Microfiltration Of Suspensions Research Articles

Modeling of fouling in cross‐flow microfiltration of suspensions

Cross‐flow filtration of fine suspensions through microsieves occurs in microprocessing. The interaction of particles with surfaces in microenvironments has been extensively studied, but predominantly in monolayers and not with an eye to microfiltration. Here, we introduce a microfiltration model that pertains to particles that might be seen as fine in a macroscopic environment, but are large enough to intrude significantly into the shear layer of a microchannel. Thus, particle accumulation upon the sieve couples the steady‐state filtrate flux and the suspension flow through the microchannel that feeds the sieve. We envision and create a stable, stationary multilayer of particles whose thickness is shear‐limited and we identify and verify the structure and parameters that limit steady filtration in this environment. At first, a packed bed of particles forms, growing into and regulated by the micro channel's shear flow. A critical shear stress is shown to determine the thickness of the bed, seen as a stationary and stable multilayer of particles through which filtration may occur. As the bed thickens, at the expense of channel area for suspension flow, surface shear stress increases until no further particle adherence is possible. We built a simple example using hard noninteracting polymer microspheres and conducted cross‐flow filtration experiments over Aquamarijn™ microsieves (uniform pore size of 0.8 μm). We observed a steady cake‐layer thickness and because of the simple geometry afforded by uniform spheres, we could approximate the force balance, cake resistance, and filtration rate from first principles. The good fit of our data to the proposed mechanism lays a firm basis for the semiquantitative analysis of the behavior of more complex suspensions. © 2018 American Institute of Chemical Engineers AIChE J, 65: 207–213, 2019

Mitigation of particle deposition onto membrane surface in cross-flow microfiltration under high flow rate

Abstract We investigated the effects of flow rate, particle diameter and initial flux on fouling mitigation in cross-flow microfiltration of suspensions containing silica and PMMA particles. Regardless of the difference in PMMA and silica, the fouling mitigation was more effective at a larger flow rate and larger particle diameter, due to sufficient hydrodynamic lift force. Lower initial flux was also shown to be better for the mitigation of fouling. Fouling was completely prevented when cross-flow filtration of particles with 1.5 μm of diameter was carried out under a flow rate of 30 L min −1 and 4.0 × 10 −5 m 3 m −2 s −1 of initial flux. We also demonstrated that classification of bi-dispersed particles using membranes could be achieved by the cross-flow microfiltration, where fouling by larger particles than the pore size was completely prevented because of the sufficient hydrodynamic lift force and only the smaller particles permeated through the membrane. This classification remained stable for 3 h while maintaining the flux and permeation of the smaller particles.

