Melbourne
11.4 Wastewater collected

Supporting information

a. Wastewater collected

The volume presented in the water accounting statements (341,462 ML) represents the volume of wastewater collected within the Melbourne region by retail water authorities City West Water, South East Water, Yarra Valley Water and Western Water during the 2012–13 year.

The value represents the metered wastewater volume collected in the region.  This volume includes wastewater discharged to the sewer after usage and any variation due to (a) ingress of stormwater; (b) infiltration of groundwater; (c) wastewater overflows to stormwater; and (d) exfiltration of wastewater to groundwater.  

Wastewater collected by retail water authorities
Authority Volume (ML)
City West Water

84,634

South East Water

120,521

Western Water

8,157

Yarra Valley Water

128,150

Total

341,462


b. Wastewater system overview

The wastewater system is one of three subcomponents of Melbourne's urban water system. The three subcomponents are the:

  • urban water supply system
  • wastewater system
  • recycled water system.

In the Melbourne region, wastewater is collected (line item 11.4) from users by the four retail water authorities within the region:

  • City West Water
  • South East Water
  • Western Water
  • Yarra Valley Water.

Following collection, wastewater is either delivered to smaller, local wastewater treatment plants operated by the authorities, or delivered to one of the major wastewater treatment plants: Melbourne Water Eastern Treatment Plant or Melbourne Water Western Treatment Plant. During the 2012–13 year, Melbourne Water received and treated almost 90% of the wastewater collected within the region.

During the 2012–13 year the majority 75% (line item 19.7) of wastewater system outflows was treated wastewater discharged to sea; approximately 17% was recycled (an increase from 11% in 2011–12); discharge to surface water was < 3% (line item 19.5 ), evaporative losses and other accounted for about 5% (line item 19.1).

The following figure shows all the inflows and outflows associated with the wastewater system. The small misbalance shown (< 1%) can be attributed to metering inaccuracies, unaccounted losses, and inaccuracies in the estimation of the recycled water on-site in process use.

For more detail on a particular flow associated with the wastewater system, refer to the line item notes. Note that volumes annotated with an asterick (*) indicate flows between subcomponents and are not reported in the account. As such, these flows do not have an associated line item number.

Schematic diagram of water inflows and outflows for Melbourne's wastewater system during the 2012–13 year; line item numbers are provided in brackets
Schematic diagram of water inflows and outflows for Melbourne's wastewater system during the 2012–13 year; line item numbers are provided in brackets

Quantification approach

City West Water

Data source

Supervisory Control and Data Acquisition (SCADA) database.

Provided by

City West Water.

Method

The volume of wastewater collected by City West Water was calculated from the following components:

  • wastewater collected from the City West Water service area and transferred to the Melbourne Water Western Treatment Plant, metered by Melbourne Water
  • wastewater collected at the Altona treatment plant, metered by City West Water
  • wastewater taken at the Sunshine sewer mining plant, metered by City West Water.

Melbourne Water bulk meters are read daily. The location of the meters and details of the network are contained in the bulk supply agreements for each water authority.  

City West Water meter flows are read daily at the Altona treatment plant and Sunshine sewer mining.

City West Water–wastewater collected 
Wastewater collected 2013 Volume (ML)
Collected and delivered to Melbourne Water Western Treatment Plant

84,558

Volume taken from Sunshine sewer mining plant

76

Total

84,634

Assumptions, limitations, caveats and approximations

Melbourne Water has a suite of bulk meters and formulas in order to attribute volumes to the three retailers. The meter network and locations are contained in a bulk supply agreement with City West Water.

Uncertainty information

The uncertainty is estimated to be +/– 10% based on meter specifications.

South East Water

Data source

Internal database.

Provided by

South East Water and Melbourne Water.

Method

The volume of wastewater collected by South East Water was calculated from the following components:

  • Wastewater collected from the South East Water service area and transferred to Melbourne Water's eastern and western treatment plants, metered by Melbourne Water
  • Wastewater collected at South East Water's sewage treatment plants and metered by South East Water.

Melbourne Water bulk meters are read daily. The location of the meters and details of the network are contained in the bulk supply agreements for each water authority.

South East Water meters record flows daily at their sewage treatment plants.

South East Water–wastewater collected
Wastewater collected 2013 Volume (ML)
Collected and treated at South East Water's treatment plants

12,194

Collected and delivered to the Melbourne Water Western Treatment Plant

28,461

Collected and delivered to the Melbourne Water Eastern Treatment Plant

79,866

Total

120,521

Assumptions, limitations, caveats and approximations

Melbourne Water has a suite of bulk meters and formulas in order to attribute volumes to the three retailers. The meter network and locations are contained in a bulk supply agreement with South East Water.

Uncertainty information

The uncertainty is estimated to be +/– 5% in accordance with the Water Industry Regulatory Audits 2013 independent annual audit report.

Western Water

Data source

Recycled water plant data.

Provided by

Western Water.

Method

The volume of wastewater collected was calculated from metered daily flows at Western Water's recycled treatment plants. Meters are located at the entrance to the plant and record all incoming water. Meters are read daily by the treatment plant operators.


Western Water–wastewater collected
Wastewater treatment plant  2013 Volume (ML)
Total

8,157

Assumptions, limitations, caveats and approximations

The volume does not include wastewater collected from Woodend. The volume of wastewater added via the recycled water onsite in the process of recirculation for treatment cannot be estimated accurately as some recycled water is used for onsite irrigation purposes. 

Uncertainty information

The uncertainty is estimated to be +/– 5% in accordance with the Summary Audit Report, October 2010 Essential Services Commission 2011.

Yarra Valley Water

Data source

Internal database.

Provided by

Yarra Valley Water.

Method

The volume of wastewater collected by Yarra Valley Water was calculated from the following components:

  • Wastewater collected from the Yarra Valley Water service area and transferred to Melbourne Water's Eastern and Western treatment plants, metered by Melbourne Water
  • Wastewater collected at Yarra Valley Water's local treatment plants and metered by Yarra Valley Water.

Melbourne Water bulk meters are read daily. The location of the meters and details of the network are contained in the bulk supply agreements for each water authority.

Yarra Valley Water–wastewater collected
Wastewater collected 2013 Volume (ML)
Collected and treated at Yarra Valley Water's treatment plants

10,073

Collected and delivered to Melbourne Water Western Treatment Plant

67,796

Collected and delivered to Melbourne Water Eastern Treatment Plant

50,281

Total

128,150

This total volume includes wastewater discharged to the sewer after usage and any variation due to (a) ingress of stormwater; (b) infiltration of groundwater; (c) wastewater overflows to stormwater; and (d) exfiltration of wastewater to groundwater.

Yarra Valley Water estimated that 14,701 ML of stormwater and groundwater entered the wastewater system—components (a) and (b), 34 ML of wastewater overflowed to stormwater from the emergency relief structures of the wastewater system—component (c).

Assumptions, limitations, caveats and approximations

Melbourne Water has a suite of bulk meters and formulas in order to attribute volumes to the three retailers. The meter network and locations are contained in a bulk supply agreement with Yarra Valley Water.

Uncertainty information

The uncertainty is estimated to be +/– 10% based on meter specifications.