Commercial Ultrafiltration Membranes Research Articles

Treatment of wastewaters from the cork process industry by using ultrafiltration membranes

Wastewaters produced in the cork process industry were treated by means of two commercial ultrafiltration membranes with MWCO of 10 kDa and 5 kDa, respectively. Previous experiments were conducted for the evaluation of the water hydraulic permeability of the membranes. Experiments with total recycling of the retentate and permeate streams, as well as experiments in batch concentration with partial recycling of the retentate stream were conducted. In both procedures, the influence of the main operating variables (transmembrane pressure, feed flow rate, temperature and nature of the membranes) on the permeate flux was established. The purification levels reached by the membranes were also evaluated by determining the rejection coefficients referred to several parameters which measure the global pollutant content of the effluent: COD, absorbance at 254 nm, tannic content, colour, and ellagic acid, one of the organic pollutant compounds which is present in this wastewater. Finally, experiments in continuous mode, without recycling of both streams, were also carried out. After the determination of the rejection coefficients, the fouling mechanism of the membranes was established by considering some filtration fouling models which are proposed in the literature.

High-performance thin-layer hydrogel composite membranes for ultrafiltration of natural organic matter

Thin-layer hydrogel composite (TLHC) ultrafiltration (UF) membranes were synthesized by photo-grafting of either poly(ethylene glycol) methacrylate (PEGMA) or N,N-dimethyl-N-(2-methacryloyloxyethyl-N-(3-sulfopropyl) ammonium betaine (SPE) onto commercial polyethersulfone (PES) UF membranes. The performance of TLHC UF membranes was evaluated for natural organic matter (NOM) filtration and compared to commercial PES UF membranes. The fouling evaluation was done by investigation of membrane–solute interactions (adsorptive fouling) and membrane–solute–solute interactions (UF). The results suggest that the TLHC membranes convincingly displayed a higher adsorptive fouling resistance than unmodified PES UF membranes. In long-term stirred dead-end UF, a much lower fouling was observed for TLHC membranes than for commercial membranes with the same flux and rejection. Further, water flux recovery was also much higher. An analysis using an existing blocking model was performed in order to elucidate the effect of a polymer hydrogel layer on fouling mechanism as well as cake layer characteristics. The TLHC membranes synthesized by photo-grafting of PEGMA (40g/L) and PEGMA with a low concentration of cross-linker monomer in the reaction mixture (ratio: 40/0.4 (g/L)/(g/L)) showed a much better performance than the other composite membranes. Those membranes could reduce the cake resistance on the membrane surface. This work has relevance for the design of high-performance UF membranes for applications in water treatment.

Protein antifouling mechanisms of PAN UF membranes incorporating PAN- g-PEO additive

The antifouling mechanism of a novel polyacrylonitrile (PAN) ultrafiltration (UF) membrane incorporating the amphiphilic comb copolymer additive, polyacrylonitrile- graft-polyethylene oxide (PAN- g-PEO), has been investigated using a laboratory-scale cross-flow test unit and atomic force microscopy (AFM). In fouling tests with a bovine serum albumin (BSA) solution, PAN UF membranes incorporating 20% PAN- g-PEO possessed excellent antifouling characteristics, whereas a commercial PAN UF membrane showed severe pore blocking that followed with surface cake formation. The PAN- g-PEO/PAN blend membranes also exhibited fouling reversibility and constant BSA retention, which indicate their ability to separate macromolecules without altering the molecular weight cut-off. An AFM analysis with a model carboxylated colloid-probe measured no adhesion force with the blend membrane, while the commercial PAN membrane exhibited strong adhesion to the probe, consistent with the fouling properties of the membranes. The antifouling character of the blend membrane is attributed to the surface segregation and local orientation of PAN- g-PEO molecules at the membrane surface and pore walls during membrane casting, creating a dense PEO brush layer that provides a steric barrier to protein adsorption.

