The steady-state operation of a fixed bed reactor (FBR) with microencapsulated urease for the regeneration of a dialysate solution was modeled at various enzyme activities to improve the understanding of performance factors. The limiting effects of pH, product inhibition and substrate depletion were also studied individually and in combination under eight case studies for two different microcapsule diameters, 5 and 500 mu m. The rapid depletion of substrate at high enzyme activities for a Michaelis-Menten kinetic model lowered the residual substrate concentration (S-r) to a value below the Michelis-Menten constant K-m,K-0 resulting in dramatic reductions in the intracapsular reaction rate. When the limiting factors were considered (pH, product inhibition and substrate depletion) in the reaction process, reduced urea conversion values were encountered for the level of enzyme activity under consideration. These limiting factors maintained S-r at a higher value relative to K-m,K-0. Hence, the efficiency of the fixed bed reactor decreased from the inlet to the outlet when a Michaelis-Menten kinetic model was considered, and vice versa for other models which accounted for product inhibition and pH-dependent kinetics.