# Exam Study Guide: RBC Troubleshooting; and Noncarbonate Hardness

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 Confined Space Protocol. This time, you can test your knowledge about RBC troubleshooting, and noncarbonate hardness.

## Wastewater Treatment Sample Question

What is the condition found on a rotating biological contractor (RBC) that is identified by uneven shaft rotation, usually by uneven biofilm growth causing unbalanced weight distribution?

A. Chaining
B. Loping
C. Fouling
D. Tepidity

Answer: The answer to this question is B. Although RBCs are not as commonly in use as they were in the past, knowledge of the operation and troubleshooting conditions are still important to a well-rounded operator.

Loping is a common problem found on RBCs. It is caused by uneven biofilm growth, and the unbalanced weight condition causes the rotational speed to vary cyclically with each rotation, causing the wheels to seem to jump or jerk. Damage may occur to the gears if this is not corrected.

## Water Treatment Sample Question

How can an operator determine the approximate amount of noncarbonate hardness in a water sample?

A. Taking the average of the total hardness and total alkalinity
B. Subtracting the total alkalinity from the total hardness
C. Adding the total alkalinity and the total hardness
D. Dividing the total hardness by 2

Answer: The correct answer is B. After analyzing a water sample for total hardness and total alkalinity, an operator can determine the approximate amount of noncarbonate hardness by subtracting the total alkalinity from the total hardness.

The difference between the two indicates the approximate amount of calcium and magnesium ions linked to other ions, such as sulfate and chloride (noncarbonated hardness). When the total hardness is less than or equal to total alkalinity, calcium and magnesium ions are linked to carbonate and bicarbonate ions (carbonate hardness) and the amount of carbonate hardness is equal to total hardness, which indicates noncarbonate hardness is not present.

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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