Tennessee Wastewater Operator Practice Exam

What can be inferred from observing undisturbed foam in one quadrant of an aerobic digester?

1. The digester is operating efficiently

2. The quadrant with foam has clogged diffusers

3. The foam indicates excessive nutrient feed

4. The digester needs more aeration

The correct answer is: The quadrant with foam has clogged diffusers

Observing undisturbed foam in one quadrant of an aerobic digester suggests that there may be a problem with the aeration system in that specific area, which likely indicates clogged diffusers. In an aerobic digester, diffusers are essential for introducing air into the system and maintaining a homogeneous mixture of the sludge. If the diffusers are clogged, the air distribution may become uneven, resulting in areas where foam accumulates but does not disperse. This undisturbed foam can indicate a lack of sufficient mixing and aeration in that quadrant, which is critical for maintaining the health of the microbial population necessary for effective waste treatment. The presence of such foam is an important visual cue for operators and signifies the need to investigate the aeration system further, ensuring that all parts of the digester are functioning properly for optimal performance.