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 Optimal Bacterial Growth Conditions and Water Membrane Classifications. This time you can test your knowledge about mean cell residence time and water separation processes.
Wastewater Treatment Sample Question
What is the mean cell residence time (MCRT) of the following activated sludge process, given the following data:
Aeration tank volume 2.5 mgd
Influent flow (Q) 2.25 mgd
Influent TSS 300 mg/L
Effluent TSS 5 mg/L
Influent BOD 280mg/L
Effluent BOD 10 mg/L
Aeration MLSS 2,800 mg/L
RAS MLSS 4,400 mg/L
Solids in Clarifiers (2) 836 pounds each
Wasted Act. Sludge 124,000 gallons
Settleometer reading after 30 minutes: 380
A. 6 days
B. 13 days
C. 18 days
D. 31 days
Water Treatment Sample Question
The passage of a liquid containing dissolved solids to become more concentrated after passing through a semipermeable membrane best describes which process?
A. Reverse osmosis
B. Osmosis
C. Forward osmosis
D. Ultrafiltration
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 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.
Ron Trygar is the program manager for water and wastewater at the University of Florida Training, Research and Education for Environmental Occupations (TREEO) Center. He is also a certified master environmental trainer through the National Environmental Safety and Health Training Association.