Removal of heavy metals from waste water using a hybrid membrane process

Soil and water pollution by heavy metals is currently a very important problem in environmental and other sectors. The origin of metals in water may be of either natural character (erosion of rocks and sediments, leaching of mineral resources) or anthropogenic character (mining and extraction of metals, industry, agriculture, etc.) (Martins et al. 2010). Many heavy metals, such as Pb, Cd, Cu, Zn, etc., are the most polluting factors in industrial wastewater and may get into the ground water. Subsequently they are bio-accumulated in living organisms and cause various diseases and disorders (Jamil et al. 2010). These problems need to be responded by developing new and more efficient methods for wastewater treatment (Martins et al. 2010). In practice several methods are used for removal of heavy metals from water. One of the promising methods for the removal of metal ions from water is a hybrid membrane processes. This method includes two processes – adsorption of metal ions on the natural zeolite and microfiltration of zeolite suspension through ceramic membrane. Experiments were carried out using model solutions containing Cu 2+ ions (from CuSO 4 .5H 2 O and Cu(NO 3 ) 2 .3H 2 O) and Zn 2+ ions (from ZnSO 4 .7H 2 O and Zn(NO 3 ) 2 .6H 2 O). In the experiments zeolite from Nižný Hrabovec localization (Zeocem JSC Bystre), Slovakia was used. Zeolite is mainly composed of mineral clinoptilolite (84%), other mineral are cristobalite (8%), clay (4%) and plagioclase (3-4%). Its structure is formed by three-dimensional network. Clinoptilolite is composed from silicate tetrahedron (SiO 4 ) 4- bound together by oxygen atoms, where part of the Si atoms is replaced with aluminum (AlO 4 ) 5- . This creates space structures with a number of cavities and channels, in which are accommodate metal cations and water molecules. The total volume of cavities is 24 to 32%. Zeolite has a bulk density of 1600 to 1800 kg.m -3 , a specific gravity of 2200 to 2440 kg.m -3 and the specific surface of 30 to 60 m 2 .g -1 ( www.zeocem.com ). Adsorption experiments on model solutions were performed with the zeolite with particle size 20 microns. Before and after the experiments the concentrations of Cu and Zn were determined by atomic absorption spectrophotometry (AAS) using iCE 3300 AA Spectrometer Thermo Scientific. Solutions with concentrations of 10 to 5000 mg.l -1 were prepared from each of the chemicals. The solutions were shaken with 1 g of zeolite in 100 ml PET flasks on a shaker for 2.5 hours at 25°C and 220 rpm. The amounts of metals (Cu or Zn) in solutions were measured after stabilization, filtration and required dilution by AAS. The equilibrium between the concentration in solution and the adsorbed substance was evaluated using Langmuir, Freundlich and Redlich-Peterson models. According to the results of the adsorption experiments zeolite adsorbed of both the nitrates ions (Cu 2+ and Zn 2+ ) (equilibrium concentrations 1.48 mg.g -1 and 1.49 mg.g -1 , respectively) best and the sulfate ions (0.34 mg.g -1 and 0.85 mg.g -1 , respectively) less. Due to better adsorption capacities of zeolite for ions derived from nitrates, further experiments were made from chemicals Cu(NO 3 ) 2 .3H 2 O and Zn(NO 3 ) 2 .6H 2 O. The next step was microfiltration of suspension of zeolite since a hybrid process for removal of Cu and Zn ions was used. Microfiltration was carried out at a constant pressure of 50 kPa, the flow rate of suspension 2.2 m.s -1 and various concentrations of zeolite (1 g.l -1 to 6 g.l -1 ). Tubular Membralox ceramic membrane was used, with length of 25 cm, internal diameter of 0.5 cm, external diameter of 0.7 cm and porosity of 50 nm. Active surface of the membrane was 49.48 cm 2 . Zeolite was added to the solution of ions circulating in the cross-flow microfiltration system. Metal ions were adsorbed by zeolite and the suspension was filtered by the membrane. The adsorbed metal remained circulating in the system and the permeat was purified water. Using this method, at suitable selection of the experimental conditions, up to 90 to 100% of metal ions can be removed from the solution.

Influence of Transmembrane Pressure on Microfiltration of Suspensions

The influence of transmembrane pressure on the permeate flux, and the critical and limiting fluxes in microfiltration of two sorbents Bentonite a natural sorbent, montmorillonite based clay and Lewatit S1468 a synthetic sorbent, styrene-divinylbenzene based copolymer were studied. An asymmetric single-channel inorganic ceramic membrane based on α-Al2O3 was used. The experimental data were obtained by continuous microfiltration equipment. According to the results the limiting flux ranged from 37 to 70 l.m-2.h-1 for Bentonite suspensions. It was not possible to estimate the limiting flux for Lewatit S1468 suspension.

Influence of Inner Configuration of Membrane on Microfiltration of Suspensions

The influence of membrane type on the permeate flux in microfiltration of two sorbents Bentonite a natural sorbent, montmorillonite based clay and Lewatit S1468 a synthetic sorbent, styrene-divinylbenzene based copolymer was studied. Two types of membranes, single-and multi-channel, both asymmetric inorganic ceramic membranes based on α-Al2O3, were used. The experimental data were obtained by continuous microfiltration equipment. According to the results use of multi-channel membrane has more advantages higher permeate flux, lower energy consumption, and lower flow rate than disadvantages longer time period to reach the steady state and higher pressure loss.

