Regenerated Cellulose Ultrafiltration Membranes Research Articles

Performance investigation of hydrophilic regenerated cellulose ultrafiltration membranes with excellent anti-fouling property via hydrolysis technology

To obtain ultrafiltration (UF) membranes with excellent separation performances and antifouling properties, regenerated cellulose (RC) membranes with intrinsic hydrophilicity and dense structures immensely attract the attention of researchers. Herein, a novel modified RC membrane, which has high water permeability and antifouling capability, is prepared using cellulose acetate (CA) via non-solvent induced phase separation (NIPS) and green hydrolysis technology. The as-prepared membranes were investigated comprehensively by scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR) analyses and protein adsorption, etc. As a result, the RC membranes showed higher hydrophilicity (WCA=25.95°), thus they possessed a lower protein adsorption value of 1.9 ± 0.1 μg/cm2. The filtration performances were evaluated by bovine serum albumin (BSA) and endotoxin separation with dead-end filtration system. The results exhibited greater selectivity of RC membranes that BSA rejection over 98% and endotoxin remove below 0.25 EU/mL, and excellent anti-fouling properties that the flux recovery rate (FRR) over 95% and even as high as 100%. Simultaneously, the common polyethersulfone (PES) composite membranes were prepared via NIPS technology, and comprehensively compared with RC membranes to provide a theoretical basis for the practical application of RC membranes in pharmaceutical and biotechnological industries.

Modification of regenerated cellulose ultrafiltration membranes with multi-walled carbon nanotubes for enhanced antifouling ability: Field test and mechanism study.

Although ultrafiltration (UF) has been extensively employed for drinking water purification, it is crucial to further develop novel membrane materials to improve the antifouling capacity and satisfy the practical usage. Multi-walled carbon nanotubes (MWCNTs) have characteristics that could potentially improve the membrane antifouling performance. Therefore, in this study, modified cellulose UF membranes were prepared using MWCNTs of various outer diameters ranging from 10 to 20nm to 40-60nm. The antifouling properties of the modified membrane and natural organic matter (NOM) removal mechanism were investigated while treating water from a local drinking water source river. Overall, the antifouling ability increased by more than one-fold when the nascent cellulose membrane was coated with MWCNTs (outer diameter of 40-60nm) at a loading of 17.4g/m2. The molecular weight distribution profiles of the NOM in the raw water and permeates suggest the superior performance of the modified membranes in removing two major NOM fractions with molecular weights ranging from approximately 5k-30k and 500k-1000k. Based on its hydrophobicity, the NOM of the raw water was fractionated into the strong hydrophobic (SHPO), the weak hydrophobic, the strong hydrophilic and the moderately hydrophilic (MHPI) fractions. The WHPO fraction caused the highest fouling compared with the other fractions under consistent experimental conditions. Meanwhile, the modified membranes showed a preference for removing the MHPI and SHPO fractions. These results imply that MWCNTs can be employed to improve the antifouling property of cellulose UF membranes and have the potential to selectively remove moderately hydrophilic contaminants from water.

Tailoring and Remotely Switching Performance of Ultrafiltration Membranes by Magnetically Responsive Polymer Chains.

Magnetically responsive ultrafiltration membranes were prepared by grafting poly(2-hydroxyethyl methacrylate) chains from the outer surface of 100-kDa regenerated cellulose ultrafiltration membranes. Surface-initiated atom transfer radical polymerization was used to graft the polymer chains. Grafting from the internal pore surface was suppressed by using glycerol as a pore-filling solvent during initiator immobilization at varied densities. Glycerol suppresses the initiator attachment to the pore surface. Polymerization times of up to four hours were investigated. Superparamagnetic nanoparticles were covalently attached to the chain end. Membrane performance was determined using bovine serum albumin and dextran as model solutes. Increasing the grafted polymer chain density and length led to a decrease in the permeate flux and an increase in the apparent rejection coefficient. In an oscillating magnetic field, movement of the grafted polymer chains led to a decrease in the permeate flux, as well as an increase in the apparent rejection coefficient of the model solutes.

