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Water Environment & Technology (WE&T) is the premier magazine for the water quality field. WE&T provides information on what professionals demand:
cutting-edge technologies, innovative solutions, operations and maintenance, regulatory and legislative impacts, and professional development. |
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October 2007, Vol. 19, No. 10 |
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Certification Quiz
Test Your Knowledge of Disinfection
True or False
1. Typical secondary treatment processes can remove as much as 95% of waterborne microorganisms from raw wastewater.
2. Ultraviolet light kills bacteria and viruses in wastewater at a wavelength of 200.0 nm without significantly altering the physical and chemical properties of the effluent.
3. Visual clarity of water is not a good indicator of ultraviolet transmission because water appearing clear in visible light might actually absorb invisible ultraviolet wavelengths.
4. In an ozone disinfection work area, ambient air meters should be calibrated to sound an alarm at 0.5 ppm.
Multiple Choice
5. Which of the following is NOT typically a disadvantage of chlorine disinfection?
a. Lasting toxic effect on aquatic life.
b. Potential hazards issues for employees and the public.
c. Expense.
d. Potential formation of disinfection byproducts.
6. Which of the following components does NOT impair chlorine’s ability to disinfect wastewater?
a. Hydrogen sulfide.
b. Copper ions
c. Ammonia.
d. Organic materials.
7. Where is the proper sampling point to measure total chlorine residual?
a. Just inside the chlorine contact chamber.
b. The middle of the chlorine contact chamber.
c. Just before the point of discharge.
d. Downstream of the discharge point.
8. Bromine chloride is sometimes used for wastewater disinfection. In solution, how does the oxidizing power of bromine chloride compare to that of chlorine gas?
a. Bromine chloride’s oxidizing power depends on water temperature.
b. Chlorine gas is a much stronger oxidant.
c. The two are about the same.
d. Bromine chloride is much stronger.
9. What is the detention time for a 110-ft long, 30-ft wide, and 10-ft deep chlorine contact chamber in a facility operating at 20 mgd?
a. 9.7 minutes.
b. 15.4 minutes.
c. 17.9 minutes.
d. 21.3 minutes.
Questions were developed by Steve Spicer and reviewed by the Association of Boards of Certification (Ames, Iowa) Validation and Examination Committee.
Answer Key
1. True.
2. False. Most ultraviolet systems are calibrated to a wavelength of 253.7 nm
3. True.
4. False. Ambient air alarms should be calibrated to sound at 0.1 ppm. Further, at a reading of 0.3 ppm, shutdown and ventilation should be triggered.
5. c.
6. b.
7. c.
8. d.
9. c. Detention time = chamber volume ÷ (flow × 92.4 ft3/min•mgd). Calculate the chamber volume: 110 ft × 30 ft × 10 ft = 33,000 ft3. Calculate the detention time: 33,000 ft3 ÷ (20 mgd × 92.4 ft3/min•mgd) = 17.9 minutes. Detention times for average flows should range between 30 and 60 minutes; detention times during peak flows should be at least 15 minutes. |
References
Water Environment Federation (1996). Operation of Municipal Wastewater Treatment Plants; Manual of Practice No. 11, Fifth Ed. Alexandria, Va.: Water Environment Federation.
©2007 Water Environment Federation. All rights reserved. |
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