![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?
Abstract and Figures
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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... This short-range atomic repulsion prevents F LvdW from reaching infinity, instead creating the primary attractive force minimum that is characteristic of electrostatic systems under most conditions. The hard-sphere approximation assumes that the electrostatic force is immediately cut off at some minimum atomic separation and is a common choice for attenuating F LvdW in numerical simulations (Mitchell & Leonardi 2016;Lohaus, Perez & Wessling 2018;Vowinckel et al. 2019). A more realistic approximation applies the assumption of pairwise additivity to integrate the repulsive potential of two macroscopic bodies, similar to Hamaker's derivation of the LvdW potential (Feke et al. 1984). ...
Hydrodynamic clogging in planar channels is studied via direct numerical simulation for the first time, utilising a novel numerical test cell and stochastic methodology with special focus on the influence of electrostatic forces. Electrostatic physics is incorporated into an existing coupled lattice Boltzmann-discrete element method framework, which is verified rigorously. First, the dynamics of the problem is governed by the Stokes number, $St$ . At low $St$ , the clogging probability, $P$ , increases with $St$ due to increasing collision frequency. At high $St$ , however, $P$ decreases with $St$ due to quadratic scaling of hydrodynamic force acting on arches. Under electrostatic forces, clogging is well represented by the wall adhesion number, $Ad_w$ . For $Ad_w \lesssim 4$ , the mechanical dependence on $St$ is exhibited, while for $4 < Ad_w < 20$ , there is a transition to high $P$ as sliding along, and attachment to, the channel surface occurs increasingly. For $Ad_w \gtrsim 20$ , clogging occurs with $P > 0.95$ . Particle agglomeration, however, can also decrease $P$ due to diminished interaction with channel walls. Distinct parametric regions of clogging are also observed in relation to the channel width, while a critical width $w/d^*=2.6$ is reported, which increases to $w/d^*=4$ with strong electrostatic surface attachment. The number of particles that form stable arches across a planar channel is determined to be $n=\left \lceil {w/d}\right \rceil + 1$ . Finally, sensitivity to the Coulomb friction coefficient is determined in favour of calibrating numerical parameters to bulk system behaviour. The greatest sensitivities occur in situations where the arch stability is lowest, while clogging becomes independent of friction for strong wall adhesion.
... Various physicochemical processes such as electrocoagulation (Chou et al. 2009;Elazzouzi et al. 2018;Estahbanati et al. 2021;Gomes et al. 2007;Han et al. 2002;Holt et al. 2005;Hu et al. 2003;İrdemez et al. 2006;Janpoor et al. 2011;Kabdaşlı et al. 2009;Kumar et al. 2004;Larue et al. 2003;Mollah et al. 2001;Yüksel et al. 2009;Zaroual et al. 2006), membrane filtration (Ahn & Song 1999;Bhattacharyya et al. 1978;Bilad et al. 2020;Carbonell-Alcaina et al. 2016;Corbatón-Báguena et al. 2015;Gitis et al. 2006;Guilbaud et al. 2010;Manouchehri & Kargari 2017), adsorption (Ahmad et al. 2012;Chen et al. 2008;Corona et al. 2021;Veli et al. 2019Veli et al. , 2021; biological processes (Andersen et al. 2002;Ashfaq et al. 2017;Bagheri & Mirbagheri 2018;Deowan et al. 2015;Emaminejad et al. 2019;Hamedi et al. 2019;Hoinkis et al. 2012;Iorhemen et al. 2016;Lohaus et al. 2018;Madaeni et al. 1995;Mahmoudi et al. 2020;Paris & Schlapp 2010) and combined treatment processes (Bokhary et al. 2018;ElSherbiny et al. 2019;Emaminejad et al. 2019;Fan et al. 2001;Hamedi et al. 2019;Howe & Clark 2006;Huang et al. 2019;Jia et al. 2014;Kamarudin et al. 2003;Kim et al. 2014;Mostafazadeh et al. 2019;Siswoyo et al. 2019) have been applied for the treatment of LWW. Biological processes are inefficient in eliminating persistent organic pollutants. ...
The problem of management and treatment of wastewater from commercial laundries is a matter of concern. The present study provides an effective and eco-friendly solution to the treatment of wastewater from commercial laundries in Quebec (Canada) by using the extracellular polymeric substance (EPS) as a bio-flocculant. EPS was produced from the valorization of crude glycerol and paper mill sludge by a bacterial strain (BS-04). Two different types of EPS: Slime EPS (S-EPS) and Broth EPS (B-EPS) were used for the treatment of commercial laundry wastewater (CLWW). This is the first study for the treatment of CLWW using bio-flocculant EPS. A comparison between the conventional treatment of laundry wastewater (LWW) by chemical coagulants (FeSO4, CaCl2, Alum) and enhanced treatment by bio-flocculant EPS has been drawn in the study. Moreover, LWW treatment by a combination of EPS and chemical coagulants was also investigated. It was observed that S-EPS (0.6 g/L) gave better flocculation activity (FA) than B-EPS. S-EPS alone can remove 83.20% of turbidity, 77.69% of suspended solids (SS), and 76.37% of chemical oxygen demand (COD). The best results were obtained by combining S-EPS (0.6 g/L) with alum (300 mg/L) at pH 7 for a treatment time of 30 min. This combination was able to remove 98% of turbidity, 95.42% of SS, and 83.08% of COD from LWW. When treatment time has been increased to 4 h at pH 7, it resulted in more than 88% COD removal from CLWW.
