This paper deals with the order reduction of the dynamical models of a class of propagation bioprocesses. Since these bioprocesses are described by partial differential equations either for simulation but mainly for control, a possible method consists of approximation of their infinitely order associated models by finite order models. These approximate models consist of a set of ordinary differential equations obtained here by orthogonal collocation method. Since it is difficult to know the connections between the original distributed parameter model and its approximate version, our objective is to analyse the behaviour of both models to view their dynamical properties. Numerical simulations conducted in the case of a fixed bed reactor without dispersion are included to illustrate the dynamical behaviour of the two classes of models.

Keywords: Nonlinear systems, Bioprocesses, Distributed parameter systems, Orthogonal collocation, Fixed bed reactor.