The presence of white pillowing foam on an aeration tank indicates what condition?

The presence of white pillowing foam on an aeration tank typically indicates that the aeration tank is underloaded organically. This condition arises when there is insufficient organic material for the microorganisms responsible for the treatment process to consume. When the organic loading is low, the microbial population may not have enough substrates to metabolize, leading to the formation of foam, commonly referred to as "white pillowing foam."

This type of foam is often characterized by its light color and fluffy appearance, which is a result of the excess aeration and the presence of certain microbial populations that proliferate under low organic load conditions. The foam can be problematic as it may lead to operational issues in the aeration tank and can also cause problems downstream in the treatment process if not addressed promptly.

Thus, recognizing this foam serves as an important indicator for operators to assess the loading conditions of the aeration tank and make necessary adjustments to optimize biological treatment processes.