Abstract
In this paper a general design procedure of activated sludge plants for nitrogen removal is presented. The general criteria followed involve solving the algebraic system obtained considering the kinetic, stoichiometric and mass balance equations for all the components. The equation used to describe the nitrification and denitrification processes kinetics is the‐classic Michaelis & Menten expression for the enzyme catalyzed reactions considering only the active fraction of the biomass. This fraction has been evaluated introducing a corrective factor (<l) function of θc, for the biomass concentration expressed as VSS.