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Concentratin Polarization with Membrane Ultrafiltration
Abstract
Unusually high ultrafiltrate flux values have been observed by use of thin-channel ultrafiltration in the dewatering and purification of colloidal suspensions. Polymer latices, paints, metal oxides, starch, and even cellular suspensions have all exhibited higher flux values than would be predicted by the now recognized gel-polarization model. Theoretical reasons for these anomalies are discussed in conjunction with experimental data obtained with thin-channel devices utilizing anisotropic noncellulosic membranes.
... Eventually a pressure will be reached where the rate of solute convection towards the membrane exceeds the rate of back transport, the limiting flux is then reached, and the flux is then unchanged by further increases in PxM^ the membrane is then said to be concentration polarised. This form of flux behaviour was reported for ultrafiltration systems by Porter (1972), and has been seen in many microfiltration applications (e.g. Kavanagh, 1987, Shimizu et a l, 1993). ...
... The theory of polarisation during ultrafiltration was outlined by Porter (1972). It is based essentially on the mass balance of retained species, with the rate of convection towards the membrane being balanced by diffusive back transport. ...
... It is generally accepted that in ultrafiltration the concentration of proteins at the membrane will increase until a gel layer forms at a concentration C q, and that once this point is reached no more protein can enter the polarised layer (Porter, 1972). This concentration of protein can be estimated from the linear plot of J]jni, the limiting flux vs In C g as the intercept on the In C g axis. ...
This thesis uses studies on the recovery of a recombinant periplasmic α-amylase from Escherichia coli to illustrate process development for the recovery of biological products for purification. Fermentations have been carried out in batch mode using defined or complex medium at up to 450 L scale, and also at 20 L scale in fed-batch mode using a defined medium. Centrifugal whole cell recovery led to cell damage in each of the types of centrifuges tested. Damage was highest in the tubular bowl centrifuge, intermediate in a disk stack centrifuge, and least in a multichamber centrifuge. The breakage in the disk stack centrifuge occurred mainly in the solids discharge. There was little breakage during microfiltration of a complex medium broth. 0.2 µm or 0.8 µm ceramic membranes were used to filter the spheroplast stream produced by a combined lysozyme-osmotic shock treatment on the recovered cells. No additional release of retentate protein was seen during microfiltration. Transmembrane pressure appeared to have little impact on the flux, but higher pressures reduced the transmission levels. The α-amylase transmission was higher than total protein transmission with the 0.2 µm membrane. No α-amylase selectivity was seen with the 0.8 µm membrane. The transmission performance during the trials has been correlated with the flux by means of a 'transmittance' term. Permeate backpulsing has led to a significant improvement in the performance of a 0.2 µm filtration. An investigation of the properties of the pulse has shown that there exists an optimum pulse frequency, and that a reverse flow of liquid is required for improved performance. Scale-up of microfiltration using constant wall shear rate has been demonstrated. Centrifugal removal of cell spheroplasts showed a lower degree of protein release than with the whole cells. However chromatography grade material could only be produced by centrifugation at low flowrates.
... The water flow through rectangular channel on membrane surface (width × length × channel height = 4.5 cm × 10 cm × 2.5 mm) with cross flow velocity 1 LPM is found to be a laminar flow behavior (Reynolds number = ~690). Thus, Leveque's solution [34][35] can be explored to obtain the mass transfer coefficient of solute (K, m 2 /s) for rectangular conduit in laminar flow region as below: Eq. 3 can be rearranged in Eq. 4 as below: ...
... The mass transfer boundary layer thickness is much lower in this study compared to the ultrafiltration membrane described using various macromolecules like protein, fruit juice and polymers in literature [34][35]. This lower δ value suggests insignificant membrane flux decline during long run of membrane operation. ...
... From Eq. 4, K is estimated in this study for cross flow velocity of 1 LPM as 4.05 × 10 -4 m/s. The thickness (δ) of the boundary layer of concentration polarization is estimated using following Eq.6[34][35]. ...
The scientific community is yet to find a cost-effective solution for the widespread problem of fluoride contamination in groundwater. In this study, cellulose acetate based mixed matrix membrane (MMM) was prepared through a phase inversion method using mixed metal oxides nanoparticles-polymer composite (Fe–Al–[email protected]) as nanofiller. Adsorption is the commonly known mechanism of fluoride removal through MMMs and also a reason for its limited performance in real applications. Fe–Al–[email protected] loaded cellulose acetate-based mixed matrix membrane (1 m²) is capable to treat 4000 L fluoride contaminated water. It has been observed that fluoride ions rejection occurs initially through adsorption. Subsequently, membrane surface experiences electrostatic repulsion due to the development of negative surface charges. Excellent defluoridation performance was obtained due to the electrostatic repulsion between F⁻ and negatively charged MMM surface. The antibacterial test reveals that the MMM is less susceptible to microbial attack compared to cellulose acetate membranes. Fluoride rejection through membrane confirms that mixed oxide nanoparticles-polymer-composite loaded MMM is capable of removing F⁻ from water quite efficiently.
... Broths can consist of a number of phases. For example, solid media constituents, which can block membrane systems, the continuous aqueous phase which can be polarising at the membrane pores (Porter 1972;Brose et al. 1996) and liquid organic phases, such as oils which can cause entrapment blocking of the pores. ...
... Optimisation of process parameters of MF can lead to increases in permeate flux (Porter 1972). Russotti et al. (1995) ...
... It has been proposed (Porter 1972;Brose et a l 1996;Okec 1998) that flux can be predicted by: ...
The causes of the interactions between fermentation and microfiltration were first examined experimentally by investigating erythromycin production using two different media. Soluble complex media (SCM) broths reached maximum erythromycin concentrations more rapidly (64.2 0.3 h) than the less expensive and therefore industrially preferred oil based media (OBM) broths (176 15 h) but also attained lower titres (241 55 g.L-1 compared to 617 104 g.L-1). The OBM broths showed oxygen limitation due to the high apparent viscosity. Both broths were found to be shear thinning and exhibited different time dependant rheological profiles which could impact on the performance of the subsequent microfiltration operation. The microfiltration performance of the two broths was subsequently examined using a flat sheet membrane system (area = 60 - 120 cm2). This small-scale unit allowed the determination of flux and transmission profiles as a function of fermentation time and for membrane operation over a range of transmembrane pressures and crossflow velocities. The OBM broths were quicker to blind the membrane, achieved lower values of steady state permeate flux, which decreased over fermentation time as apparent viscosity increased. SCM broths showed no time dependant variation in steady state permeate flux. Transmission of product was higher in SCM (96.4 1.6 %) than OBM broths (89.6 1.4 %). This was attributed to the high solids content of the OBM broth in the form of the undissolved soya flour. The mass transfer of erythromycin across the membrane was similar in both cases (SCM: 1.47 0.28 x 10-6 kg.m-2.s-1, OBM: 1.38 0.20 x 10-6 kg.m-2.s-1) due to the differences between erythromycin titre and permeate flux. For the SCM broths image analysis was also used to determine if there was a relationship between bacterial morphology and microfiltration performance. No such relationship could be adequately determined. In OBM broths image analysis was used to predict the biomass concentration. Modelling of the process using on- and off-line measurements, combined with scale-down methodologies, allows unit operations to be rapidly assessed and optimised, thus reducing product lead times through the development process. The performance of the microfiltration step was successfully predicted using a simple gel polarisation model which was reliable within a fermentation 9.5 % and a model modified to take account of operation at pressure below cTMP 6.2%. This allowed prediction of steady state permeate flux at the harvest time and the critical transmembrane pressure.
... where k B is the Boltzmann's constant; T represents the absolute temperature; µ represents the solution viscosity; and d p is the particle size. In addition, the term D/δ in the right part of Equation (2) is recognized as the mass transfer coefficient k [10]: ...
... Equations (5) and (6) are the typical CP models, which were widely applied to scale the CP in processes such as reverse osmosis (RO), nanofiltration (NF), ultrafiltration (UF), and microfiltration (MF) [5,6,10,19]. ...
