Exam Study Guide - January 2023

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By Rick Lallish

When using sand beds to dry biosolids, what is the probable cause of excessive odor when the material is applied, and what is the best solution?

A. Clogged wedge wires in underdrain, high pressure spray at discharge point

B. Over-digested biosolids, change the digester temperature settings

C. Inadequate digestion, correct the digestion problem

D. Inadequate polymer mixing, allow more mixing before biosolids application

ANSWER: C. When operating a drying bed, proper digestion is very important before the material is applied. Inadequately digested biosolids will have offensive odors and will attract vectors, such as flies. Properly digested biosolids should have little to no odors when applied to the drying beds or taken to land application. More information may be found in the WEF textbook: Wastewater Treatment Fundamentals II: Solids Handling and Support Systems, Chapter 5.


By Drew Hoelscher

Which of these is a characteristic of 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 versus packing because they don’t drip water.

ANSWER: A. To prevent damage to a mechanical seal, there must be some water leakage across the two sealing faces. The amount of water allowed to wedge between the two sealing faces is determined by the stuffing box pressure, atmospheric pressure and spring tension of the seal. The amount of water that wedges between the two sealing faces should be sufficient for lubrication but not enough visually see. If the pressure in the stuffing box and/or spring overcomes the pressure from the water for lubrication, the seal will eventually be damaged. This is sometimes referred to as a hydraulically unbalanced seal.


Rick Lallish is water pollution control program director and Drew Hoelscher is program director of drinking water operations at the Environmental Resources Training Center of Southern Illinois University Edwardsville.   


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