Three-dimensional numerical study on the correlation of spatial structure, hydrodynamic conditions, and mass transfer and conversion in biofilms

A three-dimensional model for convection, diffusion, and reaction in a porous, heterogeneous system has been implemented. It is used to analyze the influence of hydrodynamics and structural heterogeneities on mass transfer and conversion processes of solutes in biofilm systems. The mathematical model comprises the full incompressible Navier-Stokes equations and mass transfer with nonlinear reactions in the biofilm. It is found that increased biofilm surface roughness means decreased mass conversion in the solid biofilm. Secondly, a correlation between bulk flow Reynolds number and the Sherwood number for mass transfer across the irregular liquid/solid interface is formulated. In a further study the contribution of convective transport to overall mass transfer from bulk liquid into the biofilm was analyzed. The main result was that the experimental observation of high convective flux of solutes in biofilm channels not necessarily is coupled with an equally high net convective contribution to mass transfer from bulk liquid into biofilm.