Abstract
The heterogeneity and the complexity of activated sludge processes pose a continuous challenge to developing models that can incorporate all the necessary
levels of information concerning the process, and be accurate enough for the
adequate control and safe operation of the bioreactor. The complete quantification of the microbial system requires the understanding of the complex biological and physico-chemical interactions in the process, and the measurement
of a large number of reaction rates, which is often beyond the scope of reasonable measurement techniques. This task is particularly complicated when
dynamic modeling is sought. Simple and unstructured steady-state models
are generally sufficient for the purpose of plant design. However, these models
are generally inadequate for dynamic analysis. Because of the generally low
levels of substrate in the chemostat, a transient experiment, such as change
in flow rate, can result in drastic changes in the cell environment, and the
unstructured model may break down [110, 264]. Moreover, as was shown in
Chapter 4, the basic unstructured model fails to predict periodic behavior for
any growth rates.