Exam Study Guide: Flow Velocity; and Confined Space Protocol

Maintaining your education is important, especially in a career that demands licensing exams. Prove you’re an expert operator by answering these questions and others from our Exam Study Guide Series.

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Welcome back to TPO magazine's Exam Study Guide Series, which offers a pair of water/wastewater study questions with in-depth explanations of the answers. Last time, we covered a set of wastewater and drinking water treatment questions on the topics of Trickling Filter Components; and Corrosion Control. This time, you can test your knowledge about flow velocity, and confined space protocol.

Wastewater Treatment Sample Question

What is the expected or recommend time it should take for the contents in an oxidation ditch to travel the complete circuit of the ditch or go from rotor to rotor?

A. 30 seconds to 1.5 minutes
B. 2 minutes to 2.5 minutes
C. 3 minutes to 6 minutes
D. 7.5 minutes to 9 minutes

Answer: The answer to the question is C. For proper treatment time and flow velocities, the textbooks say the velocity in the ditch should be maintained at 1 to 1.5 feet per second. This will prevent the organics from settling in the ditch and should allow the treatment contents to flow around the ditch or rotor to rotor in 3 to 6 minutes.  In an oxidation ditch, the treatment time is related to the flow of the mixed liquor and is typically controlled by an adjustable weir. Knowledge of how operation of different systems work will help the operator in preparation of certification examinations.

Water Treatment Sample Question

Atmospheric oxygen is deficient at a concentration of less than ______________ by volume.

A. 23.5% 
B. 23.5 mg/L
C. 19.5%
D. 19.5 mg/L

Answer: The correct answer is C. An individual working in the water utility field will most likely enter a confined space at some point during his or her career. Performing tasks in a confined space is a serious safety risk. It is important to follow all required checklists and entry permit instructions to help eliminate such risks. With an approved and calibrated device, test in this order for oxygen, combustible gases, and toxic gases and vapors. Normal air contains 20.9% oxygen, which is only 1% to 2% higher than the oxygen deficient concentration of 19.5%. However, even this slight decrease in percent by volume can cause a healthy individual to feel the effects of an oxygen deficient environment. 


About the authors: Rick Lallish is the Water Pollution Control program director at the Environmental Resources Training Center (ERTC) of Southern Illinois University Edwardsville. He provides training for entry-level operators in the wastewater field and operators throughout the state looking to further their education. Lallish was also named the 2017 Illinois Operator of the Year and 2018 president of the Illinois Association of Water Pollution Control Operators.

Drew Hoelscher is the program director of drinking water operations at the Environmental Resources Training Center in Edwardsville, Illinois.



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