Methodology To Determine Residence Time
Distribution And Small Scale Phenomena In
Settling Tanks
Author(s)
T. Karches & K. Buzas
Abstract
Hydraulic residence time is a crucial parameter of any wastewater treatment tank
planning, operation and optimisation. Calculation of the residence time
distribution at every point within the tank gives information about the deadzones
and short circuits and well-operating zones. Using the advective-diffusive
transport equation supplemented with a scalar source term local mean age
(LMA) can be detected if the flow field is given. Combining LMA with a tracer
study the exact residence time can be determined. This method supports problem
detection in a small wastewater treatment plant (2 dead zones and one shortcircuiting
path were detected) and also gave us better understanding of the
operation of settling tanks.
Keywords: CFD, LMA, residence time, settling tank design.
1 Introduction
Computational fluid dynamics (CFD) in wastewater treatment processes has a
significant role in recent years. Several studies demonstrate that CFD is an
effective tool in design (Greenfield [8]), optimization (Bratchley et al. [3]) and
operation (Brouckaert and Buckley [4]) Furthermore CFD studies revealed that
with an extensive knowledge of fluid flow not only the hydraulic performance of
e.g. an oxidation ditch could be improved (Yang et al. [17]) but we could have a
closer look into the biological processes, too (Bartrand et al. [2]) For a few
decades researchers used to focus only on the biology and chemistry in
wastewater treatment, and hydraulics was mostly neglected.
Keywords
CFD, LMA, residence time, settling tank design
Related Book
Other papers in this volume
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