This mail is regarding the heterogeneity of biofilms and their relevance.
There was a poster paper presented at the biofilm conference (ASM) at Utah
on the effect variations of the biofilm parameters (due to the
heterogeneity of the biofilm) on the biofilm model predictions (this
theoretical work was based on the outstanding experimental work by Bishop
et al., at
Cincinnati) and it was found that for biofilm thicknesses up to 40 microns
the heterogeneity did not have much effect on the biofilm model
predictions but beyond that thickness there were significant deviations.
Bishop et al (water science tech, 31, 143-152, 1995) define biofilms as
multiphase systems which consist of solids and of a liquid phase between
solids. This definition for fungal fermentation on solids or semi solids
(Solid
State Fermentation (SSF) practised widely in the oriental countries) has
to include the gas phase also since the void space is not necessarily
filled with liquid. We has also presented a paper on the effect of this
biofilm heterogeneity on SSF and found wide deviations due to the
homogeneous assumptions.
While our work is completely theoretical, it does throw
light on the significance of heterogeity research. If we can find a 'safe
biofilm thickness' within which we can best predict the concentrations of
species inside and outside the biofilm, it will be of great industrial
importance (waste water treatment). Needless to say that
this 'safe limit' will vary from species to species but is a worthwhile
study. While it has been known for a while that this heterogeneity would
alter model predictions, there has been no quantitative report on the
amount of deviations and also there has been no report on the safe limit
underwhich a homogeneous model can best describe the transport phenomena
inside the biofilm (to my knowledge).
regards,
Raj.
