Exam Study Guide - February 2023

Licensing exams can be challenging. Our Exam Study Guide helps you prepare by presenting questions similar to those on an actual exam. You can find many more sample questions on the TPO website at www.tpomag.com/study.

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By Rick Lallish

What type of diffuser gives the best oxygen transfer but less efficient mixing?

A. Coarse-bubble

B. Fine-bubble

C. Volcano pressurized

D. Mechanical

ANSWER:  B. Diffusers to provide aeration are common in various wastewater treatment operations. Fine diffusers typically produce 1-3 mm bubbles and have much greater oxygen transfer, but they are less efficient at mixing than coarse-bubble diffusers, which produce 5-12 mm bubbles. When choosing the best diffuser, operators must determine what attribute is most important to the plant. Many varieties of each are available, with all information needed to make the best choice. More information may be found in the WEF textbook: Wastewater Treatment Fundamentals I: Liquid Treatment, Chapter 6.


By Drew Hoelscher

Which component helps prevent motor bearing damage from water leakage inside the stuffing box?

A. Lantern ring

B. Slinger ring

C. Snap ring

D. Wear ring

ANSWER: B. The slinger ring is located toward the back of the stuffing box and is sometimes referred to as the deflector. There is always leakage inside the stuffing box when mechanical packing is installed. Leakage may also occur inside the stuffing box when a mechanical seal fails. The water leaking in the stuffing box follows the shaft until it contacts the slinger ring. Motor bearing damage is prevented by the slinger ring redirecting the water away from the electric motor. 


Rick Lallish is water pollution control program director and Drew Hoelscher is program director of drinking water operations at the Environmental Resources Training Center of Southern Illinois University Edwardsville.  


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