# DBT JRF 2022 — Question 103

Exam: DBT JRF 2022 · Section: B · Topic: Bioprocess Engineering › CSTR Biomass & Product Concentration · Difficulty: Medium

## Question

A Continuous Stirred Tank Reactor (CSTR) is running at a dilution (D) of 0.3 $h^{-1}$ and the product formed is growth associated with $Y_{P/X}$ = 0.2 g/g. In order to obtain productivity = 1.2 $gl^{-1}h^{-1}$ we need to have at steady state a biomass concentration of:

## Options

- **A.** 0.8 g/l
- **B.** 1.8 g/l
- **C.** 0.072 g/l
- **D.** 20 g/l

## Answer

Option D

## Explanation

Cell concentration in continuous fermentation: Given parameters: • Volumetric productivity = $D \times C_x \times Y_{P/X} = 1.2\,\text{g/L/h}$ • Dilution rate $D = 0.3\,\text{h}^{-1}$ • Yield coefficient $Y_{P/X} = 0.2\,\text{g product/g cell}$ Solve for cell concentration $C_x$ : $1.2 = 0.3 \times C_x \times 0.2$ $1.2 = 0.06 \times C_x$ $C_x = \frac{1.2}{0.06} = 20\,\text{g/L}$ Answer: Cell concentration $C_x = 20\,\text{g/L}$ .

Source: https://mypyqbuddy.com/questions/a-continuous-stirred-tank-reactor-cstr-is-running-6a104cd5920734408bc0c776