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In Sparged stirred-tank bioreactor, the stirrer facilitates mixing and oxygen availability throughout the bioreactor – NCERT
Simple Stirred Tank Bioreactor
- Oxygen enters only at the liquid surface.
- Agitator helps mixing but no air sparging.
- Best for low oxygen-demand processes.
- Lower oxygen transfer efficiency.
Sparged Stirred Tank Bioreactor
- Sterile air is sparged directly into liquid.
- Agitator breaks bubbles into smaller ones.
- Massive increase in oxygen transfer area.
- Ideal for high oxygen-demanding cultures.
Why Sparged Tank is Better?
- Oxygen supplied deep inside the liquid.
- Higher surface area = faster oxygen transfer.
- Efficient gas entrainment improves mixing.
- Boosts growth of aerobic microbes and cells.
Bubbles & All-Directional O₂ Supply
- Each bubble supplies oxygen in 360° around.
- Smaller bubbles = larger total surface area.
- More bubbles mean better oxygenation.
- Ensures uniform oxygen for all cells.
How Bubbles Dramatically Increase Oxygen Transfer
- When sterile air is sparged into the liquid, it forms many small bubbles.
- Each bubble has surface area where oxygen dissolves into liquid.
- Smaller bubbles = greater total surface area (many small bubbles > few big ones).
- Stirring further breaks bubbles smaller and distributes them evenly.
- This massively increases oxygen transfer area for cells and microbes.
- Think of 1 big bubble vs 100 tiny ones — combined surface is much larger, allowing more oxygen transfer.
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| Feature | Simple Stirred Tank | Sparged Stirred Tank |
|---|---|---|
| Oxygen Entry | Surface only | Bubbles + surface |
| Oxygen Transfer Rate | Low | High |
| Best For | Low O₂ demand cultures | High O₂ demand microbes |
| Bubble Advantage | Not applicable | Smaller bubbles = more area |
| Gas Entrainment | No | Yes |