Membrane fouling can cause severe flux drops and affect the quality of produced water, which is a major obstacle for membrane applications. Great efforts have been made to examine theoretical models and numerical simulations for fouling behavior and mechanisms in the past decades, but there is a lack of literature providing a systematic summary. This work aims to present a state-of-the-art review of the principles, applicability and advantages of fouling theoretical models (i.e., the concentration polarization, cake layer formation and blocking models), and numerical simulations (i.e., computational fluid dynamics, Monte Carlo simulation, and artificial neural networks) for fouling behavior and mechanisms. Through these models and simulations, the behaviors of foulant particles at the microscopic level are analyzed in detail from the perspective of force, energy, and particle trajectory during the fouling process. The concise summary of fouling modeling in this review gives guidelines for the selection and application of models to simulate the membrane fouling process accurately, and the optimization of the operation in membrane-based processes.
... That non-gelling macromolecules also displayed the same experimental behavior of flux being approximately proportional to − ln(C b ) and to mass transfer coefficient, k, coupled with the characteristic plateauing of flux at high TMP led to the emergence of other theories as discussed elsewhere [8,13,14]. Also gel-polarisation theory could not and cannot explain why for one given solute, the limiting concentration determined from a plot of J lim versus − ln(C b ) as the point where flux would go to zero, varies when that solute is filtered in two different filtration-cells [8,15]. Also as pointed out by others the supposedly constant value of C gel . ...
... When this is coupled with a mention that viscosity increases with solute concentration, there is the clear impression that the relevant viscosity is that of the feed solution rather than that of the permeate. Indeed, in some papers the viscosity used in the calculation of resistance (e.g., Equation (15) in [32]) is clearly stated to be that of the feed, which is erroneous for the following reason. The permeate is passing through the membrane and thus, to be consistent with Darcy's law the relevant viscosity should be that of the permeate, as clearly set out by the majority of researchers, e.g., [8,27,33]. ...
Concentration polarization refers to the rapid emergence of concentration gradients at a membrane/solution interface resulting from selective transfer through the membrane. It is distinguishable from fouling in at least two ways: (1) the state of the molecules involved (in solution for concentration polarization, although no longer in solution for fouling); and (2) by the timescale, normally less than a minute for concentration polarization, although generally at least two or more orders of magnitude more for fouling. Thus the phenomenon of flux decline occurring over a timescale of tens of minutes should not be attributed to concentration polarization establishing itself. This distinction and a number of questions surrounding modelling are addressed and clarified. There are two paradigmatic approaches for modelling flux, one uses the overall driving force (in which case allowance for osmotic effects are expressed as additional resistances) and the other uses the net driving force across the separating layer or fouled separating layer, although often the two are unfortunately comingled. In the discussion of flux decline models’ robust approaches for the determination of flux-time relationships, including the integral method of fouling analysis, are discussed and various concepts clarified. The final section emphases that for design purposes, pilot plant data are vital.
... The downwelling flows are associated with the back transport of foulants near the membrane surface. The primary factor governing the filtration performance of a membrane module is the rate of foulant transport in a feed solution near the membrane [45,46]. If a flow system is globally chaotic, the back transported foulants will be redistributed uniformly in the entire domain, which suppresses the accumulation of foulants on the membrane surface. ...
... In this section, the growth rate of the wall concentration is characterized by adopting the film theory for a fully developed laminar flow in a thin rectangular channel [45,46]. In the film theory, the dimensionless concentration difference is represented by ...
Fouling mitigation using chaotic advection caused by herringbone-shaped grooves in a flat membrane module is numerically investigated. The feed flow is laminar with the Reynolds number (Re) ranging from 50 to 500. In addition, we assume a constant permeate flux on the membrane surface. Typical flow characteristics include two counter-rotating flows and downwelling flows, which are highly influenced by the groove depth at each Re. Poincaré sections are plotted to represent the dynamical systems of the flows and to analyze mixing. The flow systems become globally chaotic as the groove depth increases above a threshold value. Fouling mitigation via chaotic advection is demonstrated using the dimensionless average concentration (c¯w*) on the membrane and its growth rate. When the flow system is chaotic, the growth rate of c¯w* drops significantly compared to that predicted from the film theory, demonstrating that chaotic advection is an attractive hydrodynamic technique that mitigates membrane fouling. At each Re, there exists an optimal groove depth minimizing c¯w* and the growth rate of c¯w*. Under the optimum groove geometry, foulants near the membrane are transported back to the bulk flow via the downwelling flows, distributed uniformly in the entire channel via chaotic advection.
... Michaels [98] and Blatt et al. [2] presented models for the concentration polarization of macrosolutes and colloids, in which the back-transport rate of concentrated solute controls the permeate flux. On the other hand, Porter [99] reported that the mass transfer from the membrane surface into the bulk stream is influenced by some forces other than the concentration gradient. This author described the so-called tubular pinch effect (effect appreciated in many colloidal suspensions in which a lesser frictional pressure drop would be expected from the fluid viscosity) is responsible for the increase in the mass transfer [99]. ...
... On the other hand, Porter [99] reported that the mass transfer from the membrane surface into the bulk stream is influenced by some forces other than the concentration gradient. This author described the so-called tubular pinch effect (effect appreciated in many colloidal suspensions in which a lesser frictional pressure drop would be expected from the fluid viscosity) is responsible for the increase in the mass transfer [99]. In this regard, other authors have also reported that film theory is not suitable for permeate flux prediction. ...
In any membrane filtration, the prediction of permeate flux is critical to calculate the membrane surface required, which is an essential parameter for scaling-up, equipment sizing, and cost determination. For this reason, several models based on phenomenological or theoretical derivation (such as gel-polarization, osmotic pressure, resistance-in-series, and fouling models) and non-phenomenological models have been developed and widely used to describe the limiting phenomena as well as to predict the permeate flux. In general, the development of models or their modifications is done for a particular synthetic model solution and membrane system that shows a good capacity of prediction. However, in more complex matrices, such as fruit juices, those models might not have the same performance. In this context, the present work shows a review of different phenomenological and non-phenomenological models for permeate flux prediction in UF, and a comparison, between selected models, of the permeate flux predictive capacity. Selected models were tested with data from our previous work reported for three fruit juices (bergamot, kiwi, and pomegranate) processed in a cross-flow system for 10 h. The validation of each selected model's capacity of prediction was performed through a robust statistical examination, including a residual analysis. The results obtained, within the statistically validated models, showed that phenomenological models present a high variability of prediction (values of R-square in the range of 75.91–99.78%), Mean Absolute Percentage Error (MAPE) in the range of 3.14–51.69, and Root Mean Square Error (RMSE) in the range of 0.22–2.01 among the investigated juices. The non-phenomenological models showed a great capacity to predict permeate flux with R-squares higher than 97% and lower MAPE (0.25–2.03) and RMSE (3.74–28.91). Even though the estimated parameters have no physical meaning and do not shed light into the fundamental mechanistic principles that govern these processes, these results suggest that non-phenomenological models are a useful tool from a practical point of view to predict the permeate flux, under defined operating conditions, in membrane separation processes. However, the phenomenological models are still a proper tool for scaling-up and for an understanding the UF process.
... These relations highlight that flux may increase if flowrate increases or cross-section reduces. From a general standpoint, all hydrodynamics techniques to increase flow velocity and the shear rate at the membrane surface enable to increase flux [238]. In microfiltration, various recent theories take into account the hydrodynamics: i) lateral migration of particles (tubular pinch effect), ii) axial migration of deposit (flowing cake) or hydrodynamic diffusion generated by shear rate (shear-induced diffusion). ...
... and in turbulent regime Sh = A''Re α Sc β [6] (D: diffusion coefficient, k m : transfer coefficient, d h : hydraulic diameter, L: channel length, δ: thickness of limiting layer, μ: viscosity, u: velocity, ρ: density).For laminar flow in a thin rectangular channel[238][239][240], Sherwood was presented with Graezt-Lévêque's correlation): Sh = ...
By maintaining a high shear rate, dynamic filtration (DF) provides excellent performances in controlling fouling and improving flow during filtration. Many DF devices comprising a mechanical movement generated by the rotation, oscillation and/ or vibration of one element have thus been developed. Based on the bibliometric analysis, new applications and technologies related to DF have become new research hot spots. Major applications were reported in food processing, water treatment and bioprocess engineering. With a precise definition of the concepts of oscillation and vibration, 55 DF modules have been classified into 15 different types according to movement and shape (filtration cell, membrane, impeller, disk…). But it appears that it remains a great challenge to complete the knowledge on the flow of fluid inside DF modules because of their complex geometries. Global, semi-local and local investigation of hydrodynamics have been detailed. They not only make it possible to estimate performances but also to help to calculate energy consumption according to operating conditions. In this review, the main characteristics of DF devices and existing applications are presented. These empirical results are already very useful for the selection of DF devices for a dedicated application. However, a better understanding of local temporal variations in pressure and shear stress is still necessary to refine the choice of a device and the operating conditions. The overarching aims propose to report the main criteria that will help engineers to select DF module or to identify the scientific and/ or technological bottlenecks about hydrodynamics or applications.
