11.4 Wastewater collected
a. Wastewater system overview
The total wastewater volume collected was 38,429 ML during the 2011–12 year. Approximately 88% of the collected wastewater discharged to surface water after treatment (34,325 ML).
During the 2011–12 year, approximately 11% of treated wastewater was recycled; the rest was the losses. The following figure shows all the inflows and outflows associated with the wastewater system.
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 * indicate flows between sub-components 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 during the 2011–12 year for Canberra's wastewater system. Line item numbers are provided in brackets.
b. Supporting information
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 is treated at five wastewater treatment plants (WWTPs) in the Canberra region: the Lower Molonglo Water Quality Control Centre (LMWQCC), Fyshwick, Urriara, Outward Bound, and the Queanbeyan WWTPs. Some wastewater from Fyshwick and surrounding suburbs industrial area is treated at Fyshwick WWTP and returned to sewer for further treatment at LMWQCC.
For the 2012 year, ACTEW Water estimated that the metered wastewater volume at LMWQCC included 4,749 ML of stormwater and groundwater that entered the wastewater system, comprising; (a) ingress of stormwater and (b) infiltration of groundwater.
|Wastewater treatment plant||Inflow (ML)|
|add||Fyshwick Sewage Treatment Plant (STP)
||Discharge from Fyshwick STP to LMWQCC||616|
This volume is calculated by comparing calculated annual dry weather inflow to measured annual inflows, with the difference assumed to be ingress to the sewer system. The dry weather inflow volume is calculated by multiplying the volume of inflows to LMWQCC during a dry week by 365/7 to give an annual volume. The dry week used was 1–7 November 2011, when inflows were 562.8 ML. The dry weather inflow would be 29,347 ML.
|Total inflows into LMWQCC||34,096|
|less||Base-flow inflows over year||29,347|
Assumptions, limitations, caveats and approximations
- This line item is based on the assumption that in the dry reference week, there is no net gain or loss of stormwater and/or groundwater into or out of the sewer system.
- Only the inflow to the LMWQCC is considered. Data for Queanbeyan WWTP were not available.
These data are calculated from measured and estimated data using broad assumptions; the uncertainty is estimated to be of the order of +/–20 %.