Q.16
The unit for specific substrate consumption rate in a growing culture is
- (A) g / L·h
- (B) g / h
- (C) g / g·h
- (D) gmol / L·h
Unit of Specific Substrate Consumption Rate in Growing Cultures
Specific substrate consumption rate measures how efficiently microbial cells use substrates during growth, expressed per unit biomass per time. The correct answer is option (C) g/g·h, standard in bioprocess engineering for normalized rates.
Correct Answer
The unit is g/g·h (grams of substrate per gram of biomass per hour). This “specific” rate normalizes consumption to biomass concentration (X), calculated as qs = (1/X) × (dS/dt), where S is substrate concentration.
Option Explanations
| Option | Unit | Explanation |
|---|---|---|
| (A) | g/L·h | Represents volumetric substrate consumption rate (-dS/dt), not specific to biomass; used for total reactor rates, not per cell mass. |
| (B) | g/h | Absolute consumption rate without volume or biomass normalization; lacks context for culture density or scale. |
| (C) | g/g·h | Correct: Grams substrate consumed per gram dry cell weight per hour; standard for specific rates in microbial kinetics like Monod models. |
| (D) | gmol/L·h | Molar volumetric rate; applies to stoichiometry but not mass-based specific consumption in growing cultures. |
Biotech Applications
In fermentation, this rate (qs) links to growth via yield coefficients: μ = YX/S × qs, aiding scale-up and optimization. Track it in chemostats for process control, vital for antibiotic or enzyme production.
