Scale-up techniques in fermentation MCQs With Answer

Scale-up techniques in fermentation MCQs With Answer

Introduction: This quiz collection is designed for M.Pharm students studying Bioprocess Engineering and Technology. It focuses on scale-up principles used in fermentation processes, covering critical aspects such as mixing, oxygen transfer, hydrodynamics, power input, scale-up criteria, and bioreactor design considerations. Questions probe theoretical foundations and practical decision-making: choosing scale-up rules (constant P/V, constant kLa, constant tip speed, etc.), interpreting dimensionless numbers (Reynolds, Froude), and anticipating common scale-up issues like oxygen limitation, shear damage, heat removal and non-Newtonian behavior. Each MCQ includes concise options and a clear correct answer to reinforce learning and prepare students for exams and practical scale-up tasks.

Q1. What is the primary dimensionless number used to characterize the flow regime in stirred tanks during scale-up?

• Froude number
• Power number
• Reynolds number
• Sherwood number

Correct Answer: Reynolds number

Q2. Which scale-up criterion maintains similar oxygen transfer performance between scales for aerobic fermentation?

• Constant tip speed
• Constant volumetric power input (P/V)
• Constant volumetric oxygen transfer coefficient (kLa)
• Constant impeller diameter

Correct Answer: Constant volumetric oxygen transfer coefficient (kLa)

Q3. The power consumption for an agitated vessel is commonly estimated by which correlation?

• P = μ N D
• P = Np ρ N^3 D^5
• P = kLa × C*O2
• P = ρ g V

Correct Answer: P = Np ρ N^3 D^5

Q4. Which factor most directly increases the gas–liquid interfacial area (a) in a sparged fermenter?

• Increased medium viscosity
• Reduced superficial gas velocity
• Smaller mean bubble diameter
• Lower agitator speed

Correct Answer: Smaller mean bubble diameter

Q5. For scale-up by constant tip speed, which operating parameter is adjusted when reactor diameter increases?

• Impeller speed is reduced proportionally to diameter
• Power per volume is kept constant
• kLa is kept constant
• Agitator geometry is changed

Correct Answer: Impeller speed is reduced proportionally to diameter

Q6. Which criterion is most appropriate when scale-up must avoid shear damage to shear-sensitive cells?

• Constant Reynolds number
• Constant Kolmogorov microscale or maximum shear rate
• Constant P/V
• Constant Froude number

Correct Answer: Constant Kolmogorov microscale or maximum shear rate

Q7. The dynamic gassing-out method is used in fermentation to determine which parameter?

• Volumetric mass transfer coefficient (kLa)
• Power number (Np)
• Bubble rise velocity
• Mixing time

Correct Answer: Volumetric mass transfer coefficient (kLa)

Q8. Which of the following is a common cause of reduced oxygen transfer when scaling up from lab to pilot scale?

• Increase in surface-to-volume ratio
• Higher impeller Reynolds number
• Reduced gas residence time and larger bubble sizes
• Decreased medium conductivity

Correct Answer: Reduced gas residence time and larger bubble sizes

Q9. When scaling-up using geometric similarity, which of these must be preserved between vessels?

• Same impeller speed (rpm)
• Same relative dimensions and geometry (all linear dimensions scaled equally)
• Same volumetric power input (P/V)
• Same kLa

Correct Answer: Same relative dimensions and geometry (all linear dimensions scaled equally)

Q10. Which dimensionless group is most relevant for predicting gas entrainment and free-surface vortex formation in large stirred tanks?

• Reynolds number
• Schmidt number
• Froude number
• Damköhler number

Correct Answer: Froude number

Q11. In a power-law non-Newtonian fermentation broth, scaling based on which parameter often gives better mixing similarity?

• Constant tip speed
• Constant power per unit volume (P/V)
• Constant Reynolds number defined for power-law fluids
• Constant geometric similarity only

Correct Answer: Constant Reynolds number defined for power-law fluids

Q12. Which impeller feature primarily enhances axial flow and bulk mixing in a fermenter?

• Pitched-blade or hydrofoil impellers
• High disk thickness
• Small diameter flat-blade turbine
• Top-mounted gas sparger

Correct Answer: Pitched-blade or hydrofoil impellers

Q13. For scale-up where heat removal is limiting, which approach is commonly used to maintain similar temperature control?

• Decrease gas flowrate to reduce cooling
• Increase heat transfer surface area per volume (e.g., internal coils or external exchangers)
• Reduce inoculum size
• Operate at higher agitation without additional cooling

Correct Answer: Increase heat transfer surface area per volume (e.g., internal coils or external exchangers)

Q14. The typical correlation to estimate kLa as a function of power input and gas flow is of the form kLa = A (P/V)^α (Q/V)^β. What do P and Q represent?

• P is pressure, Q is heat flux
• P is power input, Q is superficial gas flowrate
• P is impeller diameter, Q is liquid viscosity
• P is protein concentration, Q is volumetric flow

Correct Answer: P is power input, Q is superficial gas flowrate

Q15. Which scale-down strategy is used to mimic large-scale gradients (oxygen, substrate) in lab reactors to study robustness?

• Operating at constant tip speed in lab reactors
• Using scale-down bioreactors with intermittent feed or divided compartments to generate heterogeneities
• Increasing inoculum and reducing working volume
• Using only geometric similarity without changing control loops

Correct Answer: Using scale-down bioreactors with intermittent feed or divided compartments to generate heterogeneities

Q16. Which of the following is NOT a typical consequence of inadequate scale-up in aerobic fermentation?

• Oxygen limitation leading to reduced productivity
• Excessive shear causing cell lysis
• Improved substrate utilization resulting in higher yield
• Poor temperature control causing metabolic shifts

Correct Answer: Improved substrate utilization resulting in higher yield

Q17. During scale-up, the Power number (Np) for an impeller is primarily a function of which parameter?

• Liquid osmolarity
• Impeller Reynolds number (flow regime)
• Culture pH
• Gas composition

Correct Answer: Impeller Reynolds number (flow regime)

Q18. Which method gives a rapid experimental estimate of kLa by temporarily stopping aeration and observing dissolved oxygen recovery?

• Static headspace method
• Dynamic gassing-out (oxygen re-saturation) method
• Bubble counting method
• Computational fluid dynamics (CFD)

Correct Answer: Dynamic gassing-out (oxygen re-saturation) method

Q19. In the context of scale-up, which statement about tip speed is correct?

• Tip speed scales proportionally with power number for similar mixing
• Maintaining constant tip speed may lead to different P/V and mixing patterns at different scales
• Tip speed is irrelevant for shear-sensitive cultures
• Tip speed is equivalent to kLa

Correct Answer: Maintaining constant tip speed may lead to different P/V and mixing patterns at different scales

Q20. When selecting a scale-up criterion for a recombinant protein production process sensitive to oxygen but tolerant to shear, the best choice is likely:

• Constant tip speed to minimize shear
• Constant kLa to ensure oxygen supply
• Constant geometric similarity only
• Constant Reynolds number to preserve turbulence

Correct Answer: Constant kLa to ensure oxygen supply

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