Tennessee Wastewater Operator Practice Exam

If the SVI has increased from 120 to 180 and a microscope examination reveals many H. Hydrossis filaments, what should the operator do?

1. Decrease DO concentration

2. Increase clarifier flow rate

3. Increase DO concentration

4. Reduce MLSS concentration

The correct answer is: Increase DO concentration

An increase in the Sludge Volume Index (SVI) from 120 to 180 indicates that the solids in the wastewater treatment process are settling poorly, often associated with bulking problems caused by the presence of filamentous organisms, such as H. Hydrossis filaments. These filaments increase the buoyancy of the biomass, preventing it from settling efficiently during the clarification phase. Increasing the Dissolved Oxygen (DO) concentration can help improve the settling characteristics of the mixed liquor. Higher DO levels can promote a healthier condition for the active microorganisms that compete with filamentous species, often leading to better floc formation and settling. This is particularly important because many filamentous organisms thrive in low-oxygen environments, so increasing the DO can shift the balance in favor of the desirable floc-forming bacteria. This approach directly addresses the root cause of the problem and aids in restoring the system's ability to effectively settle solids during the clarification process. It can also enhance the overall treatment performance of the facility by encouraging the growth of organisms that contribute to floc formation rather than those that lead to bulking issues.