50 Water & Wastewater OIT Exam Prep Questions
Water Treatment
1. What is the primary purpose of coagulation in water treatment?
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To destabilize suspended particles for removal.
2. Which chemical is most commonly used as a coagulant in drinking water treatment?
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b) Aluminum sulfate
3. What is the typical pH range for effective coagulation with alum?
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pH 5.5–7.5
4. Define “turbidity.” What unit is it measured in?
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Cloudiness of water caused by suspended solids, measured in NTU.
5. What does CT stand for in disinfection, and why is it important?
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Contact time × disinfectant concentration; ensures proper disinfection.
6. Which chlorine form provides the strongest disinfection: free chlorine, combined chlorine, or total chlorine?
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Free chlorine.
7. Which gas is commonly used to adjust pH in water treatment?
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a) CO₂
8. What is breakpoint chlorination?
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Adding chlorine until demand is met and free chlorine residual appears.
9. What is the purpose of a fluoride feed system in water treatment plants?
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To prevent dental cavities.
10. If a plant operator adds 10 mg/L of chlorine and measures 2 mg/L of residual, what is the chlorine demand?
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8 mg/L
Wastewater Treatment
11. What does BOD stand for, and why is it important?
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Biochemical Oxygen Demand; measures organic pollution.
12. In an activated sludge process, what does F/M ratio represent?
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Food-to-Microorganism ratio.
13. Which process removes phosphorus from wastewater biologically?
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Enhanced Biological Phosphorus Removal (EBPR).
14. What is the purpose of a grit chamber in a wastewater treatment plant?
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Remove sand, grit, and heavy inorganic solids.
15. Which organisms are responsible for nitrification?
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a) Nitrosomonas & Nitrobacter
16. What does MLSS stand for in activated sludge?
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Mixed Liquor Suspended Solids.
17. What is the primary purpose of secondary clarifiers?
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To settle biomass (sludge) after aeration.
18. Which type of sludge digestion produces methane gas?
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Anaerobic digestion.
19. What does TSS stand for, and why is it measured?
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Total Suspended Solids; indicates solids concentration.
20. In wastewater treatment, what does SVI measure?
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Sludge Volume Index; measure of settleability.
Safety
21. What does WHMIS stand for?
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Workplace Hazardous Materials Information System.
22. What is the maximum allowable noise exposure for 8 hours in Ontario?
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b) 85 dBA
23. What is the first step you should take if chlorine gas is leaking in the chemical room?
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Evacuate the area and activate emergency response.
24. Which type of fire extinguisher should be used for electrical fires?
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Class C extinguisher.
25. Confined space entry requires three key roles: entrant, attendant, and ______?
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Supervisor/Rescue person.
Regulations & Compliance
26. In Ontario, which regulation governs drinking water systems?
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Ontario Regulation 170/03.
27. What agency issues water and wastewater operator licenses in Ontario?
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Ontario Water Wastewater Certification Office (OWWCO).
28. What does MOECP stand for?
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Ministry of the Environment, Conservation and Parks.
29. What is the minimum amount of free chlorine residual required in a distribution system in Ontario?
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0.05 mg/L free chlorine.
30. Which document provides operators with standard methods for water and wastewater testing?
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Standard Methods for the Examination of Water and Wastewater.
Math & Calculations
31. How many litres are in 1 cubic metre of water?
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1,000 L
32. A tank is 10 m long, 5 m wide, and 3 m deep. What is its volume in cubic metres?
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150 m³
33. Convert 5 mg/L into g/m³.
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5 g/m³
34. A pump delivers 500 L/min for 2 hours. How many cubic metres of water is pumped?
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60 m³
35. A reservoir has a volume of 2,000 m³ and a flow rate of 200 m³/day. What is the detention time?
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10 days
General Knowledge
36. What is the main purpose of a SCADA system?
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Supervisory Control and Data Acquisition – remote monitoring and control.
37. What is cavitation in pumps?
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Formation of vapor bubbles in pumps causing damage.
38. What does cross-connection control protect against?
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Prevents backflow contamination.
39. What is the difference between raw water and finished water?
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Raw = untreated source water; finished = treated water ready for distribution.
40. What is the purpose of backwashing a filter?
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To clean and restore filter media.
Advanced Treatment & Processes
41. What is the main advantage of membrane filtration over sand filtration?
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Removes smaller particles (viruses, bacteria).
42. What gas is used in ozone disinfection?
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Oxygen (O₂) converted into ozone (O₃).
43. What is the typical range of UV dose for water disinfection?
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30–40 mJ/cm²
44. What is reverse osmosis primarily used for in water treatment?
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Removing dissolved salts/minerals.
45. What does tertiary treatment remove that primary and secondary may not?
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Nutrients, trace organics, pathogens.
Sludge & Solids Handling
46. What is the main purpose of sludge thickening?
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To increase solids concentration and reduce volume.
47. What does dewatering accomplish in sludge management?
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Removes water to reduce sludge weight/volume.
48. What is the difference between aerobic and anaerobic digestion?
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Aerobic = with oxygen, anaerobic = without oxygen.
49. What is lime stabilization used for in sludge treatment?
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To reduce pathogens and stabilize sludge.
50. What is land application of biosolids?
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Recycling treated biosolids as fertilizer.
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