Activator Generated Electron Transfer Combined Atom Transfer Radical Polymerization (AGET-ATRP) for Controlled Grafting Location of Glycidyl Methacrylate on Regenerated Cellulose Ultrafiltration Membranes

This investigation indicates the ability to selectively graft glycidyl methacrylate (GMA) only from the external surface of regenerated cellulose (RC) ultrafiltration (UF) membranes using activator generated electron transfer (AGET) atom transfer radical polymerization (ATRP). This controlled polymerization resulted in epoxy functionalized polymer brush ends. Further reaction of the terminal epoxy groups provides a flexible platform to introduce desired functionalities either by electrophilic or nucleophilic epoxy ring opening. Selective grafting from the external membrane surface was achieved by using an appropriate pore filling solvent prior to modification. A high viscosity pore filling solvent that is immiscible with the reactive monomer solution used during surface modification was the most effective in supressing grafting from the internal pore surface. The effects of grafting on membrane performance were evaluated by determining water permeability and protein rejection.

Designing Electric Field Responsive Ultrafiltration Membranes by Controlled Grafting of Poly (Ionic Liquid) Brush.

Electric responsive membranes have been prepared by controlled surface grafting of poly (ionic liquid) (PIL) on the commercially available regenerated cellulose ultrafiltration membrane. The incorporation of imidazolium ring on membrane surface was evidenced by FTIR (Fourier transformed infra-red) and EDX (energy-dispersive X-ray) spectroscopy. The PIL grafting resultedin a rougher surface, reduction in pore size, and enhancement in hydrophilicity. The interaction of the electric field between the charged PIL brush and the oscillating external electric field leads to micromixing, and hence it is proposed to break the concentration polarization. This micromixing improves the antifouling properties of the responsive membranes. The local perturbation was found to decrease the water flux, while it enhanced protein rejection. At a higher frequency (1kHz) of the applied electric field, the localized heating predominates compared to micromixing. In the case of a lower frequency of the applied electric field, more perturbation can lead to less permeability, whereas it will have a better effect in breaking the concentration polarization. However, during localized heating at a higher frequency, though perturbation is less, a heating induced reduction in permeability was observed. The electric field response of the membrane was found to be reversible in nature, and hence has no memory effect.

Effects of protein properties on ultrafiltration membrane fouling performance in water treatment

Protein-like substances always induce severe ultrafiltration (UF) membrane fouling. To systematically understand the effect of proteins, regenerated cellulose UF membrane (commonly used for protein separation) performance was investigated in the presence of bovine serum albumin (BSA) under various water conditions. Results showed that although trypsin enhanced the membrane flux via proteolysis, catalysis took a long time. Membrane fouling was alleviated at high solution pH and low water temperature owing to the strong electrostatic repulsion force among BSA molecules. Both Na+ and Ca2+ could increase membrane flux. However, Ca2+ played a bridging role between adjacent BSA molecules, whereas membrane fouling was alleviated via a hydration repulsion force with Na+. The order of influence on membrane fouling was as follows: Ca2+ concentration > Na+ concentration > pH > temperature > trypsin concentration. Furthermore, a polyvinylidene fluoride UF membrane experiment showed that Ca2+ could reduce the fouling induced by BSA. Thus, the differences in UF membrane performance will have application potential for alleviating UF membrane fouling induced by proteins during water treatment.

Application of the liquid-phase polymer-based retention technique to the sorption of molybdenum(VI) and vanadium(V)

This research is focused on molybdate and vanadate removal from aqueous solutions by the liquid-phase polymer-based retention (LPR) technique. In this technique, a cationic water-soluble polymer based on the ammonium quaternary group poly(diallyldimethylammonium chloride), PDDA, was used as a polymeric sorbent, and a regenerated cellulose ultrafiltration membrane was used as a filter. The removal of molybdenum and vanadium using the LPR technique was analyzed by both the washing and enrichment methods. The removal experiments using the washing method were conducted by varying the pH, polymer/metal molar ratio, concentration of metal ions, pressure and presence of interfering ions. In addition, the enrichment method was used to determine the maximum retention capacity of PDDA. The obtained results showed the highest retention capacity of molybdate (100%, using 30 mg/L in the feed) for PDDA at pH 3 and 9. The optimum molar ratio was 20:1 polymer/Mo(VI). The efficient vanadate retention (approximately 90%) was obtained at pH 6 with 10:1 polymer/V(V) molar ratio. The effect of metal concentration on the retention showed a higher retention of Mo(VI) independent of its concentrations. In the case of V(V), the maximum retention was reached when 60 mg/L of vanadium was used in the feed. The enrichment method showed the maximum retention capacities of 370 mg Mo(VI)/g PDDA and 520 mg V(V)/g PDDA. The presence of interfering ions did not affect the retention capacity of PDDA. These results showed that the combination of PDDA with ultrafiltration membranes could represent an alternative method for the removal of molybdate and vanadate from water.

