Tennessee Wastewater Operator Practice Exam

What range of velocity is typical for vortex grit basins?

1. 0.1 - 0.3 m/s (0.3 - 1 ft/sec)

2. 0.3 - 0.6 m/s (1 - 2 ft/sec)

3. 0.45 - 1.1 m/s (1.5 - 3.5 ft/sec)

4. 1.0 - 1.5 m/s (3.3 - 5 ft/sec)

The correct answer is: 0.45 - 1.1 m/s (1.5 - 3.5 ft/sec)

The typical range of velocity for vortex grit basins is between 0.45 to 1.1 m/s (1.5 to 3.5 ft/sec). This range is effective for the removal of grit and settleable solids within wastewater treatment processes. At these velocities, the flow can create the necessary conditions for gravitational settling of particles while maintaining the turbulent flow required to keep lighter materials in suspension. Vortex grit basins utilize their design to create rotational flow patterns that help enhance the settling of heavier particles, such as grit, while allowing lighter organic materials to be carried along in the effluent. This optimizes the grit removal process and helps prevent blockages and damage further along the treatment process. Other velocity ranges may not be effective for grit removal. Lower velocities, such as those between 0.1 to 0.3 m/s or 0.3 to 0.6 m/s, may not provide sufficient energy to lift and suspend the lighter organic material, leading to ineffective operation. Conversely, higher velocities, such as 1.0 to 1.5 m/s, may result in the risk of scouring off materials that should remain settled, thereby reducing the efficacy of the grit removal process.