This set of Waste Water Engineering Multiple Choice Questions & Answers (MCQs) focuses on “Advanced Oxidation Process – Ozonators”.
1. How many oxygen atoms are present in the ozone?
Explanation: Ozonation is a chemical water treatment technique based on the infusion of ozone into water. Ozone is a gas composed of three oxygen atoms, which is one of the most powerful oxidants.
2. Ozone is one of the powerful oxidants.
Explanation: Ozone is a gas composed of three oxygen atoms, which is one of the most powerful oxidants. Ozonation is a type of advanced oxidation process, involving the production of very reactive oxygen species.
3. _______ is produced by subjecting oxygen to high electric voltage.
c) Pure oxygen
Explanation: Ozone is produced with the use of energy by subjecting oxygen or high electric voltage or to UV radiation. The required amounts of ozone can be produced at the point of use but the production requires a lot of energy and is therefore costly.
4. Which of the following can be inactivated using ozone?
d) All microbes
Explanation: Ozone is excellent and can even be used to inactivate microorganisms such as protozoa, which are very resistant to conventional disinfectants.
5. Ozone is an unstable gas.
Explanation: Ozone is an unstable gas. Under suitable conditions, it splits into O2 and O. Ozonation helps in removing colour, odour and taste of the water.
6. Which of these is not an advantage of Ozonation?
a) Reaction with bacteria
b) Organics degradation
c) Equipment costs
Explanation: The advantages of Ozonation is that it rapidly reacts with bacteria, viruses and protozoa over a wide pH range, no chemicals are added to water and also efficient for organics degradation and inorganics removal.
7. Which of the following is not a disadvantage of Ozonation?
d) Fire hazard
Explanation: There are various disadvantages of Ozonation such as the equipment costs are really high, requires large amounts of energy, no residual effect, etc.
8. Which of the following is not removed by Ozonation?
Explanation: Ozone is a colourless gas that has an odour similar to the smell of the air after a major thunderstorm.
9. What is the maximum time required for ozone degradation?
a) 15 minutes
b) 30 minutes
c) 45 minutes
d) 60 minutes
Explanation: Organic particles and chemicals will be eliminated through either coagulation or chemical oxidation. Ozone is unstable, and it will degrade over a time frame ranging from a few seconds to 30 minutes. The rate of degradation is a function of water chemistry, pH and water temperature.
10. What is the average ozone concentration created during Ozonation?
a) 1000 mg/l
b) 5000 mg/l
c) 10000 mg/l
d) 15000 mg/l
Explanation: In general, an ozonation system includes passing dry, clean air through a high voltage electric discharge, i.e., corona discharge, which creates and ozone concentration of approximately 1% or 10,000 mg/L.
11. Which of the following is not correct regarding Ozonation?
a) Does not requires chemicals
b) Eliminates bad taste
c) Eliminates odour
d) Operational costs are low
Explanation: The process of Ozonation does not require chemicals, it eliminates bad taste and odour and the operational costs of ozonation are really high.
12. What is the colour of ozone?
Explanation: Ozone (O3) or trioxide is a colourless odourless gas made of oxygen. It is sometimes called the activated oxygen. It contains three atoms of oxygen rather than the two atoms we normally breathe.
13. Ozone is formed by the interaction of _______
a) UV or O2
b) O and O2
c) O and UV
d) O2 and CO
Explanation: Stratospheric ozone is formed naturally through the interaction of solar ultraviolet (UV) radiation with molecular oxygen (O2). The stratospheric “ozone layer” extends from approximately six to thirty miles above the earth’s surface and reduces the amount of harmful UV radiation reaching the Earth’s surface.
14. In which year was the structure of ozone determined?
Explanation: Ozone’s odour is sharp, reminiscent of chlorine and detectable by many people at concentrations of as little as 100 ppb in air. Ozone’s O3 structure was determined in 1865.
15. In which year was the ozone named?
Explanation: In1839, he succeeded in isolating the gaseous chemical and named it “ozone”, from the Greek word ozein meaning “to smell”. For this reason, Schoenbein is generally credited with the discovery of ozone.
16. At what pH ozonation is carried out?
Explanation: At pH 8, ozonation is carried out using UV rays. This produces free OH radical. These OH radical oxidizes the organic content present in the waste water.
17. Photo catalysis uses which of the following methods to produce free radicals?
a) UV rays
b) UV + TiO2
c) Ozone + UV
Explanation: Photocatalysis utilizes TiO2 and UV to produce free radical OH. This method doesn’t involve ozone directly in order to produce OH radicals. This is a non- ozone based method to produce OH radicals.
18. How is the electrical requirement for the ozonation process expressed mathematically?
a) EE/O =EEt/ Vlog(Ci-Cf)
b) EE/O =EEt/ (Ci-Cf)
c) EE/O =EEt Vlog(Ci-Cf)
d) EE/O =EEt(Ci-Cf)
Explanation: EE/O =EEt/ Vlog(Ci-Cf) is the mathematical representation of the electrical requirement for the ozonation process. Here EE/O is electrical requirement for the ozonation process. V is the volume of the liquid to be treated.
19. What are the byproducts of the breakdown of the organic compounds by UV rays?
b) CO2 + H2O
c) H2CO3 and water
d) CO + H2O
Explanation: The byproducts of the breakdown of these organic compounds is H2O and CO2. In most cases, it is broken down into aldehydes. In certain cases, it is broken down into carboxylic acids also.
20. In what range is the EE/O present in order to reduce one log of reduction?
a) 0-20 KWH
b) 20-265 KWH
c) 265-365 KWH
d) 365-650 KWH
Explanation: The EE/O is present in between 20-265 KWH in order to reduce one log reduction. This requires around 5-6 ppm of H2O2. In some cases the H2O2 is also not necessary.
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