Disinfection of Water MCQ – Environmental Engineering

1. A good disinfectant

  1. Should be persistent enough to prevent re-growth of organisms in the distribution system.
  2. Must be toxic to micro-organisms at concentrations well above the toxic thresholds of humans and higher animals.
  3. Should have a fast rate of kill of micro-organisms.

Select the correct answer using the codes given below:

  1. i and ii only
  2. i, ii and iii
  3. ii and iii only
  4. i and iii only
Answer. d

2. A method of disinfection of drinking water

  1. Treatment with excess lime
  2. Treatment with ozone
  3. Electra-Katadyn process
  4. All the above
Answer. d

3. The efficiency of disinfection by chlorine in water treatment increase by

  1. decrease in time of contact
  2. decrease in temperature of water
  3. increase in temperature of water
  4. pre-chlorination
Answer. d

4. 4 disinfectants in increasing order of their disinfection power?

  1. Ozone < HOCl < monochloramine < NCl3
  2. Ozone < NCl3 < monochloramine < HOCI
  3. NCl3 <HOCI < monochloramine < Ozone
  4. NCl3 < monochloramine < HOCI < Ozone
Answer. a

5. Disinfection of water results in

  1. removal of turbidity
  2. removal of hardness
  3. killing of pathogenic bacteria
  4. removal of odour
Answer. c

6. Disinfection of drinking water is carried out to remove

  1. Turbidity
  2. Colour
  3. Odour
  4. Bacteria’s
Answer. d

7. The suitable method for disinfection of swimming pool water is

  1. Ultraviolet rays treatment
  2. Lime treatment
  3. By using potassium permanganate
  4. Chlorination
Answer. a

8. The compounds of chlorine commonly used for disinfection are

  1. Chloramines
  2. Bleaching powder
  3. Both chloramines and bleaching powder
  4. None of these
Answer. c

9. Disinfection of water helps in

  1. Removing turbidity
  2. Removing hardness
  3. Killing pathogenic bacteria
  4. Complete sterilization

Which of the above is/are correct?

  1. ii and iii only
  2. iii only
  3. i and iv only
  4. i, ii, iii and iv
Answer. b

10. Disinfection depends on pH of water such that the disinfection efficiency is

  1. Highest at pH of 7
  2. Increases at higher pH value of water
  3. Reduces at higher pH value of water
  4. None of the above
Answer. c

11. Generally most water are satisfactorily disinfected if the free available residual chlorine, at the end of 10 minute contact period is about

  1. 0.5 mg/l
  2. 0.2 mg/l
  3. 2 mg/l
  4. 1 mg/l
Answer. b

12. Disinfection is the only required treatment when the source of water is

  1. lake
  2. slow moving ver
  3. deep tubewell
  4. impounded reservoir
Answer. a

13. One of the disadvantages associated with the use of O3 as a disinfectant is that the necessary residual ozone

  1. can severely corrode pipes
  2. cannot be maintained
  3. can impart strong taste to water
  4. can induce cancer
Answer. d

14. The disinfection efficiency of chlorine in water treatment

  1. is not dependent on pH value
  2. is increased by increased pH value
  3. remains constant at all pH value
  4. is reduced by increased pH value
Answer. d

15. Potassium permanganate is not desirable for disinfecting drinking water because it imparts

  1. Reddish yellow colour
  2. Colourless
  3. Yellow colour
  4. Pink colour
Answer. d

16. Chlorine demand of water is equal to

  1. applied chlorine
  2. residual chlorine
  3. sum of applied and residual chlorines
  4. difference of applied and residual chlorine
Answer. d

17. Chlorine usage in the treatment of 25,000 m3/day of water has been 9 kg/day. The residual chlorine after 10 minutes contact is 0.2 mg/l. The chlorine demand of water would be nearly

  1. 0.28 mg/l
  2. 0.22 mg/l
  3. 0.16 mg/l
  4. 0.12 mg/l
Answer. c

18. The amount of residual chlorine left in public water supply for safety against pathogenic bacteria is about

  1. 0.01 to 0.05 ppm
  2. 0.05 to 0.5 ppm
  3. 0.5 to 1.0 ppm
  4. 1.0 to 5.0 ppm
Answer. b

19. The percentage of chlorine in fresh bleaching powder is about

  1. 10 to 15
  2. 20 to 25
  3. 30 to 35
  4. 40 to 50
Answer. c

20. Super chlorination is done

  1. In day to day practice
  2. During an epidemic
  3. During winter
  4. During summer
Answer. b

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