Exam Study Guide: Common Lagoon Types; and Collecting Total Coliform Samples

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 Proper Grit Disposal; and Disinfection Profile Development. This time, you can test your knowledge about common lagoon types, and collecting total coliform samples.

Wastewater Treatment Sample Question

What is the most common type of lagoons currently in use to treat municipal wastewater?

A. Anaerobic lagoons
B. Aerated lagoons
C. Polishing lagoons
D. Facultative lagoons

Answer: The answer to the question is D. Currently the most common lagoon treatment system in use is the Facultative lagoon. These lagoons are typically 3 to 8 feet deep. They have dual layers — the upper layer is an aerobic layer and the bottom is an anaerobic layer. The algae found in the aerobic layer supply the dissolved oxygen. Light penetration determines the aerobic layers depth. The waste byproducts from the aerobic layer trickle down to the anaerobic layer where digestion takes place. Both layers supplement each other. Controlled discharges of these lagoons may provide detention times of up to 180 days. Identifying different types of lagoons are key for the wastewater operator’s certification studies.

Water Treatment Sample Question

What is the best approach when collecting a routine total coliform sample?

A. Flushing the hot-water tap for approximately 5 minutes before collecting
B. Flushing the cold-water tap for approximately 5 minutes and rinsing out the bacteriological sample bottle before collecting
C. Flushing the cold-water tap for approximately 5 minutes before collecting
D. Collecting a first-draw sample from the cold-water tap

Answer: The correct answer is C. One way of monitoring the quality of potable water flowing through the distribution system is by collecting routine coliform samples every month. Thoroughly flushing the cold-water service line before collecting a bacteriological sample ensures the operator the water collected is from the distribution main. In addition, the operator should always measure and record the chlorine residual before collecting the bacteriological sample. 

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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