Control of the biodegradation of mixed wastes in a continuous bioreactor by a type-2 fuzzy logic controller

Type-2 fuzzy logic control is proposed for nonlinear processes characterized by bifurcations. A control simulation study was conducted for a bioreactor with cell recycle containing phenol and glucose as carbon and energy sources in which a pure culture of Pseudomonas putida is carried out. The model developed by Ajbar [Ajbar, A. (2001). Stability analysis of the biodegradation of mixed wastes in a continuous bioreactor with cell recycle. Water Research, 35(5), 1201–1208] was used for the simulations.The particular dynamics of the bioreactor, characterized by two saddle-node bifurcations, makes its control difficult, since it may become unstable also for small variations of some parameters.The design of the type-2 fuzzy logic controller, with Sugeno inference method, was based on the knowledge of the more relevant continuity diagrams of the process. The proposed controller was compared by simulation with a type-1 fuzzy logic controller and a PI controller.The simulation results show that the type-2 fuzzy logic controller has a higher performance, in terms of robustness and response speed, compared with the other controllers. It is proved that the use of type-2 fuzzy controllers can be a good choice for the control of nonlinear processes with bifurcations, in particular when uncertainties on some parameters of the controlled system are present.