June 2006, Vol. 18, No.6

Certification Quiz

Test Your Knowledge of Activated Sludge

    True or False Questions:
  1. In an activated sludge system, particulat matter is referred to as mixed liquor volatile suspended solids.
  2. With typical municipal wastewater, a well-designed and well-operated activated sludge system, at best, can achieve a CBOD effluent quality of 20 to 25 mg/L.
  3. Nitrification removes ammonia from wastewater as nitrogen gas.
  4. Aeration blowers represent the single largest energy consumer in the activated sludge facility.

  5. Multiple Choice Questions:
  6.  While effective nitrification can occur at other pH levels, the optimum growth of nitrifiers has been observed in what pH range?

  7. A. 3.8 to 4.6
    B. 4.7 to 6.5.
    C. 6.5 to 8.0.
    D. 8.0 to 9.2.

  8.  Which of the following is an indicator of low dissolved-oxygen conditions?

  9. A. Low pH.
    B. Clear effluent.
    C. Dark-gray or black activated sludge, often associated with a putrid odor.
    D. Foaming.

  10. Which of the following conditions would most likely result in stiff, white, billowing foam on the biological reactor?

  11. A. Low MLSS.
    B. High DO.
    C. High MCRT.
    D. Low F:M.

  12. Mixed liquor solids are wasted from the biological reactor.  Effluent solids are negligible. The volume of the activated sludge reactor is 9.24 million gal, and 2.64 mgd of mixed liquor are wasted. What is the system’s mean cell residence time? 

  13. A. 1.5 days.
    B. 3.5 days.
    C. 4 days.
    D. 2.3 days.

Questions were developed by Steve Spicer and reviewed by the Association of Boards of Certification (Ames, Iowa) Validation and Examination Committee.

Answer Key:
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Water Environment Federation (2002). Activated Sludge; Manual of Practice No. OM-9, Second Edition, Alexandria, Va.: Water Environment Federation.