![Experimental results showing the influence of the geometry of the micro-channel on the clogging process of 5 µm sized polystyrene particles, reprinted with permission from Bacchin et al. [25]. Copyright 2014 Springer Verlag.](https://www.researchgate.net/profile/Johannes-Lohaus/publication/323282308/figure/fig1/AS:606820431302657@1521688673974/Experimental-results-showing-the-influence-of-the-geometry-of-the-micro-channel-on-the_Q320.jpg)
![Simulation results of the clogging of the connected channel performed by Bacchin et al. [25], adopted and redrawn with permission from Bacchin et al. [25]. Copyright 2014 Springer Verlag.](https://www.researchgate.net/profile/Johannes-Lohaus/publication/323282308/figure/fig2/AS:606820435492864@1521688674154/Simulation-results-of-the-clogging-of-the-connected-channel-performed-by-Bacchin-et-al_Q320.jpg)
![a) Schematic drawing of a particle adsorption on the edges of the pillars in the simulations. b) Experimental results of particle deposition on the edges, reprinted with permission from Lee et al. [36]. Copyright 2017 Elsevier](https://www.researchgate.net/profile/Johannes-Lohaus/publication/323282308/figure/fig5/AS:606820435505152@1521688674626/a-Schematic-drawing-of-a-particle-adsorption-on-the-edges-of-the-pillars-in-the_Q320.jpg)
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What are the microscopic events of colloidal membrane fouling?
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Due to the complex interplay between surface adsorption and hydrodynamic interactions, representative microscopic mechanisms of colloidal membrane fouling are still not well understood. Numerical simulations overcome experimental limitations such as the temporal and spatial resolution of microscopic events during colloidal membrane fouling: they help to gain deeper insight into fouling processes. This study uses coupled computational fluid dynamics - discrete element methods (CFD-DEM) simulations to examine mechanisms of colloidal fouling in a microfluidic architecture mimicking a porous microfiltration membrane. We pay special attention to how particles can overcome energy barriers leading to adsorption and desorption with each other and with the external and internal membrane surface. Interparticle interaction leads to a transition from the secondary to the primary minimum of the DLVO potential. Adsorbed particles can show re-entrainment or they can glide downstream. Since particles mainly re-suspend as clusters, the inner pore geometry significantly affects the fouling behavior. The findings allow a basic understanding of microscopic fouling events during colloidal filtration. The methodology enables future systematic studies on the interplay of hydrodynamic conditions and surface energy contributions represented by potentials for soft and patchy colloids.
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... NSE assume Newtonian fluid behaviour and constant thermophysical properties, applicable in this isothermal study. Particle-fluid interactions involve various forces, including DLVO forces, gravitational forces, and fluid impact [10]. ...
... Coupling DEM with CFD is experience-based, often using a ratio of 100 between CFD and DEM time steps [10]. Equation ...
... For 2-D models, 3-D surfaces were split to accommodate 2-D meshing. DEM meshing depended on particle size, following a criterion suggesting the mesh base size should be 3 -4 times the particle size for stability [10]. The minimum mesh base size was set to 100% of the base mesh size. ...
Microfiltration membrane technology has been widely used in various industries for solid-liquid separation. However, pore clogging remains a persistent challenge. This study employs (CFD) and discrete element method (DEM) models to enhance our understanding of microfiltration membrane clogging. The models were validated by comparing them to experimental data, demonstrating reasonable consistency. Subsequently, a parametric study was conducted on a cross-flow model, exploring the influence of key parameters on clogging. Findings show that clogging is a complex phenomenon affected by various factors. The mean inlet velocity and trans-membrane flux were found to directly impact clogging, while the confinement ratio and cosine of the membrane pore entrance angle had an inverse relationship with it. Two clog types were identified: internal (inside the pore) and external (arching at the pore entrance), with the confinement ratio determining the type. This study introduced a dimensionless number as a quantitative clogging indicator based on trans-membrane flux, Reynolds number, filtration time, entrance angle cosine, and confinement ratio. While this hypothesis held true in simulations, future studies should explore variations in clogging indicators, and improved modeling of clogging characteristics. Calibration between numerical and physical times and consideration of particle volume fraction will enhance understanding. How to cite this paper: Al Qahtani, A.R. (2023) Flow-Induced Clogging in Microfil-tration Membranes: Numerical Modeling and Parametric Study. Journal of Water Resource and Protection, 15, 692-705.