Microfiltration of suspensions of microparticulate boron adsorbent through a ceramic membrane

Suspensions of a microparticulate boron adsorbent Dowex XUS can be effectively concentrated by microfiltration (MF) to relatively high concentrations of about 24 mass% of dry adsorbent. This is important for formation of a hybrid process combining adsorption or ion-exchange and MF. A tubular ceramic membrane with the mean pore size of 0.1 μm and the ground boron adsorbent with the mean particle size of 4.7 mm have been used. Analysis of the flux decline data revealed that the dominant membrane fouling mechanism is cake formation. A more detail analysis showed that a pore blocking by initial layer of deposit is dominant at the beginning of MF and the resistance of growing cake becomes more important with increasing filtration time. With the increasing suspension velocity, the permeate flux significantly increases. The velocity of suspension above 2m s −1 should be used to achieve a reasonable flux. The limiting flux was reached at a pressure difference of about 60 kPa at higher suspension concentrations. The critical permeate flux was achieved at pressure difference below about 40 kPa. Even at concentrations as high as 20 mass% of dry adsorbent in the suspension, the permeate flux of about 43 dm −3m −2 h −1 was achieved.

Production of a Highly Concentrated CaCO3 Suspension by Cross‐Flow Microfiltration in the Presence of a Dispersant

This article presents the study of the cross‐flow microfiltration of an aqueous calcium carbonate suspension in the presence of dispersant in order to obtain the highly concentrated retentate. In the absence of a dispersant, the cross‐flow microfiltration with cylindrical ceramic membrane permitted to increase the CaCO3 suspension concentration from 27 to 36.5%. The retentate concentration is increased markedly in the presence of the dispersant (up to 70%). In the presence of the dispersant, the productivity of cross‐flow microfiltration of CaCO3 suspension is almost 30% higher than the productivity of dead‐end microfiltration of this suspension at the same pressure of 1 bar. However, the permeate contamination by the dispersant could not be avoided and a subsequent separation must be provided to purify the permeate.

Microfiltration of suspensions of microparticulate ion exchanger through ceramic membrane

Removal of xenobiotics present at low concentrations in water and wastewater is frequent and sometimes not an easy task, which can be solved in many cases by application of adsorption techniques. Application of microparticulate suspensions of adsorbents can be an effective way of intensification of the adsorption process [1]. The aim of this work was to study microfiltration (MF) characteristics of microparticulate ion exchanger suspensions in NaCl aqueous solution to gain data for the design of a hybrid adsorption–microfiltration process.

セラミック精密ろ過膜によるサブミクロン粒子の捕捉性能の評価

In order to establish a method for evaluating the particle retention performance of a ceramic membrane, microfiltration of suspensions of submicron polystyrene latex is performed, and the time changes in filtration rate, the particle rejection and the particle retention rate are evaluated. The rejection at the filtrate volume of 100cm per unit membrane area, R100, is plotted against the ratio of particle diameter to pore diameter, dp/dm, for various membranes and particles. The plots clearly demonstrate that the transition to almost complete particle rejection from partial particle transmission through the membrane occurs at dp/dm of about 0.1. Furthermore, the filtrate volume at which the rejection reaches 0.9, v0.9, is found to be one of the criteria for the evaluation of particle retention performance. This paper also proposes a method to evaluate the properties of filter cake formed on the membrane.

