# DBT JRF 2022 — Question 98

Exam: DBT JRF 2022 · Section: B · Topic: Bioprocess Engineering › Immobilized Cell Bioreactor - Ethanol Production · Difficulty: Medium

## Question

Yeast cells are immobilized in a column and glucose is fed through the inlet at a concentration of 90 g/l. If all the glucose is consumed and we can treat this as an anaerobic fermentation with negligible cell growth, then the ethanol concentration at the outlet will be:

## Options

- **A.** 90 g/l
- **B.** 60 g/l
- **C.** 36 g/l
- **D.** 46 g/l

## Answer

Option D

## Explanation

Ethanol yield from glucose fermentation (Embden-Meyerhof-Parnas / yeast fermentation): Glycolysis + alcoholic fermentation (Saccharomyces cerevisiae): $\text{C}_6\text{H}_{12}\text{O}_6 \rightarrow 2\,\text{C}_2\text{H}_5\text{OH} + 2\,\text{CO}_2$ Molecular weights: Glucose = 180 g/mol; Ethanol = 46 g/mol Given: 90 g/L glucose = 90/180 = 0.5 mol/L glucose From stoichiometry: 1 mol glucose → 2 mol ethanol $[\text{Ethanol}] = 0.5 \times 2 = 1.0\,\text{mol/L}$ $\text{Ethanol concentration} = 1.0\,\text{mol/L} \times 46\,\text{g/mol} = 46\,\text{g/L}$ Note: This is the theoretical maximum (100% yield). Actual fermentations achieve 90–95% of theoretical yield. Answer: 46 g/L ethanol from 90 g/L glucose.

Source: https://mypyqbuddy.com/questions/yeast-cells-are-immobilized-in-a-column-and-6a104cd5920734408bc0c771