April 2007, Vol. 19, No.4
Test Your Knowledge of Odor Control
True or False Questions:
- T F Most concrete sewer corrosion is caused by the absorption of atmospheric carbon dioxide into the moisture on the sewer head space where it forms carbonic acid that reacts with the concrete.
- T F Increasing wastewater pH by injection of a base chemical, such as sodium hydroxide (NaOH) or magnesium hydroxide (Mg(OH)2), will cause an increase in the emission of hydrogen sulfide (H2S) gas.
Multiple Choice Questions:
Which description below best defines the gas phase measurement of parts per million?
A. milligrams of gas pollutant per kilogram of gas mixture.
B. milligrams of gas pollutant per liter of gas mixture.
C. number of pollutant molecules for each million molecules in the gas mixture.
D. milliliter of gas pollutant per thousand liters of gas mixture.
Where is the most sulfide in a sewer produced?
A. In flowing wastewater with dissolved oxygen less than 1.0 mg/L.
B. In the biological slime layer on the sewer wall submerged in wastewater with dissolved oxygen less than 0.1 mg/L.
C. On the moist pipe wall above the wastewater.
D. Inside lateral connections.
What is the Dilution-to-Threshold (D/T) value of a 1.0-L odor sample if it requires 9.0 L to dilute the sample to the detection threshold as determined with a field olfactometer?
What is the control efficiency of an odor control scrubber that receives an airflow with a concentration of 15 ppm H2S and discharges 0.13 ppm H2S?
Estimate the useful life of a carbon bed air filter removing H2S from a foul airflow assuming the characteristics from the table below.
Airflow at 70º F 500 ft3/min
Hydrogen sulfide concentration 5 ppm
Carbon in filter 1000 lb
Molecular weight of H2S 34 lb/mol
Volume of 1 lb•mol of any gas at 70ºF 387 ft3
The carbon used can adsorb 30% of its weight in H2S
A. 31.6 months.
B. 8.3 months.
C. 12.0 months.
D. 11.3 months.
What is olfactory fatigue and why is it particularly dangerous with respect to hydrogen sulfide?
What is meant by the term dilution-to-threshold (D/T) as determined with a field olfactometer?
Questions were developed by Dirk Apgar and the Water Environment Federation (Alexandria, Va.) Air Quality and Odors Control Committee and reviewed by the Association of Boards of Certification (Ames, Iowa) Validation and Examination Committee.
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Water Environment Federation (2004). Control of Odors and Emissions from Wastewater Treatment Plants, Manual of Practice No. 25. Alexandria, Va.: Water Environment Federation.