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 d iffusion-limited penetration of nitrate and nitrite into the immobilized-ce ll biocatalyst particle, uniform intraparticle cell density, equivalent sla b geometry for the spherical particle, zero-order intrinsic reaction kineti cs 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-flo w bioreactor can be described by a half-order kinetics, and the process is characterized by the half-order reaction rate constants for nitrate and nit rite reduction. These constants incorporate the intrinsic reaction kinetics of the immobilized cells, the size and packing density of biocatalyst part icles in the reactor, and the effective diffusion coefficients of nitrate a nd nitrite in the particle matrix.