... Fouling is caused by the particles contained in the feed solution that block membrane pores, and creates a cake layer due to deposited particles on the membrane surface. Concentration polarization (CP) refers to a phenomenon in which the species concentration rapidly increases within a boundary layer close to the membrane surface due to the selective transport of species through the membrane [2][3][4][5][6]. Both fouling and concentration polarization leading to a decline in the filtration performance and lifespan of a membrane module are critical issues that should be overcome or alleviated in most filtration processes [7][8][9]. ...
A numerical study was conducted to investigate the effect of rotating patterned disks on the flow and permeate flux in a dynamic filtration (DF) system. The DF system consists of a rotating patterned disk and a stationary housing with a circular flat membrane. The feed flow is driven by the rotating disk with the angular velocity ranging from 200 to 1000 rpm and the applied pressure difference between inlet and outlet ports. Wheel-shaped patterns are engraved on the disk surfaces to add perturbation to the flow field and improve the permeate flux in the filtration system. Five disks with varying numbers of patterns were used in numerical simulations to examine the effects of the number of patterns and the angular velocity of the disk on the flow and permeate flux in the DF system. The flow characteristics are studied using the velocity profiles, the cross-sectional velocity vectors, the vortex structures, and the shear stress distribution. The wheel-shaped patterns shift the central core layer in the circumferential velocity profile towards the membrane, leading to higher shear stresses at the membrane and higher flux compared to a plain disk. When the number of patterns on the disk exceeded eight at a fixed Reynolds number, there were significant increases in wall shear stress and permeate flux compared to a plain disk filtration system with no pattern.
... (1) Limitation 1: Concentration polarization CP refers to the phenomenon that during membrane separation, the concentration of solute near the membrane surface is different from that of the body solution. CP not only reduces the effective driving force across the membrane, but also leads to membrane fouling (Porter, 1972;Sablani et al., 2001). CP is considered as the largest problem of the FO technology. ...
Forward osmosis (FO) is an emerging permeation-driven membrane technology that manifests advantages of low energy consumption, low operating pressure, and uncomplicated engineering compared to conventional membrane processes. The key issues that need to be addressed in FO are membrane fouling, concentration polarization (CP) and reverse solute diffusion (RSD). They can lead to problems about loss of draw solutes and reduced membrane lifetime, which not only affect the water treatment effectiveness of FO membranes, but also increase the economic cost. Current research has focused on FO membrane preparation and modification strategies, as well as on the selection of draw solutions. Unfortunately, these intrinsic solutions had limited success in unraveling these phenomena. In this paper, we provide a brief review of the current state of research on existing external field-assisted FO systems (including electric-, pressure-, magnetic-, ultrasonic-, light- and flow-assisted FO system), analyze their mitigation mechanisms for the above key problems, and explore potential research directions to aid in the further development of FO systems. This review aims to reveal the feasibility of the development of external field-assisted FO technology to achieve a more economical and efficient FO treatment process.
... The concentration polarization of large organic molecules, for example, was found to be dependent on solute-membrane interactions. [30][31][32] Additionally, Weinman and Husson observed different rejection trends on patterned membranes with a surface coating. 18 Here, we aim to give a comprehensive study on the concentration polarization of surface patterned membranes through rejection tests. ...
Surface pattern is a promising approach to enhance membrane performance while contradictory results have been reported on its impact on concentration polarization. Here, we provide an experimental and modeling study of the concentration polarization on patterned membranes by varying pattern size, solute size, surface hydrophilicity, and membrane orientation. Interesting trends were observed when comparing different membrane orientations, where relative concentration polarization degree (CPD) was found depend on molecular weight. Salts and small organic molecules encountered more severe CPD in the transverse mode, while molecules larger than a threshold value showed a different trend. Such threshold molecular weight increased at larger pattern size. Simulation results were consistent with experimental observations, and revealed the critical role of diffusivity on such phenomena. Results also showed more severe concentration polarization on patterned membranes in both parallel and transverse modes in most cases, compared to smooth membrane.
... The effect of concentration polarization is usually very small in hollow-fibre RO systems because of relatively low product flux, which is sufficient to reduce the effect of concentration polarization [27]. Where high membrane flux leads to a rapid buildup of retained solutes on the membrane surface and results in concentration polarization [28]. The interface concentration CM at the membrane surface can be replaced by the local brine concentration CB. ...
The aim of this work is to produce cellulose acetate (CA) hollow-fine-fibre membranes with good water flux performance in the 95-96% salt retention range for brackish water desalination from first principles. First, the acceptable range of fibre dimensions was determined by means of a collapse pressure calculation using the elastic buckling pressure equation (thin shell assumption). Second, the pressure drop across the fibre wall in the hollow-fine fibre was determined by using the Hagen-Poiseuille equation to determine how this would affect the chosen fibre dimensions. It was determined that the acceptable range of fibre dimensions was 222-247 μm, and the wall thickness was 50 μm. Fibres with these dimensions exhibited a high resistance to brackish water operating pressure of 20-25 bar, without collapse. The pressure drop calculations of these dimensions showed a sufficiently low pressure drop across the fibres.
... In the mBLA method, the flow outside the CP boundary layer is determined basically by the, in general, hyperbolic axial pressure profile caused by the permeate flux through the membrane, as described in [16][17][18]. The inner flow solution is obtained in a similar way as in classical film theory [4,5,19,20], however with the concentration-dependence of the dispersion properties accounted for. The mBLA method is computationally fast, and different from computational fluid dynamics methods, it offers analytic insight into the functional behavior of concentration and flow properties. ...
Cross-flow membrane ultrafiltration (UF) is used for the enrichment and purification of small colloidal particles and proteins. We explore the influence of different membrane geometries on the particle transport in, and the efficiency of, inside-out cross-flow UF. For this purpose, we generalize the accurate and numerically efficient modified boundary layer approximation (mBLA) method, developed in recent work by us for a hollow cylindrical membrane, to parallel flat sheet geometries with one or two solvent-permeable membrane sheets. Considering a reference dispersion of Brownian hard spheres where accurate expressions for its transport properties are available, the generalized mBLA method is used to analyze how particle transport and global UF process indicators are affected by varying operating parameters and the membrane geometry. We show that global process indicators including the mean permeate flux, the solvent recovery indicator, and the concentration factor are strongly dependent on the membrane geometry. A key finding is that irrespective of the many input parameters characterizing an UF experiment and its membrane geometry, the process indicators are determined by three independent dimensionless variables only. This finding can be very useful in the design, optimization, and scale-up of UF processes.
... The elevation in the concentration on the feed side of the membrane surface due to the flow toward the membrane is termed as concentration polarization, which significantly decreases the filtration efficiency. Instead of the direct measurement of the concentration on the membrane, the boundary film theory (Sablani et al. 2001;Porter 1972), used for concentration polarization, with non-dimensional correlation formulae (Berg et al. 1989;Lévêque 1928) or velocity variation method (Nakao and Kimura 1981) is used to predict the concentration value on the membrane surface. In the theoretical studies on the membrane transport, the Kedem-Katchalsky model has been modified to include the effect of the concentration boundary layer (Kargol 1996(Kargol , 2000Bryll and Ślȩzak 2017). ...