... Colloidal transport and retention in porous media constitutes a major and persistent problem in hydrology and water management (Harvey and Garabedian 1991;Adin and Alon 1986), carbon sequestration (Sokama-Neuyam et al. 2017), and in a wide range of filtration applications in chemical and energy engineering (Ravikumar and Scott 2012;Lohaus et al. 2018;Tang et al. 2023). The colloid filtration theory (CFT) (Yao et al. 1971) is commonly used to describe colloid retention behaviour in saturated porous media. ...
... To save computational cost, simulations of fluid flow were not coupled with particle motion; hence, the variations of fluid pathways caused by pore-clogging phenomena were not taken into account. Lohaus et al. (2018) included the colloid-colloid and colloid-solid electrostatic surface interactions in the unresolved CFD-DEM method to investigate the clogging phenomenon during a fouling process. However, the unresolved approach falls short in capturing flow dynamics at colloid size scale, specifically important in the regions of colloid clustering, which is likely to and may severely impair simulation results. ...
Colloidal transport and clogging in porous media is a phenomenon of critical importance in many branches of applied sciences and engineering. It involves multiple types of interactions that span from the sub-colloid scale (electrochemical interactions) up to the pore-scale (bridging), thus challenging the development of representative modelling. So far published simulation results of colloidal or particulate transport are based on either reduced set of forces or spatial dimensions. Here we present an approach enabling to overcome both computational and physical limitations posed by a problem of 3D colloidal transport in porous media. An adaptive octree mesh is introduced to a coupled CFD and DEM method while enabling tracking of individual colloids. Flow fields are calculated at a coarser scale throughout the domain, and at fine-scale around colloids. The approach accounts for all major interactions in such a system: elastic, electrostatic, and hydrodynamic forces acting between colloids, as well as colloids and the collector surface. The method is demonstrated for a single throat model made of four spherical segments, and the impact of clogging is reported in terms of the evolution of the critical path diameter for percolation and permeability. We identified four stages of clogging development depending on position and time of individual colloid entrapment, which in turn correlates to a cluster evolution and local transport.
Pressure-driven membrane filtration systems are widely utilized in wastewater treatment, desalination, and water reclamation and have received extensive attention from researchers. Computational fluid dynamics (CFD) offers a convenient approach for conducting mechanistic studies of flow and mass transfer characteristics in pressure-driven systems. As a signature phenomenon in membrane systems, the concentration polarization that accompanies the permeation process is a key factor in membrane performance degradation and membrane fouling intensification. Multiple fouling models (scaling, biofouling and colloidal particle fouling) based on CFD theory have been constructed, and considerable research has been conducted. Several representative antifouling strategies with special simulation methods, including patterned membranes, vibration membranes, rotation membranes, and pulsatile flows, have also been discussed. Future studies should focus on refining fouling models while considering local hydrodynamic characteristics; experimental observation tools focusing on the internal structure of inhomogeneous fouling layers; techno-economic model of antifouling strategies such as vibrational, rotational and pulsatile flows; and unfavorable hydraulic phenomena induced by rapidly changing flows in simulations.
Particles that flow through porous environments like soils, inside a filter or within our arteries, often lead to pore clogging. Even though tremendous efforts have been made in analysing this to circumvent this issue, the clog formation and its dynamics remain poorly understood. Coupling two experimental techniques, we elucidate the clogging mechanism at the particle scale of a slit pore with its height slightly larger than the particle diameter. We identify all the particle deposition modes during the clog formation and accurately predict the corresponding deposition rate. We show how the geometrical features of the pores and the competition between deposition modes can profoundly change the clog morphology. We find that the direct capture of particles by the pore wall is rather limited. The clog formation is more closely related to the short range hydrodynamic interaction between flowing particles and those which are already immobilized within the pore. Finally we demonstrate that all the clogging regimes can be gathered on a single phase diagram based on the flow conditions and the filter design.
Understanding the separation, concentration and purification processes of soft nanoparticles is essential for numerous applications in water filtration, bioprocessing and blood separation. Here we report unique translocation and rejection features of sub-micron sized microgels during frontal filtration using membranes having micron-sized porosity. Simultaneously measuring the increase in hydraulic resistance and electrical impedance change allows us to clearly distinguish two deposition phases: (a) microgel accumulation within the depth of the membrane porosity and (b) subsequent formation of a thin gel layer on the membrane surface. Such distinction is impossible using only classical hydraulic resistance analysis. The methodology only requires the ratio of microgel to solution conductivity as an input parameter.
Nearly all tubes and pores used to transport solids in fluids, such as arteries and filters, are subject to clogging. The length scales and geometries of these tubes are well defined. In spite of this knowledge, the collective clogging behavior of multiple tubes has not yet been connected to their shapes and sizes. We investigate the clogging behavior of ten parallel tubes, which we model with ten parallel tapered microchannels using poly(styrene) beads to induce clogging events. The clogging behavior depends on the channel geometry as well as the shear stress particles are subjected to. Although our microchannels model filters, our results can be applied to the clogging behavior of a broad range of applications such as the clogging in arteries, inkjets, or xylem in trees.
