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.
| 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
Quantification approach
City West Water
Data source
Provided by
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.
| 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
Provided by
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.
| 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
Provided by
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.
| 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 on–site in the process of recirculation for treatment cannot be estimated accurately as some recycled water is used for on–site irrigation purposes.
Uncertainty information
Yarra Valley Water
Data source
Provided by
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.
| 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.