A concise and accurate prediction method is required for membrane permeability in chemical engineering and biological fields. As a preliminary study on this topic, we propose the concentration polarization model (CPM) of the permeate flux and flow rate under dominant effects of viscosity and solute diffusion. In this model, concentration polarization is incorporated for the solution flow through a semi-permeable membrane (i.e., permeable for solvent but not for solute) in a circular pipe. The effect of the concentration polarization on the flow field in a circular pipe under a viscous-dominant condition (i.e., at a low Reynolds number) is discussed by comparing the CPM with the numerical simulation results and infinitesimal Péclet number model (IPM) for the membrane permeability, strength of the osmotic pressure, and Péclet number. The CPM and IPM are confirmed to be a reasonable extension of the model for a pure fluid, which was proposed previously. The application range of the IPM is narrow because the advection of the solute concentration is not considered, whereas the CPM demonstrates superior applicability in a wide range of parameters, including the permeability coefficient, strength of the osmotic pressure, and Péclet number. This suggests the necessity for considering concentration polarization. Although the mathematical expression of the CPM is more complex than that of the IPM, the CPM exhibits a potential to accurately predict the permeability parameters for a condition in which a large permeate flux and osmotic pressure occur.
... In addition, very concentrated protein solutions will show 'jamming'; forming a gel like layer due to close stacking of the protein molecules. For this case a parallel may be drawn to membrane processes, where, due to the same phenomenon a gel layer is formed on top of an ultrafiltration membrane (Porter 1972). In progressive freeze concentration this gel layer impedes the mass transfer in the boundary layer, resulting in a shift from heat transfer limitation to mass transfer limitation. ...
... Hence, appropriate estimations of kf are necessary to accurately report 331 membrane performance data[70]. Values for kf can be estimated experimentally by the osmotic 332 is the solute diffusion coefficient, Dh is the hydraulic diameter of the cell, Re is the 336 dimensionless Reynolds number, Sc is the dimensionless Schmidt number, and a, b, c are 337 adjustable dimensionless parameters that change based on system geometry and laminar or 338 turbulent conditions[73]. The diffusivity of NaCl in water at 25 °C varies nonequations defined for laminar and turbulent conditions in cross-flow and stirred cell (i.e., 341 dead-end filtration) conditions is reported elsewhere[70]. 3424. ...
Since the advent of thin-film composite polyamide membranes brought forth a breakthrough in desalination and water purification membranes nearly half a century ago, recent years have only witnessed marginal improvements in the water-salt selectivity of these membranes. The slow progression is partly attributable to limited understanding of membrane synthesis–structure–performance relationships. A centralized archive of reverse osmosis membrane (RO) characterization data may lead to a shared understanding of features that maximize RO performance and unify research efforts. The Open Membrane Database (OMD), which can be found at www.openmembranedatabase.org, is a growing database of over 600 water purification and desalination membranes that are sourced from peer-reviewed journals, patents, and commercial product data. Here, we outline the detailed functionality of the database, the transport theory underlying the membrane performance calculations, and best practices for membrane performance testing and reporting. The user-sourced, open-access database may be used to benchmark novel RO membranes against the state of the art, conduct meta-analyses, and develop synthesis–structure–performance relationships, each of which will be critical to advancing membrane development.
... The film theory approach for describing concentration polarization was developed by Michaels et al [11][12]. The film theory simplifies the complex transfer problem to a one-dimensional mass transfer problem by assuming that the axial convection of the solute near the membrane surface is insignificant. ...
This work describes the appearance of a concentration polarizing boundary layer on the membrane surface during the separation of the H2/CO2 gas mixture. Concentration polarization occurs when the rejection solution accumulates near the surface of the membrane, forming a boundary layer. The inclusion of concentration polarization effects in the processing of porous walls creates additional difficulties. The boundary layer formed by concentration polarization can be considered as a type of a second porous wall with a lower permeability than the membrane. The main difficulty in modeling this situation is to determine the appropriate boundary conditions for the concentration on the wall, since the concentrations on the wall will constantly change, and the wall geometry itself may change over time due to particle deposition. To account for this effect, a numerical approach was developed, which is discussed in this work
... The mass-transfer coefficient can be determined using the Leveque solution for the Sherwood relation for developed laminar flow in tubular systems, 28 as shown in eq 4. Sh is the dimensionless Sherwood number describing the ratio of convective mass transport over diffusive mass transport. Furthermore, in eq 4, d in is the inner diameter of the tube or hollow fiber in m, L is the length of the tube in m, Re is the dimensionless Reynolds number, and Sc is the dimensionless Schmidt number, as shown in eqs 5 and 6, respectively. ...
Polyelectrolyte multilayers (PEMs) are highly promising materials as selective separation layers on the inside of hollow fiber membranes. We investigate the forward osmosis (FO) performance of poly(4-styrene sulfonate) (PSS)/poly(allylamine) (PAH)- and PSS/poly(ethylene imine)-based PEM membranes and apply different draw solutions. The PEM membranes show different separation properties, demonstrated by their retention behavior under nanofiltration conditions against five relevant draw solutions (NaCl, MgCl2, MgSO4, Na2SO4, and trisodium citrate (TSC)). Subsequently, the relation between PEM properties and FO performance was studied for various draw solutions. PSS/PAH membranes showed the lowest reverse salt flux for MgCl2 and MgSO4, while the PSS/PEI membranes showed the lowest reverse salt flux for Na2SO4 and TSC. Combining the right PEM membrane with the right draw solution is thus key to getting low reverse salt fluxes in FO. Cross-linking of the PEMs resulted in an overall lower salt and water flux; however, the reverse salt flux selectivity was not affected.
... Concentration polarization at a membrane surface.3 Y. Li et al. / Desalination and Water Treatment (2017) 1-10where Sc is the Schmidt number, defined as µ ρD ; a, b, c are constants and vary with the flow regime[26][27][28]; the Sherwood number may change under different flow condi- ...
... Under the FO mode ( Figure 13.3(a)), the diffusion of water dilutes the draw solution in the pores of the support layer. This phenomenon is called as the diluted internal concentration polarization (ICP) that not only sharply declines the effective osmotic pressure difference but also reduce the water flux (Chen et al. 2004;Gray et al. 2006;McCutcheon and Elimelech 2006;Porter 1972). The extent of ICP is closely related to the structure of the support layer, which is usually described by the S parameter . ...
... Under the FO mode ( Figure 13.3(a)), the diffusion of water dilutes the draw solution in the pores of the support layer. This phenomenon is called as the diluted internal concentration polarization (ICP) that not only sharply declines the effective osmotic pressure difference but also reduce the water flux (Chen et al. 2004;Gray et al. 2006;McCutcheon and Elimelech 2006;Porter 1972). The extent of ICP is closely related to the structure of the support layer, which is usually described by the S parameter . ...
... Segundo Magalhães et al (2005), para membranas de nanofiltração, ultrafiltração e microfiltração a permeabilidade é definida pela relação entre o tamanho/forma dos solutos e a distribuição de poros das membranas, sendo assim cada um dos processos se adequa a uma faixa de dimensões. Caso a membrana seja mal selecionada ocorrem problemas operacionais, podendo não haver separação alguma ou então ocorrerem fenômenos que afetam negativamente o fluxo, como incrustação excessiva ou a formação de uma grande camada de polarização (Porter, 1972;Sablani et al., 2001) acima da superfície da membrana. ...
Diante do constante avanço das membranas industriais e tendo em vista que métodos de separação concorrentes se encontram consolidados há mais tempo, sendo muitas vezes o uso de membranas descartado antes mesmo de uma análise prévia, deseja-se criar um protocolo para a avaliação do uso das membranas industriais. Tal protocolo tem como objetivo conduzir o leitor a uma análise do emprego de separação por membranas por etapas apresentadas sequencialmente, visando a simplificação da avaliação, promovendo ganhos econômicos e de tempo. Para a estruturação do protocolo, foi realizada uma ampla revisão bibliográfica, coletando informações necessárias para conduzir o projeto de processos de separação com membranas e então dispondo as informações em sequência, sendo algumas vezes apresentados fluxogramas facilitando a visualização das etapas. Enfim, chega-se ao protocolo que em seis etapas de avalição permite construir a estrutura básica de um processo de separação por membranas candidato à operação desejada.
... CP, caused by rejection of salt ions on the membrane surface, has been 54 widely studied in RO systems [13][14][15]. It is influenced by salt properties, membrane properties, and 55 hydrodynamics [16,17]. It can be an important indicator of flux decline, and is a phenomenon that is 56 related to the occurrence of fouling [18][19][20]. ...
