Tennessee Wastewater Operator Practice Exam

For filamentous bacteria to proliferate in activated sludge, what environmental condition must be met?

1. High temperature

2. Sludge age must be long enough

3. High DO levels

4. Low MLSS concentration

The correct answer is: Sludge age must be long enough

Filamentous bacteria tend to thrive in conditions where the sludge age is extended. When sludge age is longer, there is a more substantial retention of bacterial populations, which allows filamentous bacteria to proliferate. These organisms often flourish in environments where they have more time to establish themselves, typically due to lower organic loading rates or slower decay rates of solids. Long sludge age can provide an environment favorable for filamentous growth, as these bacteria can outcompete floc-forming bacteria in certain circumstances, particularly when there are nutrient imbalances. When sludge age is short, rapid turnover of biomass can impede the establishment of filamentous populations, leading to predominantly floc-forming bacteria. In contrast, high temperatures do not directly correlate with filamentous growth, and oxygen levels (high dissolved oxygen) are generally more conducive to aerobic degradation rather than specifically promoting filamentous bacteria. Similarly, a low MLSS (Mixed Liquor Suspended Solids) concentration would not support the proliferation of filamentous bacteria, as the higher density of microorganisms often aids in their growth. Overall, the condition of maintaining a longer sludge age is critical for the proliferation of filamentous bacteria in activated sludge systems.