Microbial production of enzymes: Nonlinear state and kinetic reaction rates estimation

• Estimation strategies for microbial production of enzymes (e.g. lipase) are designed.
• An asymptotic observer that reconstructs the unavailable state variables is proposed.
• A nonlinear high-gain observer is designed to estimate imprecisely known kinetics.
• The tuning of high-gain observer is reduced to the calibration of a single parameter.
• Realistic simulations are provided to test the proposed estimation strategies.

The nonlinearity of the biotechnological processes and the absence of cheap and reliable instrumentation require an enhanced modelling effort and estimation strategies for the state and the kinetic parameters. This work approaches nonlinear estimation strategies for microbial production of enzymes, exemplified by using a process of lipase production from olive oil by Candida rugosa. First, by using a dynamical mathematical model of this process, an asymptotic observer which reconstructs the unavailable state variables is proposed. The design of this kind of observers is based on mass and energy balances without the knowledge of kinetics being necessary; only minimal information concerning the measured concentrations is used. Second, a nonlinear high-gain observer is designed for the estimation of imprecisely known kinetics of the bioprocess. An important advantage of this high-gain estimator is that the tuning is reduced to the calibration of a single parameter. Numerical simulations in various scenarios are provided in order to test the behaviour and performances of the proposed nonlinear estimation strategies.