Creating membranes with engineered surface features has been shown to reduce membrane fouling and increase flux. Surface feature patterns can be created by several means, such as thermal embossing with hard stamps, template-based micromolding, and printing. It has been proposed that the patterns create enhanced mixing and irregular fluid flow that increases mass transfer of solutes away from the membrane. The main objective of this paper is to explore whether enhanced mixing and improved mass transfer actually do take place for reverse osmosis (RO) membranes operated in laminar flow conditions typical of full-scale applications. We analyzed velocity, concentration, shear stress, and concentration polarization (CP) profiles for flat, nanopatterned, and micropatterned membranes using computational fluid dynamics. Our methods coupled the calculation of fluid flow with solute mass transport, rather than imposing a flux, as has often been done in other studies. A correlation between Sherwood number and mass-transfer coefficient for flat membranes was utilized to help characterize the hydrodynamic conditions. These results were in good agreement with the numerical simulations, providing support for the modeling results. Models with flat, several line and groove patterns, rectangular and circular pillars, and pyramids were explored. Feature sizes ranged from zero (flat) to 512 μm. The ratio of feature length, between-feature distance, and feature height was 1:1:0.5. Results indicate that patterns greatly affected velocity, shear stress, and concentration profiles. Lower shear stress was observed in the valleys between the pattern features, corresponding to the higher concentration region. Some vortices were generated in the valleys, but these were low-velocity flow features. For all of the patterned membranes CP was between 1% and 64% higher than the corresponding flat membrane. It was found that pattern roughness correlated with boundary layer thickness and thus the patterns with higher roughness caused lower mass transfer of solute away from the surface. Rather than enhancing mixing to redistribute solute, the patterns accumulated solute in valleys and behind surface features. Despite the elevated CP, the nominal permeate flux increased by as much as 40% in patterned membranes due to higher surface area compared to flat membranes. The advantageous results seen in other studies where patterns have helped increase flux may be caused by the additional surface area that patterns provide.
This paper numerically explores the potential of patterned membranes inducing chaotic advection to enhance the efficiency of reverse osmosis (RO) filtration. We compared the filtration performance of four different membrane patterns: flat surface (FS), lateral pattern (LP), herringbone pattern (HP), and staggered herringbone pattern (SHP). The dimensionless pattern depth (dp∗) and the Reynolds number (Re) were chosen as key parameters with influence on the flow and mass transfer characteristics. The numerical scheme was validated by comparing concentration profiles and permeate flux to the experimental data. Poincaré sections were used to represent the dynamical systems in spatially periodic filtration modules. Numerical simulations were conducted for an RO process with an aqueous NaCl solution, varying dp∗ and Re within the ranges of dp∗≤ 0.3 and 100≤ Re≤ 1000. The HP and SHP significantly enhanced filtration performance compared to the FS and LP, regardless of Re. Chaotic advection induced by the HP and SHP effectively suppressed concentration polarization by transporting solutes away from membrane surfaces and uniformly redistributing them back to the feed stream. Furthermore, this study demonstrates that the patterned membranes inducing chaotic advection can enhance the energy efficiency of RO filtration as well.
Background:
Extracorporeal organ assist devices provide lifesaving functions for acutely and chronically ill patients suffering from respiratory and renal failure, but their availability and use is severely limited by an extremely high level of operational complexity. While current hollow fiber-based devices provide high efficiency blood gas transfer and waste removal in ExtraCorporeal Membrane Oxygenation (ECMO) and hemodialysis, respectively, their impact on blood health is often highly deleterious and difficult to control. Further challenges are encountered when integrating multiple organ support functions, as is often required when ECMO and ultrafiltration are combined to deal with fluid overload in critically ill patients, necessitating an unwieldy circuit containing two separate cartridges.
Methods:
We report the first laboratory demonstration of simultaneous blood gas oxygenation and fluid removal in single microfluidic circuit, an achievement enabled by the microchannel-based blood flow configuration of the device. Porcine blood is flowed through a stack of two microfluidic layers, one with a non-porous, gas-permeable silicone membrane separating blood and oxygen chambers, and the other containing a porous dialysis membrane separating blood and filtrate compartments.
Results:
High levels of oxygen transfer are measured across the oxygenator, while tunable rates of fluid removal, governed by the transmembrane pressure, are achieved across the ultrafiltration layer. Key parameters including the blood flow rate, transmembrane pressure and hematocrit are monitored and compared with computationally predicted performance metrics.
Conclusions:
These results represent a model demonstration of a potential future clinical therapy where respiratory support and fluid removal are both realized through a single monolithic cartridge.
In membrane technology for water/wastewater treatment, the concepts of critical flux (JC) and limiting flux (JL) suggest the existence of a threshold flux below which no fouling occurs. However, their important roles on stable flux duration have not been sufficiently understood. This work adopts a collision-attachment approach to clarify the relationship of JC, JL to metastable (i.e., short-term stable) and long-term stable fluxes based on their dependence on initial flux (J0), foulant-clean-membrane energy barrier (Ef-m), and foulant-fouled-membrane energy barrier (Ef-f). When J0 is below JL, water flux remains stable over a long time even for the case of J0 over JC, thanks to the strongly repulsive Ef-f. At J0 > JL and J0 > JC, the water flux is unstable at the beginning of filtration, and the flux ultimately decreases to JL as the long-term stable flux. Under the condition of JL < J0 ≤ JC, an initial metastable flux appears owing to the high Ef-m, with longer metastable period observed at lower J0 and for more hydrophilic/charged membrane or colloids. Nevertheless, rapid flux decline occurs subsequently due to the energy barrier shifting to weak Ef-f, and the water flux eventually degenerates to JL in long-term fouling duration. Our results provide significant guidelines for fouling control strategies with respect to membrane design, feedwater pretreatment, and operational optimization.
Membrane technology is widely used in dairy and food industry. The membrane processes like microfiltration (0.1 to 10 μm); ultrafiltration (0.01 to 0.1 μm); nano‐filtration (nano‐voids or less than 1 nm) & reverse osmosis (0.001 – 0.0001 μm) are generally being used for pre‐treatment, separation, fractionation, purification, recovery, standardization, clarification, concentration, partial or full demineralization, cold pasteurization, etc. which are owing to their property to produce high‐value biological products, low temperature processing, retention & rejection selectivity, economy, and their environment friendly operation in comparison to conventional methods. Additionally, the knowledge of various factors related to the membrane operation and the feed like the nature of feed & foulants, configuration, requirement & material of membrane, density & size of pores, operational conditions like pressure, temperature, velocity & concentration factor, retention & rejection phenomenon, etc. are also the key components for the optimum application and diversification of membrane technology.
In the last decades, consumers have shown great interest in products that provide convenience, diversity, long shelflife, low cost and are produced in an environmentally correct way. Cold plasma technology has been use as an alternative for thermal treatments by the food industry. In this chapter we will cover the principles and methods of plasma generation and the cold plasma applications in food systems. Cold plasma technology can modify food components’ functionality (such as protein and carbohydrates), can be used for decontamination purposes and also seems promising on enzyme inactivation. Also, cold plasma has been used in the sterilization and modification of polymers in food packaging and the in‐package treatment has gained great interest from industries. The biofilm control and treatment of waste, processing surfaces, and effluent is also under investigation. This chapter reviews the mechanisms associated with cold plasma in these applications and discuss future perspectives of its utilization by food industry.
Extensive industrialization, agricultural development, and continued population growth have triggered economic and physical water scarcity. Advanced water treatment and desalination technologies with high ion removal capacity and energy efficiency are highly desirable to mitigate water pollution and shortage. Electrochemical separation techniques have exciting features such as chemical selectivity, versatility, compact size, decreased generation of secondary waste, and broad applicability in ion separation and water purification. Electrodeionization (EDI), which combines the synergistic properties of ion exchange resins (ion exchange, IX) and ion-selective membranes (Electrodialysis, ED), is one such promising electrochemical process. Herein, we briefly introduce the fundamentals of the EDI process, including its configuration, working principle, ion removal mechanism, and critical evaluation metrics for EDI performance. Various advantages and drawbacks of EDI are also discussed, along with scientific strategies to mitigate the bottleneck and improve the process. Furthermore, novel tailored applications are specifically addressed, including heavy metal ion removal, water desalination, and low-level radioactive waste removal. On top of that, the review also compares EDI with other conventional techniques regarding removal efficiency, energy consumption, and resin regeneration. Lastly, the current global market, remaining challenges, and potential research directions are summarized to offer strategies for future development in this promising field.
