Charged Ultrafiltration Membranes Research Articles

Glycomacropeptide: A comprehensive understanding of its major biological characteristics and purification methodologies.

Glycomacropeptide (GMP) is a bioactive peptide derived from whey protein, consisting of 64 amino acids. It is a phenylalanine-free peptide, making it a beneficial dietary option for individuals dealing with phenylketonuria (PKU). PKU is an inherited metabolic disorder characterized by high levels of phenylalanine in the bloodstream, resulting from a deficiency of phenylalanine dehydrogenase in affected individuals. Consequently, patients with PKU require lifelong adherence to a low-phenylalanine diet, wherein a significant portion of their protein intake is typically sourced from a phenylalanine-free amino acid formula. GMP has several nutritional values, numerous bioactivity properties, and therapeutic effects in various inflammatory disorders. Despite all these features, the purification of GMP is an imperative requirement; however, there are no unique methods for achieving this goal. Traditionally, several methods have been used for GMP purification, such as thermal or acid treatment, alcoholic precipitation, ultrafiltration (UF), gel filtration, and membrane separation techniques. However, these methods have poor specificity, and the presence of large amounts of impurities can interfere with the analysis of GMP. More efficient and highly specific GMP purification methods need to be developed. In this review, we have highlighted and summarized the current research progress on the major biological features and purification methodologies associated with GMP, as well as providing an extensive overview of the recent developments in using charged UF membranes for GMP purification and the influential factors.

Leaf-like ZIF-L as self-sacrificed template via acid induced removal for stronger negatively charged PES membranes based on RTIPS method

In this paper, ZIF-L was blended with citric acid (CA) and polyethersulfone (PES) to prepare a casting solution. A novel negatively charged ultrafiltration (UF) membrane (ZIF-L/CA/PES) was obtained using the reverse thermally induced phase separation (RTIPS) method. The hydrophilic carboxyl groups present in CA not only imparted high hydrophilicity and negative charge to the membrane surface, enhancing the membrane’s selectivity and contamination resistance, but also created an acidic environment to attack the Zn atoms in ZIF-L by the ionized H+ from CA, resulting in the generation of micro-defective pores and an improvement in permeability. Additionally, the results showed that membranes generated through the RTIPS process exhibit uniform porous surfaces and spongy cross-sections, enhancing membrane performance. The optimized membranes demonstrated the capability to achieve a pure water flux of up to 2267 L/m2h with 93.1 % humic acid (HA) retention, and a remarkable membrane flux recovery rate of 75.8 %, suggesting the crucial roles played by CA and ZIF-L in the separation process. In conclusion, hydrophilic anti-fouling UF membranes with a high negative charge and excellent permeation selectivity were fabricated by establishing micro-defective channels through the incorporation of carboxylic acid and ZIF-L, combined with the RTIPS process.

膜工学研究を振り返って– 膜を創る

Last time, the author described the study of membrane fouling and the transport equation for membrane permeation. This time, the author would like to introduce his research on creating membranes. Polymer membranes and inorganic membranes have been developed. The polymer membranes are negatively and positively charged ultrafiltration membranes, which are polysulfone membranes with sulfonic acid groups and quaternary ammonium groups. The charged membranes have a complex separation mechanism, that is combination of separation by membrane pores and by charge repulsion between the membrane and solute. It was possible to separate not only salts but also various substances such as amino acids, peptides, and proteins. The transport equations of charged membranes were also studied. Inorganic membranes are mainly silica membranes produced by chemical vapor deposition, and zeolite membranes have also been produced, but they will not be introduced here. The author started with low–temperature deposition using ozone, and finally deposited membranes at high temperature (600 ℃) using various silica sources, and was able to obtain high–performance membranes. Since the advantages of inorganic membranes can be applied to membrane reactors, membrane reactors have been applied to steam reforming of methane, dehydrogenation of cyclohexane and methylcyclohexane, and thermal decomposition of hydrogen sulfide. In particular, the cyclohexane dehydrogenation membrane reactor operated continuously for 1,054 hours, and a small membrane reactor equipped with six 50 cm membranes was also developed.

