Data obtained through the application of the Clarifier Research Technical Committee (CRTC) protocol were used to perform simulations using a mechanistic dynamic model of the secondary clarifier. The model is verified against field data, and the simulation results are used to analyze clarifier behavior. The information from the CRTC protocol provides a foundation for model‐based analysis. Limitations of clarifier analysis based solely on empirical observation are discussed.
Previous work by the authors suggested that activated sludge sedimentation might be highly sensitive to underflow geometry. Field, physical model, and stratified flow numerical model tests were conducted to evaluate this hypothesis. Field work included solids settling velocity, dye dispersion, and flow pattern/solids distribution tests. Physical tests included operation of a pie‐shaped 1:12.5 scale model of a circular, center‐feed tank with sludge withdrawal simulating countercurrent, uniform, and cocurrent geometries. A stratified flow numerical model that simulated the effects of density currents was calibrated to the results of the full‐scale testing. The results failed to confirm the experimental hypothesis. Model performance was relatively insensitive to underflow geometry in a circular tank when density effects were simulated.
An integrated dynamic model and control system are presented for the activated sludge process. The integrated model is comprised of separate models for the influent pump station, air supply and distribution system, biological reactor, and solids-liquid separator. The models for the pump station and for the air supply and distribution system were based on those for a full-scale plant, the Sagemont plant, Houston, Texas, and use standard engineering equations. The models for the biological reactor and solids-liquid separator are more research oriented and were obtained primarily from the literature. Predictions using these models are therefore expected to be more qualitative than quantitative. The integrated model will be used in part II of the paper to explore process control strategies by computer simulation.
Clarifier hydrodynamics plays an important role in the activated sludge process. Attention has long been focused on the biological behavior of the aeration basin in the secondary treatment system. One-dimensional settler models or empirical relationships have typically been coupled in wastewater treatment plant simulation systems to represent the clarifier. The research on the hydrodynamic aspects of the process are currently restricted to a clarifier uncoupled from the aeration basin. In this paper, a dynamic model of the activated sludge process is presented in which balanced emphasis is put on the hydrodynamic aspect of the system. The model integrates a biological reaction submodel for an aeration basin with a two-dimensional hydrodynamic solids transport submodel for the secondary clarifier. A verification of the model is carried out against a set of field data and shows good agreement. The model has been used to investigate the response and the interdependency of the aerator and clarifier in the activated sludge system. Water Environ. Res., 68, 329 (1996).
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