Immobilization of Peroxidase from Cauliflower Stem on Ultrafiltration Membrane for Phenol Removal

The aim of this work is to investigate phenol removal by immobilized peroxidase extracted from cauliflower stem. Peroxidase was partially purified by membrane filtration and diafiltration. Almost four-fold increase in the measured activity of partially purified peroxidase was obtained. The enzyme was then immobilized on to the surface of regenerated cellulose ultrafiltration membrane (molecular weight cut-off 30 kDa) using a dead-end filtration unit. Three different immobilization methods (physical adsorption, cross-linking and covalent-bonding using glutaraldehyde as a membrane activator) were tested. The immobilization and enzymatic reaction efficiency were evaluated in terms of the immobilization yield, the enzyme leakage from the system, the phenol removal and the permeate flux. Results showed that the immobilization methods did not much affect the permeate flux of the membrane. The peroxidase immobilization by covalent-bonding on regenerated cellulose membrane produced the highest immobilization yield and the lowest enzyme leakage. The immobilized enzymatic reaction efficiency on phenol removal was 100% at operational time 60 min and reduced to 96.4% at 600 min.

Binding of Methylene Blue to two types of water soluble polymer and its removal by polyelectrolyte enhanced ultrafiltration

The interactions of water soluble polymers with dye are studied by ultrafiltration using a molecular weight cut off of 10 KDa regenerated cellulose ultrafiltration membrane. Two water-soluble polymers, namely Poly (Sodium-4 Styrenesulfonate) (PSS) and Poly (Vinyl Alcohol) (PVA) were selected for this study. The effects of process parameters, such as, polyelectrolyte concentrations, transmembrane pressure, ionic strength and pH of solution on dye retention and permeation flux were examined. PSS enhanced ultrafiltration achieved dye retention as high as 99% as a result of complexation between polyanion containing aromatic groups and cationic dye. This result was confirmed by the red shift. The retention of dye decreases as the salt concentration increases, a high retention was obtained at pH above 4. However, in case of PVA, relatively low retention (50%) was observed. Ionic strength and pH has no significant effect on the removal of MB. The permeate flux depended slightly on polyelectrolytes concentrations, transmembrane pressure, salt concentration and pH.

The use of micellar-enhanced ultrafiltration (MEUF) for fluoride removal from aqueous solutions

Abstract Fluorine is a common chemical element. Due to the harmful influence on human health, the World Health Organization determined the permissible level of fluoride in drinking water to be 1.5 mg F−/L. Fluorine can be removed from water solutions by various methods (i.e. ion-exchange, precipitation, adsorption and membrane techniques). One membrane technique that can be effective in fluoride removal is micellar enhanced ultrafiltration (MEUF). This method involves the ability of surfactants to create micelles, which are retained by classic ultrafiltration membranes. In the presented paper, the suitability of the MEUF process for fluoride removal was verified. Polyethersulfone and regenerated cellulose ultrafiltration membranes, as well as two cationic surfactants (cetylpyridinium chloride – CPC, octadecylamine acetate – ODA) were used in the batch experiments. The fluoride content in the model solutions amounted to 10 and 100 mg F−/L, whereas surfactant concentration varied in the range of 1–3 CMC. The MEUF tests were performed under a pressure of 0.2 MPa with and without a salt (NaCl) dosage to the treated solutions. The results obtained showed that for a low fluoride content (10 mg F−/L) and a high CMC value (3CMC), the polyethersulfone membrane allowed F− ions below the permissible level for drinking water to be removed. The presence of NaCl in the model solutions resulted in a significant worsening of fluoride removal efficiency.

