Wastewater Treatment Operator Certification Practice Test

What could happen if the dissolved oxygen content in the aeration tank is too low?

1. Pinpoint floc will develop

2. Filamentous organisms could thrive and prevent the sludge floc from settling properly in the secondary clarifier

3. Settling will improve in the secondary clarifier

4. Sludge bulking will be eliminated

The correct answer is: Filamentous organisms could thrive and prevent the sludge floc from settling properly in the secondary clarifier

When the dissolved oxygen content in the aeration tank is too low, it creates a condition that can allow filamentous organisms to flourish. Filamentous organisms are a type of bacteria that can form long strands or filaments. In an adequately aerated system, these organisms are typically kept in check by the more desirable, floc-forming bacteria. However, when oxygen levels dip, these filamentous organisms can outcompete the floc-formers, leading to an imbalance in the microbial community. The increase in filamentous organisms can result in ineffective settling and compaction of sludge in the secondary clarifier. Instead of the sludge forming a dense, coherent mass that settles to the bottom, the presence of long filaments can create a "fluffier" sludge blanket. This can lead to poor settling characteristics and may allow sludge to wash out of the clarifier, reducing the overall efficiency of the wastewater treatment process. Thus, maintaining adequate dissolved oxygen levels is crucial for ensuring that the beneficial bacteria can thrive while keeping filamentous organisms under control, ultimately promoting proper sludge settlement in the secondary clarifier.