Carbonaceous Biochemical Oxygen Demand (CBOD)
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 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 wastewater treatment plant in accordance with requirements of their Texas Pollutant Discharge Elimination System (TPDES) permit.
FY 2015-16 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 and 10.0 mg/l for a monthly average. The goal of staying below 3.0 mg/l will support AW’s commitment to protecting the environment through exceptional wastewater treatment. The annual average for FY 2015-16 was 2.16 mg/l.
Assessment of Results
The City of Austin’s effluent quality measure CBOD has consistently been well below permitted levels. 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) and have a combined discharge of approximately 100 mgd of treated effluent to the Colorado River. Additionally, these plants provide treated effluent to the AW Reclaimed Water Program. Improvements are ongoing to adjust to rain patterns, floods, and regulatory changes to keep the released wastewater effluent at levels that will ensure AW remains a good steward of the Colorado River downstream.
The wastewater treatment program will continue to provide Austin residents and downstream users with the highest possible quality of treated wastewater effluent, to identify cost savings, and increase efficiencies. Looking forward, the program will also continue to provide treated effluent to the expanding reclaimed water program.
For more information contact Ayman Benyamin, Operations Manager, at (512) 972-2040.