What does the presence of light, stiff, and billowy white foam on the surface of an aeration tank indicate?

The presence of light, stiff, and billowy white foam on the surface of an aeration tank typically indicates a high food-to-microorganism (F:M) ratio. When there is an abundance of food (organic matter) available in relation to the population of microorganisms, the microbes are stimulated to grow rapidly. This rapid growth can lead to the production of excessive amounts of scum and foam on the surface of the aeration tank.

In such scenarios, the foam is often composed of microbial cells and can result from the overproduction of extracellular polymeric substances (EPS) by the microorganisms in response to an excess of nutrients. This situation creates conditions that favor foam formation, indicating that operational adjustments may be necessary, such as modifying the F:M ratio or improving the management of organic loading.

This foam is a visible indication that the aerobic processes are actively breaking down organic waste but that the system may be imbalanced due to the high levels of organic substrates available compared to the microbial biomass present. Adjustments to decrease the organic loading or to categorize the solids present would typically be required to restore balance to the aeration process.