Charge- and size-based separation of macromolecules using ultrathin silicon membranes

Commercial ultrafiltration and dialysis membranes have broad pore size distributions and are over 1,000 times thicker than the molecules they are designed to separate, leading to poor size cut-off properties, filtrate loss within the membranes, and low transport rates. Nanofabricated membranes have great potential in molecular separation applications by offering more precise structural control, yet transport is also limited by micrometre-scale thicknesses. This limitation can be addressed by a new class of ultrathin nanostructured membranes where the membrane is roughly as thick (approximately 10 nm) as the molecules being separated, but membrane fragility and complex fabrication have prevented the use of ultrathin membranes for molecular separations. Here we report the development of an ultrathin porous nanocrystalline silicon (pnc-Si) membrane using straightforward silicon fabrication techniques that provide control over average pore sizes from approximately 5 nm to 25 nm. Our pnc-Si membranes can retain proteins while permitting the transport of small molecules at rates an order of magnitude faster than existing materials, separate differently sized proteins under physiological conditions, and separate similarly sized molecules carrying different charges. Despite being only 15 nm thick, pnc-Si membranes that are free-standing over 40,000 microm2 can support a full atmosphere of differential pressure without plastic deformation or fracture. By providing efficient, low-loss macromolecule separations, pnc-Si membranes are expected to enable a variety of new devices, including membrane-based chromatography systems and both analytical and preparative microfluidic systems that require highly efficient separations.

Natural organic matter fouling due to foulant–membrane physicochemical interactions

An extended DLVO (XDLVO) force analysis was introduced to predict natural organic matter (NOM) fouling in ultrafiltration (UF) membrane processes. Ultrafiltration membrane fouling experiments were performed using two NOM extracts from real waters and two commercial polymeric UF membranes. The hydrodynamic force by permeation drag and three interfacial forces of XDLVO (van der Waals, electrostatic, acid–base energy) were used for the force analysis. Acid–base interaction forces between NOM and UF membranes were dominant in short range (separation distances < 5 nm) and appear to determine the potential of NOM deposition. Relative extents of flux decline were successfully predicted using the short-range force analyses.

Gas and water liquid transport through nanoporous block copolymer membranes

ABC triblock terpolymers containing polylactide, poly(dimethylacrylamide) and polystyrene, which can self-assemble as aligned cylinders, are etched to give nanoscopic pores. The diffusion of gases through these pores is quantitatively consistent with Knudsen diffusion. The flow of water liquid in the pores is consistent with the Hagen–Poiseuille law. If these polymers can be produced as commercial ultrafiltration membranes, they should give a larger hydraulic permeability and a sharper molecular weight cut-off.

Toward nanoporous composite membranes with tailored block copolymers as selective layer

The development of synthetic membranes featuring transport selectivity for molecules different from water is a challenge of outstanding relevance. This field is strongly inspired by nature where highly specific transport through biological membranes is based on molecular recognition processes within macromolecular assemblies. In this collaborative project we are preparing and characterizing novel composite membranes for sizeor charge-based membrane separation processes with higher selectivity. Commercially available porous membranes are used as support for thin layers of self-assembled block copolymers. The tailored diblock or triblock copolymers are synthesized by living ionic or controlled radical polymerization [1], so that they can form microphase-separated nanostructures which may even be aligned into cylindrical morphologies with the characteristic axis perpendicular to the film surface [2,3]. Supported nanoporous films may then be obtained either via the selective dissolution of another polymer which had been added to form a polymer blend and which is compatible with the block of the copolymer forming the cylindrical domains, or via selective degradation of the copolymer block forming the cylindrical domains [3]. Depending on the precursor block copolymer those pores may be also charged, and this charge may depend on the pH so that permeability and selectivity can be controlled by size or charge. As support membranes we use track-etched poly(ethylene terephthalate) (PET) membranes (Fig. 1) and commercial ultrafiltration membranes with barrier pore diameters ranging from ~5 to 3000 nm. In order to provide methods for anchoring and stabilizing the block copolymer film on the support membranes, surface functionalisations of the membranes by polymer-analogous reactions or graft copolymerization of thin functional copolymer layers are investigated [4]. Various surfaces are created to that the requirements in terms of surface energy and reactivity (by mixing/entanglement, by chemical reaction or by UV irradiation) for orienting and anchoring the block copolymer films on the support can be explored. *Corresponding author.