Influence of adsorbent particles on a dynamic protein membrane in cross flow filtration

In industry, when operations of separation, concentration, purification or sterilisation are necessary, membrane processes can be applied. In the food industry, a tangential process is used in many sectors (milk, gelatine, vinegar, juice, wine, etc.). Other fields are also concerned with these processes among which are the control of suspension concentration before evaporation or drying stages, recycling of fluids (used water), treatment of fluids for the recovery of particle products (pigments). This work is a study of tangential microfiltration of suspensions in protein solutions on the one hand and the solid/liquid adsorption phenomenon, on the other hand. A porous mineral membrane with a 0.2 μm diameter was used, and a protein solution (β-lacto globulin, 10 mg/l concentration) with an active coal suspension ofvariable concentration. The microfiltration ofpure products (ultrapure water, activated coal, protein) has led to a better understanding of the role of each component in the process of separation. The adsorption of proteins with an active coal powder was studied afterwards in a microfiltration loop in an agitated cell. Experiments of the influence of the hydrodynamic parameters (transmembrane pressures, tangential speed) and composition ofthe suspension and/or solution (concentration) were necessary to detennine the performances and the effectiveness of the operation. Globally, the results obtained show the importance of the ionic force in the fluid and the existence of strong interactions between membrane and solvent on the one hand, and membrane and protein on the other hand. The application of models for the formation of the filling phenomenon opposed to the transfer of material and isotherm adsorption are proposed. The conformity of the test results with classical law (tangential filtration) predictions confirm the validity of the models and the established experimental protocol.

The Effect of Large Particles on Microfiltration of Small Particles

The effects of the presence of large latex (1 μm) particles on the microfiltration of small gold (50 nm) colloidal suspensions have been investigated using hydrophobic 0.22 μm polyvinylidene fluoride (GVHP) micro-filtration (MF) membranes. Gold sol was filtered through the membrane with or without prefiltration of latex suspension. The characteristics of the cake formed on the membrane surface depends not only on the intrinsic properties of the particles in the feed but also depends on the nature of the mixture. The type of cake formation (e.g. a cake of small particles on the top of large particles or a cake of mixed particles) affects the cake properties due to the combination effect. This can be explained by the type of filling of the voidage between large particles with small particles. Various combinations of these particles result in cakes with different resistances. The understanding of the combination effect and the type of cake formation has a potential application for fouling minimization.Fouling is surprisingly serious in microfiltration of the feeds containing mixed particles. Separation of large particles prior to the microfiltration of suspension of small particles can reduce cake resistance and minimize fouling.

Characteristics of microfiltration of suspensions

Characteristics of microfiltration of suspensions

Characteristics of microfiltration of suspensions with inter-fiber two-phase flow

Injecting air into hollow fibers and tubular membranes has been proved to be effective in order to control flux decline caused by concentration polarization and particle deposition. This paper presents a study of the characteristics of filtration with inter-fiber two-phase flow. The enhancement of flux by bubbling, the effect of the total superficial velocity and gas and liquid velocities, the effect of fiber spacing and orientation, and the concept of critical flux were investigated. A specially designed crossflow hollow fiber cell connected to a light microscope and video-camera system has been used to monitor particle deposition on the fibers. The results showed that injecting air could enhance the permeate flux and control the deposition of particles on the membrane fibers. Changes in the hydrodynamics of two-phase flow considerably affected the filtration resistance caused by reversible fouling but was ineffective for the resistance caused by irreversible fouling. The extent of deposition was mainly controlled by the flux level in the range of wall shear rates examined. A critical flux of about 10 dm3 m−2 h−1 was identified through direct observation of particle deposition on fibers. This value correlated with the flux at which the irreversible fouling became negligible. These results should be significant for optimizing the operation of submerged membrane bioreactor wastewater systems in which bubbling is used as a hydrodynamic technique to improve the performance of the membrane process. © 2000 Society of Chemical Industry

Prediction of deposit depth and transmembrane pressure during crossflow microfiltration

Most crossflow microfiltrations of suspensions of significant solids volume concentration exhibit non-Newtonian flow behaviour, and may lead to the deposition of appreciable cake depths. The cake depth may even extend to the full filter tube diameter, thus blocking any further filtration. Crossflow filtration modelling also requires knowledge of the cake depth, and the transmembrane pressure. Experiments have been performed for both the crossflow microfiltration of non-Newtonian talc suspensions, and an investigation of the pressures and flow rates in impermeable tubes of diameters similar to the crossflow filters. The investigation also illustrates how the transmembrane pressure drop can be corrected to take account of differences in cross-sectional area between where the pressure measurements are recorded and the filter flow channel. A method is demonstrated for the estimation of the depth of deposit on a fouled filter tube from pressure and flow measurements, when combined with a knowledge of the suspension rheology. The pseudo-equilibrium steady-state flux has been shown to correlate with shear stress at the filter or deposit surface, after the above corrections have been performed.

