Airlift bioreactor anatomy: which set correctly lists the standard zones and flow paths used to describe an airlift system?

Introduction / Context:
Airlift bioreactors use gas buoyancy to circulate liquid without mechanical impellers. Understanding standard terminology—riser, downcomer, and disengagement zone—is essential for discussing hydrodynamics, mass transfer, and shear environment for sensitive cells.

Given Data / Assumptions:

• Gas is injected into a defined region to create a low-density riser.
• Liquid returns via a higher-density downcomer.
• At the top, a disengagement zone allows gas to separate from liquid.

Concept / Approach:
Gas introduction lowers the effective density in the riser, producing circulation. The downcomer completes the loop as degassed, denser liquid descends. The disengagement zone at the headspace promotes bubble release, stabilizing circulation and reducing carryover.

Step-by-Step Solution:

Verification / Alternative check:
Design schematics for split-column or internal-loop airlifts consistently use these three labels; correlations for circulation velocity and kLa are written in terms of riser/downcomer properties.

Why Other Options Are Wrong:

• Invented terms like flotsam/jetsam/downzone: not engineering terminology.
• Misspellings (air comer, downsizer) and nonstandard “disentanglement zone”.
• “All of the above”: incorrect because only one set is valid.
• Draft tube alone: does not replace zone nomenclature.

Common Pitfalls:
Confusing internal vs external-loop designs; mixing airlift terms with stirred-tank nomenclature.

Final Answer:
Disengagement zone, air riser, downcomer