Waste Water Engineering Questions & Answers for Exams on “Disinfection Process – 2”.
1. Which of these is used as the most common disinfectant?
a) Chlorine
b) Chlorine dioxide
c) Ozone
d) UV rays
Answer: a
Clarification: The most common disinfectant is chlorine. This is used as a disinfectant to remove bacteria. 91% of the utilities uses disinfectant as chlorine.
2. Which of these is the strongest disinfectant?
a) Ozone
b) Chlorine
c) Chlorine dioxide
d) UV rays
Answer: a
Clarification: The strongest disinfectant is ozone. The usage as a disinfectant has increased to 1%. This method is quiet expensive compared to the other conventional methods.
3. Which of these methods do not form any byproduct?
a) UV
b) Ozone
c) Chlorine
d) Chlorine dioxide
Answer: a
Clarification: The UV method doesn’t produce any byproducs while disinfection. Hence the efficiency of this method is considered to be superior compared to the other methods. This is the most efficient method to remove viruses.
4. What is the most effective dosage of chlorine to be used as a disinfectant?
a) 1-6 mg/L
b) 6-8 mg/L
c) 8-10 mg/L
d) 10-12 mg/L
Answer: a
Clarification: Chlorine is the most popular method used in disinfection. 1-6 mg/L chlorine dosage is the most effective dosage used in disinfection. Free chlorine is more effective than combined chlorine when used as a disinfectant.
5. What is the most effective dosage of ozone to be used as a disinfectant?
a) 1-5 mg/L
b) 5-10 mg/L
c) 10-12 mg/L
d) 12-14 mg/L
Answer: a
Clarification: The most effective dosage of ozone to bring about disinfection is 1-5 mg/L. Ozone disinfects bacteria very efficiently. Viruses are also killed by ozone very efficiently.
6. What is the most effective dosage of UV to be used as a disinfectant?
a) 20-100 mJ/cm2
b) 10-20 mJ/cm2
c) 100-120 mJ/cm2
d) 130-150 mJ/cm2
Answer: a
Clarification: The most effective dosage of UV is 20-100 mJ/cm2. Low pressure and high intensity of 254 mm is used as a disinfectant. Sometimes the UV is also operated at medium pressure.
7. Which of these produce chlorite as the byproduct?
a) Free chlorine
b) Ozone
c) Chlorine dioxide
d) Combined chlorine
Answer: c
Clarification: Chlorine dioxide produces chlorite as the byproduct. In some cases chlorate is also formed. Chlorine dioxide is used as a disinfectant to kill bacteria and virus in water.
8. Free chlorine is used to destroy bacteria. This reaction is classified as which order reaction?
a) First
b) Pseudo first
c) Second
d) Zero
Answer: b
Clarification: Free chlorine is used as a disinfectant to reduce bacteria. This reaction is classified as a pseudo first reaction. Similarly, the ozone which reduces bacteria is also classified as a pseudo first reaction.
9. Which type does the following reaction belong to?
Chlorine dioxide added to destroy bacteria.
a) Accelerating rate reaction
b) Decelerating rate reaction
c) Pseudo first order
d) First order reaction
Answer: a
Clarification: Chlorine dioxide is used as a disinfectant to remove bacteria is virus. This is usually an accelerating rate reaction. This is observed at the low concentration of chlorine dioxide dosage.
10. Which type does the following reaction belong to?
Chlorine dioxide added to destroy bacteria.
a) Accelerating rate
b) Decelerating rate
c) Pseudo first order
d) First order reaction
Answer: b
Clarification: Chlorine dioxide is a disinfectant used to remove virus and bacteria. This is a decelerating rate reaction. Removal of virus and bacteria by UV is also a decelerating rate reaction.
11. What is the EE/O for TCA in kWh/1000 US gal/order?
a) 15
b) 20
c) 10
d) 30
Answer: a
Clarification: The EE/O for TCA in kWh/1000 US gal/order is 15. This is also called tricarboxylic acid. This requires a reduction catalyst prior to the UV dosage.
12. What is the process of removal of contaminating pathogenic micro-organisms from the articles called?
a) Decontamination
b) Sanitization
c) Disinfection
d) Sterilization
Answer: a
Clarification: Decontamination is the use of physical or chemical means to remove, inactivate, or destroy living organisms on a surface so that the organisms are no longer infectious.
13. What is the technique used to achieve microbe-free environment?
a) Bacteriostasis
b) Bactericidal
c) Sanitization
d) Asepsis
Answer: d
Clarification: Asepsis is the employment of techniques (such as usage of gloves, air filters, UV rays etc) to achieve microbe-free environment. Antisepsis is the use of chemicals (antiseptics) to make skin or mucus membranes devoid of pathogenic micro-organisms.
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