Speciation and Chemical Interactions in Nitrifying Biofilms. II: Sensitivity Analysis

Abstract

Steady-state models of nitrifying biofilms have been developed that take into account the mass transfer of neutral and ionic species, electroneutrality, pH-dependent Monod kinetics, chemical equilibrium, and the presence of a boundary layer. Under the conditions investigated, the models predict significant changes in the biomass speciation and percent conversions in nitrifying biofilms as functions of pH, buffer capacity [in terms of total inorganic carbons], and, for the reactor models, volumetric flow rate per unit surface area of biofilm and total ammonium loading. To a lesser extent, the models also predict sensitivity to biofilm thickness, total ammonium, total nitrite, dissolved oxygen concentration, and total biomass density. Nitrogen conversions are only a very weak function of boundary layer thickness, total nitrate concentration, and the ratio of the chemical species' diffusivity in the biofilm to its diffusivity in water.