A fed batch culture was operated with intermittent addition of glucose solution at a flow rate of $\text{200 ml h}^{-1}$. The values of $K_s,\: \mu_m$ and $D$ are $\text{0.3 g l}^{-1}, 0.4\:h^{-1}$ and $\text{0.1 h}^{-1}$, respectively. Determine the concentration of growth limiting substrate $(gl^{-1})$ in the reactor at quasi-steady state. ______________