Graphical Abstract
The problem of management and treatment of wastewater from commercial laundries is a matter of concern. The present study provides an effective and eco-friendly solution to the treatment of wastewater from commercial laundries in Quebec (Canada) by using extracellular polymeric substance (EPS) as bio-flocculant. EPS was produced from valorization of crude glycerol and paper mill sludge by a bacterial strain (BS-04). Two different types of EPS: Slime EPS (S-EPS) and Broth EPS (B-EPS) were used for treatment of commercial laundry wastewater (CLWW). This is the first study for treatment of CLWW using bio-flocculant EPS. A comparison between the conventional treatment of laundry wastewater (LWW) by chemical coagulants (FeSO 4 , CaCl 2 , Alum) and enhanced treatment by bio-flocculant EPS has been drawn in the study. Moreover, LWW treatment by combination of EPS and chemical coagulants was also investigated. It was observed that S-EPS (0.6 g/L) gave better flocculation activity (FA) than B-EPS. S-EPS alone can remove 83.20% of turbidity, 77.69% suspended solids (SS) and 76.37% chemical oxygen demand (COD). The best results were obtained by combining S-EPS (0.6 g/L) together with alum (300 mg/L) at pH 7 for treatment time of 30 min. This combination was able to remove 98% of turbidity, 95.42 % of SS and 83.08% of COD from LWW. When treatment time has been increased to 4 h at pH 7, it resulted in more than 88% COD removal from CLWW.
Cross-scale polydisperse particulate-fluid flows are widely practised yet their multi-resolution simulations are not achieved due to the lack of reliable numerical methods. In this work, a novel so-called hybrid CFD-DEM model is developed for the high-fidelity multi-resolution simulations of cross-scale polydisperse particulate-fluid flow systems, for the first time featuring no limit on the grid size to particle diameter ratio (lm/dp). The hybrid CFD-DEM method collaboratively considers the fluid-coarse particles interaction (lm/dp <0.1), fluid-medium particles interaction (0.1< lm/dp < 3), and fluid-fine particles interaction (lm/dp >3) by means of the FD (fictitious domain)-based resolved method, semi-resolved method, and unresolved method, respectively. Three typical polydisperse particulate-fluid flow scenarios are simulated for model validation and effectiveness demonstration, i.e., sedimentation of single particle in liquid; drafting, kissing, and tumbling (DKT) process of two particles; and the migration of fine glass through the pores of the coarse particles. The results confirm the ability of the hybrid CFD-DEM model of capturing both the detailed flow fields of fluid and particles and particle-fluid interactions in the particulate-fluid flow with a cross-scale size distribution. Moreover, the hybrid CFD-DEM model shows excellent capability in mesh convergence, wide applicability, and high accuracy. It provides a promising tool for the modelling of many cross-scale particulate-fluid flow systems.
The Derjaguin-Landau-Verwey-Overbeek (DLVO) model, as well as the extended model (XDLVO), is popularly employed to quantify the interfacial interactions underlying membrane fouling. However, disagreements between membrane fouling extent and the interaction energies derived from DLVO or XDLVO models have been reported, which suggests gaps in the understanding. This study demonstrates that the Derjaguin-Landau-Verwey-Overbeek (DLVO) approximation methods for predicting the interfacial foulant-membrane interaction are sensitive to the boundary condition assumptions (e.g., constant charge versus constant potential). In particular, while both the Poisson-Boltzmann (P–B) and linear superposition approximation (LSA) equations can quantify the electrostatics (EL) interaction energy component, the former assumes constant potential, while the latter additionally considers constant charge scenarios. The relative accuracy of these two equations were evaluated here. For dead-end filtration tests, flux decline trends, OCT analysis results and fouling model parameters were obtained. Regarding fouling of pristine PCTE membrane by latex particles of opposite charge signs, both the P–B and LSA equations predict relative fouling extents correctly. However, for the case of the BPEI-coated membrane, the P–B equation failed whereas the LSA equation gave good agreements. For cross-flow filtration tests in organic solvents, LSA also out-performed the P–B equation in providing more accurate predictions of membrane fouling. The results here highlight the shortcomings in the commonly used P–B equation and are expected to be potentially valuable in the development of better equations for quantifying interfacial interaction energies.
The migration of fines suspended in the liquid through porous media represents a key challenge in many chemical engineering processes, yet the inherent fundamentals and roles of clusters were not well elucidated. In this work, we numerically study the formation, growth, and connection of clusters in a porous medium and unveil the clogging mechanism of fines at pore-scale, i.e., bridging and locking essentially. A saturation volume fraction of fines in the entrance occurs at the critical transition point from depth filtration to caking, where the volume fraction is calculated by the spherical cap method. An inter-particle contact pair method is developed to quantify the cluster size growth. Inherently, an exponential correlation between clogging ability and size ratios is obtained using the cluster information - growth rate of clusters. A probabilistic model of clogging ability and performance is derived and used to verify the exponential formula. This work provides an effective method to quantify clogging ability and could be applied to more complex systems.
In this study, the focused ion beam scanning electron microscope (FIB-SEM) technique is utilized to obtain a realistic microstructure geometry of mullite and α-alumina membranes, which are commercially available microfiltration (MF) membranes, for implementation in a high-resolution numerical simulation model based on coupled direct numerical simulation (DNS) and the discrete element method (DEM). The flow and particle permeation through the membrane pores are evaluated for different particle sizes. The developed simulation model is a powerful tool for enhancing our understanding of the MF process because it introduces the realistic microporous structure of an actual MF membrane rather than the simplified membrane model structures such as straight cylindrical pores and particle packing structures that have been used in previous numerical studies. The application of the developed model is discussed for the prediction of the rejection curve, which shows the importance of considering a realistic microporous structure for the accurate prediction of the MF process. The results showed different rejection curves for the mullite and α-alumina membranes, which mainly contributed to the difference in the local pore size distributions of the two membranes. Furthermore, detailed particle permeation through the membrane is evaluated, which is not feasible in experimental analyses for realistic MF membranes.
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.