This set of Fermentation Technology Problems focuses on “Aeration and Agitation – Factors Affecting Kla Values”.
1. Which of the following is not the factor affecting the value of KLa?
a) Bubble size
b) Temperature
c) Solubility
d) pH
View Answer
Explanation: The factors affecting KLa include the gas bubble size, temperature, pressure, solubility, agitation speed, type of agitator, etc. The pH value does not affect the value of KLa. It is independent of pH.
2. The smaller the size of the bubble the __________ is the value of KLa.
a) Higher
b) Lower
c) Zero
d) Constant
View Answer
Explanation: The smaller the size of the bubble the higher is the value of KLa. The bubbles with smaller size occupy the larger interfacial area and the smaller bubbles start to coalesce, leading to a higher value of KLa.
3. The value of KLa increases with ____________ in agitation speed (rpm).
a) Decrease
b) Increase
c) Constancy
d) Zero
View Answer
Explanation: The value of the mass transfer coefficient increases with an increase in the speed of agitation. It also depends on the type of impeller blades used and also the number of blades.
4. What happens to the value of KLa if aeration is lowered in the fermenter?
a) Becomes zero
b) Increases
c) Becomes constant
d) Decreases
View Answer
Explanation: The value of volumetric mass transfer increases most significantly with the increase in air supply or aeration. Higher the availability of oxygen higher is the value of KLa. Although higher flow rate can also cause cell damage due to forces.
5. What results in impeller flooding?
a) Increase impeller speed
b) Increases gas velocity
c) Decrease impeller speed
d) Decrease gas velocity
View Answer
Explanation: If the gas flow rate is very high, it would not allow oxygen to be dissolved in the medium and the gas may exit without dissolving. Therefore, most of the gas remains unutilized and this results in impeller flooding.
6. Who reported that sparger design does not affect KLa?
a) Hassan and Robinson
b) Tuffile and Pinho
c) Taguchi and Roels
d) Riet and Tramper
View Answer
Explanation: Hassan and Robinson in 1977 reported that the design of sparger does not have any effect on gas-liquid dispersion. The effect of gas sparger has not been studied much deeper.
7. Which of the following agitator is required for mixing of highly viscous liquid and slurries?
a) Turbine
b) Vaned discs
c) Paddle
d) Anchor
View Answer
Explanation: Anchor is used for the mixing of highly viscous liquids and slurries. The anchor agitators are of many types like U-shaped, flat blade, etc. They are used for moderate to highly viscous liquids mixing.
8. What happens to the value of KLa if the temperature is raised more than 40°C?
a) Decreases
b) Become zero
c) Increases
d) Becomes constant
View Answer
Explanation: The value of the volumetric mass transfer coefficient decreases as the temperature is raised to more than 40°C. However, in the range of 10-40°C the value of mass transfer increases.
9. Which of the following law affects the mass transfer due to pressure?
a) Henry’s law
b) Kohlrausch law
c) Hardy-Weinberg law
d) Hardy-Schulze law
View Answer
Explanation: Pressure affects the mass transfer by increasing the solubility of the gases. This is given by Henry’s law. It states that the amount of gas dissolved in a liquid is directly proportional to the partial pressure of the gas in that liquid.
10. What is the change of using antifoaming agents on KLa?
a) KLa increases
b) KLa decreases
c) KLa becomes constant
d) No effect
View Answer
Explanation: The antifoaming agents reduce or prevent the formation of foam. It prevents the coalescence of smaller bubbles into larger bubbles. This increases the interfacial area and hence the volumetric mass transfer increases.
11. Which of the following does not influence the mass transfer?
a) Types of cells
b) Anatomy of cells
c) Morphology of cells
d) Concentration of cells
View Answer
Explanation: Anatomy of cells does not affect the value of the volumetric mass transfer. The influence of cells on enhancing mass transfer depends on the types of cells, the concentration of cells, and the morphology of cells.
12. Which of the following is not a surface active solute?
a) Alcohol sulfates
b) Alkylbenzene sulfonates
c) Phosphoric acid esters
d) Halogen salts
View Answer
Explanation: Surface active solutes or surfactants are the substances that are used to lower the surface tension of the medium in which it gets dissolved. They also do not allow the gas bubbles to coalesce and therefore increases the interfacial area. This leads to an increase in KLa. Examples are alcohol sulfates, phosphoric acid salts, etc.
13. Smaller bubbles are a nuisance to the fermenters.
a) True
b) False
View Answer
Explanation: The smaller bubbles are a nuisance to the fermenters. They occupy the larger interfacial area and coalesce into larger bubbles. The gas hold-up is also higher in smaller bubbles and thus have low bubble rise velocity. This increases the value of KLa.
14. Which of the following organism broth has Bingham plastic rheology?
a) Penicillium chrysogenum
b) Endomyces sp.
c) Streptomyces kanamyceticus
d) Streptomyces scabies
View Answer
Explanation: Penicillium chrysogenum has Bingham plastic rheological type. Bingham plastics are similar to Newtonian liquids. In Bingham plastics, the shear rate will not increase until a threshold shear stress is exceeded.
15. The rheological type of Endomyces sp. is ____________
a) Pseudoplastic rheology
b) Bingham plastic rheology
c) Dilatant rheology
d) Casson body
View Answer
Explanation: The rheological type Endomyces sp. is Pseudoplastic rheology. The viscosity of pseudoplastic rheology increases with increasing shear rate. Most polymer solutions act as pseudoplastics.
16. Casson body rheology is a Newtonian type fluid.
a) True
b) False
View Answer
Explanation: Casson body rheology is a type of non-Newtonian fluid. It behaved as a pseudoplastic in which viscosity decreases with increasing shear stress and displayed yield stress. It also resembles a Bingham plastic.
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