Tennessee Wastewater Operator Practice Exam

Which of the following conditions is conducive to the proliferation of filamentous bacteria in activated sludge?

1. High DO levels

2. Short sludge age

3. Long sludge age

4. Low water temperature

The correct answer is: Long sludge age

Filamentous bacteria are microorganisms that can form long, thread-like structures and are often associated with various issues in activated sludge systems. The proliferation of filamentous bacteria is influenced significantly by the age of the sludge. When the sludge age is long, there are several consequences that foster conditions favorable for these bacteria. During extended sludge ages, the competition for nutrients and food sources can change, allowing filamentous bacteria to thrive. As the activated sludge system ages, it tends to become more selective in the types of bacteria that can flourish. Filamentous bacteria are often more resilient under low-nutrient conditions and can outcompete floc-forming bacteria for limited resources. The longer retention time allows these bacteria the opportunity to grow, as they can develop filamentous structures that help them maintain their position in the mixed liquor, thereby increasing their access to nutrients and ensuring their survival. In contrast, shorter sludge ages would generally favor floc-forming bacteria, which are typically more efficient at aggregating and settling out of the system. High dissolved oxygen (DO) levels and low water temperatures tend not to favor filamentous growth, as sufficient oxygen and warmer temperatures generally promote the growth of more stable floc-forming microorganisms. Understanding the specific conditions that allow filamentous