DYNAMIC MODELING OF THE ACTIVATED-SLUDGE PROCESS - A CASE-STUDY

Description of the unsteady-state behaviour of the activated sludge pr ocess of wastewater treatment has attracted much attention, yet there have been few exhaustive assessments of the resulting models against f ield data from full-scale plants. This paper presents results for the evaluation of a model for carbonaceous and nitrogenous substrate remov al with reference to a comprehensive set of data obtained from a 10-da y monitoring exercise at the Norwich Sewage Works in eastern England. The model of the aerator is a simplified version of the IAWPRC model o f the activated sludge process. The model of the secondary clarifier e mploys a conventional empirical expression for clarification and a con ventional flux theory for thickening. Solute transport through both th e aerator and clarifier is characterized by appropriate arrangements o f fixed and variable-volume CSTR elements. Substrate removal and the p roduction, thickening and recycle of biomass (suspended solids) are we ll replicated by the model. However, fundamental weaknesses are appare nt in the currently available representations of the clarification fun ction. Impacts of recycled flows from a sludge consolidation tank are also examined; sensitivity tests with the model suggest that these flo ws are a significant factor in the longer-term maintenance of aerator biomass concentration.