Ontario Operator-in-Training (OIT) Practice Exam

In an activated sludge process, what configuration is used to maintain the mass of the mixed liquor?

1. aeration tank

2. primary sedimentation tank

3. force main

4. grit channel

The correct answer is: aeration tank

The aeration tank is integral to the activated sludge process because it facilitates the growth of microorganisms that help to decompose organic matter in wastewater. In this configuration, air is introduced into the mixed liquor, which is a combination of wastewater and suspended solids that contains microorganisms. This aeration provides the necessary oxygen for the microorganisms to thrive and break down the organic compounds. Maintaining the mass of the mixed liquor is crucial because a consistent population of microorganisms is needed for effective treatment. Operation of the aeration tank enables this by providing an environment where the microorganisms can reproduce and maintain a stable concentration of biomass. This concentration is necessary to ensure that enough microorganisms are present to treat incoming wastewater effectively. The other options, while part of the overall wastewater treatment process, do not play a direct role in maintaining the mass of the mixed liquor. The primary sedimentation tank is primarily involved in the initial settling of solids and does not support the ongoing functionality of the microbial population. The force main is a type of piping system used to transport wastewater under pressure but has no role in the aeration process or in the preservation of mixed liquor mass. Lastly, the grit channel is designed for the removal of sand, gravel, and other heavy materials from incoming wastewater, which is important for