Biofilm formation: Hydrodynamic effects on internal diffusion and structure

Diffusion in microbial films produced by Pseudomonas fluorescens under turbulent flow conditions was studied using an inert substance (LiCl). Mass transfer coefficients in the biofilm were measured during formation of the biological deposits and for biofilms developed under different fluid velocities. Mass transfer rates in the biofilm decreased with time, and more quickly in the case of biofilms subjected to high shear stresses. The latter show lower final thicknesses and lower internal diffusivities. The so‐called “active layer”;, if it exists, does not seem to have a fixed thickness (as proposed by some authors), since it will depend on the environmental conditions, particularly on fluid velocities.