Numerical simulation of a sedimentation basin.  1.  Model development

In this short communication, the erosion process of the fine, cohesive sediment collected from the upper River Taw in South West England was studied in a rotating annular flume located in the National Water Research Institute in Burlington, Ontario, Canada. This study is part of a research project that is underway to model the transport of fine sediment and the associated nutrients in that river system. The erosion experimental data show that the critical shear stress for erosion of the upper River Taw sediment is about 0.09 Pa and it did not depend on the age of sediment deposit. The eroded sediment was transported in a flocculated form and the agent of flocculation for the upper River Taw sediment may be due to the presence of fibrils from microorganisms and organic material in the system. The experimental data were analysed using a curve fitting approach of Krone and a mathematical model of cohesive sediment transport in rotating circular flumes developed by Krishnappan. The modelled and measured data were in good agreement. An evaluation of the physical significance of Krone’s fitting coefficients is presented. Variability of the fitting coefficients as a function of bed shear stress and age of sediment deposit indicate the key role these two factors play in the erosion process of fluvial cohesive sediment.

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“…The collision frequency functions for the individual collision mechanisms can be found in Valioulis and List [27].…”

Section: Flocculation Stagementioning

confidence: 99%

Experimental Investigation of Erosion Characteristics of Fine-Grained Cohesive Sediments

Krishnappan¹,

Stone

Granger

et al. 2020

Water

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“…Numerous attempts have been made to develop mathematical models [99][100][101][102][103][104][105][106][107] to describe particle settling. Settling velocities of impermeable spheres are generally derived by balancing gravity F g , buoyant F b , and drag F d forces.…”

Section: Impermeable Aggregatesmentioning

confidence: 99%

Fractal Structures and Mechanisms in Coagulation/Flocculation Processes in Environmental Systems: Theoretical Aspects

Stoll

Silvia

2008

Biophysical Chemistry of Fractal Structures and Processes in Environmental Systems

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“…Adequate modeling of particle transport and aggregation is a necessary component of any realistic attempt to predict the fate of contaminants and nutrients. Engineering processes, such as sedimentation, flocculation, and filtering, rely on particle-particle interactions [Valioulis and List, 1984;Wilson and Barfield, 1985] and would also benefit from improvements in the predictive capabilities of models dealing with particle transport and aggregation.…”

Section: Introductionmentioning

confidence: 99%

“…Natural systems, such as lake hypolimnions, and engineered systems, such as settling tanks and sedimentation ponds, can then be treated as quiescent, where settling controls particle transport. First-order finite difference schemes for solving particle settling [Lawlet et al, 1980;Valioulis and List, 1984; Wilson and Barfield, 1985; Gardner, 1995] are prevalent in practice. The limitations of such schemes for solving fluid advection have been the focus of great attention [Warming et al, 1973;Tannehill, 1988;Islam and Chaudhry, 1997] but not in the context of solving particle settling and aggregation.…”

Section: Introductionmentioning

confidence: 99%

Modeling particle transport and aggregation in a quiescent aqueous environment using the residence‐time scheme

Perigault¹,

Leckie²,

Kitanidis³

2000

Water Resources Research

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Abstract. Suspended particles are a ubiquitous component of aqueous environments and are found over broad ranges of size and density. Particle transport and fate have an important role in the regulation of contaminants and nutrients in natural settings. The mechanisms that control the transport and size of particulate material in solution also play a fundamental role in the successful operation of engineered systems, such as sedimentation ponds and flocculation tanks, as well as flotation and filtering reactors. Adequate modeling of particle transport and aggregation is required for better understanding and prediction of the effects of particulate material in natural aqueous systems, as well as for designing efficient physicochemical processes to deal with suspended solids. In this paper we illustrate how numerical diffusion produced by the use of first-order finite difference schemes can introduce significant errors in the modeling of particle settling in quiescent systems and how this error is compounded when aggregation is considered. To model settling without introducing numerical diffusion, while preserving numerical efficiency, we propose the residence-time scheme, a simple numerical scheme based on the residence time of each size fraction in the elements of the spatial discretization. For the solution of the settling-aggregation equation the alternatingoperator-splitting technique (AOST) is used. The inherent modularity and simplicity of AOST allows smooth incorporation of additional particle transport mechanisms such as mixing, advection, etc. The lack of adequate mathematical schemes to solve the expressions used to describe the particle transport and aggregation phenomena remains an important problem that limits our ability to predict the behavior of particulate material in suspension. Usually the set of equations used to describe particle transport and aggregation do not have general analytical solutions and must be solved numerically. However, the domain discretization required for these numerical schemes can In this study, we start by analyzing some artifacts introduced by the use of first-order finite difference numerical schemes in the modeling of particle settling and show the effect of these artifacts when particle aggregation is considered. A new numerical scheme is presented, the residence-time scheme (RTS), to adequately model particle settling. Then, we apply the alternating-operator-splitting technique (AOST), a methodology widely used for solving transport-reaction aqueous systems [Valocchi and Maimstead, 1992; Kaluarachchi and Motshed, 1995a, b], for solving the equations governing particle transport and aggregation. We discuss why AOST is a computationally efficient and flexible methodology compared with more traditional numerical frameworks used to model the fate of microscopic particles in aqueous systems. 2249

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Numerical simulation of a sedimentation basin. 1. Model development

Cited by 37 publications

References 24 publications

Experimental Investigation of Erosion Characteristics of Fine-Grained Cohesive Sediments

Experimental Investigation of Erosion Characteristics of Fine-Grained Cohesive Sediments

Fractal Structures and Mechanisms in Coagulation/Flocculation Processes in Environmental Systems: Theoretical Aspects

Modeling particle transport and aggregation in a quiescent aqueous environment using the residence‐time scheme

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