Exam Study Guide: Anaerobic Digester pH; and Removing Multivalent Ions

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 Facultative Lagoons; and Hypotonic Solutions. This time, you can test your knowledge about anaerobic digester pH levels, and removing multivalent ions in drinking water.

Wastewater Treatment Sample Question

What is the desired pH levels for a properly operating anaerobic digester?

A. 4.0 – 6.6
B. 6.8 – 7.2
C. 7.6 - 9.0
D. Above 10.0

Answer: The answer to this question is B. Anaerobic digesters can operate at pH levels from 6.0 to 8.0, with the desired range being 6.8 to 7.2. If the pH falls to levels below 6.0 or above 8.0, the methane-forming bacteria will die off and the digestion process will cease operation. The methane-forming bacteria are the key component for anaerobic digestion. The pH is controlled by amounts of volatile acids and the alkalinity. The operator should be aware for proper operation of an anaerobic digester of these fundamentals.

Water Treatment Sample Question

Which membrane filtration process is capable of removing multivalent ions (such as Ca+2 and Mg+2) from water?

A. Microfiltration
B. Ultrafiltration
C. Nanofiltration
D. None of the above

Answer: The correct answer is C. Nanofiltration membranes are capable of removing contaminants as small as 0.001 microns. The small pore size does require higher operating pressures than ultrafiltration and microfiltration. However, if the goal is to soften the water by removing calcium and/or magnesium ions without increasing the sodium ion concentration, nanofiltration may be a viable option over ion exchange softening units.

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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