Exam Study Guide: Sludge Quality; and Manganese Greensand Filters

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 purpose of screens, and different forms of iron. This time, you can test your knowledge about what influences sludge quality and how manganese greensand filters work.

Wastewater Treatment Sample Question

What process control measure has the most influence on sludge quality and determines the sludge age in an activated sludge process?

A. RAS (return activated sludge)

B. WAS (waste activated sludge)

C. SVI (sludge volume index)

D. F/M (food to mass ratio)

Answer: The answer is B, waste activated sludge. When operating an activated sludge facility, the operator must have an understanding of each process control measure. The operator has to understand how measures such as RAS and WAS impact the sludge quality. They must also know when to make adjustments and use these parameters to operate the plant to meet effluent standards. Waste activated sludge is the measure that determines how long the MLSS remains in the system (SRT), and waste activated sludge determines the MLSS concentration as well. High wasting rates leave fewer solids in the system.

Water Treatment Sample Question

Manganese greensand filters are constructed from top to bottom with:

A. Manganese greensand, anthracite coal and graded gravel

B. Anthracite coal, manganese greensand and graded gravel

C. Anthracite coal, filter sand and graded gravel

D. Manganese greensand, filter sand and graded gravel

Answer: The correct answer is B, Anthracite coal, manganese greensand and graded gravel. Manganese greensand filters typically have a layer of anthracite coal on top of the greensand to allow for deeper penetration through the filter media. The anthracite coal cap allows for longer filter runs by trapping some of the larger particulates before the water passes through the greensand.

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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