Exam Study Guide: Sludge Wasting Rate and Mechanical Seals

Exam Study Guide: Sludge Wasting Rate and Mechanical Seals

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 Excessive Odors and Identifying Illegal Water Usage From Hydrants. This time you can test your knowledge about sludge wasting rate and mechanical seals.

Wastewater Treatment Sample Question

Given the following data:

MLSS 1,900 mg/l; RMLSS 3,200 mg/l; Plant Q 1.65 mgd
Aeration tank volume 2.5 mg; RAS Q .9 mgd
Clarifier Volume .75 mg; aeration tank DO 3.2 mg/l

How much sludge should be wasted to maintain a target MLSS of 1,750 mg/l?

A. 77,5000 gallons
B. 117,000 gallons 
C. 650,000 gallons
D. 747,000 gallons

Water Treatment Sample Question

Mechanical seals:

A. Require water to pass through the stationary and rotating components.
B. Have two stationary components that are sealed together by centrifugal force.
C. Are used to couple the pump and motor shaft together.
D. Typically have a shorter operating life when compared to packing because they don’t drip water.

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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