BSA Fouling Research Articles

Nature-inspired construction of poly (vinylidene fluoride) membranes through the coordination coating of tannic acid with copper ions for oil-in-water emulsions separation

Construction of the separation membranes with underwater super-oleophobic property proposes a promising pathway in the field of oily wastewater treatment, but it is still plagued with the bottlenecks of the time-consuming preparation and the unsatisfied stability of resultant membranes. Herein, the alkali induced hydroxylation and the nature-inspired construction through the coordination coating of copper ions with tannic acid (Cu2+/TA) were performed on the poly (vinylidene fluoride) (PVDF) membrane substrate prepared by the thermally induced phase separation (TIPS). The introduced hydroxyl groups resulted from the membrane hydroxylation is beneficial for the subsequent construction of the Cu2+/TA coordination coating layer. The excellent hydrophilicity and the specifically hierarchical roughness of the immobilized coating layer endow the modified membranes with the hydrophilic/underwater super-oleophobic property. The optimized membrane correspondingly showed the improved flux of around 2000 L m−2•h−1 accompanied with the oil rejection of above 97.0% in treating two simulated oil-in-water emulsions (toluene and n-hexane). Besides, the flux recovery ratio increased from 72.4% of the pristine membrane to 93.3% of the modified membrane after the BSA fouling and regeneration test, which is also indicative of the improved antifouling behavior as a result of the hydrophilic coordination coating. The membrane stability was further demonstrated by the results of the sandpaper abrasion-resisting test and the long-term (up to 6 months) air-exposure treatment. This work might provide a straightforward strategy for designing advanced membrane for the large-scale applications of oil/water separation.

Scale up of polyamide reverse osmosis membranes surface modification with tethered poly(acrylic acid) for fabrication of low fouling spiral-wound elements

Scale up of atmospheric pressure plasma-induced graft polymerization (APPIGP) was demonstrated for surface nano-structuring (SNS) of a base polyamide (PA) reverse osmosis (RO) membrane with tethered poly(acrylic acid) (PAA) chains. Large SNS-PAA-PA membrane sheets, measuring 76.2 cm × 60.9 cm, were synthesized and used to fabricate small spiral-wound low fouling seawater RO elements (2.5 in. × 21 in.). The SNS-PAA-PA membrane sheets were of high spatial uniformity with respect to both water permeability and salt rejection. Lower SNS-PAA-PA membrane fouling propensity, relative to commercial membranes, was demonstrated in BSA and sodium alginate fouling tests of both membrane coupon and spiral-wound elements. Permeability recovery, upon water flushing of the fouled SNS-PAA-PA spiral-wound membrane elements was complete. Complete permeability recovery was also achieved for the sodium alginate fouled Dow SW30 element upon water flushing; however, permeability recovery was lower (91.6%) for the BSA fouled element, thus suggesting the need for added chemical cleaning. The study results suggest that APPIGP process scale up is feasible for fabrication of commercial-scale low fouling spiral-wound RO elements. However, further scale up toward continuous APPIGP will be required for larger size elements and automated element fabrication should be employed to minimize membrane and element construction imperfections.

Effect of the Incorporation of ZIF-8@GO into the Thin-Film Membrane on Salt Rejection and BSA Fouling.

A series of Zeolitic imidazole framework-8 (ZIF-8) clusters supported on graphene oxide (ZIF-8@GO) nanocomposites were prepared by varying the ratios of ZIF-8 to GO. The resultant nanocomposites were characterized using various techniques, such as Scanning Electron Microscope (SEM), Transmission Electron Microscope (TEM), X-ray diffraction (XRD), Brunauer–Emmett–Teller (BET), thermogravimetric analysis (TGA), Fourier Transform Infrared (FTIR) and Raman spectroscopy. These nanocomposites were incorporated into the thin film layer during interfacial polymerisation process of m-phenylenediamine (aqueous phase which contained the dispersed nanocomposites) and trimesoyl chloride (TMC, organic phase) at room temperature onto polyethersulfone (PES) ultrafiltration (UF) support membrane. The membrane surface morphology, cross section and surface roughness were characterized using SEM and AFM, respectively. Compared to the baseline membranes, the thin film nanofiltration (TFN) membranes exhibited improved pure water flux (from 1.66 up to 7.9 L.m−2h−1), salt rejection (from 40 to 98%) and fouling resistance (33 to 88%). Optimum ZIF-8 to GO ratio was established as indicated in observed pure water flux, salt rejection and BSA fouling resistance. Therefore, a balance in hydrophilic and porous effect of the filler was observed to lead to this observed membrane behaviour suggesting that careful filler design can result in performance gain for thin film composite (TFC) membranes for water treatment application.