Membrane defects with low energy-barrier characteristics are unavoidable in membrane fabrication. However, their influences on fouling have not been fully understood. This work systematically investigates the critical role of membrane defects on fouling development and characteristics by adopting a collision attachment-Monte Carlo approach. Simulations show that membrane defects influencing on fouling is highly governed by foulant-clean-membrane interaction (F-M) and foulant-fouled-membrane interaction (F–F). When F–F energy barrier (Ef) is above a critical value (Ec), the long-term stability of water flux is not affected by the presence of defects, thanks to high F–F repulsion preventing further particles deposition. At low Ef (<Ec) but high F-M energy barrier Em (≥Ec), there appears an extended metastable flux for defect-free membrane. Since the local defects serve as hotspots to accelerate fouling, increased coverage or lowered energy barrier of defects shortens or even vanishes metastable period. For both low Ef (<Ec) and Em (<Ec), severe fouling occurs at the beginning of filtration with/without defects as a result of the rapid fouling transition from F-M to F–F. Furthermore, membrane defects have less remarkable influences at higher initial flux where permeate drag plays a primary role. Our simulation provides important implications to membrane design and fouling mitigation.
Membrane technology is a viable alternative to many conventional methods currently used to process traditional Chinese medicine (TCM). However, membrane fouling is a significant obstacle to the application of membrane technology in TCM. In this study, the ultrafiltration (UF) membrane fouling from TCM water extracts under constant transmembrane pressure (TMP) and constant flux operation was studied in connection with critical and threshold flux determinations. Meanwhile, the physicochemical foulant–membrane interactions were analyzed using the extended Derjaguin, Landau, Verwey, and Overbeek (XDLVO) theory. At constant TMP operation, the high pressure resulted in a rapid drop in permeate flux at the start of the filtration period, but the steady-state fluxes did not increase significantly with an increase in TMP. At constant flux operation, the TMP increased somewhat when the permeate flux was below the threshold flux. Fouling was severe above the threshold flux, and the TMP rapidly increased. By displaying fouling resistance as a function of permeate volume, the constant flux operation was compared to a constant TMP operation beginning at the same flux imposed during the constant flux operation. Below the threshold flux, fouling resistance was similar for constant TMP and constant flux operations. However, above the threshold flux, fouling resistance under constant flux operation was much greater than fouling resistance under constant TMP operation. The results of physicochemical interactions showed that there are attractive interactions between hydrophobic membrane and foulants in the TCM water extracts. These interactions should be considered a key factor leading to serious membrane fouling.
The objective of this study was to understand the influence of membrane fouling on the penetration of pharmaceutically active compounds (PhACs) in traditional Chinese medicine (TCM). Four types of TCM PhACs (palmatine, berberine, geniposide, and protocatechuic acid) and three different concentrations of bovine serum albumin (BSA) were formulated into model solutions, to evaluate the researching penetration mechanisms of PhACs under membrane fouling conditions during a cross-flow ultrafiltration (UF) process. The Hermia model was applied to analyze the membrane fouling mechanisms, and quartz crystal microbalance with dissipation (QCM-D) monitoring and molecular dynamics (MD) simulations were used to analyze the intermolecular interactions between BSA and different TCM PhACs. The results confirmed that the presence of PhACs affected the fouling mechanisms. For example, the fouling models of 10.0 g/L BSA solutions changed from cake filtration to complete blocking in the presence of berberine. Under the condition of the membrane fouling, the penetration of PhACs was mainly affected by the intermolecular interactions. The penetrations of the four PhACs studied for all tested BSA solutions were consistent with the intermolecular interaction data obtained using QCM-D and MD simulations. According to the results of the MD simulations, the intermolecular interactions between BSA and palmatine and berberine (-42.99 and -79.16 kJ/mol) were more significant than those between BSA and geniposide and protocatechuic acid (-2.68 and -3.51 kJ/mol), making penetration of the alkaloids (palmatine and berberine) more difficult. The QCM-D results were similar. This study provides a better understanding of PhAC penetration during the UF of TCM solutions.
Micro-nano bubbles (MNBs) play important roles in the reduction of membrane fouling during membrane separation; however, such improvements are always attributed to the reduced concentration polarization on the surface of membranes and little attention has been paid on the variations of physicochemical properties of the feed caused by MNBs. In this study, the separation efficiencies of the feed containing humic acid (HA), bovine serum albumin (BSA), sodium alginate (SA) or dyes can be improved by MNBs during ultrafiltration, and the normalized fluxes can be maximally increased to 139% and 127% in the dead-end and cross-flow modes, respectively in the treatment of HA solution. We further reveal that the decreased apparent viscosity of the feed in the presence of MNBs is the key factor that enhances the normalized flux during ultrafiltration. This study gives new insight on the importance of MNBs in membrane separation and provides valuable clues for other chemical processes.
When billions of people in the world still lack access to clean water, the fact remains that meanwhile more and more pollutants, emerging and old, have been found to contaminate the various water resources. The pressing issue of water scarcity and its pollution urges us to find more effective and affordable techniques to ensure that an efficient water and wastewater treatment system is in place. Electrochemical membrane technology, which integrates the electrochemistry and membrane processes, is thereby developed to meet the increasing requirements of water and wastewater treatment systems and has attracted extensive attention of the research community. This chapter aims to present an overview of the state-of-the-art electrochemical membrane technologies, mainly the ion exchange membrane- and conductive membrane-based electrochemical membrane technologies. Firstly, definitions, classifications, working principles of each technology, and the preparation methods of the employed membranes are introduced. Afterwards, the historical development of each technology as well as their primary applications in water and wastewater treatment are presented, while their advantages and disadvantages are also discussed. Finally, based on the recent advances, the challenges of and the perspectives to the future development of electrochemical membrane technologies are presented.
Global water scarcity is exacerbating owing to climate change and pollution, making the demand for clean water more challenging with the growth of the global economy and population. Membrane filtration technologies have been widely applied in drinking water purification due to their energy efficiency while facing challenges like fouling, degradation and trade-offs, such as selectivity and permeability. The sustainable development of our society demands further understanding and improvement of those membranes. In this review, the basic structures of polymer-based water purification membranes including the effective layer for separation, the support layer and the possible top protective layer are presented. Details include the conventional membranes for microfiltration (MF) and ultrafiltration (UF), the effective layers for separation in thin-film composite (TFC) membranes, electrospun nanofibrous membranes for MF, UF, and membrane distillation (MD), as well as the emerging self-assembled block copolymer membranes. Furthermore, the conventional support layers and electrospun nanofibrous support layers for reverse osmosis (RO) and forward osmosis (FO) processes, and the top protective layers are discussed. The materials, membrane structures and properties, modification strategies, possible interlayers, interconnects, interpenetration, and interactions between different layers are discussed, with the emphasis on the cost-effectiveness of various membranes.
Nanofiltration (NF) is an environmental-friendly and energetic-efficient technique for small molecule or ion separations compared to traditional energy-intensive separation processes. However, during the journey to discovering advanced NF membrane materials using a typical dead-end device, there is an obvious discrepancy on testing methodologies/protocols of NF membranes reported in contemporary literatures, which actually results in the significant data-reliability issues. This critical issue made the evaluation of various nanofiltration membranes so confusing and misleading because of the unfair comparison on NF performance. Therefore, it is urgent to guide the membrane society on the real factors affecting the data accuracy and standardize the protocol for nanofiltration test to develop advanced NF membrane materials. In this study, we have carried out a series of designed experiments to unify the standardized separation rate indicators of nanofiltration membranes by comparing flux, permeance, and permeability. The effects of external factors on separation efficiency (rejection) of NF membranes were investigated in detail, which is also analysed and discussed on the basic theory. The dead volume, rotor, and adsorption are proven to be the pivotal indicators for achieving accurate separation efficiency, which offers insight for reliable testing of nanofiltration membranes. Therefore, a protocol was proposed for evaluating accurate separation performance of nanofiltration membranes to obtain the reliable data, which benefits for fair performance comparison to advance NF membrane materials and makes the researchers to better understand the current confusing data reported in the literatures.
Graphical abstract
The accurate testing protocols of NF membranes were clarified, which is important for the development of advanced nanofiltration materials.
