Waste Water Engineering Multiple Choice Questions on “Correlation of Mass Transfer with Water Treatment”.
1. Which among the following reactors has important advantages?
a) Bubble column bioreactors
b) Fluidized bed bioreactors
c) Cylindrical orbitally shaken bioreactors
d) Continuous stirred tank bioreactors
Answer: c
Clarification: Among disposable bioreactor systems, cylindrical orbitally shaken bioreactors show important advantages. They provide a well-defined hydrodynamic flow combined with excellent mixing and oxygen transfer for mammalian and plant cell cultivations.
2. __________ is the net movement of mass from one location or component to another.
a) Osmosis
b) Mass transfer
c) Dilution
d) Reverse osmosis
Answer: b
Clarification: Mass transfer is the net movement of mass from one location, usually meaning stream, phase, fraction or component, to another. In processes like precipitation, membrane filtration, and distillation mass transfer takes place.
3. Which of the following do not involve mass transfer in terms of water treatment?
a) Clarification
b) Aeration
c) Air Stripping
d) Adsorption
Answer: a
Clarification: Clarification is the process in which the suspended solids are removed. This is done by sedimentation. Flocculants such as alum is added to obtain flocs. Then this settled down. The clear supernatant flows into the next treatment channel.
4. What is the flux not dependent on?
a) Pressure
b) Mass solute
c) Area
d) Time
Answer: a
Clarification: The flux is not dependent on the pressure. Flux is defined as the mass of solute transported through an area per unit time. Mass flow is the product of flux multiplied by area.
5. In which of the following cases the flux is considered as volumetric flux?
a) Desalination/Reverse Osmosis
b) Ion exchange
c) Adsorption
d) Aeration
Answer: a
Clarification: In desalination/ reverse osmosis, the flux is termed as volumetric flux. The material moving across the membrane is measured in terms of volume. The corresponding flux is termed as volumetric flux.
6. In water treatment what is the driving force due to which mass transfer occurs?
a) Gibbs Energy
b) Electric potential
c) Gravity
d) Pressure
Answer: a
Clarification: Gibbs Energy is the cause due to which the mass transfer occurs. The Gibbs Energy is also known as the concentration gradient. When there is a concentration gradient present between the phases there will be mass transfer from a higher concentration gradient to a lower one.
7. In case of aqueous solution which of the following mathematical formula holds good?
a) J = Na
b) J = Na x Xa
c) J = (1-1/xa) X Na
d) J = 1/xa X Na
Answer: a
Clarification: In aqueous solution, the solute is considered to be negligible. Hence J = Na holds well. In general cases J = Na(1/1-Xa).
8. How is the value for displacement value for solute calculated?
a) Vb= Dt/ x
b) Vb= 2 Dt/ x
c) Vb= Dt2/ x
d) Vb= 2 Dt2/ x
Answer: b
Clarification: Vb = 2 Dt/ x. Where Vb= Brownian velocity. Dt is dffussion coefficient in liquid phase. X is the displacement value for solute.
9. Which of these do not relate the mass transfer coefficient and diffusion coefficient?
a) Reynolds number
b) Schmidt number
c) Sherwood number
d) Boltzamn constant
Answer: d
Clarification: Sherwood number relates the mass transfer coefficient and diffusion coefficient. kf(avg)L /Df =0.664Re1/2 Sc1/3. Where kf(avg) is the mass transfer coefficient, Re is the Reynolds number and Sc is the Schmidt number.
10. Which of these is used to analyse the minimum amount of extraction phase for treatment?
a) Operating Diagram
b) Freundlich Isotherm
c) Langmuir Isotherm
d) Isobar graphs
Answer: a
Clarification: Operating diagrams are used to analyse the amount of extraction phase for treatment. For example, in case of adsorption the activated carbon amount is calculated from the V/M slope. It was found that at greater V/M slope value treatment is feasible.
11. What is the mass transfer formula for a plug flow reactor?
a) q = Ms(Co)
b) q = Q (Co-C)
c) q = Q Ms(Co-C)
d) q = Q MsC
Answer: c
Clarification: q = Q Ms(Co-C).Where q is concentration of solute adsorbed. Q is the flow rate. Ms is the feed rate of the solute.
12. The liquid phase controls the rate of mass transfer for compounds which have an H value of which of the following?
a) H>0.05
b) H=0.02
c) H<0.002
d) H=1
Answer: a
Clarification: The liquid phase controls the rate of mass transfer for compounds which have an H value >0.05. The gas phase controls the rate of mass transfer for compounds which have an H value <0.002. For compounds with H value between 0.002 and 0.05, both liquid and gas control the rate of mass transfer.