HNb3O8/g-C3N4 nanosheet composite membranes with two-dimensional heterostructured nanochannels achieve enhanced water permeance and photocatalytic activity

A photocatalytic membrane for water treatment is required to have an efficient photocatalytic functions and high membrane performances, therefore, it is necessary to design a functional membrane structure that achieves both requirements. Herein, we describe two-dimensional material engineering on heterostructured nanochannels comprising graphitic carbon nitride (g-C3N4) and HNb3O8 nanosheets and demonstrate their potential water treatment applications based on their enhanced water permeance and photocatalytic degradation of organic compounds. Laminar HNb3O8/g-C3N4 composite membranes were fabricated by vacuum filtration. The incorporation of g-C3N4 into the HNb3O8 membrane led to an eight-fold improvement in the membrane’s water permeance relative to that of the laminar HNb3O8 membrane, while maintaining high dye rejection performance. In addition, the HNb3O8/g-C3N4 composite membranes exhibited enhanced photocatalytic degradation of the cationic dye, rhodamine B, because of the formation of a heterojunction between g-C3N4 and HNb3O8 nanosheets with a suitable band-gap alignment. Furthermore, the permeance of an HNb3O8/g-C3N4 composite membrane could be completely restored via light irradiation after BSA fouling. Each type of nanosheet plays an important role as a membrane or photocatalyst component, thereby generating a synergistic effect based on the formation of two-dimensional heterostructured nanochannels in the photocatalytic nanosheet membrane.

Chitosan: Polyvinyl alcohol based mixed matrix sustainable coatings for reusing composite membranes in water treatment: Fouling characterization

This work aims at studying the potential of modifying the surface of used polyamide (PA) reverse osmosis (RO) commercial membranes by coatings made of renewable and biodegradable polymers, chitosan (CS) and polyvinyl alcohol (PVA), filled with Cu-ion-exchange layered AM-4 titanosilicate and UZAR-S3 stannosilicate to provide antifouling properties and enlarging life time of thin-film composite (TFC) membranes. The water permeation and fouling ratios were evaluated as a function of active layer material in the presence of model organic (BSA) and inorganic (NaCl) foulants. The mixed matrix membrane (MMM) coatings added on the active surface of the PA commercial membranes generally decreased the flux decline and increased the permeate flow recovery rate. The CS:PVA based coatings promote the reversible and not the irreversible fouling, especially CuAM-4CS:PVA. Beside, ATR-FTIR confirms the reversible nature of the BSA fouling and the irreversible nature of the NaCl fouling. These results may in the future open the possibility of renewing the useful lifetime of commercial RO membranes by a simple coating method in the light of the circular economy.

Impact of dithiocarbamate-based polymeric additives on the performance of polyethersulfone membrane for the treatment of arsenic contaminated waters

