Tennessee Wastewater Operator Practice Exam

In an aerated grit basin, which process control parameter primarily influences which particles sink?

1. Flow rate

2. Velocity of the roll pattern

3. Temperature

4. pH levels

The correct answer is: Velocity of the roll pattern

In an aerated grit basin, the velocity of the roll pattern significantly influences the sedimentation of particles, determining which ones will effectively sink. The roll pattern refers to the movement and circulation of water within the basin, which is created by the aeration process. This pattern plays a crucial role in keeping lighter particles in suspension while allowing denser particles, such as grit, to settle to the bottom. When the velocity of the roll pattern is properly controlled, it creates an environment that encourages the settling of larger and heavier particles while preventing smaller or lighter particles from settling too quickly or being re-suspended. This results in efficient removal of grit and ensures that the grit basin functions optimally. If the velocity is too high, it may prevent some particles from sinking, while too low a velocity may allow lighter materials to settle inadvertently. While flow rate, temperature, and pH can influence sedimentation, they do so in more indirect ways. Flow rate affects the residence time of particles in the basin but does not directly dictate which particles sink. Temperature can affect the viscosity of the water and, in turn, the behavior of particles, but it is not the primary control parameter. pH levels influence the chemistry of the water and could have some impact on certain