Fabrication of antifouling thin-film composite nanofiltration membrane via surface grafting of polyethyleneimine followed by zwitterionic modification

Carboxyl-free polyamide reverse osmosis membrane with sustainable anti-fouling performance in treating industrial coke wastewater

Carboxyl groups in polyamide (PA) reverse osmosis (RO) membrane contribute significantly to fouling and scaling, hindering the sustainable operation of RO in practical applications. Herein, we developed a novel interfacial polymerization (IP) strategy to finely engineer the molecular structure of PA with no carboxyl groups, and to significantly enhance RO membrane fouling/scaling-resistance. During IP, trimesoyl chloride (TMC) at the interface was consumed completely by the diffused m-phenylenediamine (MPD) and glycerol (GLY) under the assistance of benzalkonium chloride (BAC) surfactant. The fabricated RO membrane with no carboxyl groups exhibits sustainable anti-fouling performance with low flux decline ratios and high flux recovery ratios during the five cycles of fouling and cleaning when treating real coke wastewater, surpassing the reported anti-fouling membranes and the renowned commercial fouling-resistant RO membrane (DuPont FilmTec™ CR100). This work provides some insights to precisely tailor the molecular structure of PA RO membrane with sustainable anti-fouling performance.

Surface-engineered nanofiltration membranes for sustainable lithium recovery from real brine: Addressing fouling and scaling challenges

Nanofiltration (NF) membranes hold great promise for lithium (Li) recovery from brines, with numerous studies focusing on improving Li/Mg separation performance. However, real brine environments pose significant challenges, as fouling and scaling severely hinder Li recovery efficiency. Despite their critical impact, these challenges have received limited attention. This study addresses these issues through surface engineering of polyamide (PA) NF membranes, achieving a positively charged, ultra-smooth surface. The engineered membrane demonstrated exceptional fouling and scaling resistance during real brine treatment, exhibiting only a 12 % flux decline over 12 h, compared to 28 % and 20 % for the control and commercial NF270 membranes, respectively. This superior antifouling performance enabled sustained high Li flux (>80 mM·m⁻2·h⁻1) while reducing the Mg/Li mass ratio from 4.1 in the feed to 1.4 in the permeate. Additionally, the membrane displayed remarkable resistance to scaling in synthetic brine containing high concentrations of Ca2+ and SO42-. Systematic evaluations in both synthetic and real brines revealed that the enhanced process stability arises from the synergistic effects of reduced surface roughness and optimized surface charge, which together minimize foulant adhesion and mitigate scaling. These findings mark a significant advancement toward the practical implementation of membrane-based Li recovery, underscoring the critical importance of addressing fouling and scaling in real brine environments.

Synergistic effect of electrocoagulation and antifouling nanofiltration membranes for microcystin removal

This study aims to develop fouling-resistant membranes utilizing zwitterionic polymers for an integrated electrocoagulation (EC) and nanofiltration (NF) process to effectively remove microcystin-LR (MC-LR). The fabricated membranes were thoroughly characterized through contact angle measurements, Fourier-transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), and X-ray photoelectron spectroscopy (XPS). The efficacy of these modified membranes was investigated for synthetic microcystin removal, employing both commercial NF 270 membranes and modified NF 270 with zwitterionic polymers. Furthermore, real lake water containing microcystin was subjected to crossflow filtration using both commercial and modified NF membranes. The results indicated that the zwitterionic polymer-modified membranes demonstrated significantly better fouling resistance, with flux decline reduced from 37% to 15.5%, and improved microcystin-LR removal from 95% to 99.5% compared to unmodified membranes. To further enhance performance and meet drinking water standards, an EC step was implemented as a pretreatment for microcystin removal. The integrated EC-NF system exhibited superior performance, achieving complete MC-LR removal (below detection limit) and a 27% improvement in flux compared to the individual processes of either EC or NF. This enhancement in performance suggests the potential of this innovative integrated membrane system for applications in water treatment processes, particularly in addressing challenges related to fouling and contaminant removal. The comprehensive analysis and promising outcomes presented in this study contribute valuable insights to the advancement of membrane technology for sustainable water purification.

Preparation of Crown Ether-Containing Polyamide Membranes via Interfacial Polymerization and Their Desalination Performance

The large-scale application of aromatic polyamide (PA) thin-film composite (TFC) membranes for reverse osmosis has provided an effective way to address worldwide water scarcity. However, the water permeability and salt rejection capabilities of the PA membrane remain limited. In this work, cyclic micropores based on crown ether were introduced into the PA layer using a layer-by-layer interfacial polymerization (LbL-IP) method. After interfacial polymerization between m-phenylenediamine (MPD) and trimesoyl chloride (TMC), the di(aminobenzo)-18-crown-6 (DAB18C6) solution in methanol was poured on the membrane to react with the residual TMC. The cyclic micropores of DAB18C6 provided the membrane with rapid water transport channels and improved ion rejection due to its hydrophilicity and size sieving effect. The membranes were characterized by FTIR, XPS, SEM, and AFM. Compared to unmodified membranes, the water contact angle decreased from 54.1° to 31.6° indicating better hydrophilicity. Moreover, the crown ether-modified membrane exhibited both higher permeability and enhanced rejection performance. The permeability of the crown ether-modified membrane was more than ten times higher than unmodified membranes with a rejection above 95% for Na2SO4, MgSO4, MgCl2, and NaCl solution. These results highlight the potential of this straightforward surface grafting strategy and the modified membranes for advanced water treatment technologies, particularly in addressing seawater desalination challenges.