Two types of aliphatic and aromatic dithiocarbamate (DTC) polymers, having the thioamide groups were synthesized and used as hydrophilic agents as well as arsenic adsorbents in fabrication and modification of polyethersulfone (PES) membranes for the separation of arsenic from the contaminated water. The synthesized DTCs were characterized by nuclear magnetic resonance (NMR) and Fourier transform infrared spectroscopy (FTIR), and their arsenic adsorption test demonstrated arsenic removal of 85.5% and 91.4% for the aromatic and aliphatic DTC polymers respectively. The results indicated that by increasing the concentration of DTCs, both membrane flux and rate of arsenic removal increased compared to the bare one. The water flux reached a maximum value at 0.5 wt% DTCs and further increase lead to decreased flux. The aliphatic DTC behaved better than the aromatic one: the membrane with aromatic DTC showed better arsenic rejection than the aliphatic one, corresponding well to the adsorption results. The water contact angle was reduced by the addition of DTCs, indicating increased hydrophilicity. The fouling resistance increased by the addition of DTCs which was demonstrated by increased flux recovery ratio (FRR) after BSA fouling. The real arsenic polluted groundwater treatment for a long-time showed that tailored-made DTC polymers are excellent candidates for arsenic removal and improvement for the fouling resistance of PES membranes.

Ultrathin rigid UTSA-280/PEI-HPAN hybrid membranes with enhanced organic dye nanofiltration performance

Metal organic frameworks (MOFs) have shown widespread applications in many aspects owing to their unique structures. In this study, a thin and homogenous UTSA-280/PEI-HPAN nanofiltration membrane was fabricated by combining interfacial reaction and in-situ self-assembly reaction, which showed rejections of 83.79%, 86.17%, 99.42% and 98.93% for MO, AF, MB and CR solutions together with permeances up to 262.54, 197.51, 145.97 and 170.63 L·m−2·h−1·MPa−1, respectively. In addition, the UTSA-280/PEI-HPAN membranes demonstrated a preferable stability in 48 h continuous test, a good anti-fouling property in both HA and BSA fouling test and an outstanding reusability, and they also showed high permeances and rejections even after four cycles. The results indicate that the stable UTSA-280/PEI-HPAN hybrid membrane with high separation performances can be a promising material for wastewater treatment.

Nanocomposite cation-exchange membranes for wastewater electrodialysis: organic fouling, desalination performance, and toxicity testing

Organic fouling hinders the application of membrane treatment of alternative water. In this study, polyethyleneimine (PEI), titanium dioxide (TiO2) nanoparticles, and graphene oxide (GO) nanosheets were used for modifying cation-exchange membranes to enhance anti-organic fouling and desalination performance during electrodialysis of synthetical water and municipal wastewater. Fouling propensity of the unmodified and modified membranes was quantitatively evaluated by measuring organic accumulation on membrane surface using humic acid (HA, simulating natural organic matter) and bovine serum albumin (BSA, simulating organic matter in municipal wastewater effluent) as model foulants. Significant surface deposition of HA was observed on the unmodified, PEI-TiO2, and PEI-modified membrane surfaces while trivial HA fouling was detected on the PEI-GO membrane. BSA fouling was minor for all the modified membranes compared to the unmodified membrane. Desalination efficiency of electrodialysis with the modified membranes, except the PEI-modified membrane, was significantly improved in treating synthetical water with HA foulant compared to the electrodialysis with the unmodified membrane (20%~40% reduction of normalized salt removal). Relatively stable desalination behaviors were observed for each membrane system in treating BSA-containing synthetical water, and enhanced desalination was demonstrated with the modified membranes. Subsequent long-term fouling experiments with wastewater effluent revealed the superior antifouling capacity of the nanocomposite membranes (especially for the PEI-GO membrane) over 100-hour operation, while the unmodified membranes exhibited severe fouling (with total more than 60% decline of normalized salt removal) after approximately 50-hour treating wastewater. In a standard Microtox® acute toxicity assay, the nanocomposite membranes did not show any acute toxicity towards Vibrio fischeri due to potential leaching of PEI and nanomaterials, indicating safe utilization of the modified membranes for water treatment.

