Modeling simultaneous nitrification and denitrification (SND) in a fluidized bed biofilm reactor

Simultaneous nitrification and denitrification (SND) is a biological method for the removal of nitrogenous compounds from wastewater. This method combines the activities of nitrifying and denitrifying bacteria in one compartment to achieve near complete removal of nitrogen. Nitrifying bacteria convert NH4+ to NO3-, and denitrifying bacteria convert NO3- to N2. This method is finding widespread usage because it is highly effective and inexpensive compared to other methods. In this study the removal of NH4+, COD (Chemical Oxygen Demand) and TN (Total Nitrogen) is modeled in a three phase fluidized bed biofilm reactor. The model considers dispersion and convection in the liquid phase, simultaneous diffusion and reaction of the chemical species within the biofilm, and different types of microorganisms namely, heterotrophic aerobes, nitrifying and denitrifying bacteria. The equations of the model were derived using proper assumptions and solved by finite difference method. A set of experimental results in the literature from a bench scale bioreactor was used to verify the model. The model predicted the NH4+, COD, NO3- and TN profiles along the height of the bioreactor reasonably well. A sensitivity analysis was also performed using the model. The model is a useful tool in design and analysis of SND in a fluidized bed biofilm reactor.