A Comparison of Commercial and Experimental Ultrafiltration Membranes via Surface Property Analysis and Fouling Tests

Abstract Surface modified polyethersulfone (PES) membranes via the addition of different hydrophiLic Surface Modifying Macromolecules (LSMMs) have been developed by Matsuura, Narbaitz and co-workers. This study compares the performance of the best PES-LSMM membrane with nine commercial ultrafiltration membranes manufactured using five different types of base polymers (polyethersulfone, polysulfone, celluloseacetate, polyacrylonitrile and cellulose) in the same range of molecular weight cutoff (MWCO) (from 40 to 120 kDal). All membranes were characterized by using atomic force microscopy, contact angle measurements, solute transport analysis and then evaluated through fouling tests with Ottawa River water (ORW). While PES-LSMM membranes had much lower initial flux than the commercial membranes, they had the highest total organic carbon (TOC) rejection (80%) and the lowest flux reduction (62%). For the commercial membranes, the range of TOC rejections and flux reductions were 62 to 80% and 68 to 80%, respectively. Given their high TOC rejection and relatively high foulant deposition, fouling of the PES-LSMM membranes appears to be controlled by a surface gel.

High performance ultrafiltration composite membranes based on poly(vinyl alcohol) hydrogel coating on crosslinked nanofibrous poly(vinyl alcohol) scaffold

A new kind of high flux ultrafiltration (UF) membrane based on poly(vinyl alcohol) (PVA) electrospun nanofibrous scaffold support and PVA hydrogel coating has been demonstrated. The long-term performance of such membranes was optimized by a variation of degree of hydrolysis (i.e. 88–99%) and molecular weight (e.g. 13,000–124,000 g/mol) in the electrospun PVA scaffold in conjunction with chemical crosslinking of PVA hydrogel coating. It was found that the electrospun scaffold fabricated by 96% hydrolyzed PVA with relatively high molecular weight (e.g. 85,000–124,000 g/mol) exhibited very good overall mechanical performance before and after crosslinking. A PVA hydrogel coating, fabricated from the same material composition as the electrospun scaffold but different crosslinking conditions, was used as the anti-fouling layer for high-throughput water ultrafiltration. Results indicated that such unique hydrophilic nanofibrous composite membranes exhibited a flux rate (>130 L/m 2 h) significantly higher than commercial UF membranes but with similar filtration efficiency (rejection rate >99.5%).

Membrane treatment for palm oil mill effluent: Effect of transmembrane pressure and crossflow velocity

A pilot-scale ultrafiltration (UF) membrane study was conducted to investigate the influence of transmembrane pressure and crossflow velocity on the performance of a palm oil mill effluent (POME) treatment. Two commercial UF membranes, ceramic and polyvinylidene difluoride (PVDF), were used in this study. The permeate flux of both membranes decreased with filtration time until it reached steady-state values. The significant reduction in flux was observed during the fouling layer built up while the steady-state values were obtained once the fouling layer was developed. The steady-state flux increased with increasing crosslow velocity and transmembrane pressure. The percentage rejection for suspended solids, chemical oxygen demand (COD) and biochemical oxygen demand (BOD) were also analyzed for both membranes. The crossflow velocity significantly affected the percentage rejection of COD and BOD of the ceramic membrane. Suspended solids in the permeate obtained from both membranes were almost completely absent.

Fractionation of Lysozyme and Chicken Egg Albumin Using Ultrafiltration with 30-kDa Commercial Membranes

Lysozyme is an important protein in chicken egg white (CEW) and it is feasible to separate lysozyme from other CEW proteins using ultrafiltration. To identify suitable conditions for the fractionation of lysozyme from CEW, we studied with the model binary mixture of lysozyme and chicken egg albumin (CEA) with the composition and concentration of the two proteins similar to those in natural CEW. Two commercial ultrafiltration (UF) membranes of 30-kDa molecular weight cutoff (MWCO) made of regenerated cellulose (RC) and poly(ether sulfone) (PES) membranes were used. By systematically examining the effect of the physicochemical properties of the solution and the hydrodynamics of the membrane systems, the most suitable conditions to achieve maximum transmission and selectivity for lysozyme were identified. The PES UF membranes offer distinct advantages for the fractionation of lysozyme from this binary mixture. With the 30-kDa PES UF membrane, the suitable conditions were identified as pH 10−11, salt concentr...

