UF of pulp and paper effluent: membrane fouling-prevention and cleaning

Effluent arriving from the Mondi Kraft paper mill at Piet Retief, South Africa, was filtered through tubular poly(ether sulphone) (PES) ultrafiltration membranes under constant pressure cross-flow conditions. The effluent that was fed into the membranes and permeate produced during filtration were characterised by UV–VIS light-spectroscopy. Substances that absorbed onto membranes during filtration caused changes to the permeability characteristics of the membranes. Changes in membrane performance were monitored by pure-water and product flux (pf) measurements.A colourimetric staining technique was developed to determine the nature of foulants adsorbed onto the membranes. Membrane cleaning solutions were subsequently selected using information obtained from the characterisation studies. In addition, the anti-fouling potential of non-covalently attached coating materials was investigated as a possible membrane pretreatment technique. Results showed that foulants present in the effluent are of phenolic and hydrophobic nature. Increasing the hydrophilic characteristics of membranes prior to filtration could reduce the amount of organic foulants that adsorbed onto the membranes. Membrane pretreatment not only reduced fouling, but also improved the effectiveness of cleaning methods. Membranes were effectively cleaned by a combination of mechanical and chemical cleaning techniques.     

Chemical Cleaning of Microfiltration Membranes Fouled by Whey

Millipore hydrophobic polyvinylidene fluoride (PVDF) microfiltration membranes were used for whey processing. Fouled membranes were cleaned with acid (HCl), alkaline (NaOH) and surfactant (Triton‐X100). The latter resulted in maximum flux recovery and resistance removal. Hydrochloric acid had a moderate effect and sodium hydroxide was the weakest cleaning agent. This is due to the cleaning strength of emulsifiers compared to acid or alkali. However acids are more efficient than alkaline solutions for removal of mineral compounds which remain on the membrane surface. Cleaning efficiency depends on the concentration of cleaning agent being higher for higher surfactant concentration. For acids and alkali, the efficiency increases with increasing the concentration of the reagent reaches a maximum (optimum concentration) and then decreases. This can be explained by changes in permeability of the deposit layer with the concentration of the cleaning agent. Another explanation is the breakage of proteins by acid or alkali which produces more fouling materials and causes less cleaning efficiency. Operating conditions affect the cleaning process. At higher stirring speeds (turbulent flow) or longer cleaning time better removal of deposits and higher cleaning efficiency were observed. The sequential cleaning process may or may not improve the cleaning efficiency. When acidic cleaning was followed by washing with a surfactant an improvement was achieved. This can be attributed to the incomplete removal of deposits by acid. However further cleaning with acid can not improve the cleaning efficiency. During whey processing fouling occurs by deposition of foulants of mostly proteins and macromolecules on the membrane surface or in the membrane matrix. Large substances (compared to the membrane pores) settle on the membrane surface and the small species penetrate and are adsorbed in the membrane pores. Cleaning dissolves and removes the adsorbed foulants from the membrane.     

Chemical cleaning of oil contaminated polyethylene hollow fiber microfiltration membranes

The primary aim of this paper was to develop a more effective and economical procedure for cleaning polyethylene hollow fiber microfiltration membranes that have been used for removing oil from contaminated seawater. Alkaline cleaning showed higher recovery of operating cycle time but lower permeate flux recovery than acid cleaning. The combination of both alkaline and acid cleaning agents gave the best operating cycle time and flux recoveries (e.g. 96% and 94%, respectively). As the cleaning agent soaking time was reduced, the actual operating cycle time was reduced. However, the ratio of operating time/chemical cleaning time increased as the soaking time was reduced. The soaking time was recommended to be as short as possible (8–10 h) in the design of small capacity plants and 30 h or higher in case of large capacity plants. SEM analysis showed that in case of alkaline cleaning, most of the pores remained covered with a foulant layer, resulting in low flux recovery. The SEM results of acid cleaned membranes showed more complete removal of the foulant layer from the pores resulting in better flux recovery. Surface analysis of membranes cleaned with combined acid/base agents showed the best results. A membrane surface similar to the original one was obtained. The long-term objective is to increase the understanding of membrane fouling phenomena, preventive means and membrane cleaning processes as it applies to the clean-up and desalination of oil contaminated seawater.     

