Grey box modelling in two time domains of a wastewater pilot scale plant

Wastewater treatment processes are characterized by the existence of many different biochemical and physical processes, which partly can be controlled through operation of the wastewater treatment plant. Time series models of these processes are very useful for gaining insight into real time operation of wastewater treatment systems which deal with variable influent flows and pollution loads. In this paper nonlinear time series models based on knowledge of the processes are established. Rates of the biochemical and hydraulic processes are identified, and by statistical methods these constants for the biochemical processes are estimated assuming Monod kinetics. The models are solely based on on-line measurements of ammonia and nitrate concentrations and corresponding controlling signals from a wastewater pilot scale plant. The models only include those hydraulic and kinetic parameters which have been shown to be significant in a statistical sense, and hence can be quantified.