MODELING MASS-TRANSFER AND SUBSTRATE UTILIZATION IN THE BOUNDARY-LAYER OF BIOFILM SYSTEMS

The use of microelectrodes in biofilm research allows a better underst anding of intrinsic biofilm processes. Little is known about mass tran sfer and substrate utilization in the boundary layer of biofilm system s. One possible description of mass transfer can be obtained by mass t ransfer coefficients, both on the basis of the stagnant film theory or with the Sherwood number. This approach is rather formal and not quit e correct when the heterogeneity of the biofilm surface structure is t aken into account. It could be shown that substrate loading is a major factor in the description of the development of the density. On the o ther hand, the time axis is an important factor which has to be consid ered when concentration profiles in biofilm systems are discussed. Fin ally, hydrodynamic conditions become important for the development of the biofilm surface when the Reynolds number increases above the range of 3000-4000. (C) 1998 IAWQ. Published by Elsevier Science Ltd.