Nonlinear control of biotechnological processes with growth-production decoupling.

Nonlinear control design techniques for a class of continuous biological processes with growth and production decoupling are investigated. We establish, under realistic assumptions on the kinetics, that though neither the inlet substrate concentration nor the dilution rate can achieve linearization of the global dynamics, we can maximize the dimension of the linear system obtained after feedback and get stable zero dynamics by choosing output functions having a physical meaning. More precisely, if the manipulated variable is the inlet substrate concentration, then the output can be chosen as the biomass concentration. But if the chosen input is the dilution rate, then a suitable output corresponds to yields.