South East Queensland
9.9 Discharge from urban water system

Supporting Information

This line item consists of urban water supply system (including potable and non-potable water), wastewater collection system and recycled water supply system discharges to surface water within the South East Queensland (SEQ) region.

Urban water supply system discharges

Discharges from the urban water supply system could not be quantified in a way that is complete, neutral and free from material error, but are expected to be minor compared to wastewater and recycled water discharges. Discharges may include supply system flushing, air valve releases and tank cleaning.

Wastewater collection system discharges

A number of wastewater treatment plants (WWTPs) discharge treated wastewater to rivers and creeks within the SEQ region. This line item includes discharges to freshwater rivers and creeks that form part of the surface water system. Discharges to estuarine rivers, creeks, inlets and the sea are reported in line item 19.7 Wastewater discharge outside of region. A number of WWTPs that discharge to the Brisbane River are included in line item 19.7 Wastewater discharge outside of region, as the Brisbane River is estuarine through much of the urban Brisbane area.

Recycled water supply system discharges

Reverse osmosis brine concentrate from the Bundamba Advanced Water Treatment Plant was discharged to the Bremer River as part of the Western Corridor Recycled Water Scheme treatment process.

Excess purified recycled water discharges occurred from the Gibson Island and Luggage Point advanced water treatment plants, but as the Brisbane River is estuarine at the discharge point, these discharges were reported in line item 19.7 Wastewater discharge outside of region. No excess purified recycled water discharges to surface water occurred from Bundamba Advanced Water Treatment Plant.

There is potential for recycled water discharges from the Western Corridor Recycled Water Scheme to Lake Wivenhoe in accordance with the current SEQ System Operating Plan when SEQ Water Grid storages fall below 40%. When the total volume of water stored by key Water Grid storages falls below 40% of the total water storage capacity of these storages, the supply of purified recycled water to Lake Wivenhoe from the Western Corridor Recycled Water Scheme is to be maximised, subject to appropriate approvals from Queensland Department of Environment and Resource Management (DERM). Storages were well above this trigger level throughout the 2010–11 year, so no discharges to surface water storages occurred. If and when purified recycled water is introduced into Lake Wivenhoe, this water will then be available for use throughout the entire SEQ region via the SEQ Water Grid.

 

Wastewater and recycled water discharges to surface water
Discharge description Volume (ML)
Treated wastewater discharge       56,517
Excess recycled water discharge            – 
Reverse osmosis concentrate discharge           816
Total SEQ region       57,333

Quantification Approach

Data Source

Queensland Department of Environment and Resource Management (DERM) licensed discharge data from the Point Source Database. Qldwater Statewide Water Information Management (SWIM) system indicator WA71 (wastewater discharge) for Queensland Urban Utilities and indicator WA20, 21 and 22 (recycled water supplied) for Queensland Urban Utilities and Unitywater. Allconnex Water and Unitywater internal database of Wastewater Treatment Plant discharge volumes. Allconnex Water, Unitywater and Queensland Urban Utilities internal database of Wastewater Treatment Plant influent. Seqwater Western Corridor Recycled Water Scheme dataset.

Provided by

Bureau of Meteorology.

Method

Wastewater collection system discharges

Annual WWTP discharge volumes obtained from DERM's Point Source Database, Qldwater statewide water information management (SWIM) indicators and urban utility databases were compared with each other and with WWTP influent data and recycled water supply data. Where discrepancies between datasets occurred, the closest discharge to the influent minus the recycled water supplied was chosen. This resulted in Point Source Database data being chosen for some WWTP, SWIM data for others and urban utility data for yet others. Where the recycled water supplied was the same as the influent, the WWTP discharge was assumed to be zero.

Each WWTP discharge point was then identified and WWTP that discharge to sea, inlets, estuaries and landscape were removed from the list. The discharge from the remaining WWTP were summed to provide the total wastewater collection system discharge to surface water.

Recycled water supply system discharges

Annual advanced WWTP discharge data for reverse osmosis concentrate and excess purified recycled water was obtained from Seqwater datasets. The volume of reverse osmosis concentrate and excess purified recycled water from Bundamba Advanced WWTP was included in this line item, as it was the only plant that discharged to surface water.

 

Assumptions, Limitations, Caveats and Approximations

It was assumed that the WWTP discharge data that most closely represented the influent minus the recycled water supplied was the most accurate value. Despite this being the best choice from a water balance point of view, inaccuracies in WWTP discharge data may have occurred.

Uncertainty Information

The uncertainty estimate was not quantified.

Comparative year

This line item corresponds to line item 20.4.1 Discharge of urban wastewater to connected surface water reported in the 2010 Account. The understanding of discharge points for WWTP in the SEQ region has developed since 2010 Account publication.

In the 2010 Account a breakdown of discharge by WWTP was not available and a number of WWTP discharging to estuaries were included in this line item. With a more accurate understanding of the discharge locations and individual WWTP discharge data, a number of WWTP discharges were moved from this line item to line item 19.7 Wastewater discharge outside of region in the 2011 Account. This was particularly prevalent in the Brisbane River, as the estuary extends through most of the urban Brisbane area and there were a number of WWTPs now reported as line item 19.7 Wastewater discharge outside of region.

The 2011 Account comparison year uses the volume reported in the 2010 Account, as a breakdown of WWTP discharges for the 2010 Account data were not available.