Modification of PVDF hollow fiber membrane by co-deposition of PDA/MPC-co-AEMA for membrane distillation application with anti-fouling and anti-scaling properties

In this study, a self-prepared polyvinylidene fluoride (PVDF) hollow fiber membrane with a hierarchical structure was used for facile modification by co-deposition of polydopamine (PDA) and poly(MPC-co-2-aminoethyl methacrylate hydrochloride) (MPC-co-AEMA) for application in direct contact membrane distillation (DCMD). The facile formation of the PDA/MPC-co-AEMA layer on the membrane outer surface drastically changed the chemical and physical properties of the membrane surface. Although the membrane became hydrophilic and smooth with a low porosity and small pore size, the bulk structure of the membrane remained almost intact. For a saline solution including protein and Ca2+ as organic fouling and scaling agents, the deposition of the hydrophilic PDA/MPC-co-AEMA layer on hydrophobic PVDF led to the alleviation of the membrane fouling and scaling during long-term DCMD application. Whereas the formation of a hydrated layer on the membrane surface avoided BSA fouling by avoiding hydrophobic–hydrophobic interactions, a combination of several chemo-physical properties of the modified membrane surface resulted in anti-scaling properties.

Influence of Pore-Size/Porosity on Ion Transport and Static BSA Fouling for TiO2-Covered Nanoporous Alumina Membranes

The influence of geometrical parameters (pore radii and porosity) on ion transport through two almost ideal nanoporous alumina membranes (NPAMs) coated with a thin TiO2 layer by the atomic layer deposition technique (Sf-NPAM/TiO2 and Ox-NPAM/TiO2 samples) was analyzed by membrane potential and electrochemical impedance spectroscopy measurements. The results showed the significant effect of pore radii (10 nm for Sf-NPAM/TiO2 and 13 nm for Ox-NPAM/TiO2) when compared with porosity (9% and 6%, respectively). Both electrochemical techniques were also used for estimation of protein (bovine serum albumin or BSA) static fouling, and the results seem to indicate deposition of a BSA layer on the Sf-NPAM/TiO2 fouled membrane surface but pore-wall deposition in the case of the fouled Ox-NPAM/TiO2 sample. Moreover, a typical and simple optical technique such as light transmission/reflection (wavelength ranging between 0 and 2000 nm) was also used for membrane analysis, showing only slight transmittance differences in the visible region when both clean membranes were compared. However, a rather significant transmittance reduction (~18%) was observed for the fouled Sf-NPAM/TiO2 sample compared to the fouled Ox-NPAM/TiO2 sample, and was associated with BSA deposition on the membrane surface, thus supporting the electrochemical analysis results.

New insights into membrane fouling formation during ultrafiltration of organic wastewater with high salinity

Membrane separation technology has been generally preferred for treating high-salinity organic wastewater during the last decades of years. Despite not suitable for ion removal, ultrafiltration (UF) is quite appropriate and widely employed for retaining solids, organic matters and macromolecules etc. from high-salinity wastewater. However, limited efforts have been made to investigate the UF fouling characteristics affected by such high saline environment. In this study, sodium chloride (NaCl) with the concentration higher than 10 g/L was employed to examine its impacts on the UF fouling behaviors. The results showed that the involvement of high-concentration NaCl remarkably aggravated HA fouling formation, whereas mitigated BSA fouling development. In the presence of NaCl, HA seemed to form a more homogenous fouling layer, while substantial scattered and large NaCl crystals with different shapes appeared on BSA fouling layer. Further analysis demonstrated that NaCl at high levels induced the agglomeration of BSA foulants, leading to their slower transportation to membrane surface and alleviated the formation of cake layer. Comparatively, the electrostatic attraction and thermodynamic interactions between HA-HA and HA-membrane were substantially increased at high-salinity condition, probably facilitating HA migration to membrane and enhancing fouling layer development. Consequently, the different effects of high salinity on HA and BSA fouling were systematically revealed with their formation mechanisms proposed, which should provide an insightful guidance for membrane fouling control when high-salinity organic wastewater is treated with membrane-based technique.

