MOVEMENT OF SOLIDS IN BIOFILMS - SIGNIFICANCE OF LIQUID-PHASE TRANSPORT

In the one-dimensional mixed-culture biofilm model, volume expansion d ue to microbial growth leads to a displacement of biomass towards the biofilm surface, where solids (cells and particles) can be detached an d attached. In this model there are no suspended solids in the pore vo lume of the biofilm. In a growing biofilm, this description makes a si gnificant penetration of solids from the bulk fluid into the biofilm i mpossible and it leads to a fast elimination of attached inert particl es from the biofilm. Recent experiments with fluorescent microbeads us ed as solid tracers are in disagreement with this description. The ine rt tracer particles added to the bulk fluid penetrate the biofilm quit e fast and they show a residence time in the film that is much larger than that of the bacteria. For this reason the processes ''transport o f solids suspended in the biofilm pore volume'' and ''attachment to'' and ''detachment from the solid matrix in the biofilm interior'' were added to the mixed-culture biofilm model. These processes were also im plemented in the biofilm reactor compartment of the simulation program AQUASIM which is used here to demonstrate that the new processes make a qualitative simulation of the observed behavior possible. Therefore , the mixed-culture biofilm model with these processes added can be us ed as a tool for further research on the mechanisms which determine th e development of the biofilm solid matrix and on transport of solids i n the biofilm pore volume. (C) 1997 IAWQ. Published by Elsevier Scienc e Ltd.