Efficiency of various chemical cleanings for nanofiltration membrane fouled by conventionally-treated surface water

Nanofiltration systems are generally cleaned chemically. The optimal choice of the cleaning agent is a function of membrane material and foulant in a complex manner. This study evaluated the cleaning efficiency and effects of several cleaning agents on NF255 nanofiltration membrane. The nanofiltration pilot plant was fed with conventionally-treated surface water from a water treatment plant in southern Finland. Fouled membranes were cleaned weekly with different chemicals and procedures, and the cleaning efficiencies were compared in terms of flux recoveries and foulant removals. On the basis of the cleaning chemical analysis, the fouling material consisted of biofouling, organic deposits and metal complexes. In these circumstances, alkaline cleaners with chelatants resulted in the most efficient cleaning both in terms of flux recovery and foulant removal. Alkaline cleaning modified the membrane and improved the flux substantially in comparison to the virgin state. The results demonstrate that the choice of chemical cleaning agent is critical to cleaning efficiency, both technically and economically. The same flux recovery could be reached either by a single cleaning phase or by three sequential cleaning phases.     

An enzymatic approach to the cleaning of ultrafiltration membranes fouled in abattoir effluent

Membrane fouling severely curtails the economical and practical implementation for the purification of biologically related process streams such as abattoir effluent (Jacobs, WRC Report no. K5/362, 1991, Pretoria, South Africa [1]). Mechanical and chemical removal of foulants usually lead to membrane damage and additional pollution. Enzymes, specific for the degradation of proteins and lipids, were tested as key components of biological cleaning regimes for membranes fouled in abattoir effluent. Fouling of polysulphone membranes was assessed as previously described by Maartens et al. (J. Membrane Sci., 119 (1996) 1 [2]) and optimal enzyme concentrations and incubation times were determined for the different preparations. The ability of each cleaning agent to remove adsorbed protein and lipid material, as well as their ability to restore the water-contact angle and the pure-water flux of the fouled membranes, were determined and compared. These variables were also used to compare the cleaning efficiency of enzymatic cleaning agents with conventional chemical agents under optimal conditions. The enzymes and enzyme detergent mixtures were effective cleaning agents and the pure-water flux of statically fouled membranes could be restored by treatment with these agents.     

Probing Membrane Fouling via Infrared Attenuated Total Reflection Mapping Coupled with Multivariate Curve Resolution

Understanding membrane fouling induced by dissolved organic matter (DOM) is of primary importance for developing effective fouling control and prevention strategies. In this work, we combine multivariate curve resolution–alternating least squares analysis with infrared attenuated total reflection mapping to explore the fouling process of microfiltration and ultrafiltration membranes caused by two typical DOMs, humic acid (HA) and bovine serum albumin (BSA). The spectral contributions of different foulants and the membrane substrate were successfully discriminated, thereby enabling the diagnosis of fouling origins. Membrane fouling caused by HA is more severe than that by BSA. Three periods, the initial adsorption stage, the equilibrium stage, and the accumulation stage, were observed for the HA‐induced fouling process. The integrated approach presented herein elegantly demonstrates the spatial and temporal characterization of membrane fouling processes, along with relative concentrations of the involved species, and suggests a promising perspective for understanding the interaction mechanisms between foulant species and membranes at the molecular level.     

Critical flux in NF of high molar mass polysaccharides and effluents from the paper industry

High molar mass polysaccharides (locust bean gum and karaya gum) and effluents from a mechanical pulp mill and a paper mill were nanofiltered with commercially available nanofiltration (NF) membranes. The effect of the filtration conditions on the flux (critical flux), retention, and the fouling of the membranes was studied. The experiments were conducted by increasing and decreasing the pressure and measuring the flux thus obtained.

The critical flux was observed to increase with increasing flow velocity and decreasing concentration. An increase in pH increased the electrostatic repulsion between the membrane and the dissociated (charged) components in the paper mill effluents. As a result, a higher critical flux was obtained and also the retentions of the charged substances improved. Only a weak form of the critical flux was observed with the mill effluents. The permeate flux deviated from the pure water flux even at the lowest pressure, but increased linearly with pressure until the weak form of the critical flux was exceeded. The small decrease in flux immediately after filtration was started was probably caused by the plugging of the free spaces in the membranes or by the adsorption of foulants onto the membrane surface.

In the filtrations with the high molar mass polysaccharides, a strong form of the critical flux as well as a weak form were observed. The significant irreversible fouling of the most hydrophobic membrane was due to adsorption of the model substances by hydrophobic interaction. A precleaning of the membranes with an alkaline cleaning agent improved the pure water fluxes by up to 30%, but it had only a small effect on the critical or the limiting flux. The pure water fluxes of precleaned membranes after filtration were still higher than the pure water fluxes of the untreated membranes before filtration.     

