Biomedical Engineering Reference
In-Depth Information
It was thus noted that biofilms also have a complex three-dimensional structure like
activated sludge flocs. Biofilms are composed of cell clusters and pore channels and biofilm
structure can be affected by filamentous bacteria [26].
This new insights into biofilm structure have led to the development of two- and three
dimensional biofilm models [27-34]. Two- and three-dimensional biofilm models are
undoubtedly important tools in biofilm research, since they help to understand formation of
biofilm structures. However, the picture of biofilm structure painted by 2D and 3D models
remains schematic only - the same accounts for the 1D models. On the other hand the
development of multi-dimensional biofilm models has not led to more applications of biofilm
models in engineering practice.
Problems and Current Trends in Activated Sludge and Biofilm
Modelling
Biofilm models have evolved over the past decades with increasing complexity going
from one-dimensional to two-dimensional to three-dimensional models. Unlike in activated
sludge modelling, structure has been strongly emphasized in the biofilm modelling
community. A major reason and driving force for this development was on one hand side the
importance of diffusion and the related application of Fick's law, which crucially links
diffusion to biofilm structure. On the other hand microscopic advances using the confocal
laser scanning microscope (CLSM) have revealed that biofilms have a complex three-
dimensional structure. This revelation indicates that one-dimensional (stratified) biofilm
models paint an inadequate picture of biofilm structure, which has been an additional driving
force towards two- and three-dimensional biofilm models.
However, a gap has developed in the biofilm modelling community between engineering
applications and biofilm research, i.e. biofilm models have been primarily used for research
whilst they have found little application in engineering practice. The reasons for this have
been discussed by
Noguera et al.
[35] and are as follows:
• Biofilm models are perceived as complicated mathematical entities.
• Simplifications and assumptions used in 1D models are often not supported by
experimental observations.
• There are many phenomena not considered in the models, such as the fate of
particulate substrate, the activity of higher organisms, and the role of exopolymeric
substance (EPS) production.
• There is a general lack of trust in the capability of the models to make accurate and
reliable predictions.
• The usefulness of biofilm models for the design of full scale systems is not fully
appreciated. Many engineers prefer to use simple empirical correlations for design,
while models are mostly used as troubleshooting tools when operational problems
arise.
• Biofilm models have not been adequately distributed or commercialized.
•
Parameters used in biofilm models are sometimes difficult to estimate.
