A distributed parameter fixed-bed bioreactor model with axial diffusio
n is presented. An orthogonal collocation method is applied to obtain
a lumped parameter model, i.e. a system of ordinary differential equat
ions, which consists of one subset for the biomass concentration and t
he other for the substrate concentration. An order reduction parameter
of the model is developed, giving a qualitative correlation between t
he number of collocation points and the accuracy of the steady state s
olution. The sensitivity of a static state feedback control law is int
roduced. Some simulation results are presented.