Polytetrafluoroethylene (PTFE) hollow fibers modified by hydrophilic crosslinking network (HCN) for robust resistance to fouling and harsh chemical cleaning

Polytetrafluoroethylene (PTFE) hollow fibers are considered as robust membranes for wastewater treatment due to its comprehensive chemical, thermal and mechanical stability. However, the intrinsic strong hydrophobicity impeded its application because of severe organic matter fouling. Therefore, hydrophilic PTFE hollow fiber membrane especially with robust resistance to chemical washing is highly desirable. Herein, we feasibly enhance the chemical washing resistance of hydrophilic PTFE hollow fiber membrane via the interface impregnation and crosslinking of poly (vinylpyrrolidone-vinyltriethoxysilane) (P (VP-VTES)). The hydrophilic crosslinking network (HCN) endowed PTFE membrane with better resistance to BSA, HA and soybean oil fouling compared to ethanol pre-wetted PTFE membrane. More importantly, the HCN modified membrane maintains its hydrophilic and chemical stability after strong acidic (pH = 2), alkaline (pH = 12) and oxidization artificial accelerated cleaning (2000 ppm NaClO) for 2 weeks. Overall, the facile preparation and excellent performance of robust hydrophilic PTFE membrane highlights its great potential in treating highly contaminated wastewater.

Nanoscale polyelectrolyte/metal ion hydrogel modified RO membrane with dual anti-fouling mechanism and superhigh transport property

The anti-fouling polyamide (PA) reverse osmosis (RO) membranes modified by hydrophilic polymer are trapped in the problems of declined flux, single anti-fouling mechanism, high cost or complex fabrication. Here the nano-sized sodium alginate/Cu2+ hydrogel prepared with the layer-by-layer (LBL) method was firstly applied for PA RO membrane modification to solve these contradictions. The combination of passive and active antifouling capabilities can be imparted by the polyelectrolyte hydrogel cross-linked with metal ions. In addition, remarkable transport properties can be achieved by brilliant hydrophilicity of hydrogel layer and LBL method which can control the thickness of the modified layer at nanometer level to minimize the transmembrane resistance of water molecules. The modified membrane possesses a water flux of 71.40 LMH up to 192.97% of the unmodified membrane without sacrificing salt rejection at 25 °C, 1.6 MPa. In the BSA and DTAB fouling tests, the flux recovery rate of the modified membrane was 26.44% and 29.14% greater than that of the unmodified membrane, respectively. Moreover, the modified PA membrane exhibited great bactericidal potential to S. aureus and E. coli. Besides prominent comprehensive performance, this strategy is low cost and simple in operation, shining a light on preparing new generation of high-performance RO membrane.

The hierarchical flower-like MoS2 nanosheets incorporated into PES mixed matrix membranes for enhanced separation performance

Membrane fouling is an issue of concern due to the hydrophobic properties of polyethersulfone (PES) membrane when applied in water treatment. In this work, a facile hydrothermal method was utilized to synthesize hierarchical flower-like structured molybdenum disulfide nanosheets (HF–MoS2 NSs) that then incorporated into PES membranes as composite membranes. We characterized their permeability, the separation performance, the antifouling performance, and the antibacterial activity systematically. Results showed that composite membranes exhibited a better pure water flux (286 LMH/bar) at the HF–MoS2 NSs content of 0.4 wt%, which was 1.8 times higher than the control membrane. Also, composite PES membranes achieved 98.2% and 96.9% rejection of BSA and HA in comparison with the control PES membrane (87.3%, and 84.5%, respectively). Compare to the control PES membrane, the flux recovery ratio of the composite membrane increased from 69% to 88% for BSA fouling and increased from 84% to 93% for HA fouling. The retention rate for the organic dyes also improved slightly after HF–MoS2 NSs incorporation into the membrane. Additionally, the composite membranes exhibited a relatively high antibacterial activity against E. coli and B. subtilis with antibacterial rates of 67.8% and 82.5%, respectively. In conclusion, HF–MoS2 NSs incorporated composite membranes were shown to have outstanding filtration performance and could be a promising candidate for practical application in water filtration.

