Certification Quiz
Test Your Knowledge of Chemical Safety and Dosing
True or False
1. T F Sodium hypochlorite solutions decompose over time and lose available chlorine for disinfection, so storage considerations are extremely important.
2. T F One air change per hour (24 air changes per day) is considered adequate ventilation when personnel occupy chlorine storage and feed areas.
3. T F Liquid ammonia is considered a fire hazard.
4. T F Secondary containment, such as concrete structures, should be provided for spills and leaks of chemicals. Containment volume should be a minimum of the largest bulk storage tank volume.
Multiple Choice
5. In an ammonia storage room, where should intakes for forced mechanical ventilation be located?
a. On the floor.
b. On the ceiling.
c. Midway up the wall.
d. Placement doesn’t matter.
6. Which of the types of pipe listed below should be used for sodium hypochlorite applications?
a. PVC.
b. Stainless steel.
c. Ductile iron.
d. Copper.
7. Calculate the chlorine dosage, in parts per million, of the wastewater, using the following information.
| Average daily wastewater flow |
treated 0.5 mgd |
| Average daily chlorine use |
15 lb/d | a. 36.0 ppm.
b. 7.2 ppm.
c. 6.3 ppm.
d. 3.6 ppm.
8. If adding 40.0 gal/d of ferric chloride solution to a primary clarifier for coagulation resulted in a concentration of 3.8 ppm, how many gallons per day would it take for a concentration of 6.0 ppm?
a. 88.0 gal/d.
b. 75.6 gal/d.
c. 63.2 gal/d.
d. 58.7 gal/d.
Answer Key (Highlight black box to reveal answers)
1. True.
2. False. One air change per minute (60 air changes per hour) is considered adequate ventilation when personnel occupy chlorine storage and feed areas.
3. False. However, vapors may form an explosive mixture with air.
4. False. Containment volume should be a minimum of the largest bulk storage tank volume plus, at least, an additional 10%.
5. b. Because ammonia is lighter than air, vents should be placed near the ceiling of its storage room.
6. a. Certain metals can cause the sodium hypochlorite solution to decompose to oxygen and salt, resulting in a pressure buildup.
7. d. Dosage in ppm = (million lb chemical/d) ÷ (million lb of wastewater treated/d) = (15 lb/d) ÷ (0.5 mgd × 8.34 lb/gal) = 3.6 ppm.
8. c. Gallons of chemical needed = (desired concentration/known concentration) × rate of application = (6.0 ppm/3.8 ppm) × 40 gal/d = 63.2 gal/d. |
Reference
Water Environment Federation (2005). Operation of Municipal Wastewater Treatment Plants (Manual of Practice No. 11), Sixth Ed. Alexandria, Va.: Water Environment Federation.
©2006 by the Water Environment Federation. All rights reserved. |