Positively charged PVC ultrafiltration membrane via micellar enhanced ultrafiltration for removing trace heavy metal cations

One of the major focuses in the field of sewage is the development of low-pressure driven and high-efficiency filtration membrane, particularly for removing extremely low-concentration heavy metals cations. A new type of polyvinyl chloride (PVC) blended ultrafiltration (UF) membrane was fabricated to reject heavy metal cations (e.g., Cd2+, Co2+, Ni2+, Cu2+, and Zn2+) from simulated waters using micellar enhanced ultrafiltration (MEUF) in this research. The positively charged PVC UF membrane was fabricated by blending PVC and amphiphilic poly (methyl methacrylate-co- dimethylaminoethyl methacrylate) (PMD) which was in-situ quaternized by methyl iodide (CH3I), then the PVC/PMD blended membrane was fabricated via nonsolvent induced phase separation (NIPS) process. The membranes' pore morphology, surface chemical compositions, surface charge, water contact angle, mechanical strength and water flux were investigated in detail. The influence of pH, transmembrane pressure, sodium dodecylbenzene sulfonate (SDBS) concentration on the filtration of pure SDBS solution was studied. SDBS was subsequently used as surfactant to remove heavy metal ions by micellar enhanced ultrafiltration (MEUF). For a molar ratio of 40:1 (SDBS: metal cation), the rejection of feed solution containing 10 ppm metal cations (e.g., Cd2+, Co2+, Ni2+, Cu2+, and Zn2+) surpassed 96% with MEUF method. The results showed that the prepared membrane had low-pressure driven and high-efficiency performance, which provided a potential solution for the high-efficiency removal of trace heavy metals cations.

High Purity of α-Lactalbumin from Binary Protein Mixture by Charged UF Membrane Far from the Isoelectric Point to Limit Fouling

Separation and high recovery factor of proteins similar in molecular mass is a challenging task, and heavily studied in the literature. In this work, a systematic study to separate a binary protein mixture by charged ultrafiltration membranes without affecting membrane performance was carried out. α-lactalbumin (ALA, 14.4 kDa) and β-lactoglobulin (BLG, 18.4 kDa) were used as a binary model system. These two proteins are the main proteins of whey, a very well-known byproduct from the dairy industry. Initially, a systematic characterization of individual proteins was carried out to determine parameters (protein size and aggregation, zeta potential) which could influence their passage through a charged membrane. Then, the influence of operating parameters (such as initial protein concentration, pH, and critical pressure) on the UF process was investigated, so as to identify conditions that limit membrane fouling whilst maximizing protein recovery factor and purity. The study permitted to identify process conditions able to fully separate ALA from BLG, with high purity (95%) and recovery factor (80%), in a single UF step. Compared to studies reported in literature, here, the main approach used was to carry out a charged UF process far from proteins isoelectric point (pI) to limit protein aggregation and membrane fouling.

Positively charged ultrafiltration membranes fabricated via graft polymerization combined with crosslinking and branching for textile wastewater treatment

2-methacryloyloxy ethyl trimethylammonium chloride (DMC) was successfully grafted with 2-hydroxyethyl methacrylate (HEMA) as branching agent and N, N'-methylenebisacrylamide (MBAA) as crosslinker onto the surface of hydrolyzed polyacrylonitrile (HPAN) ultrafiltration membrane with high density via ceric ion (Ce4+)-induced graft polymerization. The successful graft polymerizations were confirmed by characterization of attenuated total reflectance spectrophotometer, X-ray photoelectron spectroscopy, scanning electron microscope and atomic-force microscopy. The obtained membranes showed surface positive charges and favorable hydrophilicity, which resulted in an ultrahigh permeability, distinguished rejection for positively charged dyes (>99%) and almost no retention for divalent salts (<4%), as well as excellent stability in multiple cycles of filtration. This work provided an efficient and facile approach to tailor the structure and properties of ultrafiltration membranes.

Recent Advancements of UF-Based Separation for Selective Enrichment of Proteins and Bioactive Peptides—A Review

Proteins are one of the primary building blocks that have significant functional properties to be applied in food and pharmaceutical industries. Proteins could be beneficial in their concentrated products or isolates, of which membrane-based filtration methods such as ultrafiltration (UF) encompass application in broad spectra of protein sources. More importantly, selective enrichment by UF is of immense interest due to the presence of antinutrients that may dominate their perspicuous bioactivities. UF process is primarily obstructed by concentration polarization and fouling; in turn, a trade-off between productivity and selectivity emerges, especially when pure isolates are an ultimate goal. Several factors such as operating conditions and membrane equipment could leverage those pervasive contributions; therefore, UF protocols should be optimized for each unique protein mixture and mode of configuration. For instance, employing charged UF membranes or combining UF membranes with electrodialysis enables efficient separation of proteins with a similar molecular weight, which is hard to achieve by the conventional UF membrane. Meanwhile, some proposed strategies, such as utilizing ultrasonic waves, tuning operating conditions, and modifying membrane surfaces, can effectively mitigate fouling issues. A plethora of advancements in UF, from their membrane material modification to the arrangement of new configurations, contribute to the quest to actualize promising potentials of protein separation by UF, and they are reviewed in this paper.

