50 Class 4 Water Treatment Exam Prep Questions
Water Treatment Basics
1. What is the primary source of surface water contamination?
Runoff carrying organic material, nutrients, and microorganisms.
2. What does NTU stand for in turbidity measurement?
Nephelometric Turbidity Unit.
3. What is the purpose of coagulation in water treatment?
To destabilize suspended particles so they can clump together.
4. Which chemical is commonly used as a coagulant in water treatment?
Aluminum sulfate (alum).
5. What is flocculation?
The gentle mixing process that allows microflocs to collide and form larger flocs.
Disinfection
6. What does CT value represent in disinfection?
Concentration × Time; ensures effective pathogen inactivation.
7. Which form of chlorine provides the most effective disinfection?
Free chlorine.
8. What is breakpoint chlorination?
The point where chlorine demand is satisfied and free residual begins to appear.
9. What is the minimum free chlorine residual required in Ontario distribution systems?
0.05 mg/L free chlorine.
10. What is chloramine used for in distribution systems?
To maintain longer-lasting residual and reduce disinfection by-products.
Filtration
11. What is the purpose of filter backwashing?
To remove trapped particles and restore filter performance.
12. What is filter-to-waste?
Initial water discharged after a filter is returned to service, to prevent turbidity spikes.
13. What is a typical effective size of sand in a rapid sand filter?
0.4–0.6 mm.
14. What does head loss across a filter indicate?
Resistance to flow caused by accumulated solids.
15. What type of filtration is most effective at removing viruses?
Membrane (ultrafiltration or nanofiltration).
Water Chemistry
16. What is alkalinity?
The capacity of water to neutralize acids, mainly due to bicarbonates, carbonates, and hydroxides.
17. What is the ideal pH range for coagulation with alum?
5.5–7.5.
18. What is hardness in water caused by?
Calcium and magnesium salts.
19. What is the Langelier Saturation Index used for?
To predict if water will be scale-forming, neutral, or corrosive.
20. What chemical is often used to raise pH?
Lime or sodium hydroxide.
Pumps & Equipment
21. What is cavitation in pumps?
The formation and collapse of vapor bubbles causing damage.
22. What is the difference between static head and dynamic head?
Static head = vertical lift; dynamic head = total pressure including friction losses.
23. What does VFD stand for?
Variable Frequency Drive.
24. What is the purpose of a foot valve on a pump?
To prevent backflow and keep the pump primed.
25. What is the efficiency range of a centrifugal pump?
60–85% depending on design and operating conditions.
Math & Calculations
26. How many litres are in 1 cubic metre of water?
1,000 L.
27. A tank is 20 m long, 10 m wide, and 5 m deep. What is its volume?
1,000 m³.
28. Convert 25 mg/L into g/m³.
25 g/m³.
29. A pump delivers 1,000 L/min for 3 hours. How many cubic metres is pumped?
180 m³.
30. A reservoir of 5,000 m³ has an outflow of 1,000 m³/day. What is the detention time?
5 days.
Regulations & Safety
31. What does WHMIS stand for?
Workplace Hazardous Materials Information System.
32. What does SDS stand for?
Safety Data Sheet.
33. What is the maximum noise level allowed for 8 hours in Ontario?
85 dBA.
34. What agency certifies operators in Ontario?
Ontario Water Wastewater Certification Office (OWWCO).
35. Which regulation governs drinking water systems in Ontario?
Ontario Regulation 170/03.
Advanced Treatment
36. What is reverse osmosis used for?
To remove dissolved salts and impurities.
37. What is the typical pressure range for RO membranes?
200–400 psi (varies by application).
38. What is the primary disinfecting agent in UV treatment?
Ultraviolet light at 254 nm damages microbial DNA.
39. What is ozone primarily used for in water treatment?
Oxidation and disinfection.
40. What is GAC filtration used for?
To remove taste, odor, and organic compounds.
Operations & Monitoring
41. What is the purpose of jar testing?
To determine the optimal coagulant dose.
42. What parameter does a nephelometer measure?
Turbidity.
43. What is the maximum acceptable concentration (MAC) for nitrate in drinking water in Canada?
10 mg/L as nitrogen.
44. What is the MAC for arsenic in drinking water in Canada?
0.01 mg/L.
45. What does HPC testing measure?
Heterotrophic Plate Count – general bacterial population.
Miscellaneous
46. What is a cross-connection?
A physical link between potable and non-potable water systems.
47. What is a backflow preventer?
A device to prevent contamination from reverse flow.
48. What is the purpose of fluoridation?
To reduce tooth decay.
49. What is the Safe Drinking Water Act?
Ontario legislation ensuring safe drinking water standards.
50. What is SCADA used for in water plants?
Supervisory Control and Data Acquisition – monitoring and controlling processes.
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