Effects of operating conditions on biofouling in crossflow ultrafiltration membrane processes

Abstract We evaluated the effects of operating conditions on the biofouling behaviors in ultrafiltration (UF) membrane processes with respect to biofilm formation and decrease in permeate flux. The biofouling experiment was performed by filtering nutrient-containing feed water with a crossflow membrane cell through a regenerated cellulose UF membrane consisting of pre-adhered bacteria. The nutrient concentration, initial permeate flux, flow rate of feed water, and trans-membrane pressure (TMP) were controlled as the operating conditions. The permeate flux was monitored during the filtration, and the adhesion of bacteria and extracellular polymeric substances (EPS) to the membrane surfaces was observed using confocal laser scanning microscope. The increase in the medium concentration and initial permeate flux facilitated both the decline of the permeate flux and the biofilm formation by causing concentration polarization of the medium. The TMP and flow rate of the feed water also affected the permeate flux and bacterial adhesion. The biofilm thickness on the membrane surface after the biofouling tests was positively related to the decline ratio of the permeate flux.

Enhanced purification of plasmid DNA isoforms by exploiting ionic strength effects during ultrafiltration.

The solution structure of plasmid DNA is known to be a strong function of solution conditions due to intramolecular electrostatic interactions between the charged phosphate groups along the DNA backbone. The objective of this work was to determine whether it was possible to enhance the use of ultrafiltration for separation of different plasmid isoforms by proper selection of the solution ionic strength and ion type. Experiments were performed with a 3.0 kbp plasmid using composite regenerated cellulose ultrafiltration membranes. The transmission of the linear isoform was nearly independent of solution ionic strength, but increased significantly with increasing filtrate flux due to the elongation of the highly flexible plasmid in the converging flow field into the membrane pores. In contrast, the transmission of the open-circular and supercoiled plasmids both increased with increasing NaCl or MgCl2 concentration due to the change in plasmid size and conformational flexibility. The effect of ionic strength was greatest for the supercoiled plasmid, providing opportunities for enhanced purification of this therapeutically active isoform. This behavior was confirmed using experiments performed with binary mixtures of the different isoforms. These results clearly demonstrate the potential for enhancing the performance of membrane systems for plasmid DNA separations by proper selection of the ionic conditions.

Scrutinizing the Nanostructural and Nanomechanical Features of Regenerated Cellulose Ultrafiltration Membranes

Ultrafiltration (UF) membranes have been widely used for many separation processes in which high performance is required. Commercial regenerated cellulose UF membranes with variable molecular weight cut-offs were characterized by high performance atomic force microscopy (AFM) using the novel quantitative nanomechanical mapping mode and the versatility of its signal channels towards nanoscale features elucidation of the materials surface. In addition, Raman spectroscopy was applied in order to investigate some possible chemical behavior changes associated with the UF membranes’ cut-offs. Overall, the results showed that the proposed AFM method was reliable to gain qualitative and quantitative data at unprecedented nanoscale resolution and such information can be used to distinguish UF membranes according to their specific molecular weight cut-offs and properties even on situations in which the molecular behavior were not influenced by the UF membrane’ cut-off. This approach can be useful on quality control procedures of researchers and manufacturers producing or modifying these polymeric materials.

Ultrasonically Assisted Ultrafiltration of Whey Solution

The ultrafiltration of whey solutions is a common feature of dairy processes. However, the frequent fouling of ultrafiltration membranes and the subsequent cleaning cycle significantly affects the economics of the process. In this work, we investigated the effect of ultrasonically assisted ultrafiltration. The ultrafiltration of whey solution was investigated in order to determine the main parameters affecting the flux, retention and membrane fouling. The experiments were carried out with an ultrasonic combined laboratory ultrafiltration device, using regenerated cellulose ultrafiltration membranes. The results showed that increasing resistance during filtration is predominantly caused by the concentration polarization, while the participation of membrane fouling in the total resistance is negligible. The ultrasonically assisted ultrafiltration actively reduces the concentration polarization layer resistance. The retention changed slightly with ultrasound power. Practical Applications Combination of ultrasound and ultrafiltration processes in dairy industry may enhance the efficiency of whey separation processes during ultrafiltration of why solutions. The given model for describing the filtration mechanism and modified Reynolds number for ultrasonically assisted batch reactor allow the scale up of coupled ultrafiltration process for dairy industry.

