Measurement of local effective diffusivity in heterogeneous biofilms

We have developed a novel technique to measure local effective diffusivity distribution in heterogeneous biofilms. Mobile microelectrodes (tip diameter 10 mu m) and the limiting current technique were employed to measure the effective diffusivity of electroactive species introduced to natural and artificial biofilms. We calibrated the microelectrodes in artificial biofilms of known effective diffusivity and known density. In mixed population biofilms, local effective diffusivity varied from one location to another and decreased toward the bottom of the biofilm. We related local effective diffusivity to local biofilm density using an empirical equation. Surface-averaged biomass density depended on liquid flow velocity at which the biofilms were grown. The higher the flow velocity, the denser were the biofilms. Our technique permits fast evaluation of local effective diffusivity and biofilm density in heterogeneous biofilms. (C) 1998 Published by Elsevier Science Ltd. All rights reserved.