Exam Study Guide: Rotating Biological Contactor

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When faced with a licensing exam, don't struggle with test anxiety! Use the question below and others from our Exam Study Guide series to study and prepare for exam questions. Take a look at this sample wastewater treatment licensing question along with an explanation of the correct answer.

Sample question:

When using a rotating biological contactor (RBC), which two conditions are required for effective operation?

A. The rotating drum(s) must be 50 percent submerged and rotate at a speed greater than 2 rpms.
B. The rotating drum(s) must be 40 percent submerged and rotate at a speed no greater than 1.5 rpms.
C. The rotating drums must be parallel to the flow and totally submerged.
D. The rotating drum(s) must be completely enclosed and rotate at a speed greater than 2 rpms.


The correct answer is B. The rotating drum(s) should never be submerged more than 40 percent of the diameter to allow for adequate air contact for microorganisms. The drums should never rotate faster than 1.5 rpms so the biological mass is not dislodged during operation. The drums should always be perpendicular to the flow, and they only need to be enclosed when used in extreme climate conditions.


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