April 18, 2012
Lower Temperatures Mean Lower Secondary Aeration Costs at Your Wastewater Treatment FacilityBy: Evan Bowles
As Ron Eisele discussed in a previous blog post, operation of a wastewater treatment facility varies from season to season. Although engineers attempt to design treatment facilities for an optimal, cost effective operation, we all know that field operations are never as simple as they’re conceptualized in the office. Therefore, it’s up to the operators to further optimize the plant performance, and account for these seasonal variations. Some of the major changes in secondary biological performance include variation of MLSS concentrations, WAS flow rates, and solids retention times (i.e. sludge age or MCRT).
However, another very key item is the change in operation of the blowers that deliver D.O. to the aeration basins in the secondary biological treatment. As the temperature of wastewater varies with the seasons, its capacity to reach saturation of molecular oxygen also fluctuates. In the colder winter months, the wastewater is able to reach desired D.O. concentrations with less blower capacity than is required in the summer months. Therefore, in the warmer months, the blowers are typically required to deliver a higher airflow to the diffusers in the basin. Conversely, this means that colder months typically require less air from the blowers. Since aeration requirements can often account for the majority of a facility’s energy costs, this likely decrease in blower performance can yield a significant, welcome decrease in the power bill. Although this change must be carefully balanced with the necessary biological performance requirements (e.g. BOD oxidation, nitrification), it could potentially be obtained by usage of variable frequency drive, blower cycling, or any number of creative operational practices. Some of these basic alterations can save a significant chunk of change, and free up funds in the operations budget for that new lab equipment you’ve been eyeballing!