250+ TOP MCQs on Factors Affecting Chlorination and Answers

Environmental Engineering Assessment Questions on “Factors Affecting Chlorination”.

1. When turbidity in water increases, the efficiency of chlorine?
a) Decreases
b) Increases
c) Slightly increases
d) Remains constant
Answer: a
Clarification: The presence of turbidity in water makes it difficult to obtain free residual chlorine. So, it is preferred to apply chlorine after filtration when water is free from turbidity.

2. The presence of metallic compounds in water _______ the efficiency of chlorine.
a) Decreases
b) Increases
c) Slightly decreases
d) Remains constant
Answer: a
Clarification: The presence of metallic compounds like iron and manganese utilized a large amount of chlorine and decrease the efficiency of chlorine for disinfection.

3. The amount of hypochlorous acid formed when pH of water is 8 is _______________
a) 95% of total free chlorine
b) 80% of total free chlorine
c) 30% of total free chlorine
d) 5% of total free chlorine
Answer: c
Clarification: When chlorine is added to water, the amount of hypocholorous acid decreases as pH of water increases. It is 95% of total free chlorine when pH < 6.7 and 30% of total free chlorine when pH of water is 8.

4. Which type of chlorine is represented by the green line as shown in the following figure?

Figure: Kill rates of E-coli
a) Free residual chlorine
b) Ammonia chlorine
c) Combined residual chlorine
d) Residual chloramine
Answer: a
Clarification: Free residual chlorine composed of dissolved hypochlorite ions, hypochlorous acid and chlorine gas present in water. It is represented by the green line in the above figure.

5. Which type of chlorine is represented by the red line as shown in the following figure?

Figure: Kill rates of E-coli
a) Free residual chlorine
b) Ammonia chlorine
c) Combined residual chlorine
d) Residual chloramine
Answer: b
Clarification: Ammonia chlorine is represented by the red line in the figure which results in speedy disinfection, it contains ammonia and chlorine in the ratio of 1:1 in the following figure.

6. The efficiency of chlorine increase by ______________
a) Presence of metallic compounds
b) When the pH of the water increases
c) When the pH of the water decreases
d) Turbid water
Answer: c
Clarification: The efficiency of chlorine is inversely proportional to the pH of water. When the pH of the water containing chlorine decreases, the efficiency of chlorine increases.

7. The contact time for disinfection by free chlorine is ______________
a) 20 minutes
b) 30 minutes
c) 40 minutes
d) 60minutes
Answer: a
Clarification: The contact time for disinfection by free chlorine is 20 minutes and it depends on pH, temperature, type and concentration of microorganism.

8. The contact time for disinfection by combined chlorine is ______________
a) 20 minutes
b) 30 minutes
c) 40 minutes
d) 60 minutes
Answer: d
Clarification: The contact time for disinfection by combined chlorine is 60 minutes. The % kill of bacteria depends upon the time of contact between chlorine and microorganism.

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