This set of Environmental Engineering Multiple Choice Questions & Answers focuses on “Mechanical Aeration System, Treatment of Sludge”.
1. The device used for the aeration in the combined aerator is ___________
a) Header pipe
b) Diffuser plate and paddles
c) Cone with spiral vanes
d) Diffuser plate
View Answer
Explanation: In combined aeration, both diffused air aeration and mechanical aeration take place using both diffuser plate and paddles.
2. The detention period of the Sheffield mechanical aeration tank is ___________
a) 15 hours
b) 1minute
c) 1 hour
d) 4 hours
View Answer
Explanation: The detention period of a Sheffield mechanical aeration tank is 15 hours. Its return sludge is 15-20% of sewage flow.
3. The minimum detention period of combined aerator is ___________
a) 1 hour
b) 2 hours
c) 3 hours
d) 4 hours
View Answer
Explanation: The detention period of combined aerator lies between 3 to 4 hours and the minimum detention period is 3 hours.
4. The speed at which the bubbles are formed in the simplex aerator?
a) 15rpm
b) 20rpm
c) 60rpm
d) 30rpm
View Answer
Explanation: The cones, with spiral vanes rotates at a high speed of 60rpm that results in the formation of bubbles in a simplex aerator resulting in the aeration of sewage.
5. Dorroco aerator is a type of ___________
a) Combined aerator
b) Mechanical aerator
c) Ridge and furrow type aerator
d) Spiral flow type aerator
View Answer
Explanation: Dorroco aerator is a type of combined aerator which is efficient in comparison to diffused air and mechanical aerator.
6. Simplex aerator is a type of ___________
a) Combined aerator
b) Mechanical aerator
c) Ridge and furrow type aerator
d) Spiral flow type aerator
View Answer
Explanation: Simplex aerator is a type of mechanical aerator where a square or rectangular tank with a hopper bottom is used.
7. Which gas is produced in aerobic digestion of sludge?
a) NO2
b) CO2
c) O2
d) H2S
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Explanation: Carbon dioxide gas is produced in the aerobic digestion of sludge by the oxidation of organic matter by bacteria into CO2.
8. Which of the following process is not involved in the treatment of sludge?
a) Dewatering
b) Drying
c) Flocculation
d) Conditioning
View Answer
Explanation: The process involved in the treatment of sludge are thickening, stabilization, dewatering and dying.
9. Which of the following is the final stage in the sludge treatment process?
a) Digestion
b) Dewatering
c) Drying
d) Thickening
View Answer
Explanation: Drying of the sludge is the final stage in the sludge treatment process where the most stable form of sludge is obtained.
10. In which sludge treatment process, the organic solids are converted into more stable form?
a) Dewatering
b) Thickening
c) Digestion
d) Conditioning
View Answer
Explanation: In the sludge digestion process, the organic solids are converted into more stable form. It makes the dewatering and drying process of sludge simpler.
11. The sludge treatment process to increase the solid content of sludge is ___________
a) Dewatering
b) Thickening
c) Conditioning
d) Drying
View Answer
Explanation: In sludge thickening, the solid content of sewage is increased by gravity flotation and clarifier.
12. The process of removal of water from the sludge is called ______
a) Dewatering
b) Thickening
c) Digestion
d) Drying
View Answer
Explanation: Dewatering is the process of removal of water from the sludge. It can be done by drying or subjected the sludge with pressure.
13. In which sludge treatment process, the sludge is treated with chemicals?
a) Dewatering
b) Thickening
c) Conditioning
d) Drying
View Answer
Explanation: In sludge conditioning, the sludge is treated with chemicals in order to separate the water from the sludge and improving the dewatering characteristics of the sludge.
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