This set of Waste Water Engineering Puzzles focuses on “Different Types of Reactors in Water Treatment – 2”.
1. Which type of reactor is used for mixing chemicals in water treatment?
a) Continuous reactor
b) Batch reactor
c) Plug flow reactor
d) Fixed bed reactor
View Answer
Explanation: Batch reactors are used while mixing chemicals for water treatment. When chemicals such as alum, ferric ammonium sulphate are required for coagulation, chemical mixing is done. For the preparation of flocculants and other pH controlling chemicals also the same batch reactor process is used for chemical mixing.
2. Which reactors are characterized by non-continuous reactions?
a) Plug flow reactor
b) Continuous reactor
c) Batch reactor
d) Fluidized bed reactor
View Answer
Explanation: Based on the operation, the reactors are classified as batch and continuous. Batch reactors follow non-continuous mode of reaction. While in a continuous flow reactor, the continuous reaction takes place.
3. In which type of reactor, mixing is uniform?
a) Ideal reactor
b) Batch reactor
c) Non-ideal reactor
d) Fixed bed reactor
View Answer
Explanation: Ideal reactors are those in which the mixing is uniform. The reactors in which the mixing is not uniform, those reactors are known as non-ideal reactors. Ideal reactors have uniform hydraulic conditions.
4. Which type of reactor is not used for oxidation?
a) Packed bed reactor
b) Stirred tanks
c) Tank in series
d) Venturi reactor
View Answer
Explanation: Packed bed reactors are not used for the oxidation reaction. Oxidation is carried out in a venturi reactor, tank in series and stirred tank reactors. Oxidation of Iron, Oxidation of manganese, dechlorination of SO2 and ozone reactions are carried out in these reactors.
5. Which type of reactor is not subjected to back mixing?
a) Plug flow
b) Completely stirred reactor
c) Batch reactors
d) Venturi reactor
View Answer
Explanation: Plug flow reactors are not subjected to back mixing. They are designed for a specific detention time. Disinfection of water is carried out in a plug flow reactor.
6. Which type of reactor is used for stripping off gases from water?
a) Venturi reactor
b) Packed bed reactor
c) Plug flow reactor
d) Continuous stirred reactor
View Answer
Explanation: Packed bed reactors are used in stripping off gases from water. These are used to strip off undesirable gases or organic compounds from water. Counter current flow is usually encountered in such reactors.
7. Which type of reactor is used in ion exchange or adsorption?
a) Fixed bed reactor
b) Venturi reactor
c) Plug flow reactor
d) Continuous flow stirred reactor
View Answer
Explanation: Ion exchange takes place in a fixed bed reactor. This reaction takes place within the solid phase. These type of reactions also take place in a fluidized bed reactor.
8. Which type of reactor is used in precipitation reactions?
a) Fluidised bed reactor
b) Plug flow reactor
c) Venturi reactor
d) Recycle reactor
View Answer
Explanation: Recycle reactors are predominantly used in precipitation reactions. In these reactions, a part of the solid precipitated is recycled. This is done in order to increase the rate of reaction as in the case of softening.
9. In which type of reactor diffusion and dispersion contribute to solid fluxes into and out of the reactor?
a) Venturi reactor
b) Open reactor
c) Closed reactor
d) Recycle reactor
View Answer
Explanation: In open reactors diffusion and dispersion contribute to solute fluxes into and out of the reactor. An example of an open reactor is ground water with contaminant plume. In this case, the plume flows along with the ground water by diffusion.
10. Which of these is the mathematical representation of a condition of a plug flow reactor after a tracer is added?
a) ŧ=V/Q
b) C=C0e-1/ŧ
c) ŧ=Q/V
d) C0=Ce-1/ŧ
View Answer
Explanation: The mathematical representation of a plug flow reactor after a tracer is added is ŧ=V/Q. Plug flow reactors have uniform mixing. Also, there’s no back mixing in these reactors.
11. What is the mathematical representation of a completely stirred reactor after a tracer is added?
a) ŧ=V/Q
b) C=C0e-1/ŧ
c) ŧ=Q/V
d) C0=Ce-1/ŧ
View Answer
Explanation: The completely stirred reactor is represented as C=C0e-1/ŧ. In most of the water treatment process completely stirred reactors are used. To improve the hydraulic performance, a series of completely mixed stirred reactors are employed.
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