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
