Which of the following statements is $ALWAYS\; CORRECT$ about an ideal chemostat?
- Substrate concentration inside the chemostat is equal to that in the exit stream
- Optimal dilution rate is lower than critical dilution rate
- Biomass concentration increases with increase in dilution rate
- Cell recirculation facilitates operation beyond critical dilution rate
- $P$ and $Q$ only
- $P, R$ and $S$ only
- $P$ and $S$ only
- $P, Q$ and $S$ only