Filtration of natural and colloidal matter is an essential process in today's water treatment processes. The colloidal matter is retained with the help of micro- and nanoporous synthetic membranes. Colloids are retained in a "cake layer" - often coined fouling layer. Membrane fouling is the most substantial problem in membrane filtration: colloidal and natural matter build-up leads to an increasing resistance and thus decreasing water transport rate through the membrane. Theoretical models exist to describe macroscopically the hydrodynamic resistance of such transport and rejection phenomena; however, visualization of the various phenomena occurring during colloid retention is extremely demanding. Here we present a microfluidics based methodology to follow filter cake build up as well as transport phenomena occuring inside of the fouling layer. The microfluidic colloidal filtration methodology enables the study of complex colloidal jamming, crystallization and melting processes as well as translocation at the single particle level.
In this study, the clogging mechanism of poly(styrene) particles in the flow through a single micro-pore was investigated. Together with the microscopic observation, the pressure drop was also measured. The pressure drop fluctuated according to the amount of particles deposited inside the channel. When the particles deposited and blocked the channel, the channel was clogged and the pressure drop increased sharply. During the clogging process, the particles were often detached by the flow, and interesting behaviors, such as “rolling” and “stick and detach”, were found to be the key factors that determine whether the clogging completely occurs or not. Above a certain flow rate, the channel was not clogged and the pressure drop did not increase further. The particles deposited in the upstream had an influence on the flow path. When the particles were deposited in the upstream, the flow detoured and the vortex was formed. The effect of viscosity was examined by controlling the concentration of glycerol solution. As the viscosity and the flow rate increased, the shear stress applied to the particles became larger and it was more difficult for the particles to get accumulated. The normalized clogging pressure drop decreased exponentially with shear stress. It was unity above a certain shear stress, in which the particles did not clog the channel completely.
The transport of suspensions of microparticles in confined environments is associated with complex phenomena at the interface of fluid mechanics and soft matter. Indeed, the deposition and assembly of particles under flow involve hydrodynamic, steric and colloidal forces, and can lead to the clogging of microchannels. The formation of clogs dramatically alters the performance of both natural and engineered systems, effectively limiting the use of microfluidic technology. While the fouling of porous filters has been studied at the macroscopic level, it is only recently that the formation of clogs has been considered at the pore-scale, using microfluidic devices. In this review, we present the clogging mechanisms recently reported for suspension flows of colloidal particles and for biofluids in microfluidic channels, including sieving, bridging and aggregation of particles. We discuss the technological implications of the clogging of microchannels and the schemes that leverage the formation of clogs. We finally consider some of the outstanding challenges involving clogging in human health, which could be tackled with microfluidic methods.
This reference describes the role of various intermolecular and interparticle forces in determining the properties of simple systems such as gases, liquids and solids, with a special focus on more complex colloidal, polymeric and biological systems. The book provides a thorough foundation in theories and concepts of intermolecular forces, allowing researchers and students to recognize which forces are important in any particular system, as well as how to control these forces. This third edition is expanded into three sections and contains five new chapters over the previous edition.
The purpose of this work is to examine the interplay between hydrodynamic conditions and physicochemical interactions from filtration experiments of microparticles. Experiments are performed in microfluidic filters with real time visualization at pore scale. Both flow rate and pressure are measured with time to analyse the dynamics of pore clogging and permeability. Flux stepping experiments are performed at different physicochemical conditions to determine the different clogging conditions. The results allow distinguishing different clogging behaviours according to filtration conditions which are discussed by considering particle-particle and particle-wall colloidal interactions whose main characteristics are an important repulsive barrier at 0.01 mM, a significant secondary minimum at 10 mM, and low repulsive barrier at 100 mM. Clogging delay at moderate ionic strength and deposit fragility and associated sweeping out of aggregates of particles at high ionic strength are discussed from the deposit structure, specific resistance, and deposit relaxation analyses. It has also been observed that an opening angle at microchannel entrance causes rapid clogging; this effect being more pronounced when the repulsion is partially screened. Three different scenarios are discussed by analogy to crowd swarming: panic scenario (0.01 mM) where repulsion between particles induce pushing effects leading to the creation of robust arches at pore entrances; herding instinct scenario (10 mM) where the attraction (in secondary minima) between particles enhances the transport in pores and delays clogging; sacrifice scenario (100 mM) where the capture efficiency is high but the aggregate formed at the wall are fragile.