Florida Wastewater Practice Test

What is the first corrective action to take for floating sludge conditions in a secondary clarifier with high SVI and filamentous organisms?

1. Decrease DO

2. Increase DO

3. Reduce inflow rates

4. Increase aeration time

The correct answer is: Increase DO

Increasing dissolved oxygen (DO) levels is often the first corrective action to consider when addressing floating sludge conditions in a secondary clarifier that exhibits high Sludge Volume Index (SVI) and the presence of filamentous organisms. A higher DO concentration promotes better aerobic conditions that can suppress the growth of filamentous bacteria, which are often responsible for settling issues and floating scum in the clarifier. Filamentous organisms thrive in low-DO environments, which can lead to the formation of a less dense sludge blanket; this blanket is unable to settle properly, causing the sludge to float. By increasing DO, you enhance the growth of floc-forming bacteria, which can help improve the settling characteristics of sludge and reduce the SVI. If DO levels were decreased instead, it could exacerbate the problem, allowing filamentous organisms to flourish even more, which would worsen the floating sludge situation. Reducing inflow rates may not address the root cause of the problem, and while increasing aeration time could be beneficial, it may not provide an immediate solution to the filamentous growth if the DO levels are not optimal. Thus, initiating the process with increased DO levels tackles the primary issue effectively.