The main aim of this paper is to investigate the ability of hollow fiber ultrafiltration membrane of MWCO of 5 KD made of polysulfone to remove reactive dyes from wastewater. Two reactive dyes, violet 5R and C.I red 222.1, were studied under different experimental conditions of flow rate, temperature, concentration, pH, and transmembrane pressure to determine the best conditions under which the highest percentage of dye removal can be achieved. Binary systems of the two dyes prepared in different ratios to study the ability of membrane to treat solutions containing dye mixtures. It was showed that 91% of violet dye removal and 88% of red dye removal were achieved when both dyes were treated individually. Flow rate and pH proved to have great effects on membrane performance in the case of violet dye whereas solution pH showed the greatest effect for red dye removal. For the binary systems, it was found that interactions between dyes are not significant. Solutions with properties similar to that of the effluents from textile industry were prepared and 6% of violet dye removal as well as 20%-80% of red dye removal were achieved. Resistance In Series model was applied to find the flux theoretically which showed agreement with experimental values
with a variable error ranging from 2-21%.
Cross-flow filtration mode can greatly alleviate the membrane fouling due to the presence of shear stress. In this paper, a new flux prediction model for steady cross-flow microfiltration has been established by considering the effect of shear stress as function of the geometry of filtration module and the suspension properties in the particle mass balance. The results showed that this model possessed higher accuracy in both laminar and turbulent flow regime (relative error σ = 4.43%/1.91%) than Glen Bolton’s model (σ = 11.88%/6.42%) and Makardij’s model (σ = 9.44%/12.92%). Meanwhile, the validity of the proposed model was approved by using other suspensions (yeast suspension and activated sludge suspension) (σ<3.43%) and other membranes (PVDF and PES microfiltration membrane) (σ<4.63%). Moreover, new criterion relationships between Sherwood number (Sh), Reynolds number (Re) and Schmidt number (Sc) in both laminar and turbulent flow regime were also established.
Colloidal size affects the whole process of particle transport and membrane filtration. However, its compound effect on fouling remains controversial. In the present study, we adopt a collision-attachment approach to systematically investigate the role of colloidal size on fouling. Our study highlights the critical importance of four competing mechanisms: reduced specific cake resistance and enhanced foulant-membrane interaction of larger particles tend to mitigate flux decline, while the simultaneously increased hydrodynamic drag and reduced particle back-transport tend to promote fouling. The net effect of particle size on fouling is governed by the competition among these mechanisms. When strong foulant-membrane repulsion prevails, we show enhanced flux stability for larger particles as a result of a greatly increased energy barrier to resist particle deposition. Nevertheless, this trend could be reversed for weak foulant-membrane interaction. Our study reconciles the contradictory experimental observations of the effect of particle size on colloidal fouling and provide important insights for effective fouling mitigation.
A sustainable and cost-effective supply of contamination-free, clean, safe, and enough water is one of the major needs of living things. This is one of the most challenging issues facing the world. Several practices have been developed for treatment of wastewater, such as reverse osmosis, nanofiltration, ultrafiltration, and microfiltration. All of these techniques have been based on a membrane separation system. The application of membrane systems for waste water treatment is inexpensive and extensively applied technologies for water purification. These polymeric membranes are mainly made up of cellulose acetate, cellulose nitrate, polysulfone, polyvinylidenefluoride, and thin-film composite. The basic principle of separation is based on adsorption, pore size, molecule size, and surface hydrophilicity or hydrophobicity of a membrane. The developed membrane system have been used for removal of pathogens, colloidal materials, and salt from sea water to obtain drinkable water and also used for water recovery from industrial effluents and product recovery. All of these applications are important for pollution control in the chemical, electronic, food, and biotechnology industries to avoid harmful effects on the environment as well as human health.
Radioactive wastes from nuclear fuel processing are stored in large underground storage tanks at the Hanford Nuclear Reservation. Treatment and remediation require that waste feed from the storage tanks be delivered to the Hanford Tank Waste Treatment and Immobilization Plant continually for the duration of the treatment mission. The complex physical and chemical processes required for this mission, the significant scale, and the hazardous nature of the waste necessitate the use of simulants in process testing. A new class of simulants, “performance-based simulants,” has been developed to match the process performance of the simulant to actual waste performance data.
Though electrodialysis (ED) and reverse osmosis (RO) are both mature, proven technologies for brackish water desalination, RO is currently utilized to desalinate over an order of magnitude more brackish water than ED. This large discrepancy in the adoption of each technology has yet to be thoroughly justified in the literature, particularly from the perspective of energy consumption. Hence, in this study, we performed a direct and systematic comparison of the energy consumption of RO and ED for brackish water desalination, precisely mapping out the ideal operational space of each technology for the first time. Using rigorous system-scale models for RO and ED, we determine the specific energy consumption and energy efficiency of each process over a wide range of brackish water conditions. Specifically, we investigate the effects of varying feed salinity, extent of salt removal, water recovery, and productivity to ultimately identify the operational sweet spots of each technology. By maintaining the same separation parameters (i.e., feed salinity, salt removal, water recovery) and productivity between RO and ED throughout the study, we ensure that our comparison of the technologies is valid and fair. Our results indicate that both RO and ED are capable of operating with high energy efficiency (>30%) for brackish water desalination, though for differing conditions. Particularly, we show that whereas ED excels for low feed salinities (<3 g L–1) and extents of salt removal, RO operates optimally for high salinity feeds (>5 g L–1), which require more extensive desalination. Through our in-depth energetic analysis, we provide guidance for future applications of RO and ED, emphasizing that increased implementation of ED will require significant reduction in the cost of ion-exchange membranes.
A coupled XDLVO-collision attachment (CA) model is proposed to quantitatively evaluate the critical roles of zeta potential ζ and contact angle θ of foulant on colloidal fouling. In this model, the XDLVO theory is applied to relate ζ and θ to foulant-membrane interaction energy barrier (ΔEb). The latter is further bridged to membrane fouling rate (dmf/dt) by the CA theory, recognizing fouling as foulant colliding with a membrane surface followed by its attachment. XDLVO-CA model predictions agree well with the experimental water flux declines under various solution pHs. Modelling results show that severe fouling occurs at low ζ², and increasing ζ² can substantially lower dmf/dt as a result of the increased ΔEb. Interestingly, a negative linear relationship is observed between ζ² and logarithm of dmf/dt at high ζ². For the role of contact angle for water, glycerol and diiodomethane, there exists a critical θ, below (or above) which little fouling occurs owing to the dramatically increased ΔEb and thus decreased dmf/dt by orders of magnitude. Furthermore, the threshold θ corresponds to the acid-base interaction energy transiting from attraction to repulsion. Our modelling results reveal the importance of optimally tailoring foulant ζ and θ for fouling control.
The initial behavior of colloidal fouling is governed by foulant-clean-membrane interaction (F-M), and its long-term behavior is determined by foulant-fouled-membrane interaction (F-F). Nevertheless, the transitional fouling behavior from F-M to F-F has not been fully understood. This study reports a novel collision attachment (CA)-Monte Carlo (MC) approach, with the stochastic colloid-membrane collision events modelled by MC and the probability of colloidal attachment to the membrane determined by the interplay of flux and the energy barrier arising colloid-membrane interaction (Em for F-M and Ef for F-F). The long-term membrane flux remains stable for large Ef, whereas severe fouling occurs when both Em and Ef are small. Our study reveals the existence of a metastable flux behavior for the combination of large Em but small Ef. The time evolution of flux behavior and colloidal deposition pattern shows a nearly constant flux for an extended period, with the high energy barrier Em retarding initial colloidal deposition. However, accidental random deposition of a colloidal particle could reduce the local energy barrier (towards the smaller Ef), seeding for further colloidal deposition in its vicinity. This initiates an uneven patch-wise fouling and eventually leading to a complete transition to F-F dominated behavior. The metastable period can be effectively extended by increasing the energy barrier (Em or Ef) or lowering flux, which provides important implications to membrane design and operation.
