Tennessee Wastewater Operator Practice Exam

What is the primary function of draft tubes on mechanical mixers?

1. Create velocity currents close to the bottom of the tank

2. Maintain optimal pH levels in the digester

3. Reduce the need for additional mixing

4. Increase the temperature of the digested material

The correct answer is: Create velocity currents close to the bottom of the tank

The primary function of draft tubes on mechanical mixers is to create velocity currents close to the bottom of the tank. Draft tubes are designed to enhance the flow patterns within the tank, promoting effective mixing by drawing fluid from the lower regions and pushing it towards the surface. This movement helps in uniformly distributing solids and ensures that the entire volume of liquid is adequately mixed. By facilitating this circulation, draft tubes contribute to improving biochemical reactions, which are crucial in wastewater treatment processes. The generation of these velocity currents prevents sedimentation, maintains a homogeneous mixture, and optimizes the overall efficiency of the treatment system. In contrast, maintaining optimal pH levels, reducing the need for additional mixing, and increasing the temperature of the digested material relate to different operational aspects of wastewater treatment and do not encompass the primary function associated with draft tubes.