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Roden JC, Goddard BD, Pearson JW. Dynamic density functional theory for sedimentation processes on complex domains: Modelling, spectral elements, and control problems. J Chem Phys 2023; 159:154102. [PMID: 37846952 DOI: 10.1063/5.0166458] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/05/2023] [Accepted: 09/22/2023] [Indexed: 10/18/2023] Open
Abstract
Modelling of many real-world processes, such as drug delivery, wastewater treatment, and pharmaceutical production, requires accurate descriptions of the dynamics of hard particles confined in complicated domains. In particular, when modelling sedimentation processes or systems with driven flows, it is important to accurately capture volume exclusion effects. This work applies Dynamic Density Functional Theory to the evolution of a particle density under diffusion, external forces, particle-particle interaction, and volume exclusion. Using a spectral element framework, for the first time it is possible to include all of these effects in dynamic simulations on complex domains. Moreover, this allows one to apply complicated no-flux, and other non-local, non-linear, boundary conditions. The methodology is also extended to control problems, addressing questions of how to enhance production set-up in industrially-motivated processes. In this work the relevant models are introduced, numerical methods are discussed, and several example problems are solved to demonstrate the methods' versatility. It is shown that incorporating volume exclusion is crucial for simulation accuracy and we illustrate that the choice of boundary conditions significantly impacts the dynamics.
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Affiliation(s)
- Jonna C Roden
- School of Mathematics and Maxwell Institute for Mathematical Sciences, The University of Edinburgh, Edinburgh EH9 3FD, United Kingdom
| | - Benjamin D Goddard
- School of Mathematics and Maxwell Institute for Mathematical Sciences, The University of Edinburgh, Edinburgh EH9 3FD, United Kingdom
| | - John W Pearson
- School of Mathematics and Maxwell Institute for Mathematical Sciences, The University of Edinburgh, Edinburgh EH9 3FD, United Kingdom
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Opitz J, Bauer M, Alte M, Schmidtmann J, Peiffer S. Sedimentation Kinetics of Hydrous Ferric Oxides in Ferruginous, Circumneutral Mine Water. ENVIRONMENTAL SCIENCE & TECHNOLOGY 2022; 56:6360-6368. [PMID: 35507770 DOI: 10.1021/acs.est.1c07640] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/14/2023]
Abstract
Transport, transformation, and removal of iron in aqueous environments is primarily controlled by ferrous iron oxidation followed by aggregation and sedimentation of the resultant hydrous ferric oxides. The latter mechanisms are particularly important for passive iron removal in mine water treatment systems, yet the interrelation and underlying kinetics are poorly understood. In this study, the sedimentation behavior of natural hydrous ferric oxides was systematically investigated under different hydrogeochemical conditions via laboratory-based column experiments. The objective was to determine a robust model approach for the approximation of aggregation/sedimentation kinetics in engineered systems. The results showed that sedimentation is governed by two interrelated regimes, a rapid second-order aggregation-driven step (r1) at high iron levels followed by a slower first-order settling step (r2) at lower iron levels. A mixed first-/second-order model was found to adequately describe the process: -d[Fe]dt=kr2[Fe]+kr1[Fe]2 with kr1 = 9.4 × 10-3 m3/g/h and kr2 = 5.4 × 10-3 h-1. Moreover, we were able to demonstrate that the removal of particulate hydrous ferric oxides at low particulate iron levels (<10 mg/L) may be reasonably well approximated by a simplified first-order relationship: -d[Fe]dt=ksed[Fe] with ksed = 2.4 (±0.4) × 10-2 h-1, which agrees well with incipient literature estimates. Only minor effects of pH, salinity, and mineralogy on kinetic parameters were observed. Hence, the results of this study may be broadly transferrable among different mine sites.
