Oxygen transfer prediction in aeration tanks using CFD

Fayolle, Yannick; Cockx, Arnaud; Gillot, S.; Roustan, M.; Héduit, A.

doi:10.1016/j.ces.2007.08.082

Cited by 135 publications

(75 citation statements)

References 10 publications

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“…However, as the suspended phase is neglected in this approach, the use of neutral-density models may lead to over-prediction of the degree of mixing when translating the CFD results directly to fullscale agitated AS systems operating at high mixed liquor suspended solids (MLSS) concentrations, and where the occurrence of regions characterized by low liquid velocities has been identified. Therefore, work has been undertaken on the development of numerical tools based on a Eulerian twofluid model, which is able to assess the impact of the gas-liquid hydrodynamics on the global and local mass transfer coefficients in pilot-and full-scale oxidation ditches (one of several well-known modifications to the AS process) aerated with diffusers and agitated with slowspeed mixers (Cockx, Do-Quang, Audic, Liné, & Roustan, 2001;Do-Quang, Cockx, Liné, & Roustan, 1998;Fayolle, Cockx, Gillot, Roustan, & Héduit, 2007). The results from the simulations based on the fixed bubble size show that the gas holdup and oxygen transfer in closed-loop AS tanks depend on the axial velocity of the fluid imparted by the mixers.…”

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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“…In this process, aeration can represent up to 70% of the total energy expenditure [33]. Pure oxygen passes through the membrane wall.…”

Section: Treatments To Hypoxiamentioning

confidence: 99%

“…The activated sludge process is the main method for treating nitrogen and organic components in urban wastewater treatment because of its efficiency in reducing organic pollutants by over 90% and converting them to biogas [33,34]. In this process, aeration can represent up to 70% of the total energy expenditure [33].…”

Section: Treatments To Hypoxiamentioning

confidence: 99%

Solar Water Purification System Design: Application Study in Lake Taihu, China

You¹,

Zheng²,

Ho³

2017

JRST

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Through investigation and comparison of the methods of water purification, salvage and aeration were confirmed to be the most effective methods in treating the pollution in Lake Taihu. A solar water purification system was designed to achieve the effects of salvage and aeration. To collect algae as "salvage," this purification system employed a combination of a water pump and filter screen. To increase the dissolved oxygen, the water pump lifted water and sprayed it into the air, and an air pump was equipped to inject oxygen bubbles into the water. After a one-year test at Lake Taihu, the effectiveness of this purification system was confirmed. It could effectively lower the levels of permanganate, NH NH 3 4 + / , and chlorophyll a and increase the level of dissolved oxygen in the lake water.

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“…Activated sludge plants can account for up to 70% of total energy consumption of a WWTP, due mainly to the aeration process through the air diffusers [1]. So it is necessary a knowledge of the fluid dynamic phenomena which occur in the plant.…”

Section: Introductionmentioning

confidence: 99%

Effects of the aeration on the fluid dynamic behaviour of a multi-zone activated sludge system

Sánchez

Kaiser

Viedma

et al. 2016

WIT Transactions on Ecology and the Environment

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Conventional wastewater treatment plants (WWTP) are necessary to modify the wastewater properties in order to make it acceptable for a safe discharge into the environment or a certain reuse purpose. Biological oxidation is the most important of the processes involved in conventional WWTP. Organic substances dissolved in the water are removed by means of bacteria presented in the biological reactor. Air is necessary to enable the reduction of the organic content of the water by the bacteria. Bubbles of air are introduced into the reactor through air diffusers. Air diffusers can account up to 70% of WWTP total energy consumption.So a deep understanding of the dynamic behaviour of the flow is necessary for optimizing the process and saving energy.A numerical analysis of the effects of the aeration in the fluid dynamics behaviour of a real multi-zone activated sludge reactor is carried out. The purpose is to identify and analyse the changes originated in the velocity field by the aeration.A numerical modelling of the activated sludge system located in San Pedro del Pinatar (Murcia, Spain) is developed throughout a general-purpose computational fluid dynamics (CFD) code. The multiphase flow is simulated with a EulerLagrange approach; modelling the bubbles as discrete phase. Two simulations, one with aeration and the other without it, are carried out. The numerical results show that the aeration has a notable effect in the performance of the reactor. Changes in velocity field, stagnant zones, residence time distribution or even free surface level originated by the aeration in the reactor are studied. In general, the aeration reduced the amount of stagnant volume in the reactor. However, when the aeration is activated, some re-circulating zones are formed, reducing the residence time in the reactor.

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Oxygen transfer prediction in aeration tanks using CFD

Cited by 135 publications

References 10 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

Solar Water Purification System Design: Application Study in Lake Taihu, China

Effects of the aeration on the fluid dynamic behaviour of a multi-zone activated sludge system

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