July 2011, Vol. 23, No.7

Certification Quiz

Test your knowledge of odor control

    True or False Questions:
  1. It is possible to remove all odorous compounds from an airstream with a single wet scrubber if it is designed correctly.
  2. Raising the pH of a wastestream will inhibit the release of compounds such as hydrogen sulfide but may increase the release of compounds such as ammonia and amines.
  3. The primary concern about hydrogen sulfide in a treatment plant is its odor potential.

  4. Multiple Choice Questions:
  5. You have determined that an odorous airstream has significant concentrations of hydrogen sulfide, methylamine, and butryaldehyde. To achieve effective removal of these constituents, which of the following treatment technologies would be best? 

  6. A. An activated carbon scrubber
    B. A biotrickling filter followed by chemical or activated carbon polishing
    C. A wet scrubber with caustic
    D. A multistage biotrickling filter

  7. You are operating the primary clarifiers to thicken the primary sludge being fed to the digesters. You have begun to observe an increase in odors at the primary effluent overflow weirs. Which of the following steps will not help to reduce these odors based on the operating conditions described in the table? 

    Number of units in service


    Average hydraulic detention time

    5 h

    Influent dissolved oxygen concentration

    0 mg/L

    Average sludge retention time

    4 h

    Average sludge concentration

    6.5% total solids

    Influent temperature

    20°C (70°F)

    Physical observations

    Mats of sludge floating to the surface and rising bubbles


  8. A. Reduce the number of primary units
    B. Increase sludge pumping rate
    C. Add chemicals such as chlorine or ferric chloride to the influent
    D. Add more primary units

Questions excerpted from the Operation of Municipal Wastewater Treatment Plants Study Guide, published in 2007 by the Water Environment Federation (Alexandria, Va.). 

Answer Key:
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