Performance Assessment and Optimization of Secondary Settling Tanks Using Cfd Modeling

Featuring Krish Ramalingam                                                     
New York City Department of Environmental Protection    

Savvas Xanthos, Ph.D.
Department of Civil and Environmental
The City College of The City University of New York

Location:  McDonnell-Douglas Auditorium
Free and open to the public

Abstract:
The New York City Department of Environmental Pollution is implementing step feed biological nitrogen removal (BNR) process to meet the recent nitrogen discharge permit regulations at its Water Pollution Control Plants (WPCPs) discharging in to Long Island Sound. Such a process would require an increase in the mixed liquor concentration (MLSS) which would stress the Gould II type rectangular final settling tanks (FSTs).
To assess performance and evaluate alternatives to improve the efficiency of the FSTs, NYCDEP and the City College of New York developed a 3-D computer model depicting the actual structural configuration of the tanks and the current and proposed hydraulic and solids loading rates. Fluent 6.3.26TM was the base platform for the computational fluid dynamics (CFD) model, for which sub-models of the SS settling characteristics as well as turbulence, flocculation and rheology were incorporated. This was supplemented by field and bench scale experiments to quantify the coefficients integral to the sub-models. The 3-D model developed can be used to consider different baffle arrangements, sludge withdrawal mechanisms and loading alternatives to the FSTs. The goal of this study was to use this tool to assess the internal behavior based on different baffle configurations at the inlet and especially for the chosen 4H7V configuration. The hydrodynamic simulation for this configuration predicts plug flow behavior immediately following the influent baffles while the solids coupled model predicts a different scenario due to the density current effect. Following this outcome an additional in-tank baffle at a distance of 30ft was added and its effect on the final clarifier performance was investigated.

About the Speakers:
Krish Ramalingam has been working with waste water treatment plants in New York City for the last several years as a research consultant and has extensive experience in the area of municipal wastewater treatment.  He has also consulted with the major environmental engineering firms in the metropolitan area, and was involved in plant operators’ training courses. He has been the project manager for the Applied Research Program for New York City Department of Environmental Protection (NYCDEP) for the past 10 years and is well-versed with process control and operational issues at the WPCPs. He has also been working on asset management and sustainable infrastructure problems for NYCDEP. Current projects and challenges that are in progress include research on novel nitrogen removal technologies such as the Sharon and Anammox processes and the optimization of the final settling tanks at the WPCPs. This is a multi disciplinary effort between researchers in the Mechanical and Civil Engineering departments at the City College of New York and NYCDEP.

Savvas Xanthos is currently a research assistant professor in the Department of Civil Engineering in the Grove School of Engineering at The City College of The City University of New York. He obtained his Ph.D. degree in 2004 in the field of experimental fluid mechanics, which was followed by a two-year appointment as an assistant professor in the Department of Mechanical Engineering at CCNY. His research interests include traditional fluid mechanics and especially shock wave, expansion wave and blast wave interactions with turbulence along with hot wire anemometry techniques using 3-D velocity and fully 3-D vorticity probes. He has also been involved in modeling of atherosclerotic plaque and trying to identify the main reasons of its rupture. He is now part of the research team at CCNY involved in the optimization of final settling tanks using CFD modeling of waste water and especially in the prediction of suspended solids in final settling tanks.