Treatment Plant and Eastern Treatment Plant are shown below.

 

Wastewater treatment plant wastewater storage in the Melbourne region
Treatment Plant Component Opening volume (ML) 1 July 2009 Closing volume (ML) 30 June 2010
Western Treatment Plant 115 east lagoon 4,055 4,055
55 east lagoon 5,805 5,805
25 west lagoon 5,935 5,935
85 west C lagoon 931 931
85 west A lagoon 459 459
85 west B lagoon 736 736
145 west A lagoon 829 829
145 west B lagoon 1,065 1,065
Walsh’s lagoon 1,140 1,140
Lake Borrie north lagoon 1,139 1,139
Lake Borrie south lagoon 1,153 1,153
Western lagoon 166 166
T-section lagoon 163 163
Western Treatment Plant subtotal
  23,576  23,576
Eastern Treatment Plant Volume in storage undergoing treatment 253 253
Volume stored in effluent holding basins 490 880
Eastern Treatment Plant subtotal
  743  1,133
Total 24,319 24,709

 

Quantification approach   


Data source

Melbourne Water: Western Treatment Plant and Eastern Treatment Plant records.

Data provider

Melbourne Water.

Method

The volume of wastewater storage was the sum of the volume of wastewater held at the Western and Eastern treatment plants. A different method was used to calculate the volume of wastewater storage for each treatment plant:

  • Western Treatment Plant

The wastewater storage volume was based on surveys conducted by Melbourne Water between 1980 and 2000 to determine the approximate volume of each lagoon at Western Treatment Plant. The total storage volume at Western Treatment Plant was the sum of the individual lagoon volumes.

  • Eastern Treatment Plant

The volume in storage at Eastern Treatment Plant was determined using level gauging in effluent holding basins. Levels were interpreted as volumes using stage–storage relationships. The stage–storage relationships have been determined following surveying 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.

Uncertainty

Derived from measured data. Uncertainty is ungraded.

Approximations, assumptions, caveats/limitations

Western Treatment Plant

  • The total storage volume for the Western Treatment Plant is assumed to be the same for 01 July 2009 and 30 June 2010.
  • 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 magnitude of uncertainty as a result of these changes is approximately 20%.

Eastern Treatment Plant

  • 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.