Dynamic Model of Nitrification in Fluidized Bed

Abstract

Fixed‐film nitrification was studied in a pilot‐scale fluidized bed treating municipal secondary effluent. A mechanistic mathematical model incorporating reaction stoichiometry, diffusion, multisubstrate kinetics with product inhibition, fluidization, and a reactor model developed from the observed residence‐time distribution, was developed to predict the steady‐state and short‐term dynamic performance of the reactor. The model equations were solved using orthogonal collocation with trial functions tailored to the spherical‐shell biofilm geometry, and a semi‐implicit third‐order Runge‐Kutta integration technique. The steady‐state model closely fit measured concentration profiles using the maximum specific growth rates for Nitrosomonas and Nitrobacter as adjustable parameters. The dynamic model predicted observed responses to step and impulse changes in ammonium and nitrite concentrations to within 3 mg/L without further parameter adjustment. The fluidization model predicted the observed fluidized bed height within 1 cm. External mass transfer resistance was small for the conditions employed and was not included in the model.