Surface modification on thin-film composite reverse osmosis membrane by cation complexation for antifouling

A facile surface modification method has been developed for improving the antifouling property of TFC membranes by immobilizing poly(ethylene glycol) (PEG) onto polyamide (PA) surface. PEG has been chelated and immobilized onto PA surface by ion-dipole interaction between ether oxygen atoms in PEG backbone and –COONa in PA layer. The resulting TFC membranes were characterized by ATR-FTIR, XPS, SEM, AFM, WLI, zeta potential as well as static contact angle. The changes in chemical composition and morphology of the membrane surface indicate the successful modification process. The permeation property of the PEG modified TFC membranes dependence on PEG concentration, treatment temperature and time has been investigated thoroughly. The optimized PEG modified membrane shows a NaCl rejection of 99.04%, higher than that (97.79%) of the virgin membrane. More importantly, PEG modified membrane exhibits much more improved organic fouling-resistance ability than control sample. Typically, after BSA fouling for 12 h, PEG modified membrane loses about 19% of the initial flux, much lower than that of the virgin PA membrane (40%). Furthermore, the flux recovery of the PEG modified membrane reaches about 95% after cleaning, much higher than that of the virgin PA membrane (79%). Therefore, this simple, rapid, environment-friendly and cost-effective modification approach will provide a method for mitigating the long-term fouling of reverse osmosis membrane.

Surface modification of polyamide reverse osmosis membrane with organic-inorganic hybrid material for antifouling

Abstract A series of thin-film composite reverse osmosis membranes based on polyamide have been modified by coating the polyvinyl alcohol and 3-mercaptopropyltriethoxysilane aqueous solution prepared by a sol-gel process on the membrane surface, followed by thermal crosslinking treatment. In order to improve the hydrophilicity of the modified TFC membranes, the membranes were then immersed into H2O2 aqueous solution to convert −SH into −SO3H. The resulting TFC membranes were characterized by SEM, AFM, ATR-FTIR, streaming potential, XPS as well as static contact angle. After surface modification with the organic-inorganic hybrid material, the TFC membranes show increased NaCl rejection and decreased water flux with increasing 3-mercaptopropyltrimethoxysilane content in coating solution. The optimal modification membrane (PA-SMPTES-0.8) exhibits a NaCl rejection of 99.29%, higher than that (97.20%) of the virgin PA membrane, and a comparable water flux to virgin PA membrane (41.7 L/m2 h vs 47.9 L/m2 h). More importantly, PA-SMPTES-0.8 membrane shows much more improved fouling resistance to BSA than virgin PA and PVA modified PA (PA-PVA-1.0) membranes. PA-SMPTES-0.8 membrane loses about 13% of the initial flux after BSA fouling for 12 h, which is lower than that of virgin PA and PA-PVA-1.0 membranes (42% and 18%). Furthermore, the flux recovery of PA-SMPTES-0.8 membrane reaches 94% after cleaning. Thus the TFC membranes modified by this organic-inorganic hybrid technology show potential applications as antifouling RO membrane for desalination and purification.

Influence of an external electric field on removal of protein fouling on a stainless steel surface by proteolytic enzymes

Enzymatic cleaning is a potentially useful method for removing proteinaceous fouling from solid surfaces under mild conditions. Herein, the influence of an external electric field on the enzymatic cleaning of a metal surface fouled with a protein was investigated. The model fouling protein (BSA; lysozyme) was prepared on a stainless steel (St) surface, and the resulting surface subjected to enzymatic cleaning with an electric potential being applied to the St plate. Trypsin, α-chymotrypsin, and thermolysin were used as model proteases. The amounts of protein remaining on the plate before and during the cleaning process were measured by means of a reflection absorption technique using Fourier transform infrared spectroscopy. In the case for BSA fouling, the cleaning efficiency of the protease tended to increase at more negative applied potentials. Whereas, there was an optimum applied potential for removing the lysozyme fouling. Atomic force microscopy analyses indicated that applying an adequate range of electric potential enhanced the enzymatic removal of protein fouling inside scratches on the St plate surface. These findings suggest the existence of two modes of electrostatic interactions for the external electric field, one with protease molecules and the other with digested fragments of the fouling protein.

