A Reduced Order Model for Control of a Single Reactor Activated Sludge Process

The IAWQ activated sludge model no 1, slightly modified by adding a nitrogen limiting growth function for heterotrophic microorganisms, has been validated on a sequencing single sludge wastewater reactor doing nitrification and denitrification. However, this model is too complex to be used for control design. The main purpose of this paper is to show how it is possible to simplify the full model from biological and mathematical considerations. Properties of observability, controllability and theoretical identifiability have been analyzed. The parameter identification has been carried out by using the simplex method of Nelder & Mead. Simulation results performed over a range of six hours (two aerobic / anoxic cycles), show that there exists a good fit between the simulated solution and the actual behavior of a lab scale pilot plant.