Kinetics of nitrogen and carbon removal in a moving-fixed bed biofilm reactor

A mathematical model of nitrification and denitrification in a moving-fixed bed biofilm reactor has been developed to describe ammonium utilization by nitrifying biomass as well as nitrate and organic carbon utilization by denitrifying biomass, respectively. The model incorporates the mechanisms of diffusive mass transport and Monod kinetics. The model was solved using a combination of orthogonal collocation method and Gear’s method. The model solutions included the concentration profiles of NH4+–N, NO3-–N and glucose (as COD), the growth of suspended and attached biomasses and the effluent concentrations of NH4+–N, NO3-–N and glucose (as COD) in bulk liquid. The batch kinetic tests were independently conducted to determine biokinetic parameters used as an input in the model. A pilot-scale moving-fixed bed biofilm reactor including suspended and attached growths of nitrifying and denitrifying biomasses was set up to verify the model system. The experimental results of NH4+–N, NO3-–N and glucose (as COD) effluents show a good agreement with model prediction. The removal efficiencies of NH4+–N, NO3-–N and COD in specific area and volumetric loadings were about 75%, 92% and 70% at a steady-state condition, respectively. The approaches of modeling and experiments presented in this study could be employed for the design of a full-scale moving-fixed bed biofilm process to remove nitrogen and carbon simultaneously in waters and wastewaters.