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Title: PERFORMANCE ASSESSMENT OF SECONDARY SETTLING TANKS USING CFD MODELING

Author: S. Xanthos, M. Gong, K. Ramalingam, J. Fillos, A. Deur , K. Beckmann and J.A. McCorquodale

Year: 2009

Publisher: European Water Resources Association (EWRA)

Description:

Amongst the principal separation processes used to treat effluents in the water industry is the sedimentation of solid particulates from the carrier fluid known as mixed liquor by the force of gravity. New York City DEP is in the process of upgrading its Upper East River water pollution control plants (WPCP’s) to incorporate biological nitrogen removal (BNR). The rectangular final settling tanks (FSTs) are a central link in the treatment process and often times a limiting factor in terms of the solids handling capacity especially when high throughput requirements need to be met. The objective of this study was to develop a 3D Computational Fluid Dynamics (CFD) model based on the exact geometry of the existing Gould II type FSTs in Battery “E” at the Wards Island WPCP and calibrate and validate it with in-situ data collected at the site. The performance of the model was also evaluated by comparison with the results from one of the rectangular sedimentation tanks reported by Larsen in 1977 in Sweden, where detailed liquid flow and SS concentrations were measured experimentally and showed very good agreement. The goal of this study is to illustrate how the different modeling approaches applied on the physical phenomena that take place in the tank affect the outcome of a CFD model and its predictions. It is  common for internal baffles to be added at the inlet and within the tank to handle high flow requirements such as in wet weather storms. This model has been used as a tool to assess the internal behavior of such baffles and assess the clarifier’s performance based on different inlet baffle configurations.