An integrated process model for activated sludge processes consists of four mechanisms, namely hydraulics, mass transfer, reactions, and separations. The structural forms of the models are classified as follows:
• 'Mechanistic models', which are based upon the actual physics, chemistry and microbiology that govern the system.
• 'Empirical models', which are based upon convenient mathematical functions that reasonably represent available data from the system, also called black box or input-output models.
• 'Gray box models', which include some of the mechanisms of the system, and also empirical func tions where the mechanisms are too complex or unknown.
Most process models are gray box models. Commonly used dynamic models for activated sludge processes are classified in Table 9. In spite of the complexity and long computing time, the distributed parameter approach to the dynamics and control of activated sludge processes is to be preferred due to its generality, flexibility, and accuracy.
research has indicated that under certain conditions, 1D settler models with proper modifications can be applied to 2D settlers.
Successful operations of activated sludge processes depend on a rapid and complete separation of the biomass from the liquid supernatant. Problems encountered in sludge water separation include de flocculation, bulking, pin point floc, blanket rising, and foaming. The identified problems with possible mechanisms and consequences are listed in Table 8.
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