Effects of diffusivity on the predicted hollow fiber biofilm reactor performance

Abstract

Considerable modeling work has been done to calculate the performance of hollow fiber biofilm reactors (HFBR's). The performance of the HFBR is controlled by the biological phase (biofilm). Previous investigations of biofilm structure showed that biofilms are heterogeneous and consist of voids, and cell clusters. The biofilm activity can be modeled using the diffusion reaction model. The main design parameter in diffusion and reaction model is the effective diffusivity in biofilms. Recent studies have shown that the effective diffusivity varied in biofilms and is controlled by the biofilm heterogeneity This variation may influence the predicted activity oft he HFBRs. The existing biofilm models do not include variable effective diffusivity. The goal of this study was to compare the predicted performance of HFBR by employing 1) position dependent and, 2) constant effective diffusivity. The percentage difference between predicted activities, employing variable, and constant effective diffusivity, was approximately zero for biofilm thicknesses less than 50 mum. However, the percentage difference is significantly increased for biofilms thicker than 50 mum. The employment of constant or variable effective diffusivity in the model does not influence the predicted results for thinner biofilms. However, increased biofilm thickness significantly influences the predicted activity of the HFBR. Ir was concluded that for thicker biofilms, a variable effective diffusivity should be used in the model solutions.