Exam Study Guide: Excessive Clarifier Ashing; and Calculating MRDL for Chlorine

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.

Exam Study Guide: Excessive Clarifier Ashing; and Calculating MRDL for Chlorine

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 Trickling Filter Types; and Determining Lead Concentration. This time you can test your knowledge about excessive clarifier ashing, and calculating MRDL for chlorine.

Wastewater Treatment Sample Question

If you notice excessive ashing on the secondary clarifier in an activated sludge plant, what action might you try to correct the issue?

A. Increase the return activated sludge (RAS) to raise the mean cell residence time (MCRT)
B. Increase the waste activated sludge (WAS) to reduce the MCRT
C. Increase the sludge blanket level to allow for nitrification
D. Increase the aeration to the clarifier to allow the ash to settle out

Water Treatment Sample Question

How do you calculate the running annual maximum residual disinfectant level (MRDL) average for chlorine?

A. Average the highest distribution system chlorine residuals from each month for 12 months
B. Average the lowest distribution system chlorine residuals from each month for 12 months
C. Average the highest and lowest distribution system chlorine residuals from each month for 12 months
D. Average the four most recent quarterly distribution system chlorine residual averages

To see the answers to both the above questions, click this link.


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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