Permeability and selectivity analysis for ultrafiltration membranes

One of the major challenges facing end-users of ultrafiltration membranes is the difficulty in comparing membrane products provided by different manufacturers and made from different polymeric or ceramic materials. In this short communication, we examine the trade-off between permeability and selectivity for different ultrafiltration membranes using data for bovine serum albumin. Results for a number of different ultrafiltration membranes fall along, or below, an “upper bound” that reflects the current state-of-the-art in commercial ultrafiltration membranes, analogous to the Robeson Plot used to analyze the performance of gas separation membranes. The shape of this upper bound is consistent with a theoretical analysis of solute and solvent transport through a membrane composed of a parallel array of cylindrical pores having a log–normal pore size distribution. These results provide a framework that can be used to analyze the performance of new ultrafiltration membranes, an approach that was demonstrated using data for a prototype negatively charged ultrafiltration membrane.

Influence of the Membrane Pore Conductance on Tangential Streaming Potential

Tangential streaming potential technique is an attractive way to characterize the electrokinetic properties of various kinds of materials such as films or flat membranes with a dense or a porous structure. However, the interpretation of data in terms of zeta potential is usually carried out by doing the implicit assumption of nonconducting substrates. In the present paper, we investigate the electrokinetic properties of a commercial ultrafiltration membrane, the porous structure of which affects the streaming potential because streaming and conduction currents involved in the streaming potential process do not flow through identical paths (the streaming current flows only through the slit channel formed by the two membrane samples facing each other whereas a non-negligible part of the conduction current is likely to flow through the membrane pores filled with electrolyte solution). The correct zeta potential value is determined from an extrapolation method for which a set of measurements with various channel heights is required. A very good agreement is obtained with zeta potential values deduced from consecutive streaming potential and total conductance measurements (referred in the text as the direct method). The ratio of the correct zeta potential to the apparent one (given by Helmholtz-Smoluchowski equation) is dependent on the pH which suggests a non-negligible contribution of surface conductance within the membrane pores.

Ceramic Membranes for Water Separation from Organic Solvents

Novel hydrophilic SiOx modified alumina membranes with high separation factors and flux rates have been prepared for the separation of water from organic solvents. For the preparation of the membranes, SiOx networks are deposited inside the γ-Al2O3 layer of a commercial ultrafiltration membrane by hydrolysis of tetraethylorthosilicate in autoclaves at 250 °C. The transport resistances of the individual membrane layers for the permeation flux are described by a model. The membranes are stable towards solvents to temperatures of at least 150 °C. Pervaporation studies show that water can be separated from solvents such as acetonitrile, tetrahydrofurane, 2-propanol, ethyl alcohol, dimethylsulfoxide, N, N-dimethylformamide, and phenol. The separation performance of the membranes allows their use in technical separation processes, especially for the removal of water.

Ceramic Membranes for Water Separation from Organic Solvents

Novel hydrophilic SiOx modified alumina membranes with high separation factors and flux rates have been prepared for the separation of water from organic solvents. For the preparation of the membranes, SiOx networks are deposited inside the γ-Al2O3 layer of a commercial ultrafiltration membrane by hydrolysis of tetraethylorthosilicate in autoclaves at 250 °C. The transport resistances of the individual membrane layers for the permeation flux are described by a model. The membranes are stable towards solvents to temperatures of at least 150 °C. Pervaporation studies show that water can be separated from solvents such as acetonitrile, tetrahydrofurane, 2-propanol, ethyl alcohol, dimethylsulfoxide, N, N-dimethylformamide, and phenol. The separation performance of the membranes allows their use in technical separation processes, especially for the removal of water.

