During his doctoral thesis a methodology for retrofitting existent Anoxic/Oxic (A/O) wastewater treatment plants (WWTP) to perform the Enhanced Biological Phosphorus Removal (EPBR) in order to biologically remove organic matter (COD), nitrogen (N) and phosphorus (P) at the same time, considering process control aspects, was developed. The proposed methodology exhaustively searches a process model, using existent plant data to determine the current kinetic parameters. The plant model is calibrated using a methodology based on the Fisher Information Matrix. Using the plant model structure, new plant configurations are proposed and a set of criteria are used to identify what is the best alternative. Amongst the criteria are: the robustness of the process control structure, operating costs, investment costs to perform changes in the plant layout and equipments and the effluent quality. The feasibility of phosphorus accumulating organisms (PAO) growth and the effect of these species in the existent process control structure are also studied.