Non-linear analysis of feedback controlled aerobic cultures

In the present work, the results of a complete dynamical analysis of open- and closed-loop continuousbioreactor for cultures of substrate inhibited aerobic microorganisms were presented. In the closed loopsystem the dissolved oxygen concentration was controlled at a pre-set value by means of a proportionalintegralfeedback control scheme manipulating the inlet substrate concentration. A mathematical modelwas developed coupling the mass balance equation for the substrates (carbon-source and oxygen) andthe controller. Solutions of both open- and closed-loop systems were assessed by means of parametriccontinuation technique and bifurcational analysis tools. The dynamics behavior was studied by changingthe main operating parameters – dilution rate and gas-liquid mass transfer rate - and the controllerparameters - gain and set-point – in a wide intervals. We have found that the regimes strongly depend onthe operating conditions. In particular, the open-loop unstable steady state may be stabilized in closedloopsystem, provided the proper choice of both the gain and the reset time for the selected set-point valueof oxygen concentration