Tennessee Wastewater Operator Practice Exam

What is a key indicator that denitrification is taking place in a circular secondary clarifier?

1. Increased turbidity

2. Sludge collecting between scum baffle and weir

3. Reduction in BOD levels

4. Lower oxygen levels in the sludge

The correct answer is: Sludge collecting between scum baffle and weir

In a circular secondary clarifier, denitrification is a process where nitrates are reduced to nitrogen gas, typically occurring under anoxic conditions. The key indicator that denitrification is taking place relates to the accumulation of organic matter and the interactions between sludge and wastewater. When sludge collects between the scum baffle and the weir, it suggests that there is a buildup of biomass, which is indicative of biological activity occurring in that area. This accumulation often includes denitrifying bacteria, which thrive in the absence of oxygen and contribute to the denitrification process. As these bacteria metabolize nitrates, they can lead to an increase in the volume of sludge due to cell proliferation. While higher sludge levels between the baffle and weir may suggest issues with solids management, in the context of denitrification, it is important because it shows that the biological processes are being actively engaged in removing nitrogen pollutants from the wastewater. This relationship highlights that denitrification is an essential part of wastewater treatment, promoting not only nitrogen removal but also indicating effective microbial action within the clarifier system.