Rational transfer function models for nitrifying trickling filters

An important step towards optimization and control of wastewater treatment plants is the development of dynamic models and efficient methods of simulation. Using standard simplifying assumptions, non-rational transfer function models describing the fast dynamics of nitrifying trickling filters, are derived. With a method based on the location of their singularities, it is shown how low order rational transfer functions can approximate the non-rational ones. These transfer functions can be used in efficient simulation routines and in standard methods of controller design. Effluent concentrations from trace substance pulse response experiments and an experiment with varying flow and varying influent ammonium concentration carried out on a large pilot plant NTF show close agreement with simulated effluent concentrations using the rational transfer functions.