This set of Waste Water Engineering Multiple Choice Questions & Answers (MCQs) focuses on “Different Types of Reactors in Water Treatment – 1”.
1. In which of the following systems no flow is added or allowed to leave during the design detention time?
a) Arbitrary flow reactor
b) Fluidized bed reactor
c) Mixed batch reactor
d) Packed bed reactor
View Answer
Explanation: Arbitrary reactor is any degree of partial mixing between plug-flow and complete-mix. Where no flow is added or allowed to leave during the design detention time is called mixed batch reactor.
2. In __________ reactor the bed is filled with a packing material that expands when wastewater moves upwards.
a) Fluidized bed reactor
b) Packed bed reactor
c) Plug flow reactor
d) Mix batch reactor
View Answer
Explanation: Fluid particles pass through the tank and are discharged in the same sequence in which they enter in plug flow reactor. The packing material that expands and gets fluidized when wastewater moves upward in the reactor is provided in fluidized bed reactor.
3. What is the aspect ratio of a stirred tank bioreactor?
a) 1-2
b) 2-3
c) 2-4
d) 3-5
View Answer
Explanation: The aspect ratio of a stirred tank bioreactor is usually between 3-5. However, for animal cell culture applications, the aspect ratio is less than 2. The number of impellers depends on the size of the bioreactor and is variable.
4. The diameter of the impeller is usually 1/3 rd of the vessel diameter.
a) True
b) False
View Answer
Explanation: The diameter of the impeller is usually 1/3 rd of the vessel diameter. The distance between two impellers is approximately 1.2 impeller diameter. Different types of impellers (Rustom disc, concave bladed, marine propeller etc.) are in use.
5. In bubble column bioreactor, the flow rate of air/ gas influences the performance of oxygen transfer.
a) True
b) False
View Answer
Explanation: The air or gas is introduced at the base of the column through perforated pipes or plates, or metal micro porous sparger is in the bubble column bioreactor. The flow rate of the air/gas influences the performance factors —O2 transfer, mixing.
6. The vessel used for bubble column bioreactors is _______
a) Square
b) Rectangular
c) Cylindrical
d) Circular
View Answer
Explanation: The bubble column bioreactors may be fitted with perforated plates to improve performance. The vessel used is usually cylindrical with an aspect ratio of 4-6 (i.e., height to diameter ratio).
7. In which of the following bioreactors is the vessel divided into two interconnected zones?
a) Bubble column bioreactors
b) Airlift bioreactors
c) Continuous stirred tank bioreactors
d) Packed bed bioreactors
View Answer
Explanation: In the airlift bioreactors, the medium of the vessel is divided into two interconnected zones by means of a baffle or draft tube. Air is pumped in one of two zones. The other zone that receives no gas is the down comer.
8. Which of the following reactors is comparable to bubble column bioreactor?
a) Fluidized bed bioreactor
b) Packed bed bioreactors
c) Airlift bioreactors
d) Continuous stirred tank bioreactors
View Answer
Explanation: Fluidized bed bioreactor is comparable to bubble column bioreactor except the top position is expanded to reduce the velocity of the fluid. The design of the fluidized bioreactors is such that the solids are retained in the reactor while the liquid flows out.
9. Which of the following bioreactor consists of biocatalysts on or within the matrix of solids?
a) Photo-bioreactors
b) Packed bed bioreactors
c) Airlift bioreactors
d) Fluidized bed bioreactor
View Answer
Explanation: A bed of solid particles, with biocatalysts on or within the matrix of solids, packed in a column constitutes a packed bed bioreactor. The solids used may be porous or non-porous gels, and they may be compressible or rigid in nature.
10. Which bioreactor is designed for fermentation?
a) Photo bioreactors
b) Continuous stirred tank bioreactors
c) Fluidized bed bioreactor
d) Airlift bioreactors
View Answer
Explanation: The bioreactors designed for fermentation that can be carried out either by exposing to artificial illumination or sunlight is called Photo bioreactors.
11. The array of tubes or flat panels constitutes ________ in photo bioreactors.
a) Light receiving systems
b) Heating systems
c) Cooling systems
d) Radiation emitting systems
View Answer
Explanation: Glass or more commonly transparent plastic is used to make photo bioreactors. The array of tubes or flat panels constitutes light receiving systems (solar receivers).
12. Hydrolysis of chlorine in water has a rate constant of 11 s-1. What does this imply?
a) It is a slow reaction.
b) It is a moderate reaction
c) It is a fast reaction
d) It is a very slow reaction
View Answer
Explanation: Hydrolysis of chlorine in water is a first order reaction. Any first order reactions with rate constant > 1s-1 is considered as a fast reaction. Hence the above reaction is a fast reaction.
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