Exam Study Guide: Automatic Composite Sampling Devices; and Chemical Solution Math

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 UV Disinfection; and Total Water Hardness. This time, you can test your knowledge about automatic composite sampling devices, and chemical solution math.

Wastewater Treatment Sample Question

When operating an automatic composite sampling device, you notice elevated TSS and/or BOD levels in the effluent sample. What could be causing this problem? Pick the best answer

A. Not enough samples in the 24-hour period
B. Refrigerator temperature set too low 
C. Dirty lab-ware/operator error
D. Sample tubing residue

Answer: The answer to the question is D. Automatic samplers are outstanding and generally reliable pieces of equipment to help the wastewater operator if maintained properly. Dirty tubing can definitely lead to elevated TSS or BOD readings in the effluent samples. The residue is biological growth and unchecked will cause many problems. Periodic cleaning or changing of the rubber or plastic tubing is necessary for proper operation of automatic composite samplers. Other problems operators might look for is low battery/electric causing the sample to warm and begin bacterial growth, clogged strainers, or dirty sample bottles. Understanding the sampling equipment is often overlooked training opportunities in the wastewater facility.

Water Treatment Sample Question

An operator has a 100 gallon chemical day tank with 60 gallons of water in it. How many pounds of chemical should the operator add to the tank to prepare a 10% solution by weight?  

A. 6
B. 10
C. 35.5
D. 55.6

Answer: The correct answer is D. When asked to make a solution with a percent by weight concentration, the weight of the water plus the weight of the chemical are taken into account. For instance, 60 gallons of water weighs approximately 500.4 pounds and should only contribute to 90% of the total weight if the desired concentration is 10% chemical. 

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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