Chemical and physical aspects of organic fouling of forward osmosis membranes

The growing attention to forward osmosis (FO) membrane processes from various disciplines raises the demand for systematic research on FO membrane fouling. This study investigates the role of various physical and chemical interactions, such as intermolecular adhesion forces, calcium binding, initial permeate flux, and membrane orientation, in organic fouling of forward osmosis membranes. Alginate, bovine serum albumin (BSA), and Aldrich humic acid (AHA) were chosen as model organic foulants. Atomic force microscopy (AFM) was used to quantify the intermolecular adhesion forces between the foulant and the clean or fouled membrane in order to better understand the fouling mechanisms. A strong correlation between organic fouling and intermolecular adhesion was observed, indicating that foulant–foulant interaction plays an important role in determining the rate and extent of organic fouling. The fouling data showed that FO fouling is governed by the coupled influence of chemical and hydrodynamic interactions. Calcium binding, permeation drag, and hydrodynamic shear force are the major factors governing the development of a fouling layer on the membrane surface. However, the dominating factors controlling membrane fouling vary from foulant to foulant. With stronger intermolecular adhesion forces, hydrodynamic conditions for favorable foulant deposition leading to cake formation are more readily attained. Before a compact cake layer is formed, the fouling rate is affected by both the intermolecular adhesion forces and hydrodynamic conditions. However, once the cake layer forms, all three foulants have very similar flux decline rates, and further changes in hydrodynamic conditions do not influence fouling behavior.     

Colloidal interactions and fouling of NF and RO membranes: a review

Colloids are fine particles whose characteristic size falls within the rough size range of 1-1000 nm. In pressure-driven membrane systems, these fine particles have a strong tendency to foul the membranes, causing a significant loss in water permeability and often a deteriorated product water quality. There have been a large number of systematic studies on colloidal fouling of reverse osmosis (RO) and nanofiltration (NF) membranes in the last three decades, and the understanding of colloidal fouling has been significantly advanced. The current paper reviews the mechanisms and factors controlling colloidal fouling of both RO and NF membranes. Major colloidal foulants (including both rigid inorganic colloids and organic macromolecules) and their properties are summarized. The deposition of such colloidal particles on an RO or NF membrane forms a cake layer, which can adversely affect the membrane flux due to 1) the cake layer hydraulic resistance and/or 2) the cake-enhanced osmotic pressure. The effects of feedwater compositions, membrane properties, and hydrodynamic conditions are discussed in detail for inorganic colloids, natural organic matter, polysaccharides, and proteins. In general, these effects can be readily explained by considering the mass transfer near the membrane surface and the colloid-membrane (or colloid-colloid) interaction. The critical flux and limiting flux concepts, originally developed for colloidal fouling of porous membranes, are also applicable to RO and NF membranes. For small colloids (diameter?100 nm), the limiting flux can result from two different mechanisms: 1) the diffusion-solubility (gel formation) controlled mechanism and 2) the surface interaction controlled mechanism. The former mechanism probably dominates for concentrated solutions, while the latter mechanism may be more important for dilute solutions. Future research needs on RO and NF colloidal fouling are also identified in the current paper.     

A three mechanism model to describe fouling of microfiltration membranes

Mathematical modeling of flux decline during filtration plays an important role in both sizing membrane systems and in the understanding of membrane fouling. Protein fouling is traditionally modeled using one of three classical fouling mechanisms: pore blockage, pore constriction or cake filtration. Here, we have developed a mathematical model to describe flux decline behavior during microfiltration accounting for all three classical fouling mechanisms. Pore constriction was assumed to first reduce the size of internal pores. Pore blockage then occurs at the top of the membrane, preventing further fouling to the interior structure. Finally the foulants at the top of the membrane form a cake, which controls the late stages of the filtration. The model prediction shows excellent agreement with experimental data for 0.25 μm polystyrene microspheres filtered through 0.22 μm Isopore membranes (where pore constriction is expected to be minimal) as well as non-aggregated bovine serum albumin solution through hydrophobic Durapore membranes (where pore constriction is expected to dominate). The effects of different fouling mechanisms on the flux decline were characterized by the ratio of characteristic fouling times of the different mechanisms. In this way the model can provide additional insights into the relative importance of different fouling mechanisms as compared to an analysis by a single mechanism model or by derivative plots, and it can be used to provide important insights into the flux decline characteristics.     

