Abstract
Secondary clarifiers are demanded to separate solids created in activated sludge biological processes to achieve both a clarified effluent and to manage the biological processes itself. Indeed, the biological process may influence the sludge characteristics, and conversely, the settling efficiency of the sedimentation basin plays an important role on the biological process in the activated sludge system. The proposed model represents a tool for better addressing the design and management of activated sludge system in wastewater treatment plants. The aim is to develop a numerical model which takes into account both the conditions in the biological reactor and the sludge characteristics coupled to the hydrodynamic behavior of a clarifier tank. The obtained results show that the different conditions in the reactor exert a great influence on the sedimentation efficiency.
Highlights
Sedimentation basins are used in wastewater treatment plants to separate suspended solids from water
Secondary clarifiers are used to remove settleable solids created in biological processes such as the activate sludge process being an active part of the process itself
Development and application of numerical models to calculate the velocity pattern in sedimentation tanks assumes a remarkable importance because it is proven that the actual characteristics of flow differ strongly from the supposed uniform distribution, and they have a relevant influence on the settling efficiency
Summary
Sedimentation basins are used in wastewater treatment plants to separate suspended solids from water. Secondary clarifiers are used to remove settleable solids created in biological processes such as the activate sludge process being an active part of the process itself. Settling basins are mainly designed using simple rules based on detention time, overflow rate, and solid loadings, which ensure that flow velocities in the basins are sufficiently low to allow solid particles to settle and to be removed, and yet sufficiently high so that the basin volumes are not excessively large. Compliance with the effluent requirements depends greatly on the efficiency of the secondary clarifiers. The tank performance is strongly influenced by hydrodynamic processes together with physical effects, such as density-driven flow, gravity sedimentation, flocculation, and thickening. Development and application of numerical models to calculate the velocity pattern in sedimentation tanks assumes a remarkable importance because it is proven that the actual characteristics of flow differ strongly from the supposed uniform distribution, and they have a relevant influence on the settling efficiency
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