Particle transport in crossflow microfiltration – II. Effects of particle–particle interactions

A model previously developed for the calculation of limiting fluxes for crossflow microfiltration of non–interacting particles was extended to include the effect of physico-chemical particle–particle interactions. It was shown theoretically that the effect of particle–particle interactions on the microfiltration flux can be described by a diffusion-type equation with an effective interactioninduced diffusion coefficient. The microfiltration flux for a general situation, where particle transport is caused by convection, Brownian diffusion, shear-induced diffusion, and particle–particle interactions, was then calculated by adding the diffusion coefficients, and solving the governing convective-diffusion equation numerically. Results of these calculations agreed very well with experimental fluxes measured during crossflow microfiltration of model silica particle suspensions. The influence of wall shear stress, membrane length, particle size, and particle concentration on permeate flux was very well predicted. However, the effect of particle surface potential was quantitatively underpredicted. Shear-induced diffusion seems to be the main transport mechanism governing the flux in the microfiltration of suspensions of micron-sized particles, but charge effects can increase fluxes considerably.

Pressure effects in cross-flow microfiltration of suspensions of whole bacterial cells

The effect of Trans-Membrane Pressure (TMP) on permeate flux during cross-flow microfiltration of bacterial cell suspensions in tubular ceramic membranes is studied experimentally. Continuous filtration experiments with suspensions of whole bacterial cells (Mycobacterium M156) show a dramatic permeate flux decline with increasing TMP. During the very early stages of the filtration process, a linear relationship between permeate flux and TMP is observed, suggesting an initial surface sorption of cells on the membrane surface. At longer times, the permeate flux vs. TMP data exhibit a critical pressure beyond which the permeate flux declines with increasing trans-membrane pressure. This is interpreted in terms of the formation of a compressible cake, whose permeability can be described through the Carman-Kozeny equation.

Cross-flow microfiltration of kaolinite-in-water dispersions

The convective model of cross-flow microfiltration of suspensions with non-Newtonian viscosity (see E.F. Leonard and C.S. Vassilieff, Chem. Eng. Commun., 30 (1984) 209) predicts different qualitative behaviour depending on the mode of operation (i.e. constant inlet feed or constant inlet pressure). Experiments aimed at testing this prediction are performed with stable kaolinite-in-water dispersions (pH 10) in a small laboratory microfiltration set-up. The observed filtration behaviour follows the pattern predicted by the convective model. The shear-enhanced diffusion model fails to rationalize the experimental observations.

The calculation of microfiltration of suspensions in cartridge filters

The calculation of non-steady static microfiltration of suspensions in cartridge-type units has been developed. It is based on mass and energy balance equations and founded on sieve mechanism of separation. The model accounts for a mutual energy interdependence between flows both in feed and in permeate channels and also particle-size distribution of suspension to be separated. The model consists of analytical equations and permits stimulation or analysis of the influence of various factors to permeate flux and concentration. It also permits prediction of their behavior on time.

Measurement of cake thickness on membrane for microfiltration of yeast using ultrasonic polymer concave transducer.

An ultrasonic measurement method was applied to obtain information about the properties of cake formed on the membrane in microfiltration of suspensions of yeast. The microfiltration was carried out at low applied pressure in order to assess that the cake formed was incompressible. A spherically concave transducer made of piezoelectric films of a vinylidene fluoride-trifluoroethylene copolymer was adopted. The surface shape of the cake was found not to be flat by the reflection technique. An on-line method of measuring cake thickness was developed by using the transmission technique, and the results showed good agreement with data reported elsewhere.