A systematic insight into fouling propensity of soluble microbial products in membrane bioreactors based on hydrophobic interaction and size exclusion

Soluble microbial products (SMPs) contained in membrane bioreactor (MBR) supernatant have been proved to be main foulants. To obtain a comprehensive understanding of the fouling potential of SMPs on the basis of both hydrophilic/hydrophobic properties and molecular size, MBR supernatant of a pilot-scaled system treating municipal wastewater was partitioned into different hydrophilic/hydrophobic fractions by DAX-8 resins, with joint size partition of hydrophilic fraction also undertaken. A series of stirred dead-end filtration tests were conducted to investigate the flux decline. Hydrophilic fraction was found the dominant foulant responsible for flux deterioration, which was mainly attributed to the subclass of molecular weight above 100 kDa. The molecular weight distribution and atomic force microscopy images indicated that large molecules in hydrophilic fraction plugged the membrane pores. The backwash tests showed the flux decline caused by hydrophilic fraction was much less recoverable by hydraulic cleaning. It can be inferred that steric factor, i.e. size exclusion was the primary cause in the initial stage of fouling, while the role of hydrophobic interaction was of less significance. Additional modeling work indicates that the main fouling mechanism was complete blocking, further confirming the predominance of size exclusion contributing to membrane fouling by SMPs in MBR supernatant.     

Surface modification of polypropylene membranes by γ-ray induced graft copolymerization and their solute permeation characteristics

Porous hydrophobic polypropylene (PP) membranes were subjected to the surface modification by the γ-ray induced graft copolymerization with hydrophilic 2-hydroxyethyl methacrylate (HEMA). The structural changes and surface morphologies of the modified PP membranes were characterized by a Fourier transform infrared spectroscopy (FT-IR), elemental analysis (EA) and field emission scanning electron microscopy (FE-SEM). Peroxides produced from γ-ray irradiation were determined by a 1,1-diphenyl-2-picryl hydrazyl (DPPH) method and the surface hydrophilicities of membranes were measured by a static contact angle measurement. The contact angle of the modified membranes reduced with the degree of grafting (DG) of HEMA onto the membrane surface, and it decreased up to about half of that before modification. The permeation behaviors of all membranes were investigated by a bovine serum albumin (BSA) filtration experiment. As a result, the DG of the modified membrane increased with the reaction time. However, in the case of irradiation dosage it showed the maximum value at 20 kGy. Also, the modified membrane showed a higher solution flux, lower BSA adsorption, and the better flux recovery after cleaning than that of the unmodified membrane. Particularly, 40.6% grafted membrane showed a two-fold increase in a BSA solution flux, 62% reduction in total fouling and three-fold increase in flux recovery after chemical cleaning.     

Photografted thin polymer hydrogel layers on PES ultrafiltration membranes: characterization, stability, and influence on separation performance

Highly fouling-resistant ultrafiltration (UF) membranes were synthesized by heterogeneous photograft copolymerization of two water-soluble monomers, poly(ethylene glycol) methacrylate (PEGMA) and N,N-dimethyl-N-(2-methacryloyloxyethyl-N-(3-sulfopropyl)ammonium betaine (SPE), with and without cross-linker monomer N,N'-methylene bisacrylamide (MBAA), onto a polyethersulfone (PES) UF membrane. The characteristics, the stability, and the UF separation performance of the resulting composite membranes were evaluated in detail. The membranes were characterized with respect to membrane chemistry (by ATR-IR spectroscopy and elemental analysis), surface wettability (by contact angle), surface charge (by zeta potential), surface morphology (by scanning electron microscopy), and pure water permeability and rejection of macromolecular test substances (including the "cutoff" value). The surface chemistry and wettability of the composite membranes did not change after incubating in sodium hypochlorite solution (typically used for cleaning UF membranes) for a period of 8 days. Changes in water permeability after static contact with solutions of a model protein (myoglobin) were used as a measure of fouling resistance, and the results suggest that PEGMA- and SPE-based composite membranes at a sufficient degree of graft modification showed much higher adsorptive fouling resistance than unmodified PES membranes of similar or larger nominal cutoff. This was confirmed in UF experiments with myoglobin solutions. Similar results, namely, a very much improved fouling resistance due to the grafted thin polymer hydrogel layer, were also obtained in the UF evaluation using humic acid as another strong foulant. In some cases, the addition of the cross-linker during modification could improve both permeate flux and solute rejection during UF. Overall, composite membranes prepared with an "old generation" nonfouling material, PEGMA, showed better performance than composite membranes prepared with a "new generation" one, the zwitterionic SPE.     

