Fluidized-bed bioreactors often achieve higher gas–liquid and liquid–solid mass transfer rates than packed-bed bioreactors primarily because:

Introduction:
Choosing between packed-bed and fluidized-bed configurations for immobilized biocatalysts depends heavily on mass transfer performance. Fluidization alters hydrodynamics, boundary layers, and interfacial areas, which can markedly increase transfer rates.

Given Data / Assumptions:

• Fluidized beds maintain particles in motion due to upward flow.
• Smaller support particles are commonly used in fluidized systems.
• Mixing and contact patterns differ significantly from fixed beds.

Concept / Approach:
Higher mixing reduces external film resistance; particle motion thins boundary layers and renews liquid at surfaces; smaller particles provide larger specific surface area. Together these effects elevate overall volumetric mass transfer, provided attrition and elutriation are controlled.

Step-by-Step Solution:

Verification / Alternative check:
Residence time distribution and k_La measurements typically show higher values in fluidized systems at comparable throughputs, confirming the mechanism-based expectations.

Why Other Options Are Wrong:

• Individual statements (a), (b), or (c) each reflect only part of the reason; the comprehensive answer is all of the above.

Common Pitfalls:
Ignoring particle attrition and carryover can negate advantages. Use appropriate particle density and size to maintain stable fluidization without excessive losses.

Final Answer:
all of the above