Waste Water Engineering MCQ - Chemical Reactions Associated with Water Treatment Part-2

1. What is the rate of a chemical reaction not dependent on?
a) Stoichiometry
b) Surface area of reactants
c) Temperature
d) Pressure

Answer: d
Explanation: The rate of a reaction is independent of the pressure. Stoichiometry is the basis on which the rate of a reaction is defined. Greater the surface area of the reactants, greater is the rate of a reaction

2. How is iconic strength related to total dissolved solids?
a) I= (2.5 x 10-5)TDS
b) I = (2.5 × 105) TDS
c) I= 2.5 TDS
d) I = 2.5 x10 TDS

Answer: a
Explanation: I = (2.5×10-5) TDS .This correlation was defined by Stumm and Morgan in 1996. The ionic strength can be found if the TDS is known. TDS is measured in mg/L.

3. In solutions as ionic concentration increases a non-ideal condition arises. To account for this non-ideal condition due to the ion-ion interaction what is the effective concentration term called as?
a) Activity
b) Dielectric constant
c) Ionic coefficient
d) Ionic strength

Answer: a
Explanation: Activity is the effective concentration term used to account for the non-ideal conditions encountered due to ion-ion interaction. Activity is defined at 1 atm pressure and 298.15 K temperature. It is measured in mol/L (M).

4. In dilute solutions which are normally encountered in water treatment what is the value of the activity of coefficient assumed?
a) 0.5
b) 0.75
c) 1.0
d) >1

Answer: c
Explanation: In dilute solutions usually encountered in water treatment the activity of coefficient assumed is 1. For electrolytes the activity coefficient is assumed <1 and for non-electrolytes >1.

5. What will be the activity coefficient of a solution consisting of monovalent ions?
a) Equal to 1
b) >1
c) Close to 1
d) <0

Answer: c
Explanation: The activity coefficient of a solution consisting of monovalent ions would be close to 1. For water supplies usually, the ionic strength is <5millimole/L. The Davies Equation is used to calculate the activity for concentrated solutions <0.1 M.

6.In case of Moving Bed Bioreactor and Activated Sludge process which is the factor that limits the rate of the reaction?
a) temperature
b) pressure
c) pH
d) ionic composition

Answer: a
Explanation: Temperature limits the rate of reaction in case of both Moving bed bioreactor and Activated Sludge Process. As temperature increases the rate of the reaction increases. But beyond a value of the temperature the rate decreases, as the enzymes present in the bacteria get deactivated.

7. What is the value of activity coefficients for monovalent and divalent ions for a potable water at an ionic strength of 0.01 M?
a) 0.9 and 0.66 respectively.
b) 0.9 in both the cases
c) 0.66 and 0.9 respectively.
d) 0.66 in both the cases

Answer: a
Explanation: The value of the activity coefficient for the monovalent ion is 0.9. The value of the activity coefficient for the divalent ion is 0.66. The activity coefficients for neutral species is negligible.

8. In water treatment which factor which has a major control over reaction selectivity and product distribution?
a) pH
b) temperature
c) pressure
d) ionic concentration

Answer: a
Explanation: The pH has a major control over reaction stability and product distribution. The pH determines whether the reactant species are catalyst or ionic. Control of the pH will result in an acceleration of desired pathways.

9. The degradation of BOD is classified as what type of reaction?
a) First Order Reaction
b) Zero Order Reaction
c) Second Order Reaction
d) Third Order Reaction

Answer: a
Explanation: The degradation of Biological Oxygen Demand is classified as First Order Reaction. rL =− kLL. This is the equation that depicts the degradation of BOD. Here rL represents the rate of reaction, kL represents coefficient of rate of degradation of BOD and L represents the BOD concentration.

10. 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
Explanation: 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.