Exam Study Guide: UV Disinfection; and Total Water 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 Dissolved Oxygen Levels; and Legionella Removal Requirements. This time, you can test your knowledge about UV disinfection and determining total water hardness.

Wastewater Treatment Sample Question

What wavelength range is ultraviolet radiation most effective for wastewater disinfection?

A. No minimum wavelength
B. 100 to 200 nanometers
C. 200 to 300 nanometers
D. No maximum wavelength

Answer: The answer to the question is C. Ultraviolet radiation is most effective in the 200 to 300 nanometer (nm) range. The peak or set wavelength is usually about 253.7 nm to 264.0 nm (based on what textbook/specification is noted). This range, often called the germicidal range, will safely destroy the genetic material in the pathogenic organisms. The contact time at this UV intensity is sufficient to meet disinfection requirements. Such knowledge will help the operator understand the various properties of disinfection other than chlorination.

Water Treatment Sample Question

Titrating EDTA into a water sample to determine total hardness will cause the color of the sample to go from ______ to ______.

A. Red, blue
B. Blue, red
C. Red, clear
D. Blue, clear

Answer: The correct answer is A. In order to analyze a water sample for total hardness, the operator buffers the sample to a pH of 10.1 and then adds a hardness indicator. The added indicator reacts with a portion of the calcium and magnesium ions in the sample, leaving some hardness ions free and unbound. Initially, the titrant reacts with the free calcium and magnesium ions before reacting with the calcium and magnesium ions bound to the indicator. Through this reaction process, the sample will change from red to blue. 

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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