Diffusion in biofilms

Biofilms are widely used in biotechnology processes • production of human care and nutritional products, water and wastewater treatment, and environmental Improvement The product formation and recovery are dependent upon the performance of the biofilm. Biofilms can be harmful in other situations, such as in heat exchangers, drinking water systems, and on teeth, urinary tract and catheters causing infections. The behaviour of the immobilized microorganisms is different from the observed in bulk water, in part due to mass transfer limitations of nutrients and products formed. Diffusion in microbial films produced by Pseudomonas fluorescens (see Oliveira A. et al., this congress) under turbulent flow conditions, was studied using an inert substance (lithium cloride). The mass transfer coefficients in the biofilm were evaluated at different Instants of its formation and at different velocities. Biofifm mass transfer coefficients decrease with time as biofilm builds up. This decrease is more abrupt when the biofilm is formed under high velocities, when thinner but more compact biofilms are observed. Internal diffusion in biofilms is thus highly dependent on the hydrodynamic conditions of the flowing fluid over the microbial layer