March 2011, Vol. 23, No.3
Test your knowledge of disinfection
True or False Questions:
- Disinfection produces bacteria-free water.
- Removal of solids always improves ultraviolet transmittance.
- Disinfection is designed to kill or inactivate pathogenic bacteria and viruses.
- The first use of disinfection in a potable water supply was in New York City in 1850.
- Pasteurization is a form of disinfection.
Multiple Choice Questions:
Because of the potential for volatilization, samples collected for residual chlorine analysis should be analyzed within how long after collection?
A. 15 minutes.
B. 45 minutes.
C. 1 hour.
D. 24 hours.
According to 40 CFR 136, what is the maximum holding time for samples to analyze bacteria content?
A. 1 hour.
B. 3 hours.
C. 6 hours.
D. 24 hours.
Which of the following factors affect disinfection performance?
B. Solids content of secondary effluent.
C. Oxidation demand.
D. All of the above.
What safety equipment should all facilities using chlorine gas for disinfection contain?
A. Shower and eyewash stations near the chemical storage areas.
B. A window at the administrative offices to view grit-removal operations
C. A placard reading “Caution! Flammable chemical” at the chemical storage locations.
D. Confined-space entry equipment (tripods, harnesses, and life lines) near the chlorine storage area.
What is the typical mass ratio of chlorine residual to sodium bisulfite used for dechlorination?
Which equation correctly describes the relationship among dosage, demand, and residual chlorine?
A. Demand – dosage = residual.
B. Demand – residual = dosage.
C. Dosage – demand = residual.
D. Dosage – breakpoint = demand + residual.
How many pounds per day of chlorine will need to be added at 8 mg/L at a flow of 10 mgd?
A. 312 lb/d.
B. 594 lb/d.
C. 667 lb/d.
D. 861 lb/d.
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Questions developed by Gary Hunter, senior wastewater process engineer at Black & Veatch (Overland Park, Kan.) and past chair of the Water Environment Federation (Alexandria, Va.) Disinfection Committee, and reviewed by the Operations forum Editorial Advisory Board.