We see that if D > μ, then dCc/dt will be negative, and the cell concentration will continue to decrease until we reach a point where all cells will be washed out:
Cc = 0
The dilution rate at which wash-out will occur is obtained from Equation (9-90) by setting Cc = 0.
Flow rate at which wash-out occurs
We next want to determine the other extreme for the dilution rate, which is the rate of maximum cell production. ...