Convective mass transport in heterogeneous biofilms,consisting of
cell clusters and voids,was investigated using oxygen microelectrodes.
Oxygen concentration profiles were measured and contour plots constructed
at different (average) flow velocities (Uavg). The profiles were
used to determine the thickness of the mass transfer boundary layer
(delta h) above the voids and the cell clusters. The delta h above
the biofilm was inversely related to flow,as expected,and decreased
exponentially with increasing flow velocity. However,the delta h
above the voids decreased more rapidly than the delta h above the
cell clusters resulting in two distinct situations ; at low flow
velocities the oxygen contours were parallel to the substratum but
at high velocities were parallel to the irregular biofilm surface.
It was concluded that at low flow velocities the biofilm could be
modeled one-dimensionally,with 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 multidirectional,and
the exchange area is equal to that of the convoluted biofilm surface.
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