Tennessee Wastewater Operator Practice Exam

What condition helps maintain Sphaerotilus natans bulking in secondary clarifiers?

1. Ensure D.O. is 2 to 4 ppm in the aeration tank

2. Reduce the return sludge rate

3. Increase the temperature in the aeration tank

4. Minimize the nutrient loading

The correct answer is: Ensure D.O. is 2 to 4 ppm in the aeration tank

Maintaining dissolved oxygen (D.O.) levels in the aeration tank between 2 to 4 parts per million (ppm) is critical for controlling Sphaerotilus natans bulking in secondary clarifiers. Sphaerotilus natans is a type of filamentous bacteria that can contribute to bulking in wastewater treatment systems. When D.O. levels are maintained within this range, it promotes a balanced growth environment for beneficial microorganisms while suppressing the excessive growth of filamentous organisms like Sphaerotilus natans. If the D.O. levels drop too low, it can create anaerobic conditions that favor the growth of these filamentous organisms, leading to bulking and settling issues in the clarifier. Managing D.O. in this way ensures that the activity of the microbial population is optimal for effective floc formation, helping to maintain clear effluent quality and efficient settling characteristics in the secondary clarifier. This balance prevents the conditions that allow for the proliferation of undesired filamentous growth that would lead to operational problems within the treatment system.