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Affiliation(s)
- Joscha Opitz
- Department of Hydrology, University of Bayreuth, BayCEER, Universitätsstraße 30, Bayreuth D-95447, Germany
- BASE Technologies GmbH, Josef-Felder-Straße 53, Munich D-81241, Germany
| | - Martin Bauer
- BASE Technologies GmbH, Josef-Felder-Straße 53, Munich D-81241, Germany
| | - Matthias Alte
- BASE Technologies GmbH, Josef-Felder-Straße 53, Munich D-81241, Germany
| | - Johanna Schmidtmann
- Department of Hydrology, University of Bayreuth, BayCEER, Universitätsstraße 30, Bayreuth D-95447, Germany
| | - Stefan Peiffer
- Department of Hydrology, University of Bayreuth, BayCEER, Universitätsstraße 30, Bayreuth D-95447, Germany
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Gao H, Stenstrom MK. Development and applications in computational fluid dynamics modeling for secondary settling tanks over the last three decades: A review. WATER ENVIRONMENT RESEARCH : A RESEARCH PUBLICATION OF THE WATER ENVIRONMENT FEDERATION 2020; 92:796-820. [PMID: 31782964 DOI: 10.1002/wer.1279] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/19/2019] [Revised: 11/15/2019] [Accepted: 11/23/2019] [Indexed: 06/10/2023]
Abstract
Secondary settling tanks (SSTs) are a crucial process that determines the performance of the activated sludge process. However, their performance is often far from satisfactory. In the last 30 years, computational fluid dynamics (CFD) has become a robust and cost-efficient tool for designing new SSTs, modifying the geometries of existing SSTs and improved control techniques in wastewater treatment plants. The first part of this review paper discusses the different approaches to model the motion of particles in SSTs. The applications of different multiphase approaches and the widely applied single-phase approach in different SST studies are reviewed. The second part reviews current CFD research and engineering practice, focusing on the formation and the effect of density currents, effects of different design variables, parameter uncertainties in modeling structures, and atmospheric conditions. Finally, challenges and future improvements of sub-models (sludge settling, rheology, turbulence, and flocculation) in the SST model framework are identified. PRACTITIONER POINTS: The first journal review for the CFD applications in SSTs over the last decade. The controversy over the relationship between SOR and SST performance can be largely explained by the prediction of the CFD model. Density decoupling in the turbulence model is possible for well-baffled SSTs. The relative importance of three modeling parameters is summarized. Recommendations for future data collection are provided.
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Affiliation(s)
- Haiwen Gao
- Department of Civil and Environmental Engineering, University of California Los Angeles, Los Angeles, CA, USA
| | - Michael K Stenstrom
- Department of Civil and Environmental Engineering, University of California Los Angeles, Los Angeles, CA, USA
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Hunter TN, Peakall J, Egarr D, Cowell DM, Freear S, Tonge AS, Horton L, Rice HP, Smith I, Malone K, Burt D, Barnes M, Randall G, Biggs S, Fairweather M. Concentration profiling of a horizontal sedimentation tank utilising a bespoke acoustic backscatter array and CFD simulations. Chem Eng Sci 2020. [DOI: 10.1016/j.ces.2020.115560] [Citation(s) in RCA: 9] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
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Cui Y, Ravnik J, Steinmann P, Hriberšek M. Settling characteristics of nonspherical porous sludge flocs with nonhomogeneous mass distribution. WATER RESEARCH 2019; 158:159-170. [PMID: 31035193 DOI: 10.1016/j.watres.2019.04.017] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/05/2018] [Revised: 04/08/2019] [Accepted: 04/09/2019] [Indexed: 06/09/2023]
Abstract
The paper reports on the development of an advanced Lagrangian particle tracking model of sludge flocs that takes into account its nonspherical shape, the internal porosity and permeability, as well as the nonhomogenous mass distribution. The floc shapes, sizes and free settling velocities are determined based on the experimental measurement of settling sludge flocs originating from a wastewater treatment plant. Based on the floc shape characterization, a prolate axisymmetric ellipsoid is selected as the modelled sludge particle. In order to determine the main particle characteristics, e.g. the internal porosity, the density and the flow permeability, a Lagrangian particle tracking model is developed based on Brenner's drag model for a prolate axisymmetric ellipsoid and a buoyancy force model for a porous particle. The model is implemented for numerical simulations of the free settling process. The obtained floc characteristics are presented in the form of a two-part polynomial fitting curve, which can be used to model floc characteristics. The values of settling velocities of flocs computed by the model show very good agreement with experimental results. Futhermore, as the internal structure of a floc is seldom uniform, the nonhomogeneous mass distribution is considered, influencing the rotational and translational motions of the settling flocs. The nonhomogeneous mass distribution is introduced into the floc settling model. The parametric analyses of different barycentre offsets and shear rates are performed, and their influences on the free settling velocity are evaluated. The presented modelling approach can also be applied to flocculent settling of alum and other flocs in drinking water treatment plants. The developed Lagrangian model is suitable for use as a point source within the framework of Eulerian flow computations, and is solved as a two-phase flow model with a suitable Computational Fluid Dynamics code.
