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.
