Tennessee Wastewater Operator Practice Exam

Which variable remains constant in relation to influent flow and sludge age management?

1. MLVSS concentration

2. Influent BOD

3. SLUDGE AGE

4. MLSS concentration

The correct answer is: SLUDGE AGE

In the context of wastewater treatment, sludge age, also known as mean cell residence time (MCRT), is the average time that the microorganisms (or biomass) remain in the treatment system. This variable is critical because it directly affects the efficiency of the biological processes within the treatment plant. Sludge age remains relatively constant despite changes in influent flow and the concentration of other parameters such as mixed liquor volatile suspended solids (MLVSS) or mixed liquor suspended solids (MLSS). The reason for this is that sludge age is managed through the operation of the system, particularly by regulating the rate at which sludge is wasted from the system in relation to the influent flow and the biological activity occurring within the treatment process. As influent flow increases or decreases, adjustments in the wasting of sludge can maintain a consistent sludge age. This is essential because the performance of the biological treatment process can be significantly impacted by sludge age. For example, a longer sludge age can lead to more efficient removal of organic material, while a shorter sludge age can enhance the settling characteristics and overall operation of the system. In contrast, MLVSS concentration, influent biochemical oxygen demand (BOD), and MLSS concentration can fluctuate based on the incoming wastewater characteristics and operational changes