Which of the following conditions indicates a well-functioning aeration tank?

A well-functioning aeration tank is characterized by stable dissolved oxygen levels. This stability is crucial for promoting the growth of aerobic microorganisms responsible for breaking down organic matter in the wastewater. Aerobic conditions ensure that these microorganisms can thrive, effectively digesting pollutants and converting them into more benign substances.

When dissolved oxygen levels are stable, it indicates that the aeration process is efficient, maintaining the necessary oxygen concentration for optimal microbial activity. This is essential not only for treatment efficacy but also for preventing undesirable conditions in the tank, such as those that could lead to poor treatment performance or the release of harmful substances.

In contrast, a dark black color of mixed liquor typically signals the presence of excess sludge or poorly settled solids, which may indicate issues with the treatment process or a need for clarification. A strong odor can suggest the presence of anaerobic conditions or the accumulation of volatile organic compounds, both of which are undesirable in an aeration tank. A foamy surface might indicate issues such as the growth of certain types of bacteria or the presence of excess surfactants, which could interfere with the aeration process and the performance of the tank.

Thus, stable dissolved oxygen levels serve as a positive indicator of the aeration tank's functioning, ensuring that wastewater treatment