This, in combination with increasing loads, and limited availability of land, calls for more efficient procedures for wastewater treatment plants. In this thesis, control and estimation strategies are developed in order to improve the efficiency of the activated sludge process. Four different controllers for control of the external carbon flow rate are evaluated in a simulation study, and in pilot plant experiments.
All controllers utilize feedforward from measurable disturbances.
Different models of the nonlinear oxygen transfer function and time-varying respiration rate are discussed. The approaches are successfully applied to real data. Two strategies for designing a DO controller are developed and practically evaluated. The basic idea is to explicitly take the nonlinear oxygen transfer function into account in the controller design. A simulation study and an experiment in a pilot plant illustrate that a nonlinear DO controller outperforms a standard linear PI controller.