Melbourne
19.5 Discharge from urban water system to surface water

Supporting information

a. Discharge from urban water system

The volume presented (26,243 ML) represents the treated wastewater discharged to surface water from, Western Water's recycled water plants (RWPs) and Yarra Valley Water's local treatment plants (LTPs), and recycled water provided by the Melbourne Water Western Treatment Plant as environmental flows to the Lake Borrie Wetlands within the Melbourne Water Western Treatment Plant. 

South East Water reported 649 ML of treated wastewater discharge to surface water in 2012; however, this year the South East Water reported volume is 0 ML.

The breakdown of treated wastewater discharge to surface water in the Melbourne region during the 2012–13 year is presented in the following table.

Discharge from urban water system to surface water
Discharge type

Water authority

Volume (ML)

treated wastewater discharge to surface water Western Water

3,140

Yarra Valley Water 6,687
South East Water

0

Sub-total

9,827
recycled water discharge as environmental flow Melbourne Water

16,416

Total  

26,243

Western Water–treated wastewater discharged to surface water
Discharge location Volume (ML)
Bacchus Marsh RWP to land lot/lagoon 141
Gisborne RWP to Jacksons Creek 488
Melton RWP to Werribee River 878
Riddells Creek RWP to Riddells Creek 97
Romsey RWP to Deep Creek 280
Sunbury RWP to Jacksons Creek 1,256
Total 3,140
Yarra Valley Water–treated wastewater discharge to surface water
Discharge location  Volume (ML)
Brushy Creek LTP to Brushy Creek 3,245
Craigieburn LTP to Merri Creek 395
Healesville LTP to Yarra River 319
Upper Yarra LTP to Yarra River 739
Lilydale LTP to Olinda Creek 1,767
Monbulk LTP to Sassafras Creek 18
Wallan LTP to Merri Creek 204
Total 6,687

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

c. Recycled water system overview


The recycled water system is one of three sub-components of Melbourne's urban water system. The three sub-components are the:

  • Urban water supply system
  • Wastewater system
  • Recycled water system.

Wastewater treatment plants located within the Melbourne region produce the majority of recycled water (see 'Wastewater System Overview' for further information). A very small volume of recycled water (161 ML: line item 11.21) is received from external organisations to supplement Melbourne's recycled water system.

During the 2012–13 year, approximately 45% of the recycled water produced (including the recycled water received from external organisations) was used on-site at wastewater treatment plants throughout the Melbourne region.  Of the recycled water used on-site, approximately half that volume (15,118 ML) was recirculated back into the wastewater system (and therefore not reported in the water accounting statements). The remaining recycled water used on-site, 11,406 ML, was for irrigation/outdoor purposes or in-process and reported at (line item 19.4).

The remaining recycled water produced in Melbourne was supplied for use; 8,511 ML was supplied to urban water system users (line item 19.4); and 8,076 ML was supplied to either the Eastern Irrigation Scheme or Werribee Irrigation District (line item 19.6). Recycled water was also supplied for environmental purposes to Lake Borrie Wetlands within the Melbourne Water Western Treatment Plant (line item 19.5).Overall, 19,917 ML of recycled water was supply for urban consumption (8,511 ML) and on-site use (11,406 ML). These volumes are reported as part of (line item 19.4).

The following figure presents the inflows and outflows associated with the recycled water system. A small misbalance (1.6%) is shown, due to the difference between the volume of recycled water available for supply and the volume of recycled water supplied for use. The misbalance 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 recycled water system, refer to the line item notes. Note that volumes annotated with an asterick (*) indicate flows between urban subcomponents and are not reported in the 2013 Account.  As such, these flows do not have an associated line item number or note.

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

Quantification approach

Melbourne Water

Data source

Supervisory control and data acquisition (SCADA) database.

Provided by

Melbourne Water.

Method

Water recycled and used for conservation flows is metered using an ultrasonic level transmitter. This recycled water is measured by Melbourne Water before being discharged to the Lake Borrie Wetlands (Ramsar-listed).

Assumptions, limitations, caveats and approximations

Data are logged daily and reported quarterly, and thus metering periods align with the reporting period.

Uncertainty information

Ultrasonic level transmitters are used to measure flows and are assumed to have an accuracy of +/– 5 to +/– 10%.

Western Water

Data source

RWP data.

Provided by

Western Water.

Method

Meters are located at the outlet of the treatment plants and are read daily by the treatment plant operators. 

Assumptions, limitations, caveats and approximations

Excludes discharge at Woodend RWP to Five Mile Creek, as this is not located within the Melbourne region.

Uncertainty information

The uncertainty is estimated to be +/– 5% based on meter specifications.

Yarra Valley Water

Data source

BI reporting system, treatment plant, and trade waste dashboard and Flow and reuse summary report.

Provided by

Yarra Valley Water.

Method

Meters measuring the volume of treated wastewater discharged from local treatment plants to surface water are read daily.

Assumptions, limitations, caveats and approximations

Nil.

Uncertainty information

The uncertainty is estimated to be +/– 5% based on meter specifications.