Interaction analysis and control structure selection in a wastewater treatment plant model

This paper considers the problem of channel interaction in multivariable systems. As an application, nitrate removal in the activated sludge process (ASP) in a wastewater treatment plant is studied. To evaluate the degree of channel interaction, two different tools are compared: the well-known relative gain array (RGA) and the more recently developed Hankel interaction index array (HIIA). The results of the analysis are discussed from a process knowledge point of view, and are also illustrated with some control experiments. The main conclusion is that the HIIA gives a deeper insight about the actual cross couplings in the system. This insight is also used in order to design a suitable structured multivariable controller.