Reaction Kinetics of Immobilized-Cell Denitrification. I: Background and Model Development

A simplified, quasi-steady-state model has been formulated for groundwater denitrification using immobilized cells. The model takes into account the diffusionlimited penetration of nitrate and nitrite into the immobilized-cell biocatalyst particle, uniform intraparticle cell density, equivalent slab geometry for the spherical particle, zero-order intrinsic reaction kinetics of the immobilized cells, sequential reduction of nitrate to nitrite and nitrite to dinitrogen within the particle, no inhibition of the sequential reactions by either nitrate or nitrite, and ideal plug flow conditions in the bioreactor. As a result, the reaction in the bulk fluid of the plug-flow bioreactor can be described by a half-order kinetics, and the process is characterized by the half-order reaction rate constants for nitrate and nitrite reduction. These constants incorporate the intrinsic reaction kinetics of the immobilized cells, the size and packing density of biocatalyst particles in the reactor, and the effective diffusion coefficients of nitrate and nitrite in the particle matrix.