This set of Environmental Engineering Multiple Choice Questions & Answers (MCQs) focuses on “Design of Activated Sludge Plant”.
1. Which of the following is the correct expression of the aeration period in hours?
a) V/Q
b) 24V/Q
c) V/24Q
d) Q/V
View Answer
Explanation: Aeration period = 24V/Q where V is the volume of the tank and Q is the quantity of sewage. It is measured in hours.
2. Which of the following activated sludge process has minimum food to microorganism ratio?
a) Extended aeration
b) Step aeration
c) Modified aeration
d) Conventional
View Answer
Explanation: Extended aeration process has minimum food to microorganism ratio of 0.5 which means it has the maximum BOD removal efficiency.
3. The maximum aeration period for a conventional activated sludge system is ___________
a) 2 hours
b) 3 hours
c) 4 hours
d) 6 hours
View Answer
Explanation: The detention period for a conventional activated sludge system is between 4 to 6 hours.
4. The organic loading in an activated sludge plant is defined as ___________
a) Mass of BOD per day/Volume of the aeration tank
b) Volume of aeration tank/Mass of BOD per day
c) The mass of BOD per day/Volume of secondary clarifier
d) Aeration period * Volume of aeration tank
View Answer
Explanation: The organic loading in an activated sludge plant is defined as the mass of BOD to the aeration tank in grams per unit volume of aeration tank in m3.
5. _________ is defined as a volume in ml occupied by 1 gram of solid in the mixed liquor after 30 minutes of settling.
a) BOD loading
b) Suspended solid volume
c) Sludge volume index
d) Organic loading
View Answer
Explanation: Sludge volume index is used to indicate the settling behavior of sludge. It is measured in ml/gm.
6. The design value of food to microorganism ratio in the tapered aeration sludge process is ___________
a) 0.1
b) 0.2
c) 0.4
d) 0.8
View Answer
Explanation: The design value of food to microorganism ratio is 0.3-0.4 for a tapered aeration sludge process.
7. Which of the following sludge process has maximum aeration period?
a) Conventional process
b) Extended process
c) Step aeration process
d) Tapered aeration
View Answer
Explanation: Extended process has a maximum aeration period of 12 to 24 hours.
8. The maximum BOD removal efficiency of the Step aeration process of the activated sludge system is ___________
a) 92%
b) 80%
c) 99%
d) 78%
View Answer
Explanation: The BOD removal efficiency of the step aeration process of the activated sludge system is between 85% to 92%.
9. BOD of sewage is dependent on food to microorganism ratio.
a) True
b) False
View Answer
Explanation: If the food to microorganism ratio increases, BOD removal from the sewage will decrease.
10. _________ is the time at which sewage is detained in the aeration tank.
a) Average time
b) Detention time
c) Aeration period
d) Reaeration period
View Answer
Explanation: Aeration period decides the loading rate at which sewage is introduced in the aeration tank.
11. Which of the following has minimum hydraulic retention time?
a) Conventional process
b) Extended process
c) Modified aeration process
d) Complete mix process
View Answer
Explanation: Modified aeration process has a minimum hydraulic retention time with an aeration period of 1.5 hours.
Sanfoundry Global Education & Learning Series – Environmental Engineering.
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