Charged ultrafiltration membranes based on TEMPO-oxidized cellulose nanofibrils/poly(vinyl alcohol) antifouling coating.

This study reports the potential of TEMPO-oxidized cellulose nanofibrils (T-CNF)/poly(vinyl alcohol) (PVA) coatings to develop functionalized membranes in the ultrafiltration regime with outstanding antifouling performance and dimensional/pH stability. PVA acts as an anchoring phase interacting with the polyethersulfone (PES) substrate and stabilizing for the hygroscopic T-CNF via crosslinking. The T-CNF/PVA coated PES membranes showed a nano-textured surface, a change in the surface charge, and improved mechanical properties compared to the original PES substrate. A low reduction (4%) in permeance was observed for the coated membranes, attributable to the nanometric coating thickness, surface charge, and hydrophilic nature of the coated layer. The coated membranes exhibited charge specific adsorption driven by electrostatic interaction combined with rejection due to size exclusion (MWCO 530 kDa that correspond to a size of ∼35–40 nm). Furthermore, a significant reduction in organic fouling and biofouling was found for T-CNF/PVA coated membranes when exposed to BSA and E. coli. The results demonstrate the potential of simple modifications using nanocellulose to manipulate the pore structure and surface chemistry of commercially available membranes without compromising on permeability and mechanical stability.

Removal of model dyes on charged UF membranes: Experiment and simulation

Charged ultrafiltration (UF) membranes can repel electrically charged molecules that are smaller than the size of the membrane pores and display high rejection of solutes, high flux, and low operation pressures compared to uncharged UF, nanofiltration (NF) and reverse osmosis (RO). Here, a charged UF membrane composite (PANI/PVDF) was prepared and regulated via electrochemically reversible control in portions of amine/imine functional groups of PANI. As a result, the permeability and rejection ratios of CR2- on charged PANI/PVDF, with PVDF as a control, increased from 19.6 to a maximum of 183.3 L m-2 h-1 bar-1 and from 3.4% to 74%, which expands the trade-off confine benefited from surface potential change from-12.21 mV to-25.26 mV, furtherly, the rejection ratio of CR2- on PANI/PVDF reached up to 93% via the electrochemical regulation. Finally, a fixed-charge model was built that well describes the steric and electric repulsion effects on membrane performance and the important roles of the electrochemically controllable surface charge. Moreover, the contour map of rejection ratios containing the ratio of molecular size vs the average pore size of the membrane (r/R = 0.2-1.0) and the zeta potential (-10 to-60 mV) were taken into account, which can be used to visually understand the rejection performance of membranes. This model is also appropriate for varying molecular sizes and for molecules with different charges. Our work opens a new horizon for the design of electrochemically controllable charged membranes to remove charged compounds.

Tannic acid coating and in situ deposition of silver nanoparticles to improve the antifouling properties of an ultrafiltration membrane

ABSTRACTThe construction of antifouling membranes has been a desirable approach for addressing membrane‐fouling issues in the ultrafiltration (UF) process. Antifouling means antiadhesive and antimicrobial; however, few researchers have achieved both properties in a facile and effective manner. In this article, we report a direct tannic acid (TA) coating method combined with the in situ deposition of silver nanoparticles (Ag NPs); this was used to improve the antifouling properties of a positively charged polymeric UF membrane. The results show that the TA–Ag NP modified membranes showed improved protein resistance (flux recovery rate = 71.2% after modification vs 17.8% before modification) and less attachment of bacteria (Escherichia coli K1) on the membrane surface and reduced cell viability in the resulting bacterial suspension (reduced by ≥90%) because of the combined antimicrobial properties of both the TA and Ag NPs. This indicated that our modification method was promising for UF membrane antifouling applications. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019, 136, 47314.

