Exam Study Guide: Grit Removal Systems; and Water Pump Impellers

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.

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 Disinfection Contact Time; and Effluent Coloration. This time, you can test your knowledge about grit removal systems and types of pump impellers.

Wastewater Treatment Sample Question

What is the recommended velocity of a properly operated grit removal system?

A. 0.5 ft/sec

B. 1.0 ft/sec

C. 1.5 ft/sec

D. 2.0 ft/sec

Answer: The answer to this question is B. Properly operated grit removal systems should be operated at 1 ft/sec. This velocity allows the grit (non-organics) to settle but the majority of the organic material to remain in suspension. This is important to know in the event you notice excessive inorganic material passing through your preliminary treatment. If you note an excessive amount of organics in your grit, this could indicate your velocity is too low. 

According to the WEF Wastewater Treatment Fundamentals 1 - Liquid Treatment textbook, “The goal of process control is to maintain a velocity of 0.3 m/s (1 ft/sec).”

Water Treatment Sample Question

How many shrouds would an open impeller have?

A. 0

B. 1

C. 2

D. 3

Answer: The correct answer is A. The impeller of a pump is sometimes referred to as the heart of the pump and is composed of vanes and either zero, one or two shrouds. One way impellers are classified is by the number of shrouds. Open impellers have no shrouds, and they are primarily used to pump large volumes of heavy sludge at low pressures. Open impellers are commonly found on trash pumps used to remove sludge from sump pits or muddied water from an excavation site. 


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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