Abstract for presentation at Chemeca 2007

The activated sludge model that we analyse in this work is based on the model proposed by Henze et al. (1987). This model is regarded as one of the most popular mathematical description of the biochemical processes in the reactor for nitrogen and chemical oxygen demand. The model is amenable to describe the process of carbon oxidation, nitrification and denitrification (the latter two are the biological processes required for the removal of nitrogen). We note that the model is known to give a good description of the processes, as long as the wastewater has been characterised in detail and is of domestic or municipal in origin. The model has not been developed to fit industrial wastewater treatment.

So far the model has been investigated via simulations, that is, direct integration of the governing equations. This approach is obviously time consuming whereby parameter regions of interest (in terms of quality of effluent leaving the plant) can only be determined through laborious and repetitive calculations. More importantly, regions of parameter space that may be of interest can easily be missed. In this work we apply techniques from nonlinear dynamical systems theory to systematically analyse all the generic steady-state behaviour for the system. In particular, we determine design parameters that would enable the treatment plant to minimise the overall nitrogen concentration in the effluent leaving the treatment plant, thereby increasing the performance of the plant.