Fractionation of Glycomacropeptide from Whey Using Positively Charged Ultrafiltration Membranes.

Fractionation of the bovine glycomacropeptide (GMP) from the other proteins in cheese whey was examined using ultrafiltration membranes surface modified to contain positively charged polymer brushes made of polyhexamethylene biguanide. By placing a strong positive charge on a 1000 kDa ultrafiltration membrane and adjusting the pH of whey close to the isoelectric point of GMP, a 14-fold increase in selectivity was observed compared to unmodified membranes. A one stage membrane system gave 90% pure GMP and a three-stage rectification system gave 97% pure GMP. The charged membrane was salt-tolerant up to 40 mS cm−1 conductivity, allowing fractionation of GMP directly from cheese whey without first lowering the whey conductivity by water dilution. Thus, similarly sized proteins that differed somewhat in isoelectric points and were 50–100 fold smaller than the membrane molecular weight cut-off (MWCO), were cleanly fractionated using charged ultrafiltration membranes without water addition. This is the first study to report on the use of salt-tolerant charged ultrafiltration membranes to produce chromatographically pure protein fractions from whey, making ultrafiltration an attractive alternative to chromatography for dairy protein fractionation.

Milk Protein Concentration Using Negatively Charged Ultrafiltration Membranes.

In this work, milk protein concentrate (MPC) was made using wide-pore negatively charged ultrafiltration membranes. The charged membranes were used for a six-fold volume concentration of skim milk and subsequent diafiltration to mimic the industrial MPC process. The charged 100 kDa membranes had at least a four-fold higher permeate flux at the same protein recovery as unmodified 30 kDa membranes, which are currently used in the dairy industry to make MPC. By placing a negative charge on the surface of an ultrafiltration membrane, the negatively charged proteins were rejected by electrostatic repulsion and not simply size-based sieving. Mass balance models of concentration and diafiltration were developed and the calculations matched the experimental observations. This is the first study to use wide-pore charged tangential-flow membranes for MPC manufacturing. Additionally, a unique mass balance model was applied, which accurately predicted experimental results.

Analysis of Protein Separation Mechanism in Charged Ultrafiltration Membrane

The separation mechanism of proteins on a charged ultrafiltration membrane was analyzed using the extended Nernst–Planck (N-P) model. The model was solved numerically based on experimental data during ultrafiltration of bovine serum albumin/BSA and hemoglobin at various pH (between 5 and 8) to obtain the flux parameter ( J v ). The flux parameter was used to determine the effective charge of the membrane ( f ) and the actual membrane porosity ( A k ). These two parameters were then used to predict the transport mechanism of proteins through the charged membrane. Higher flux was obtained during the ultrafiltration of BSA compared to hemoglobin. The most effective separation of mixed proteins occurred at pH 5 ( a albumin = 5). In addition, the mobility of a single protein was lower than when it was mixed with other proteins that had different charges. The effective charges of the membranes were varied between 0.99996 to 1.0000, which means that the fixed charge on the membrane structure was higher than the concentration of proteins, thus the effective charge of the membrane was not influenced by the presence of protein charge at various pH. On the contrary, the value of A k was influenced by the type and charge of the proteins. A decrease of negative charge along with an increase of solution pH increased the porosity of the membrane, thus reducing the rejection of proteins.

Polyarylsulfone-based blend ultrafiltration membranes with combined size and charge selectivity for protein separation

Current research is actively devoted to the development of high-performance ultrafiltration membranes with high permeability at maximum selectivity for dedicated separations. This work reports the preparation of polymer blend charged ultrafiltration membranes for the improvement of fractionation selectivity. Flat sheet membranes made from polysulfone and various types of sulfonated poly(arylsulfone)s were prepared via non-solvent induced phase separation. Membrane morphology, hydrophilicity and surface charge were assessed by scanning electron microscopy, contact angle and zeta potential measurements, respectively. The separation performances, i.e. selectivity factor, permeability, and permeability recovery, were evaluated by ultrafiltration of model proteins – bovine serum albumin (BSA) and hemoglobin (Hb). Results showed that the membrane charge can be tuned by adjusting the fraction of sulfonated groups via the type of sulfonated polymer in the blend used for membrane preparation. Hence, a broad range of ultrafiltration membranes with different barrier pore sizes, permeability properties and surface charge was established. Pronounced differences between the effects of different types of sulfonated poly(arylsulfone)s at the same degree of sulfonation and mass fraction in the membranes had been found and related to different barrier structures formed during phase separation. Successful separation of protein mixtures was achieved by additionally adjusting filtration parameters. Overall, this work provides guidelines for a versatile and easy method to tailor membrane properties for the selective separation of binary mixtures of biomacromolecules with nearly identical molecular weight and potentially also to solve other separation problems.

