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GATE 2026 BT – Question 46

Fundamentals of Biological Engineering · Bioreaction Engineering: Batch, fed-batch and continuous processes, microbial and enzyme reactors, optimization and scale up · 2 marks · Multiple select

In an aerobic fermentation with air sparging, which of the following options can be used to increase the volumetric mass transfer coefficient for oxygen transfer?

  1. Using pure oxygen in place of air
  2. Increasing the volumetric flow rate of air
  3. Reducing the bubble diameter
  4. Decreasing the agitation rate

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Show answer and explanation

Correct answer: (B) Increasing the volumetric flow rate of air; (C) Reducing the bubble diameter

Explanation

The coefficient $k_La$ rises with a higher gas flow rate (more bubbles and holdup), with smaller bubbles (more interfacial area $a$), and with more agitation. Pure oxygen raises the driving force $C^* - C_L$ but does not change $k_La$ itself.