July 2010, Vol. 22, No.7
Test Your Knowledge of Odors
True or False Questions:
- Hydrogen sulfide is a whitish, toxic gas with a characteristic rotten-egg odor.
- Force mains with long hydraulic detention times can allow wastewater to become anaerobic, releasing odors at air-release valves and force-main outlets.
- Turbulent effluent launders on primary clarifiers often represent a significant portion of the total clarifier odorous emissions.
- Ensuring uniform organic loading of biological processes can control odors.
- The four classes of chemicals typically used to control odors are oxidizers, reducers, bactericides, and pH modifiers.
- Pure-oxygen aeration causes the lowest odor emissions.
Multiple Choice Questions:
What is the most common odorous gas found in wastewater collection and treatment systems?
A. Hydrogen sulfide.
B. Methyl mercaptan.
C. Acetic acid.
Which of the following steps is a general method for controlling and reducing odors from collection systems?
A. Maximizing hydraulic detention in wet wells.
B. Maintaining proper hydraulic flows.
C. Ensuring that pipes are sufficiently lined with solids.
D. Maximizing turbulence in the pipe.
What concentration of hydrogen sulfide deadens the sense of smell in 3 to 15 minutes?
A. 1 ppm.
B. 5 ppm.
C. 10 ppm.
D. 20 ppm.
What is the best time of day during a typical work week to perform potential odor-causing operations and maintenance procedures?
A. Early morning (6 a.m. to 9 a.m.).
B. Mid-day (10 a.m. to 1 p.m.).
C. Early afternoon (3 p.m. to 6 p.m.).
D. Late night (10 p.m. to 1 a.m.).
In a biofiltration system that uses soil, compost, or other media as a substrate for odor-consuming microbes, what is the typical air residence time needed to remove hydrogen sulfide?
A. 1 - 10 seconds.
B. 15 - 25 seconds.
C. 40 - 60 seconds.
D. 80 - 100 seconds.
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Questions developed by
and reviewed by the Association of Boards of Certification (Ames, Iowa) Validation and Examination Committee.
Water Environment Federation (2008). Operation of Municipal Wastewater Treatment Plants; Manual of Practice No. 11, Sixth Ed. Alexandria, Va.: Water Environment Federation.
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