A number of studies have been performed in the simulation of activated sludge systems withmany utilizing ideal reactor concepts to reduce the overall complexity of the modelframework. Observance of non-ideal behaviour in actual reactors, however, led others torecognize the importance of hydrodynamics in modelling wastewater treatment processes.More recently, new experimental studies have demonstrated the influence of floc size on thereaction environment inside a floc. However, no reported attempts have been found in theliterature in developing a mathematical model of activated sludge system that incorporateseffects of spatial variation in floc size on the biological processes. This study presents anapproach in modeling activated sludge systems that combines Computational FluidDynamics (CFD), floc dynamics, and biological reaction kinetics in simulating the carbonand nitrogen removal process at both the reactor scale and internal floc scale. The use ofCFD allowed the simulation of the flow field in a baffled flow-through reactor. Theintroduction of floc aggregation and breakup dynamics provided spatial estimates of thesteady-state sizes of flocs inside the reactor allowing for a more comprehensive descriptionof the transport and reactive processes occurring both within the reactor and inside the floc.The results showed that significant differences in reactor performance can be predicted whenspatial variation in floc size is incorporated in the model framework.
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