Environmental Engineering Multiple Choice Questions on “Methods of Disinfection”.
1. Which water treatment process is done after filtration of water?
a) Primary sedimentation
b) Disinfection
c) Secondary sedimentation
d) Flocculation
Answer: b
Clarification: Disinfection is a process which is done to kill microorganism present in the water after the filtration process.
2. Which of the following is wrong regarding disinfection?
a) It should be readily available at reasonable cost
b) Its method of application should be simple
c) It should render the water toxic for its intended use
d) It should act as safeguard against re-contamination
Answer: c
Clarification: Disinfection should not render the water toxic, objectionable and unpalatable for its intended use.
3. Boiling of water is a _____ method of disinfection.
a) Physical
b) Chemical
c) Mechanical
d) Electrical
Answer: a
Clarification: Boiling of water is a physical method of disinfection which is also called as disinfection by heat.
4. Sunlight is a ________ method of disinfection.
a) Physical
b) Chemical
c) Mechanical
d) Electrical
Answer: a
Clarification: Sunlight is a natural disinfection. Irradiation by ultraviolet rays promotes disinfection.
5. Which of the following is a chemical method of disinfection?
a) Disinfection by heat
b) Disinfection by light
c) Metal ions
d) Metal ions, Alkalis and acids
Answer: d
Clarification: Disinfection by heat and light are physical methods of disinfection whereas metal ions, alkalis and acids are chemical methods of disinfection.
6. The pathogenic bacteria do not last long at a pH ______
a) >11
b) <11
c) <8
d) >8
Answer: a
Clarification: The pathogenic get killed at pH>11 which is very alkaline in nature or at pH=3 which is highly acidic.
7. Which minor method of disinfection is effective in complete sterilization of water?
a) Boiling method
b) Excess lime treatment
c) Silver treatment
d) Ultraviolet ray treatment
Answer: a
Clarification: Boiling method is effective in complete sterilization of water as it kills all the bacteria and microorganism present in water.
8. What is the dose of lime required in the excess lime treatment?
a) 10-20ppm
b) 0-10ppm
c) 5-10ppm
d) 5-20ppm
Answer: a
Clarification: The dose of lime used in the excess lime treatment is 10-20ppm and the excess lime can be removed by the process of re-carbonation.
9. At what pH, the E-Coli bacteria will die in the water?
a) 6
b) 7
c) 9
d) >9.5
Answer: d
Clarification: The E-Coli bacteria will die at a pH>9. This can be done with the help of excess lime treatment.
10. The depth of water while using ultra violet ray treatment for disinfection should be ____
a) 35cm
b) 46cm
c) 28cm
d) 10cm
Answer: d
Clarification: The depth of water while using ultra violet ray treatment for disinfection should not exceed 10 cm and its turbidity should be in the range of 15-20ppm.
11. Which method of disinfection is mainly used in rural areas?
a) Boiling method
b) Excess lime treatment
c) Potassium permanganate treatment
d) Silver treatment
Answer: c
Clarification: The Potassium permanganate treatment is used in rural areas where most of the water is drawn from a well which contains the least amount of bacteria.
12. The dose of KMnO4 required for disinfection of water is _______ ppm.
a) 1-2
b) 2-3
c) 3-4
d) 4-7
Answer: a
Clarification: The normal dose of KMnO4 required for disinfection of water varies between 1 to 2ppm with a contact period of 4 to 6 hours.
13. Addition of KMnO4 to water imparts _____ color.
a) Blue
b) Red
c) Pink
d) White
Answer: c
Clarification: Addition of KMnO4 to water imparts pink color. It not only kills the bacteria, but also helps in oxidizing the taste producing organic matter.