City of Austin Performance Report 2014-15
Wastewater Quality: Carbonaceous Biochemical Oxygen Demand
One way of assessing the quality of treated wastewater effluent is to compare the actual level of Carbonaceous Biochemical Oxygen Demand (CBOD), in milligrams per liter (mg/l), to the permit level mandated by the Environmental Protection Agency (EPA) and the Texas Commission on Environmental Quality (TCEQ). The measure tracks the pollutants in the wastewater that the treatment plants remove, and a lower number represents fewer pollutants re-entering the river. Fish, other animals and plants in the river need oxygen to live, and this measure tracks Austin Water’s (AW) efforts to limit the amount of oxygen using pollutants that re-enter the stream through the release of treated effluent.
For this measure, the combined flow weighted average is calculated from effluent CBOD concentration and effluent flow, measured daily at each plant in accordance with the requirements of their Texas Pollutant Discharge Elimination System (TPDES) permit.
FY 2014-15 Results
The goal for this measure was established not to exceed 3.0 mg/l. This level is well below the permit level of 5.0mg/l for a yearly average. The permit level allows for a month average of 10.0 mg/l. The goal of staying below 3.0 mg/l will support the Austin Water (AW) commitment to protecting the environment through exceptional wastewater treatment. The annual average for FY 2014-15 was 2.19 mg/l.
Assessment of Results
The City of Austin’s effluent quality measure CBOD has consistently been well below the permitted level. The permit level is 10.0 mg/l (monthly average) and 5.0 mg/l (yearly average). Austin has two main wastewater treatment plants: South Austin Regional and Walnut Creek. Both plants have a rated capacity of 75 million gallons per day (mgd) each. South Austin Regional and Walnut Creek Wastewater Treatment Plants discharge approximately 100 mgd of treated effluent to the Colorado River yearly. Additionally, these two plants provide treated effluent to the Reclaimed Water Program. Improvements are ongoing at these plants to adjust to rain patterns, floods and regulatory changes to keep the released wastewater effluent at levels that will ensure AW is a good steward of the cleanliness and health of the Colorado River downstream.
The wastewater treatment program continues to provide the citizens of Austin and downstream users with the highest possible quality of treated wastewater effluent. The program continues to identify cost savings and increase efficiencies. Looking forward, the program will continue providing treated effluent to the expanding reclaimed water program.
For more information contact Ayman Benyamin, Operations Manager, at (512) 972- 2040.