Section 4: Bioprocess Engineering and Process Biotechnology
Bioreactor types, scale-up
Subtopic: Fundamentals of Bioreactor types, scale-up
Question Statement:
Correctly match the Microorganisms with their respective Nutrition and energy
requirement.
Microorganisms Nutrition and energy requirement
P. Photolithoautotrophs 1. Use organic compounds as a source of
energy, hydrogen, electron and carbon
Q. Chemoorganoheterotrophs 2. Use light energy and use CO2 as their
carbon source
R. Chemolithoautotrophs 3. Use light energy and use organic
compounds as electron donor and
carbon source
S. Photoorganoheterotrophs 4. Oxidise reduced-inorganic molecules
as energy and electron source but
derive carbon from organic sources
Options:
(A) P-2; Q-1; R-4; S-3
(B) P-2; Q-1; R-3; S-4
(C) P-1; Q-2; R-4; S-3
(D) P-4; Q-1; R-2; S-3
Official Answer Key:
A
Step-by-Step Solution & Explanation
### **Official Solution & Concept Analysis (GATE BT 2025 Q.36)**
**1. Governing Concept**:
- **Topic**: Bioprocess Engineering & Scale-Up Criteria
- Bioreactor scale-up maintaining constant volumetric mass transfer coefficient ($k_L a = \text{constant}$):
- In non-viscous coalescing media, $k_L a$ correlates with volumetric power input ($P/V$) and superficial gas velocity ($v_s$) via the empirical relation:
$k_L a = C \left(\frac{P}{V}\right)^\alpha v_s^\beta$
- When superficial gas velocity is constant, keeping $k_L a$ constant requires maintaining **constant power per unit volume ($P/V = \text{constant}$)**.
**2. Option Analysis**:
- **Option (A) is CORRECT**: Constant power-to-volume ratio ($P/V$) ensures equivalent turbulent energy dissipation rate and gas dispersion to maintain identical oxygen transfer capacity.
- **Option (B) is INCORRECT**: Constant impeller tip speed ($v_{\text{tip}} = \pi N D_i$) maintains constant maximum shear stress, which under-aerates large vessels.
- **Option (C) is INCORRECT**: Keeping Reynolds number constant severely drops agitation and mass transfer in large fermenters.
- **Option (D) is INCORRECT**: Constant mixing time requires excessively high power consumption on large scales.
**3. Final Answer**:
- **Correct Choice**: **A**
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