Stabilization of unstable steady states of a continuous stirred tank bioreactor with predator–prey kinetics

• We analyze the nonlinear dynamics of CSTBR with a developed predator–prey trophic chain.
• A method of stabilizing unstable steady states by using continuous controllers is shown.
• The oscillations can be removed by employing continuous P or PI controllers.
• A new, hitherto unknown phenomenon was observed.
• By using PI-controller, the predator can be completely eliminated from the system.

Nonlinear properties of a bioreactor with a developed microbiological predator–prey food chain are discussed. The presence of the predator microorganism completely changes the position and stability of the stationary states. A wide range of unstable steady states appears, associated with high amplitude oscillations of the state variables. Without automatic control such a system can only operate in transient states, with the yield undergoing periodic changes following the dynamics of the stable limit cycle. Technologically, this is undesirable. It has been shown that the oscillations can be removed by employing continuous P or PI controllers. Moreover, with a PI-controller, the predator can be eliminated from the system.

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