Tennessee Wastewater Operator Practice Exam

Which adjustment can operators make to influence the oxygen transfer rate (OTR) of a horizontal rotor?

1. Change the depth of submergence

2. Alter the size of the sparger

3. Change the speed of the shaft rotation

4. Adjust the oil level in the motor

The correct answer is: Change the speed of the shaft rotation

Changing the speed of the shaft rotation directly impacts the oxygen transfer rate (OTR) of a horizontal rotor. By increasing the speed of the rotor, more surface area of the rotor is exposed to the wastewater, leading to increased agitation and more interaction between the air and the wastewater. This enhances the mass transfer of oxygen from the air into the water, thereby improving the rate at which oxygen is transferred. In contrast, adjustments such as changing the depth of submergence may influence the overall operation but do not directly affect the OTR like rotor speed does. Similarly, altering the size of the sparger might affect aeration characteristics, but it is the rotor's motion that primarily enhances the mixing and oxygen transfer efficiency. Adjusting the oil level in the motor pertains to maintenance rather than operational performance concerning OTR. Thus, the most effective way to influence OTR in this context is through adjustments to the shaft rotation speed.