Fractionation of α-lactalbumin and β-lactoglobulin from bovine milk serum using staged, positively charged, tangential flow ultrafiltration membranes

Fractionation of bovine α-lactalbumin (ALA) from β-lactoglobulin (BLG) in milk serum permeate (MSP) using tangential flow ultrafiltration was examined in this work. By placing a positive charge on a 300kDa regenerated cellulose ultrafiltration membrane, it was possible to increase the selectivity for fractionating ALA and BLG by 180% compared to an uncharged membrane. Thus, like-sized proteins that differed only somewhat in isoelectric point, and that were about 15–20 times smaller than the membrane molecular weight cutoff, were fractionated using charged ultrafiltration membranes. Electrostatic repulsion was solely responsible for the improved selectivity. Protein sieving coefficients were explained by the net charge on the protein and the stagnant film model. From experimental data using a single-stage system under total recycle conditions, mass balance models were used successfully to predict the performance of a multi-stage membrane system. A three-stage system gave 87% pure ALA and 83% pure BLG. Thus, dairy protein fractions of chromatographic purity can be obtained using charged ultrafiltration membranes arranged in stages, without the wastewater generation and expense of chromatography. The results of this study will be useful for expanding the utility of ultrafiltration membranes beyond simple protein concentration to fractionation of proteins.

Modification of ultrafiltration membranes with block copolymer nanolayers for produced water treatment: The roles of polymer chain density and polymerization time on performance

► Unique, nanostructured polymer coatings developed for ultrafiltration of oily water. ► Nanolayer architecture shown to impact coating effectiveness for fouling prevention. ► Optimization of nanolayer architecture yielded membranes with high, stable flux. This contribution describes the development of advanced membranes for produced water treatment through modification of low molecular weight cut-off regenerated cellulose ultrafiltration membranes with uniquely structured block copolymer nanolayers. Poly(N-isopropylacrylamide)- block -poly((polyethylene glycol) methacrylate) (PNIPAAm- b -PPEGMA) nanolayers were grafted from the membrane using surface-initiated atom transfer radical polymerization. A focus of this study was to better understand the role of polymer nanolayer structure on performance. Specifically, the objective of this work was to use initiator grafting density and PNIPAAm and PPEGMA polymerization times as independent variables to optimize the performance of the surface-modified membranes. Membrane performance was evaluated by measuring water flux using deionized water, synthetic produced water developed from an oil-in-water emulsion, and actual oil-field produced water. Optimization of nanolayer structure yielded membranes with stable permeabilities that compare well to commercial membranes used for removal of organics with high salt passage. The results show that nanolayer structure plays an important role in determining the effectiveness of a polymer coating for fouling prevention, even for polymers that are recognized by the community to have good antifouling characteristics. The membrane surface modification protocol allows optimization of nanolayer structure in ways not achievable by standard coating methods. Visualization by confocal laser scanning microscopy shows that the modification occurs at the membrane external surface and internally within the porous cellulose layer. The modification protocol was used in this study to design highly advanced membranes to separate emulsified oils from produced water.

Recovery of galactoglucomannan from wood hydrolysate using regenerated cellulose ultrafiltration membranes

Hemicelluloses show promise as a renewable source of raw material for various industrial processes. In this study, galactoglucomannan was recovered from pressurized hot water extract of spruce-sawdust in two steps using hydrophilic regenerated cellulose ultrafiltration membranes having different molecular weight cut-off values. The first step was concentration of galactoglucomannan (GGM) by ultrafiltration using a flat sheet unit and the second step was purification of the retained galactoglucomannan by diafiltration using reverse osmosis filtered water. The highest GGM retention (88%), purity (63%) and recovery (70%) were achieved with the UC005 membrane (cut-off value 5-kDa) at a volume reduction (VR%) of 86%. The UC010 and UC030 membranes (cut-off values 10- and 30-kDa, respectively) partly separated xylan from GGM. Generally, diafiltration did not improve the purity of the GGM due to overlapping of the GGM and lignin molar mass distributions and the fact that most of free low molar mass lignin had already been removed in the concentration filtration step. However, by diafiltration, partial removal of xylan and complete removal of monosaccharides from the GGM rich concentrate was achieved.