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Affiliation(s)
- Yan Cui
- Chair of Applied Mechanics, Friedrich-Alexander Universität Erlangen-Nürnberg, Paul-Gordan-Str. 3, D-91052, Erlangen, Germany.
| | - Jure Ravnik
- Faculty of Mechanical Engineering, University of Maribor, Smetanova 17, SI-2000, Maribor, Slovenia.
| | - Paul Steinmann
- Chair of Applied Mechanics, Friedrich-Alexander Universität Erlangen-Nürnberg, Paul-Gordan-Str. 3, D-91052, Erlangen, Germany.
| | - Matjaž Hriberšek
- Faculty of Mechanical Engineering, University of Maribor, Smetanova 17, SI-2000, Maribor, Slovenia.
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Hendi E, Shamseldin AY, Melville BW, Norris SE. Experimental investigation of the effect of temperature differentials on hydraulic performance and flow pattern of a sediment retention pond. WATER SCIENCE AND TECHNOLOGY : A JOURNAL OF THE INTERNATIONAL ASSOCIATION ON WATER POLLUTION RESEARCH 2018; 77:2896-2906. [PMID: 30065142 DOI: 10.2166/wst.2018.286] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/08/2023]
Abstract
Existing studies on sediment retention ponds (SRPs) have examined the effects of pond layout, inlet and outlet geometry and the installation of baffles on the performance of the SRPs. However, the effects of a temperature difference between the ambient water in the pond and the inflow are often neglected, and the buoyancy forces arising from these differences in temperature can potentially change the flow in the pond and hence its hydraulic performance. This study has experimentally evaluated the effect of these temperature differences on the flow field and residence time in a retention pond for a range of temperature differences. As expected a cold inflow sinks to the bottom of the pond while a hot inflow remains at the surface, but in both cases the inflow flows more rapidly towards the outlet than is the case for isothermal inflow. A counter-current was observed at the bottom or the surface of the pond for colder or hotter influents, respectively. These thermally induced flows significantly reduced the residence time of the pond, reducing the hydraulic performance of the pond and causing severe short-circuiting. The results have also shown that the temperature differences in the pond decrease with time, yet small temperature differences persist with the pond remaining thermally stratified.
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Affiliation(s)
- Ehsan Hendi
- Department of Civil and Environmental Engineering, The University of Auckland, Private Bag 92019, Auckland 1142, New Zealand E-mail:
| | - Asaad Y Shamseldin
- Department of Civil and Environmental Engineering, The University of Auckland, Private Bag 92019, Auckland 1142, New Zealand E-mail:
| | - Bruce W Melville
- Department of Civil and Environmental Engineering, The University of Auckland, Private Bag 92019, Auckland 1142, New Zealand E-mail:
| | - Stuart E Norris
- Department of Mechanical Engineering, The University of Auckland, Private Bag 92019, Auckland 1142, New Zealand
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Analysis of seasonal temperature influence on hydraulic processes in a waste water sedimentation tank. MONATSHEFTE FUR CHEMIE 2017. [DOI: 10.1007/s00706-016-1898-0] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 10/20/2022]
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Guo H, Ki SJ, Oh S, Kim YM, Wang S, Kim JH. Numerical simulation of separation process for enhancing fine particle removal in tertiary sedimentation tank mounting adjustable baffle. Chem Eng Sci 2017. [DOI: 10.1016/j.ces.2016.09.022] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/21/2022]
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Xiang L, Wu J, Song Y, Liu R, Yu H, Gao Q, Yang Y, Dai Y. Variation in water density related to pollutants removal in wastewater treatment processes and its use in explaining the working principles of the Unifed SBR. WATER SCIENCE AND TECHNOLOGY : A JOURNAL OF THE INTERNATIONAL ASSOCIATION ON WATER POLLUTION RESEARCH 2016; 74:2010-2020. [PMID: 27842021 DOI: 10.2166/wst.2016.294] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/06/2023]
Abstract
The wastewater quality of several municipal wastewater treatment plants (MWTPs) in Beijing was studied, and the water densities of different processing units were also measured during the wastewater treatment process. The results clearly showed that the water density declined from influent to effluent of the wastewater treatment process. Meanwhile, the variation in water density had good statistical correlation with the concentrations of total organic carbon, total phosphorus, suspended solids and total solids. Furthermore, the variation in water density could be used to explain the working principles of the Unifed sequencing batch reactor (SBR). Tracer tests were conducted in the Unifed SBR to investigate the hydraulic characteristics of the reactor. The experimental results showed that the variable values of water density from influent to effluent in the Fangzhuang MWTPs were greater than those caused by the temperature difference of >3 °C between the influent and the liquid in the reactor at 13 °C. Moreover, the flow regime of wastewater in the Unifed SBR was affected by the variation in water density, which may lead to stratification or a density current. Ascribed to the appearance of stratification in the Unifed SBR reactor, the water quality of the effluent could not be affected by that of the influent.
