Certification Quiz
Test Your Knowledge of Activated Sludge
True or False
1. T F In an activated sludge system, particulate matter is referred to as mixed liquor volatile suspended solids.
2. T F 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. T F Nitrification removes ammonia from wastewater as nitrogen gas.
4. T F Aeration blowers represent the single largest energy consumer in the activated sludge facility.
Multiple Choice
5. While effective nitrification can occur at other pH levels, the optimum growth of nitrifiers has been observed in what pH range?
a. 3.8 to 4.6.
b. 4.7 to 6.5.
c. 6.5 to 8.0.
d. 8.0 to 9.2.
6. Which of the following is an indicator of low dissolved-oxygen conditions?
a. Low pH.
b. Clear effluent.
c. Dark-gray or black activated sludge, often associated with a putrid odor.
d. Foaming.
7. Which of the following conditions would most likely result in stiff, white, billowing foam on the biological reactor?
a. Low MLSS.
b. High DO.
c. High MCRT.
d. Low F:M.
8. 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?
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 (Highlight black box to reveal answers)
1. False. Mixed liquor suspended solids is the term for all particulate matter; mixed liquor volatile suspended solids refers only to the organic fraction of the particulate matter.
2. False. Effluent CBOD should be 5 to 15 mg/L.
3. False. Nitrification oxidizes ammonia–nitrogen to nitrate–nitrogen. Denitrification reduces nitrate–nitrogen to nitrogen gases.
4. True.
5. c.
6. c.
7. a.
8. b. MCRT = biological reactor (liquid) volume ÷ waste mixed liquor flow per day. So, 9.24 million gal ÷ 2.64 mgd = 3.5 days. |
Reference
Water Environment Federation (2002). Activated Sludge; Manual of Practice No. OM-9, Second Edition, Alexandria, Va.: Water Environment Federation.
©2006 by the Water Environment Federation. All rights reserved. |