LIQUID FLOW AND MASS-TRANSPORT IN HETEROGENEOUS BIOFILMS

Convective mass transport in heterogeneous biofilms, consisting of cel l clusters and voids, was investigated using oxygen microelectrodes. O xygen concentration profiles were measured and contour plots construct ed at different (average) how velocities (U-avg). The profiles were us ed to determine the thickness of the mass transfer boundary layer (del ta(h)) above the voids and the cell clusters. The delta(h) above the b iofilm was inversely related to flow, as expected, and decreased expon entially with increasing flow velocity. However, the delta(h) above th e voids decreased more rapidly than the delta(h) above the cell cluste rs resulting in two distinct situations; at low flow velocities the ox ygen contours were parallel to the substratum but at high velocities w ere parallel to the irregular biofilm surface. It was concluded that a t low how velocities the biofilm could be modeled one-dimensionally, w ith fluxes perpendicular to the substratum and the exchange area being equal to the substratum area, but at higher velocities biofilm voids facilitate mass transport and a more complex, three-dimensional model would be more appropriate. In this latter case fluxes are multidirecti onal, and the exchange area is equal to that of the convoluted biofilm surface. Copyright (C) 1996 Elsevier Science Ltd