Modeling and Control Design of an Activated Sludge Process: a Multi-Model Approach

Wastewater treatment systems, especially those using biochemical processes, present recently new challenges resulting from the growing awareness of environmental risks. In this paper, a multi-model-based method is proposed and successfully applied for modeling and control design of an Activated Sludge Plant (ASP). A quasi Linear Parameter-Varying (LPV) representation of such a wastewater treatment system is firstly established to build a corresponding multi-model by the use of a convex polytopic transformation. Such a global ASP's multi-model structure is then used to design state-feedback controllers based on the Parallel Distributed Compensation (PDC) formalism. Local control laws for the modeled dynamics, i.e. effluent volume and concentrations of the heterotrophic biomass, the biodegradable substrate and the dissolved oxygen are merged to obtain global PDC control laws stabilizing these nonlinear variables. Simulation results are effectuated to show the validity and efficiency of the proposed multi-model-based modeling and control approach for such a complex biochemical process.