GATE 2021 BT – Question 52
A chemostat has $D=0.8\ \mathrm{h^{-1}}$, biomass 8 mol/m³ and specific product formation 0.2 mol product/(mol biomass h). Steady product concentration (mol/m³) is _______.
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Correct answer: 2
Explanation
At the **steady state of a chemostat**, the product is formed at the same rate that it leaves with the outflow.
**Balance on the product** (feed contains no product):
$$\text{formation}=\text{outflow}\;\Rightarrow\;q_P\,X=D\,P .$$
**Numbers.**
$$P=\frac{q_PX}{D}=\frac{0.2\ \text{mol/(mol h)}\times8\ \text{mol/m}^3}{0.8\ \text{h}^{-1}}=\mathbf{2\ mol/m^3}.$$