Determination of diffuser bubble size in computational fluid dynamics models to predict oxygen transfer in spiral roll aeration tanks

Terashima, Mitsuharu; So, Magnus; Goel, Rajeev; Yasui, Hidenari

doi:10.1016/j.jwpe.2016.07.001

Cited by 23 publications

(8 citation statements)

References 29 publications

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“…Moreover, accurate prediction of the overall mass transfer coefficient, k L a, relies on correct estimation of the initial bubble size at the diffuser level, requiring either in situ bubble diameter measurements (Fayolle et al, 2010) or implementation of an add-on model to estimate inlet bubble size. Similarly, the need for bubble diameter calibration has been emphasized in more recent CFD work by Terashima, So, Goel, and Yasui (2016), involving use of the same modeling approach to determine k L a values in a number of full-scale activated sludge systems and clean water tanks that differed in their dimensions, diffuser types (coarse and fine-pore, ceramic, plastic and membrane diffusers), their configuration (single and dual spiral roll) and operating airflow rates. Others (Cockx et al, 2001;Talvy, Cockx, & Line, 2007) have explored the use of a Eulerian model to determine axial dispersion and oxygen mass transfer in a pilot-scale airlift reactor.…”

Section: Previous Modeling Approachesmentioning

confidence: 99%

Towards a robust CFD model for aeration tanks for sewage treatment – a lab-scale study

Karpinska

Bridgeman

2017

Engineering Applications of Computational Fluid Mechanics

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Detailed insight into the hydrodynamics of aeration tanks is of crucial importance for improvements in treatment efficiency, optimization of the process design and energy-efficient operation. These factors have triggered increasing interest in the use of Computational Fluid Dynamics (CFD) to evaluate performance of wastewater treatment systems. Whilst factors such as incorrect input assumptions, poor model choice and excessive simplifications have been recognized as potential sources of output errors, there remains a need to identify the most robust strategy to faithfully simulate aeration tank performance. Therefore, the focus of this work was to undertake rigorous transient simulations of the hydrodynamics and oxygen mass transfer in a lab-scale aeration tank in order to work towards the development of robust modeling guidelines for activated sludge systems. Unlike most previous CFD analyses of aeration systems, the work reported here employed the shear stress transport (SST) k − ω turbulence model to account for the turbulent interactions between the phases inducing bubble breakup and/or coalescence, and as a consequence, promoting the formation of bubbles of different sizes and shapes. The results obtained were compared with those arising from an analysis using the standard k − ε (sk − ε) model -and assuming fixed bubble diameter-the most common CFD modeling framework used within the wastewater modeling community. Model validation was achieved using acoustic Doppler velocimetry and particle image velocimetry techniques, and experimentally derived oxygen mass transfer data. Limitations of both turbulence models used and modeling assumptions concerning bubbly flow are discussed. The benefits of the SST k − ω turbulence model are demonstrated, but the need to balance the increased computational expense of this approach compared to the sk − ε model and, indeed, bubble flow modeling are recognized. Thus, this paper presents the first rigorous analysis of turbulence model and bubble flow generation models together for activated sludge system optimization.

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Section: Previous Modeling Approachesmentioning

confidence: 99%

Towards a robust CFD model for aeration tanks for sewage treatment – a lab-scale study

Karpinska

Bridgeman

2017

Engineering Applications of Computational Fluid Mechanics

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“…Bubble size also depends on the orifice or pore size of the diffusion aerator (Wang et al, 2009), although this is not modelled in this study. A uniform mean bubble size of 4 mm in this study is taken as an average value from the literature (Lei and Ni, 2014;Le Moullec et al, 2010;Terashima et al, 2016;Xu et al, 2010).…”

Section: Two Phase Flowmentioning

confidence: 99%

Computational fluid dynamics simulation of two-phase flow and dissolved oxygen in a wastewater treatment oxidation ditch

Matko

Chew

Wenk

et al. 2021

Process Safety and Environmental Protection

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This paper presents a computational fluid dynamics (CFD) model of an aerated wastewater treatment oxidation ditch, taking into account gas-liquid flow, mass transfer and dissolved oxygen. This innovative study contributes to knowledge as it considers the effect of bubble size distribution (BSD) and biochemical oxygen demand (BOD) distribution on the dissolved oxygen (DO) distribution. Species transport modelling predicts the DO and BOD distribution. De-oxygenation of local dissolved oxygen by BOD is modelled by an oxygen sink that depends on the local BOD concentration. Bubble coalescence and breakup models predict the BSD. The behaviour of the ditch is non-ideal, which is indicated by the residence time distribution (RTD) and the heterogeneous flow pattern and DO distribution. The parameters with the greatest influence on the dissolved oxygen are the BOD and bubble size. There is good agreement with the observed flow patterns and the measurements of mean DO. This study identifies that the BOD distribution and the BSD are important parameters for predicting the dissolved oxygen distribution and are also current gaps in the published research.

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“…However, fine bubbling is favored because it achieves high interfacial area, which facilitates more efficient mass transfer between phases and minimizes stripping of the liquid phase as vapor (Hasanen et al, 2006). Fine‐bubble diffusers such as perforated flexible membrane, porous rigid ceramic, jets, mechanical turbines, and perforated cap diffusers are the most commonly used in industrial applications (Terashima et al, 2016). Due to their energy efficiency, fine‐bubble diffusers made of perforated membranes and porous ceramics are the most common technology of choice in biological wastewater treatment (Rosso, 2019; Tchobanoglous et al, 2014).…”

Section: Introductionmentioning

confidence: 99%

Effects of flow velocity and bubble size distribution on oxygen mass transfer in bubble column reactors—A critical evaluation of the computational fluid dynamics‐population balance model

Khalil

Rosso

DeGroot

2021

Water Environment Research

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Computational fluid dynamics (CFD) is used to simulate a bubble column reactor operating in the bubbly (homogenous) regime. The Euler–Euler two‐fluid model, integrated with the population balance model (PBM), is adopted to compute the flow and bubble size distribution (BSD). The CFD‐PBM model is validated against published experimental data for BSD, global gas holdup, and oxygen mass transfer coefficient. The sensitivity of the model with respect to the specification of boundary conditions and the bubble coalescence/breakup models is assessed. The coalescence model of Prince and Blanch (1990) provides the best results, whereas the output is shown to be insensitive to the breakup model. The CFD‐PBM study demonstrates the importance of considering the BSD in order to correctly model mass transfer. Results show that the constant bubble size assumption results in a large error in the oxygen mass transfer coefficient, while giving acceptable results for gas holdup. Practitioner points Constant bubble size (CBS) and population balance model (PBM) are compared for a bubble column reactor. Both PBM and CBS can predict gas holdup; however, PBM can correctly predict gas–liquid mass transfer whereas CBS cannot. Best practices for selecting coalescence, breakup, and drag models are determined.

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Determination of diffuser bubble size in computational fluid dynamics models to predict oxygen transfer in spiral roll aeration tanks

Cited by 23 publications

References 29 publications

Towards a robust CFD model for aeration tanks for sewage treatment – a lab-scale study

Towards a robust CFD model for aeration tanks for sewage treatment – a lab-scale study

Computational fluid dynamics simulation of two-phase flow and dissolved oxygen in a wastewater treatment oxidation ditch

Effects of flow velocity and bubble size distribution on oxygen mass transfer in bubble column reactors—A critical evaluation of the computational fluid dynamics‐population balance model

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