Florida Wastewater Practice Test

Which type of protozoa is not typically found in a good settling sludge?

1. Free swimmers

2. Stalk ciliates

3. Filamentous organisms

4. Stalked organisms

The correct answer is: Filamentous organisms

Filamentous organisms are not typically found in a good settling sludge because they can contribute to poor settling characteristics. In a healthy wastewater treatment system, good settling sludge should be compact and relatively free of filamentous growth. Filamentous organisms, which tend to form long, thread-like structures, can lead to filamentous bulking, making it difficult for the sludge to settle properly. This bulking results in an unstable sludge blanket and can cause issues such as increased return of solids to the aeration tank, poor effluent quality, and challenges during the clarification process. In contrast, free swimmers and stalked organisms often represent a healthy and balanced biomass in sludge, contributing to effective treatment processes. Stalk ciliates, in particular, are beneficial as they build dense aggregates that help in settling. Together, these organisms aid in the floc formation necessary for proper sedimentation in the clarifiers. Thus, the presence of filamentous organisms indicates an imbalance that can disrupt the efficiency of the wastewater treatment process.