Experimental formulation of a kinetic model describing the nitrification process in biological aerated filters filled with plastic elements

The present work reports the results of a series of experimental tests performed on cylindrically shaped biological aerated filters (BAFs) to define a new model for reactors design. The nitrification performance was analysed by monitoring a laboratory pilot plant over a six-month period; the dependence of the nitrification rate from the biomass surface density, from ammonia nitrogen concentration and dissolved oxygen concentration was determined using kinetic batch tests. The controls performed on the pilot plant exhibited a nitrification efficiency of approximately 98% at loadings up to [GRAPHICS] . Over this value, the pilot plant performance decreased without a correlation with the applied loads. In response to the inlet ammonia loading increase, the bacterial surface density showed a logistic growing trend. The results of kinetic tests proved that the nitrification rate was not affected by the ammonia nitrogen concentration; instead, a first-order kinetic with respect to the dissolved oxygen concentration was detected. Moreover, it was observed that a minimum oxygen concentration, which was proportional to the bacterial surface density, was necessary to initiate the nitrification process. The reaction rate related to bacterial surface density exhibited an increasing trend that was followed by a subsequent decreasing behaviour. The results of kinetic tests and the identification of the relationship between bacterial surface density and ammonia loading permitted the formulation of a mathematical model to predict BAFs' nitrification efficiency.