Exam Study Guide - June 2023


By Rick Lallish

When referring to odors and odor control in wastewater treatment, what is the definition of odor threshold?

A. When the odor has reached a point where a person can no longer tolerate it

B. The highest concentration at which the compound can be detected by human smell

C. The lowest concentration at which the compound can be detected by human smell

D. When the concentration meets the point of olfactory deprivation

Answer: C. Odor control has become an important topic in many wastewater treatment facilities due to surrounding community growth. The lowest concentration at which a compound can be detected by human smell is known as the odor threshold. Odors in wastewater treatment may be from anaerobic decay (fermentation) or the production of sulfides. More information may be found in the WEF textbook: Wastewater Treatment Fundamentals III: Advanced Treatment, Chapter 11. 


By Drew Hoelscher

For bacteria contamination, repeat samples are required to be collected:

A. Within 24 hours of being notified

B. Within 30 hours of being notified

C. Within 48 hours of being notified

D. Anytime, as long as it is within the same monitoring month

Answer: A. Bacteriological samples are collected from potable water distribution systems every month. These samples help ensure that the water is safe to drink. Occasionally, a system will have a sample test positive for total coliform and will be required to collect repeat samples. The repeat sample must be collected within 24 hours of being notified from the certified laboratory.

About the authors

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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