In this work, a modelling research on the separation of ammonia gas from liquid streams via vacuum membrane distillation (VMD) is conducted. An experimentally validated multi-component simulation model of a flat sheet VMD module is developed by implementing heat and mass balances through the feed, membrane and permeate channels. Continuous removal of the gases transferred through the membrane at a constant pressure in the permeate channel is assumed. The transport mechanisms through the pores under VMD conditions for both volatiles are discussed. Under studied VMD conditions and the typical concentration range in waste waters (i.e. 1-10 g TAN l⁻¹), it is observed that none of the two volatile components (ammonia and water) is preferentially transported. The resulting VMD performance is simulated and evaluated in terms of total transmembrane flux, ammonia flux, ammonia selectivity and thermal energy consumption. The model was validated experimentally and showed good agreement, with an average relative error <10%. The experiments were performed with a solution of (NH4)2SO4 in a laboratory set up under controlled conditions. The simulation, as well as the experimental results, emphasize the existing trade-off between the flux (JNH3) and selectivity (SNH3) of ammonia. Increasing feed temperature and decreasing vacuum pressure results in higher JNH3 but lower SNH3. Moreover, those parameters that enhance the heat transfer through the membrane (i.e. feed temperature, pore size, porosity, vacuum pressure, etc.) promote the water flux over ammonia. While those parameters that enhance mixing and the ammonia mass transfer in the feed (i.e. feed velocity, spacer geometry, pH, ammonia feed concentration, etc.) promote the ammonia flux over water. The only operating parameter which enhances simultaneously the JNH3 and SNH3 is the feed velocity, indicating that the spacer geometry can play an important role in designing VMD modules for ammonia separation. VMD can extract and concentrate ammonia on the permeate side at a low specific thermal energy consumption. However, the JNH3 is greatly limited by the feed ammonia concentration which will ultimately determine the cost-effectiveness of the recovery. The trends described by the model are in agreement with other authors’ observations and give insight into the mechanisms dominating ammonia separation via VMD and its performance limits.
This study designed and tested a novel type of solar-energy-integrated vacuum membrane distillation (VMD) system for seawater desalination under actual environmental conditions in Wuhan, China. The system consists of eight parts: a seawater tank, solar collector, solar cooker, inclined VMD evaporator, circulating water vacuum pump, heat exchanger, fresh water tank, and brine tank. Natural seawater was used as feed and a hydrophobic hollow-fiber membrane module was used to improve seawater desalination. The experiment was conducted during a typical summer day. Results showed that when the highest ambient temperature was 33 °C, the maximum value of the average solar intensity was 1,080 W/m 2 . The system was able to generate 36 kg (per m 2 membrane module) distilled fresh water during 1 day (8:00 am until 6:00 pm), the retention rate was between 99.67 and 99.987%, and electrical conductivity was between 0.00276 and 0.0673 ms/cm. The average salt rejection was over 90%. The proposed VMD system shows favorable potential application in desalination of brackish waters or high-salt wastewater treatment, as well.
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Segré and Silberberg1 recently observed that when an initially uniform dilute suspension of rigid spheres passes through a circular tube in laminar flow, the spheres tend to concentrate into an annular region about half-way between the tube centre and tube wall. It was suggested that the inward motion of the spheres resulted from a force, akin to the Magnus effect, which was present because the spheres rotated as they passed through the tube. Work by Tollert2, Saffmann3 and Rubinow and Keller4 has also indicated the presence of an inward force of the above type, while the ‘minimum energy dissipation’ theory of Jeffery5 shows that the spheres should move inwards and eventually travel along the tube axis. Unfortunately no satisfactory explanation has been given of the fact that, in the above experiment1, the inner spheres moved outwards while the outer spheres ceased to move inwards when they reached the region of the annulus.
The flow about a spinning sphere moving in a viscous fluid is calculated for small values of the Reynolds number. With this solution the force and torque on the sphere are computed. It is found that in addition to the drag force determined by Stokes, the sphere experiences a force F L orthogonal to its direction of motion. This force is given by [formula omitted]. Here a is the radius of the sphere, Ω is its angular velocity, V is its velocity, ρ is the fluid density and R is the Reynolds number, [formula omitted]. For small values of R, the transverse force is independent of the viscosity μ. This force is in such a direction as to account for the curving of a pitched baseball, the long range of a spinning golf ball, etc. It is used as a basis for the discussion of the flow of a suspension of spheres through a tube. The calculation involves the Stokes and Oseen expansions. A representation of solutions of the Oseen equations in terms of two scalar functions is also presented.
It is shown that a rigid sphere transported along in Poiseuille flow through a tube is subject to radial forces which tend to carry it to a certain equilibrium position at about 0.6 tube radii from the axis, irrespective of the radial position at which the sphere first entered the tube. It is further shown that the trajectories of the particles are portions of one master trajectory and that the origin of the forces causing the radial displacements is in the inertia of the moving fluid. An analysis of the parameters determining the behaviour is presented and a phenomenological description valid at low Reynolds numbers is arrived at in terms of appropriate reduced variables. These phenomena have already been described in a preliminary note (Segré & Silberberg 1961). The present more complete analysis confirms the conclusions, but it appears that the dependence of the effects on the particle radius go with the third and not the fourth power as was then reported.
It is also shown that the description of the phenomena becomes more complicated at tube Reynolds numbers above about 30.
Small spheroidal particles suspended in a sheared viscous liquid are sometimes observed to take up slowly preferred orientations, relative to the motion of the undisturbed liquid, which are independent of the initial conditions of release. These obsevations cannot be accounted for by the solution, obtained by Jeffery (1922), of the linearized Navier-Stokes equations. It is shown in this paper that the effect of the inertia of the liquid is to alter slowly the orbit of the particle in accordance with Jeffery's hypothesis that the particle ultimately moves in such a way that the dissipation of energy is a minimum, but that this effect is orders of magnitude too small to account for any of the experimental observations.
It is suggested that non-Newtonian properties of the liquid account for the observations. It is shown that the rate of orientation of a particle would then be independent of its size, and this prediction is verified experimentally. Other experimental evidence in support of this suggestion is also described.
Some remarks are also made about the possible effect of collisions between the particles when more than one particle is present.
The mechanism of macromolecular ultraflltration with microporous membranes is discussed, focusing on factors that control membrane flux and solute retention. Flux is limited by mass transfer conditions on the feed solution side of the membrane (concentration polarization). Solute retention is determined by geometric properties of the membrane pores and the macromolecules in solution, as well as concentration polarization. Ultraflltration data for solutions of Dextran fractions and a Carbowax fraction are presented and compared with theory. Agreement for turbulent flow, laminar flow, and stirred cell ultrafiltration systems is good.
Ultracentrifugal studies on polystyrene latex particles (PSL) in solutions of different densities prepared either from mixtures of H2O and D2O or from various concentrations of sucrose in water yielded a value, by interpolation, of 1.0520 for the density of solution in which the particles neither sediment nor float. Considerations of these results plus the nature of the particles lead to the conclusion that the partial specific volume of the polystyrene latex particles is (1/1.0520) cc./g., a value in agreement with the bulk specific volume of solid polystyrene. Evidence is presented for PSL to support the view that the effective hydrodynamic volume is equal to the partial specific volume, so that volume fractions can be determined from the partial specific volume and the dry weight concentration. Measurements of the viscosity of suspensions of polystyrene latex particles over a broad concentration range showed that the intrinsic viscosity was 2.5, in confirmation of the theory of Einstein. At concentrations above 2% by volume a square term in concentration, with coefficient about 10, and also a cubic term are needed to satisfy the data. From the partial specific volume of the latex particles and the value of the sedimentation coefficient extrapolated to infinite dilution, a value of 2640 ± 12 A. was calculated for the diameter of the particles from Stokes' law. This value is in excellent agreement with values obtained by electron microscopy, light scattering, and low angle x-ray scattering. This agreement amounts to a satisfactory test of Stokes' law for particles not much larger than some of the viruses. Studies of the dependence of sedimentation coefficient on concentration indicate that existing theories are not completely satisfactory and that the influence of backward flow of liquid during the sedimentation of the solute particles is appreciable.
Ultrafiltration has been used with increasing frequency in recent years in biological laboratories for concentration, separation or purification of biological material. No data have been available on the comparison of the characteristics of Ultrafiltration systems currently in use. This study compares the filtration characteristics of four systems using commercially available membranes on suspensions and solutions: suspension of protein micelles (casein), cell debris (E. coli) and catalase solution. None of the four systems considered is found to be generally superior for all the suspensions and solutions. Vibration systems were most effective when relatively large particles were involved, while laminar flow recycling systems with high wall shear rates were best for dilute suspensions and proteins in solution. It was found that shearing inactivates enzymes in both recycle and vibration systems. It was also observed that vibration actually reduces flux in dilute solutions.