February 2009, Vol. 21, No.2
Test Your Knowledge of Disinfection
True or False Questions:
- Increasing the flow rate across ultraviolet (UV) disinfection lamps decreases the contact time and lowers the inactivation rates of microorganisms
- Water’s visual clarity is always a good indicator of UV transmittance.
- Using ferric salts for enhanced coagulation–sedimentation upstream of the disinfection chamber requires considering the effect the iron has on the UV system.
- The chlorine dose that satisfies the ammonia’s chlorine demand is called the breakpoint.
- If it is necessary to store sodium hypochlorite for long periods, it should be stored in as concentrated a form as possible.
Multiple Choice Questions:
By what mechanism does ozone disinfect wastewater?
A. Cell-wall disintegration.
B. Reproduction inhibition.
C. Electron-receptor blockage.
D. Nutrient-uptake prevention.
In an ozone generating system, what function does the gas-flow rotameter serve?
A. Lowers gas temperature and lowers dewpoint.
B. Dries gas to limit nitric oxide production and maximize ozone production.
C. Adjusts air-oxygen flow rate into the ozonator.
D. Removes offgas ozone by converting it into oxygen.
Ozone is extremely reactive. Which of the following materials will it readily corrode?
D. All of the above
What is the chlorine detention time for a chlorine contact chamber that is 30-ft wide × 50-ft long × 15-ft deep at a plant that treats a flow of 7.3 mgd?
A. 17.8 min.
B. 22.0 min.
C. 33.4 min.
D. 34.1 min.
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Questions were developed by Steve Spicer and reviewed by the Association of Boards of Certification (Ames, Iowa) Validation and Examination Committee.
Water Environment Federation (2008). Operations of Municipal Wastewater Treatment Plants; Manual of Practice No. 11, Sixth Edition. New York: WEF Press–McGraw Hill.