Engineering Questions with Answers - Multiple Choice Questions

Environmental Engineering MCQ – Design of Activated Sludge Plant

1 - Question

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

Answer: b
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 - Question

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

Answer: a
Explanation: Extended aeration process has minimum food to microorganism ratio of 0.5 which means it has the maximum BOD removal efficiency.




3 - Question

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

Answer: d
Explanation: The detention period for a conventional activated sludge system is between 4 to 6 hours.




4 - Question

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

Answer: a
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 - Question

_________ 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

Answer: c
Explanation: Sludge volume index is used to indicate the settling behavior of sludge. It is measured in ml/gm.




6 - Question

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

Answer: c
Explanation: The design value of food to microorganism ratio is 0.3-0.4 for a tapered aeration sludge process.




7 - Question

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

Answer: b
Explanation: Extended process has a maximum aeration period of 12 to 24 hours.




8 - Question

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

Answer: a
Explanation: The BOD removal efficiency of the step aeration process of the activated sludge system is between 85% to 92%.




9 - Question

BOD of sewage is dependent on food to microorganism ratio.
a) True
b) False

View Answer

Answer: a
Explanation: If the food to microorganism ratio increases, BOD removal from the sewage will decrease.




10 - Question

________ 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

Answer: c
Explanation: Aeration period decides the loading rate at which sewage is introduced in the aeration tank.




11 - Question

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

Answer: c
Explanation: Modified aeration process has a minimum hydraulic retention time with an aeration period of 1.5 hours.

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