Preparation of electrically enhanced forward osmosis (FO) membrane by two-dimensional MXenes for organic fouling mitigation

In this work, a conductive thin film composite forward osmosis (TFC-FO) membrane was firstly prepared via vacuum filtering MXenes nanolayer on the outer surface of polyethersulfone membrane followed by interfacial polymerization in the other side. Moreover, its feasibility of mitigating organic fouling under electric field was evaluated. Results indicated that the addition of MXenes greatly reduced the electric resistance of membrane from 2.1 × 10¹² Ω to 46.8 Ω, enhanced the membrane porosity and promoted the membrane performance in terms of the ratio of water flux to reverse salt flux. The modified TFC-FO membrane presented the optimal performance with 0.47 g/m² loading amount of MXenes. Organic fouling experiments using sodium alginate (SA) and bovine serum albumin (BSA) as representative demonstrated that the introduction of MXenes could effectively enhance the anti-fouling ability of TFC-FO membrane under the electric field of 2 V. The interelectron repulsion hindered organic foulants attaching into membrane surface and thus effectively alleviated the membrane fouling. More importantly, the modified TFC-FO membrane showed good stability during the fouling experiment of 10 h. In all, our work proved that introducing MXenes into the porous layer of support is feasible to alleviate organic fouling of FO membrane.     

Membrane fouling and cleaning in ultrafiltration of wastewater from banknote printing works

The hollow fiber blend membrane, fouled by plant wastewater from banknote printing works, was characterized with SEM and the fouling elements were investigated by EDX. Based on analysis results, fouling process in ultrafiltration was simulated by using the model substances, which exist in the wastewater from banknote printing works, such as Turkey red oil, sodium hydroxide and calcium ion. It is observed that the reaction between Turkey red oil and calcium ion forms sediments, which leads to the beginning of membrane fouling. Furthermore, a four-step cleaning method, including de-ionized water cleaning, hydrochloric acid (0.1N) aqueous solution cleaning, second de-ionized water cleaning and sodium hydroxide (1 wt.%) aqueous solution cleaning, was used to clean the seriously fouled membrane in both lab and plant scale (membrane areas were 0.0157 and 80 m², respectively) experiments. The results show that the cleaning method is effective. The membrane surface after cleaning was also analyzed by SEM/EDX and the foulants in the cleaning solutions were identified by TOC and ICP. According to these experimental results, the mechanisms of membrane fouling and cleaning were proposed. The four-step cleaning method has been widely used in the ultrafiltration of wastewater from banknote printing works.     

Ultrasonic time-domain reflectometry as a non-destructive instrumental visualization technique to monitor inorganic fouling and cleaning on reverse osmosis membranes

Fouling is readily acknowledged as one of the most critical problems limiting the wider application of membranes in liquid separation processes. A better understanding of fouling layer formation and its monitoring is needed in order to improve on existing cleaning techniques. The overall objective of this research was to develop a non-destructive, real-time, in situ visualization technique or device for fouling layer monitoring. Ultrasonic time-domain reflectometry (UTDR) was employed as a visualization technique to provide real-time characterization of the fouling layer. The fouling experiment was carried out with 2 g/l calcium carbonate solution. Results confirmed that there is a correspondence between the flux decline behavior and the UTDR response from membranes in reverse osmosis (RO) modules. The ultrasonic technique could effectively detect fouling layer initiation and growth on the membrane in real-time at different axial velocities. In addition to the measurement of fouling, the ultrasonic technique was also successfully employed for monitoring membrane cleaning. The UTDR technique, due to its extremely powerful capabilities and its use in monitoring devices, can be of great significance in the membrane industry.     

Membrane formation mechanism and permeation properties of a novel porous polyimide membrane

The transport properties of a novel porous fluorinated polyimide membrane fabricated by a wet phase inversion process were studied with a stirred dead‐end filtration cell. The porous membrane‐forming solvents were tetrahydrofuran (THF), acetone, N,N‐dimethylacetamide (DMAc), N‐methylpyrrolidone (NMP), N,N‐dimethylformamide (DMF), and dimethylsulfoxide (DMSO). The phase separation phenomena in a ternary system of polyimide/solvent/water were investigated from cloud point curves by a titration method and binary interaction parameters. Solvent–water demixing in the system has been found to play very important roles in determining the structure and surface morphology of the polyimide membrane. The porous fluorinated polyimide membranes showed pore sizes from 4 to 500 nm and permeation properties from ultrafiltration to a microfiltration range. In this study, we particularly focused on fouling of the polyimide membranes, because fouling decreases the flux and increases the resistance. Interestingly, the porous polyimide membrane showed excellent water flux recovery after water cleaning compared with that of the polyethersulfone (PSf) membrane, which suggest that for a 6FDA‐6FAP membrane, the protein–membrane and protein–protein interaction was not so strong compared with those in a PSf membrane. Copyright © 2002 John Wiley & Sons, Ltd.     

