Exam Study Guide: F/M Ratios and Chemical Concentrations

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 ORP Readings and Basin Perimeter Calculations. This time you can test your knowledge about F/M ratios and chemical concentrations.

Wastewater Treatment Sample Question

Given the following data what is the F/M ratio?

1.5 mgd activated sludge facility
Influent BOD 230 mg/l
Effluent BOD  12 mg/l
Influent TSS 240 mg/l
Effluent TSS 6 mg/l
Flow 1,250,000 gallons
MLSS 1,400 mg/l
RasMLSS 2,300 mg/l

A. .05 F/M ratio
B. .14 F/M ratio
C. .28 F/M ratio
D. .73 F/M ratio

Water Treatment Sample Question

The sodium hypochlorite (NaOCl) bulk tank concentration has weakened over time and the operator is tasked with increasing the concentration from 4% to 10%. How many gallons of 12% NaOCl should the operator add, if the bulk tank is currently holding 20 gallons of 4% NaOCl solution?

A. 6
B. 12
C. 24
D. 60

To see answers for both of 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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