Average modeling of an alternating aerated activated sludge process for nitrogen removal

In this paper we present a novel average model for alternating (two-phase) activated sludge (AS) models. This kind of processes, where nitrification-denitrification operations occur, are represented by two (switching) consecutive dynamics: an aerobic phase followed by an anaerobic one. In particular, we study a reduced AS model for nitrogen removal. The resulting average continuous model captures the original switched dynamics, without considering the (fast) switching behavior. In contradistinction to (discontinuous) intermittently aerated AS models, the continuous nonlinear AS models thus obtained can be used straightforwardly for analysis, control design and estimation purposes.