About ten years ago a mathematical model was presented which describes
the spatial distribution and development in time of microbial species
in mixed-culture biofilms. The model was based on the continuum appro
ach and was one-dimensional in space. These two concepts still are the
basis of practically all biofilm models used today. On the experiment
al side some remarkable new findings have been made in the past years:
transport of dissolved components in the biofilm is not always due to
molecular diffusion only, transport of particulate components can not
be exclusively related to the net growth rates of the microbial speci
es in the biofilm, the liquid phase volume fraction (porosity) in the
biofilm is not a constant, and simultaneous attachment and detachment
of cells and particles at the biofilm surface is an essential process.
These experimental findings had a significant impact on our notion of
biofilm systems and called for the integration of new processes in th
e original mixed-culture biofilm model. The new processes can reproduc
e most of the experimental observations, however, they are described b
y empirical mathematical functions. Their mechanisms and significance
for biofilm behavior have not been completely elucidated yet. Thus, th
e extended mixed-culture biofilm model represents primarily a tool for
research on biofilm processes.