Surface modification of polyamide reverse osmosis membrane with sulfonated polyvinyl alcohol for antifouling

Sulfonated polyvinyl alcohol (SPVA) was synthesized by esterification reaction of PVA and sulfuric acid, and the structure was characterized by FTIR spectrum. Then a series of TFC membranes modified with cross-linked SPVA layer were fabricated by coating method, with glutaraldehyde as the cross-linker. The resulting TFC membranes were characterized by SEM, AFM, ATR-FTIR, XPS, streaming potential as well as static contact angle. The TFC membranes modified with SPVA exhibit decreased water flux and increased NaCl rejection with SPVA content increasing in the coating aqueous solution. The optimal PA-SPVA-0.5 sample exhibits a NaCl rejection of 99.18%, which is higher than the 98.32% of the virgin PA membrane. More importantly, the PA-SPVA-0.5 membrane shows much more improved fouling resistance to BSA and CTAB than virgin PA membrane and the TFC sample modified with PVA (PA-PVA-0.5). PA-SPVA-0.5 membrane loses about 8% of the initial flux after BSA fouling for 12h, which is much lower than those of virgin PA and PA-PVA-0.5 membranes (28% and 15%, respectively). Furthermore, the flux recovery of the PA-SPVA-0.5 membrane reaches above 95% after cleaning. Thus, the PA-SPVA-0.5 membrane shows potential applications as antifouling RO membrane for desalination and purification.

A new strategy to simultaneously improve the permeability, heat-deformation resistance and antifouling properties of polylactide membrane via bio-based β-cyclodextrin and surface crosslinking

The permeability and thermal stability are crucial to the application of environmentally benign, sustainable and bio-based polylactide (PLA) membrane. In the present work, we introduce a bio-based pore forming agent β-cyclodextrin to enhance the permeability of PLA membrane. Furthermore, we improve the protein resistance and heat-deformation resistance via a surface crosslinking strategy. P(VP-VTES) copolymer was first synthesized and seeded on the surface of PLA membranes steadily through the swelling, hydrolysis and condensation. The physicochemical property of PLA membrane was characterized by XPS, FTIR and SEM. The hydrophilicity, pure water flux and BSA fouling resistance were evaluated respectively. The crystallization evolution of PLA membrane was investigated by DSC and XRD. It was found that the surface crosslinked P(VP-VTES) significantly improved the hydrophilicity, dry membrane flux recovery (~98%) and BSA resistance. Meanwhile, the surface crosslinking induced the crystallization of PLA membrane up to ~38% degree of crystallinity and withstood ~100°C hydrothermal treatment without dimension deformation or filtration performance deterioration. This study suggests a simple but effective strategy to simultaneously enhance the fouling resistance and thermal stability, as well as the permeability of PLA membranes through the surface crosslinking and the pore forming agent β-cyclodextrin.

The performance of forward osmosis process in treating the surfactant wastewater: The rejection of surfactant, water flux and physical cleaning effectiveness

In this study, the rejection of surfactant (sodium dodecyl benzene sulfonate, SDBS) was investigated at different feed solution (FS) chemistries (ionic strengths and SDBS concentrations, with and without the presence of organic foulants BSA and Alg-Na), temperatures and flow velocities in the forward osmosis (FO) process. SDBS rejection increased with the increase of flow velocity and the decrease of temperature and SDBS concentration; while it had no obvious change with the increasing FS ionic strength. SDBS rejection of FO membrane was high (more than 99.77%), mainly due to the size exclusion. Moreover, the water flux and effectiveness of physical cleaning were also measured. SDBS impacted water flux by two ways: one was the positive role that SDBS micelles enhanced the hydrophilia of membrane; the other one was the negative role that SDBS formed a gel cake layer and increase the resistance. The membrane fouling caused by Alg-Na increased solute rejection and water flux in the FO mode, which was beneficial to the total membrane process. Though BSA fouling increased solute rejection in the PRO mode, it declined water flux, and caused a severe pore blocking which was hard to remove just by the simple rinse.