Modification and characterization of ultrafiltration membranes for treatment of produced water

This contribution describes the surface modification of low molecular weight cutoff regenerated cellulose ultrafiltration membranes by grafting poly(N-isopropylacrylamide) (PNIPAAm)- block-poly(oligoethylene glycol methacrylate) (PPEGMA) nanolayers from the membrane surface using surface-initiated atom transfer radical polymerization. The objective of the work was to change the membrane surface properties in ways that limit foulant accumulation on these membranes and provide an easy, chemical-free way to remove any attached foulants during produced water filtration. ATR-FTIR spectra confirmed the successful grafting of both polymers from the membrane surface. Analysis of AFM topographical images indicated that membrane surface roughness decreased slightly from 2.6 nm for the unmodified membrane to 1.7 nm following PNIPAAm- b-PPEGMA modification. The performance of the modified membranes was tested by measuring water flux using synthetic produced water developed from an oil-in-water emulsion. Polymer grafting led to a roughly 40% decrease in the water flux, but the final flux was comparable to commercial membranes used for removal of organics with high salt passage. Furthermore, modified membranes showed slower flux decline than unmodified membranes, and, hence, the modified membranes allowed a 13.8% higher cumulative volume of water to be processed over a 40 h cross-flow filtration run. To test potential for chemical-free cleaning, filtration runs were carried out before and after a temperature-controlled water rinse. Flux recovery was better for the modified membranes after a cold water rinse. The flux recovered fully to initial values for both the PNIPAAm- and PNIPAAm- b-PPEGMA-modified membranes; while only ∼81% of the initial flux was recovered for the unmodified membrane. All three membranes exhibited poor salt rejection, as would be expected for ultrafiltration membranes. However, TOC removal efficiencies were higher than 97% for PNIPAAm- b-PPEGMA-modified membranes. Taken together, results from this work indicate that PNIPAAm- b-PPEGMA modified ultrafiltration membranes could be used to separate emulsified oils from large volumes of produced water at high flux.

Improving separation capability of regenerated cellulose ultrafiltration membrane by surface modification

In this study we introduced dialdehyde groups to a commercial regenerated cellulose (RC) ultrafiltration membrane by periodate oxidation. They were further converted to nitrogen-containing derivatives by Schiff base reaction with diethylenetriamine (DETA). The modified membrane was challenged with aqueous solution containing Pb(II) metal ions. The different variables affecting the rejection of lead ion by membrane including oxidization time, concentration of DETA, initial metal ion concentration and pH of the solution were elucidated. The membranes were characterized by FTIR–ATR, SEM, EDAX and elemental analyses. The process efficiency was enhanced by improving the oxidization time up to a certain period. In our case this was diminished after 9 h due to deterioration in the membrane integrity. The Pb 2+ removal was facilitated by increasing feed pH and DETA concentration. This was diminished for more concentrated metal ion in the feed. Membrane regeneration was successfully utilized using 0.1 M HNO 3 solution. The removal capability of the regenerated membranes was maintained even after four cycles.

Concentration of Rutin Model Solutions from Their Mixtures with Glucose Using Ultrafiltration

Separation of polyphenolic phytochemical compounds from their mixtures with sugars is necessary to produce an added-value sugar-reduced extract with high biological activity from fruit juice processing industry waste streams. The separation characteristics of a binary mixture of rutin and glucose using a Pellicon-2 regenerated cellulose ultrafiltration membrane with an area of 0.1 m2 having nominal MWCO of 1,000 Da were investigated, to demonstrate the separation of phenolic compounds from sugars. The effects of the operating variables–transmembrane pressure, feed solution temperature and pH, initial feed concentration and feed flow rate–on the permeate flux and enrichment of rutin, were determined. The permeate flux increased with the increase in transmembrane pressure up to a certain limit and after that the flux remained more or less constant. The optimum transmembrane pressure was within 4–5 bar. The flux increased with the increase in feed solution temperature because of reduced feed viscosity, and better solubility. The concentration of rutin was optimum at lower temperature (30°C), with an enrichment factor of 1.3. The effect of pH on permeate flux was less obvious. Lowering the feed solution pH increased the retention of rutin and the optimum separation was obtained within pH 3–4. The permeate flux decreased with the increase in feed concentration of rutin (concentration range 0.1–0.5 g/L). The enrichment of rutin was significant in the glucose concentration range 0.35–0.5 g/L. The feed flow rate had a significant effect on the flux and separation characteristics. Higher cross-flow through the membrane reduced the fouling by providing a shear force to sweep away deposited materials from the membrane surface. At high feed flow rate, more rutin was retained by the membrane with less sugar permeating through. The optimum feed flow rate was 1.5 L/min. For the separation of rutin (in the retentate) and glucose (in the permeate), the best results were obtained at rutin enrichment of 2.9 and recovery 72.5%, respectively. The performance of this system was further improved by operating it in a diafiltration mode, in which only approx. 11% of glucose remained in the retentate.