Sensitivity Analyses of Biodegration/Adsorption Models

Abstract

The research was directed toward additional development and refinement of mathematical models of simultaneous adsorption and biodegradation in granular activated carbon (GAC) columns used in the treatment of low concentrations of synthetic organic chemicals. The sensitivity of models to individual parameters was investigated, as well as alternative formulations for mass transport resistances within the biofilm and at the biofilm/GAC interface. The sensitivity analyses identified three important parameters: the Monod half-saturation coefficient, the GAC surface diffusion coefficient, and the amount of biomass initially attached to the GAC. Small values of the half-saturation coefficient, which are characteristic of oligotrophic microorganisms, were required to simulate the entire range of experimental data. Models with and without a diffusive transport resistance through a biofilm matched the experimental data well. The substrate concentration, however, was quite low, and biofilm diffusion probably would be important at somewhat higher concentrations. A model having a transport resistance at the biofilm/GAC interface did not perform well, implying that sorbed substrate is readily available to microorganisms even under conditions that select for scattered growth of microorganisms on the GAC surface.