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Affiliation(s)
- Liancheng Xiang
- Department of Urban Water Environmental Research, Chinese Research Academy of Environmental Sciences, Beijing 100012, China and State Key Laboratory of Environmental Criteria and Risk Assessment, Chinese Research Academy of Environmental Sciences, Beijing 100012, China E-mail:
| | - Junqi Wu
- Beijing University of Civil Engineering and Architecture, Beijing 100044, China
| | - Yonghui Song
- Department of Urban Water Environmental Research, Chinese Research Academy of Environmental Sciences, Beijing 100012, China and State Key Laboratory of Environmental Criteria and Risk Assessment, Chinese Research Academy of Environmental Sciences, Beijing 100012, China E-mail:
| | - Ruixia Liu
- Department of Urban Water Environmental Research, Chinese Research Academy of Environmental Sciences, Beijing 100012, China and State Key Laboratory of Environmental Criteria and Risk Assessment, Chinese Research Academy of Environmental Sciences, Beijing 100012, China E-mail:
| | - Huibin Yu
- Department of Urban Water Environmental Research, Chinese Research Academy of Environmental Sciences, Beijing 100012, China and State Key Laboratory of Environmental Criteria and Risk Assessment, Chinese Research Academy of Environmental Sciences, Beijing 100012, China E-mail:
| | - Qiong Gao
- Beijing Drainage Group Co., Ltd, Beijing 100044, China
| | - Yingjie Yang
- Beijing Drainage Group Co., Ltd, Beijing 100044, China
| | - Yunrong Dai
- Department of Urban Water Environmental Research, Chinese Research Academy of Environmental Sciences, Beijing 100012, China and State Key Laboratory of Environmental Criteria and Risk Assessment, Chinese Research Academy of Environmental Sciences, Beijing 100012, China E-mail:
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Gila A, Beltrán G, Bejaoui M, Sánchez S, Nopens I, Jiménez A. Modeling the settling behavior in virgin olive oil from a horizontal screw solid bowl. J FOOD ENG 2016. [DOI: 10.1016/j.jfoodeng.2015.07.016] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/23/2022]
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Halalsheh MM, Abu Rumman ZM, Field JA. Anaerobic wastewater treatment of concentrated sewage using a two-stage upflow anaerobic sludge blanket- anaerobic filter system. JOURNAL OF ENVIRONMENTAL SCIENCE AND HEALTH. PART A, TOXIC/HAZARDOUS SUBSTANCES & ENVIRONMENTAL ENGINEERING 2010; 45:383-388. [PMID: 20390881 DOI: 10.1080/10934520903467824] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/29/2023]
Abstract
A two-stage pilot-scale upflow anaerobic sludge blanket - anaerobic filter (UASB-AF) reactors system treating concentrated domestic sewage was operated at 23 degrees C and at hydraulic retention times (HRT) of 15 and 4 h, respectively. Excess sludge from the downstream AF stage was returned to the upstream UASB reactor. The aim was to obtain higher sludge retention time (SRT) in the UASB reactor for better methanization of suspended COD. The UASB-AF system removed 55% and 65% of the total COD (COD(tot)) and suspended COD (COD(ss)), respectively. The calculated SRT in the UASB reactor ranged from 20-35 days. The AF reactor removed the washed out sludge from the first stage reactor with average COD(ss) removal efficiency of 55%. The volatile fatty acids concentration in the effluent of the AF was 39 mg COD/L compared with 78 mg COD/L measured for the influent. The slightly higher COD(tot) removal efficiency obtained in this study compared with a single stage UASB reactor was achieved at 17% reduction in the total volume.
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Affiliation(s)
- Maha M Halalsheh
- Water and Environmental Research and Study Centre, University of Jordan, Amman, Jordan.
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