A simple instrument to characterize convective and diffusive transport of single hollow fibers of short length

The use hollow fiber membranes for cell encapsulation is being developed as an experimental transplantation technology in which a permselective membrane physically isolates grafted cells from directly interacting with host cells or tissue. Although laboratory characterization of commercial ultrafiltration and dialysis membranes using multi-fiber test modules is well established, a simple apparatus for characterizing the transport properties of small individual segments of hollow fiber membrane has not been described. In the current study, we describe an instrument for evaluating the diffusive and convective transport characteristics of individual cell encapsulation membranes at size scales typically used in animal and human clinical studies. The performance capabilities of the instrument are described, as well as methods for determining hydropermeability, diffusive permeability, and solute rejection.

Treatment of olive mill washing water by ultrafiltration

AbstractOlive oil production requires important quantities of washing water containing low oil concentrations, but classical processes used to recover or to eliminate this oil are ineffective. This study presents a membrane technique to treat olive oil mill washing water using different commercial ultrafiltration membranes: one organic (PCI) and two ceramic (Ceraver) membranes. The influence of the hydrodynamic parameters (transmembrane pressure and flow rate) and the cut‐off membranes on the efficiency of the ultrafiltration process was evaluated, and it was shown the organic PCI membrane could reduce pollution due to organic matter by decreasing the value of the Chemical oxygen demand by about 90%. Moreover, the nature of the ultrafine pore membrane appeared to be an important parameter which may strongly increase or decrease the capacity of the membrane. The membrane cut‐off did not have a strong influence on the performance of the process but if the membrane pores were too large the stability of the dynamically formed membrane decreased at transmembrane pressures greater than 0.2 MPa.

Interesting behavior for filtration of macromolecules through EVAL membranes

The objective of this article is to investigate the permeation characteristics of several polydispersed macromolecules through the asymmetric and the particulate poly (ethylene-co-vinyl alcohol) (EVAL) membranes. The solutes in examination include two nonionic solutes, dextran and polyethylene glycol (PEG), and one anionic solute, sodium polyacrylate (SPA). The ultrafiltration results indicate that the rejection coefficients increase monotonically with the molecular weights of test solutes permeating through the asymmetric EVAL membranes. This is consistent with the behavior of normal commercial ultrafiltration membranes. For the particulate membranes, the rejection curves show different trends. In most cases, there exist two local minima in the rejection curves, having the shape of “W”. This unusual behavior is found to be associated with the dual-pore character of the particulate membrane. To this context, a parallel composite membrane model is proposed to explain this specific rejection in terms of rejection coefficients for the small and the large pores.

Theoretical Analysis of the Effect of Membrane Morphology on Fouling during Microfiltration

Previous studies of membrane fouling have often employed one of the classical blocking laws to describe the variation of filtrate flux with time. However, these models implicitly assume that the membrane has straight-through noninterconnected pores, even though most commercial microfiltration and ultrafiltration membranes have a highly interconnected pore structure. We have developed a theoretical model for the effects of pore blockage on the fluid velocity and pressure profiles within membranes having different interconnected pore structures assuming Darcy flow in the porous membrane. Model calculations are in good agreement with filtrate flux data obtained during protein microfiltration using membranes with very different pore morphologies. The results clearly demonstrate that the membrane pore connectivity has a significant influence on the flux decline due to the possibility for fluid to flow around the pore blockage, an effect which has been ignored in previous studies.

Sieving characteristics of multilayer ultrafiltration membranes

Almost all commercial ultrafiltration membranes have an asymmetric structure. However, the unusual transport characteristics of these asymmetric, or multilayer, structures has not been widely appreciated. The general equations describing solute transport through a multilayer membrane are developed and used to examine the physical basis for the unusual transport properties of these membranes. Experimental data are obtained for the transport of polydisperse dextrans through asymmetric and symmetric ultrafiltration membranes, both alone and in sandwich (series) combinations. The data clearly show that the sieving characteristics of these multilayer membranes are dependent upon both the detailed properties and the orientation of the different layers. The sieving coefficients for traditional asymmetric membranes are shown to increase by well over an order of magnitude when used in the reverse (skin-side down) direction. Experiments with appropriate sandwich arrangements demonstrate that these composite structures can have higher selectivities than conventional membranes. The implications of these transport phenomena are examined in several different ultrafiltration applications.