Simultaneous removal of humic acid and heavy metal from aqueous solutions using charged ultrafiltration membranes

ABSTRACTLab-made negatively charged ultrafiltration (UF) membranes were used for simultaneous removal of humic acid (HA) and heavy metals from water. Effects of the HA/metal ratio, solution pH and ionic strength on rejection coefficients of HA and metals were investigated. The results showed that the rejection coefficients of both HA and metals increase with the increase of pH and the HA/metal ratio, and the decrease of ionic strength. This study indicated that charged UF could be an effective method for the simultaneous removal of HA and heavy metal harnessing the principle of complexation UF and electrostatic repulsion between the membrane and the HA–M complex of the same charges.

Surfactant-stabilized oil separation from water using ultrafiltration and nanofiltration

The treatment of oily wastewater containing well-stabilized oil emulsions remains a challenge. As gravity-based separation methods cannot effectively remove emulsified oil droplets with sizes below 10µm, water polishing steps need to be applied to reduce the organic load of the treated effluent. Membrane-based separation processes ensure high permeate quality, but are prone to fouling when treating oily wastes. Surfactants play an important role in producing well-stabilized oil emulsions, but there has been limited work on the effect of surfactants on membrane fouling. To fundamentally understand the surfactant effect on fouling, we studied the fouling of model oil (hexadecane) emulsions stabilized by anionic, cationic and nonionic surfactants in a crossflow filtration system using either ultrafiltration (UF) or nanofiltration (NF) membranes. For this, we investigated the impact of membrane surface and emulsion properties on the different fouling mechanisms observed in our experiments. UF filtration experiments revealed that emulsions stabilized with cationic surfactant quickly fouled negatively charged UF membranes due to electrostatic attraction, while anionic and non-ionic surfactants stabilized emulsions experienced less fouling. In NF filtration tests, membranes exhibited exponential fouling when filtrating all types of surfactant stabilized emulsions. Permeate quality confirms that the NF process achieves better rejection of surfactants than the UF process. However, cationic surfactants are able to pass through NF membranes because of their positive charge. When salt is added to the water, electrostatic forces collapse, and the differences between the surfactants are quenched. Our experimental results combined with theoretical calculations reveal that initial membrane fouling by emulsified oil drops is dominated by a cake layer formation. However, once a critical pressure drop across the cake layer is achieved, membrane wetting occurs, which results in irreversible membrane fouling in both UF and NF.

Positively charged membrane for removing low concentration Cr(VI) in ultrafiltration process

To enhance the low concentration hexavalent chromium (Cr(VI)) removal performance in membrane filtration process, two novel positively charged ultrafiltration (UF) membranes were prepared. Firstly, a tertiary amine based UF membrane (TA membrane) was fabricated by blending tertiary amine containing block copolymer poly(methyl methacrylate-b-dimethylamino-2-ethyl methacrylate) (P(MMA-b-DMAEMA)) with poly (vinylidene fluoride) (PVDF) via a non-solvent induced phase separation (NIPS) process. Secondly, a quaternary ammonium based UF membrane (QA membrane) was prepared by surface quaternization on the TA membrane. The surface quaternization was confirmed by attenuated total reflectance Fourier transform infrared (ATR/FTIR) and X-ray photoelectron spectroscopy (XPS). While, the images from scanning electron microscopy (SEM) suggested that the quaternization had little effect on the membrane morphology. By measuring the water contact angle, surface charge, water permeation properties at different pH, Cr(VI) adsorption and desorption properties as well as the Cr(VI) removal performance in filtration process, the two membranes were compared. The results showed that compared with the TA membrane, the contact angle of the QA membrane decreased from 69° to 58°, the isoelectric point increased from pH 8.3 to more than pH 11, the fluxes changed slightly with the change of feed pH and the equilibrium Cr(VI) uptake at pH 7 increased from 6.96mg/g to 63.17mg/g, indicating enhanced hydrophilicity and surface positive charge, permeation stability, wide Cr(VI) removal pH range as well as the potential application in low concentration Cr(VI) removal.

