Exam Study Guide: Settled Sludge; and Ladder Safety

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 Flow Velocity; and Chlorine Reactions. This time, you can test your knowledge about settled sludge and ladder safety.

Wastewater Treatment Sample Question

What type of settled sludge digests more efficiently in an anaerobic digester?

A. Grit and manually removed screenings
B. Primary clarifier settled sludge 
C. Scum and mechanical screenings
D. Secondary clarifier settled sludge 

Answer: The answer to this question is B. Anaerobic digesters are more efficient with predominately sludge removed from a primary clarifier. They may be supplemented with secondary clarifier sludge. The sludge from primary clarifiers has a much higher organic composition and is better able to combine with acid-forming bacteria to form organic acids — one of the two types of bacteria to achieve anaerobic digestion. The other type is methane-forming bacteria. Aerobic digesters use almost exclusively secondary clarifier sludge.

Water Treatment Sample Question

How many ladders are required for entering and exiting a 65-foot long trench that is 4.5-feet deep?

A. 1
B. 2
C. 3
D. 4

Answer: The correct answer is B. An excavation is classified a trench when the average depth of the excavation exceeds the width of the excavation and the width does not exceed 15 feet. Working in and around trenches is common in the water utility industry. When a trench reaches a depth of four feet or more, an exit point is required every 25 feet. The ladder must also extend above the surface of the trench by three feet and be in good working order. 


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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