Effects of polyether–polyamide block copolymer coating on performance and fouling of reverse osmosis membranes

The effects of a water-permeable polymer coating on the performance and fouling of high-flux (ESPA1 and ESPA3) and low-flux (SWC4) polyamide reverse osmosis (RO) membranes were investigated. It was anticipated that the coating would create a smoother hydrophilic surface that would be less susceptible to fouling when challenged with a motor-oil/surfactant/water feed emulsion (used as a model foulant). AFM and FT-IR analyses confirm that a 1 wt.% polyether–polyamide (PEBAX^® 1657) solution applied to ESPA and SWC4 membranes produces a continuous polymer coating layer and, thereby, provides smoother membrane surfaces. However, pure-water permeation data combined with a series-resistance model analysis reveal that the coating does not only cover the surface of the polyamide membrane, but also penetrates into its porous ridge-and-valley structure. During a long-term (106-day) fouling test with an oil/surfactant/water emulsion, the rate of flux decline was slower for coated than for uncoated membranes. This improvement in fouling resistance compensated for the decrease in permeate flux for SWC4 over a period of approximately 40 days. However, the coating material is believed to penetrate more deeply into the polyamide surface layer of the high flux, high surface area ESPA membranes relative to the low-flux SWC4, resulting in significant water flux reduction.     

Membrane fouling in a submerged membrane bioreactor (MBR) under sub-critical flux operation: Membrane foulant and gel layer characterization

Membrane foulants and gel layer formed on membrane surfaces were systematically characterized in a submerged membrane bioreactor (MBR) under sub-critical flux operation. The evaluation of mean oxidation state (MOS) of organic carbons and Fourier transform infrared (FT-IR) spectroscopy demonstrated that membrane foulants in gel layer were comprised of not only extracellular polymeric substances (EPS) (proteins, polysaccharides, etc.) but also other kinds of organic substances. It was also found that fine particles in mixed liquor had a strong deposit tendency on the membrane surfaces, and membrane foulants had much smaller size than mixed liquor in the MBR by particle size distribution (PSD) analysis. Gel filtration chromatography (GFC) analysis showed that membrane foulants and soluble microbial products (SMP) had much broader distributions of molecular weight (MW) and a larger weight-average molecular weight (M_w) compared with the influent wastewater and the membrane effluent. Scanning electron microscopy (SEM) and energy-diffusive X-ray (EDX) analysis indicated that membrane surfaces were covered with compact gel layer which was formed by organic substances and inorganic elements such as Mg, Al, Fe, Ca, Si, etc. The organic foulants coupled the inorganic precipitation enhanced the formation of gel layer and thus caused membrane fouling in the MBR.     

Remarkable reduction of irreversible fouling and improvement of the permeation properties of poly(ether sulfone) ultrafiltration membranes by blending with pluronic F127

Hydrophilic modification of ultrafiltration membranes was achieved through blending of Pluronic F127 with poly(ether sulfone) (PES). The chemical composition and morphology changes of the membrane surface were confirmed by water contact angle, X-ray photoelectron spectroscopy, scanning electron microscopy, and protein adsorption measurements. The decreased static water contact angle with an increase in the Pluronic F127 content indicated an increase of surface hydrophilicity. XPS analysis revealed enrichment of PEO segments of Pluronic F127 at the membrane surface. The apparent protein adsorption amount decreased significantly from 56.2 to 0 microg/cm(2) when the Pluronic F127 content varied from 0% to 10.5%, which indicated that the blend membrane had an excellent ability to resist protein adsorption. The ultrafiltration experiments revealed that the Pluronic F127 content had little influence on the protein rejection ratio and pure water flux. Most importantly, at a high Pluronic F127 content membrane fouling, especially irreversible fouling, has been remarkably reduced. The flux recoveries of blend membranes reached as high as 90% after periodic cleaning in three cycles.