Multifunctional polyelectrolyte multilayers as nanofiltration membranes and as sacrificial layers for easy membrane cleaning

This manuscript investigates the modification of an ultra-filtration (UF) membrane support with polyelectrolyte multilayers (PEMs) consisting of the weak polyelectrolytes poly(allyl amine) hydrochloride (PAH) and poly(acrylic acid) (PAA). These prepared polyelectrolyte multilayer membranes have a dual function: They act as nanofiltration (NF) membranes and as sacrificial layers to allow easy cleaning of the membranes. In order to optimize the conditions for PEM coating and removal, adsorption and desorption of these layers on a model surface (silica) was first studied via optical reflectometry. Subsequently, a charged UF membrane support was coated with a PEM and after each deposited layer, a clear increase in membrane resistance against pure water permeation and a switch of the zeta potential were observed. Moreover these polyelectrolyte multilayer membranes, exhibited rejection of solutes in a range typical for NF membranes. Monovalent ions (NaCl) were hardly rejected (<24%), while rejections of >60% were observed for a neutral organic molecule sulfamethoxazole (SMX) and for the divalent ion SO32−. The rejection mechanism of these membranes seems to be dominated by size-exclusion. To investigate the role of these PEMs as sacrificial layers for the cleaning of fouled membranes, the prepared polyelectrolyte multilayers were fouled with silica nano particles. Subsequent removal of the coating using a rinse and a low pressure backwash with pH 3, 3M NaNO3 allowed for a drop in membrane resistance from 1.7⋅1014m−1 (fouled membrane) to 9.9⋅1012m−1 (clean membrane), which is nearly equal to that of the pristine membrane (9.7⋅1012m−1). Recoating of the support membrane with the same PEMs resulted in a resistance equal to the resistance of the original polyelectrolyte multilayer membrane. Interestingly, less layers were needed to obtain complete foulant removal from the membrane surface, than was the case for the model surface. The possibility for backwashing allows for an even more successful use of the sacrificial layer approach in membrane technology than on model surfaces. Moreover, these PEMs can be used to provide a dual function, as NF membranes and as a Sacrificial coating to allow easy membrane cleaning.

Negatively charged tangential flow ultrafiltration membranes for whey protein concentration

This work examines the use of wide-pore negatively charged ultrafiltration membranes for whey protein concentration. The hypothesis is that by placing a negative charge on the surface of an ultrafiltration membrane, negatively charged proteins are rejected by electrostatic repulsion and not simply sized based sieving. This allows using wide-pore membranes that have a higher flux without suffering a loss in protein recovery. It was found that negatively charged 100kDa ultrafiltration membranes had the same protein recovery as 10kDa unmodified membranes used in the dairy industry, but offered a flux that was at least two-fold higher. The new membranes were used for a 40-fold concentration of whey with subsequent diafiltration to mimic the industrial process for making whey protein concentrate. Mass balance models of concentration and diafiltration were developed and each agreed well with the experimental results. The experimental methods and mathematical models developed in this work can be used to design, simulate and optimize different process flow sheets, and explore the effect of various operating conditions on the membrane processing of whey.

Recovery of small dye molecules from aqueous solutions using charged ultrafiltration membranes

Recovery of reactive dyes from effluent streams is a growing environmental challenge. In this study, various charged regenerated cellulose (RC) ultrafiltration (UF) membranes were prepared and tested for removal of three model reactive dyes (reactive red ED-2B, reactive brilliant yellow K-6G, and reactive brilliant blue KN-R). Data were obtained with charged UF membranes having different spacer arm lengths between the base cellulose and the charge functionality. The effects of charge density of the dye molecules, ionic strength of the feed solution, spacer arm length of charged membranes and filtrate flux were studied. Results indicated that dye retention was greatest with the most negatively charged dye molecule. Higher rejection was also observed in low ionic strength solutions. Results were consistent with model calculations based on the partitioning of a charged sphere into a charged cylindrical pore. The membranes with longer spacer arm length had higher rejection coefficients, consistent with the greater negative charge on these membranes. This study confirms that charged UF membranes can effectively recover small reactive dye molecules at low pressures (below 100kPa) under appropriate solution conditions due to the strong electrostatic repulsion from the membrane pores.