Tailoring the Performance of a Composite PEI Nanofiltration Membrane via Incorporating Activated PDA for Efficient Dye Sieving and Salt Separation

Efficient dye sieving and salt separation can facilitate the recycling of valuable resources in textile wastewater treatment. This study focuses on developing a high-performance nanofiltration membrane (NF) by co-depositing activated polydopamine (O-PDA), oxidized with KMnO4, and polyethyleneimine (PEI) onto a polysulfone support membrane (PSF), thereby enabling effective dye sieving and salt separation. Due to the high hydrophilicity of PDA and the formation of high molecular polymers after oxidation, it was anticipated that O-PDA would crosslink the PEI layer, providing rapid permeating channels. Filtration experiments demonstrated that the formation of O-PDA significantly enhanced the salt retention rate of nanofiltration membranes, achieving a nearly threefold increase in NaCl retention from 15% to 45.7%. It was observed that the retention performance of O-PDA could be adjusted by controlling its loading or oxidation level. Furthermore, despite a notable reduction in permeability, the dye removal efficiency of the O-PDA/PEI membrane increased substantially to 99.5%. Long-term filtration experiments also confirmed both the stability and anti-fouling properties of this membrane design. Clearly, owing to its excellent operational stability and anti-fouling characteristics, the O-PDA/PEI membrane exhibits great potential for applications in dye sieving and salt separation.

Preparation of Zwitterionic Sulfobetaines and Study of Their Thermal Properties and Nanostructured Self-Assembling Features

Zwitterionic polymers have garnered significant attention for their distinctive properties, such as biocompatibility, antifouling capabilities, and resistance to protein adsorption, making them promising candidates for a wide range of applications, including drug delivery, oil production inhibitors, and water purification membranes. This study reports the synthesis and characterization of zwitterionic monomers and polymers through the modification of linear, vinyl, and aromatic heterocyclic functional groups via reaction with 1,3-propanesultone. Four zwitterionic polymers with varying molecular structures-ranging from linear to five and six membered ring systems-were synthesized: poly(sulfobetaine methacrylamide) (pSBMAm), poly(sulfobetaine-1-vinylimidazole) (pSB1VI), poly(sulfobetaine-2-vinylpyridine) (pSB2VP), and poly(sulfobetaine-4-vinylpyridine) (pSB4VP). Their molecular weights, thermal behavior, and self-assembly properties were analyzed using gel permeation chromatography (GPC), thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), transmission electron microscopy (TEM), and zeta potential measurements. The glass transition temperatures (Tg) ranged from 276.52 °C for pSBMAm to 313.69 °C for pSB4VP, while decomposition temperatures exhibited a similar trend, with pSBMAm degrading at 301.03 °C and pSB4VP at 387.14 °C. The polymers' self-assembly behavior was strongly dependent on pH and their surface charge, particularly under varying pH conditions: spherical micelles were observed at neutral pH, while fractal aggregates formed at basic pH. These results demonstrate that precise modifications of the chemical structure, specifically in the linear, imidazole, and pyridine moieties, enable fine control over the thermal properties and self-assembly behavior of polyzwitterions. Such insights are essential for tailoring polymer properties for targeted applications in filtration membranes, drug delivery systems, and solid polymer electrolytes, where thermal stability and self-assembly play crucial roles.

Selective ion channel adsorbents facilitate efficient and low environmental impact extraction of liquid lithium resources

As lithium is the cornerstone of green energy development, it is crucial to realize a low environmental impact and efficient lithium extraction process. Ion-sieve adsorption is the most widely used method to extract liquid lithium resources, but this method is only efficient under alkaline conditions for H+ and Mg2+ competing adsorption. Conventional methods are often accompanied by the consumption of quantities of alkali, the generation of solid waste, and the acidification of liquid lithium resources. To address these issues, a selective ion-channel adsorbent was constructed. The composition comprises an ion sieve adsorbent and an organic carrier with a zwitterionic quaternary ammonium base group. This group storages OH- in situ, hinders H+ diffusion, slows down Mg2+ diffusion, and accelerates Li+ diffusion by relying on the difference in binding energies, which reduces the competing adsorption and avoids acidification and solid waste generation. The saturated adsorption capacity (21.38 mg/g) and selectivity of the adsorbent are 4.7 and 24 times higher than that of conventional ion-sieve adsorbent under neutral conditions respectively. The dosage of alkali is 1/256 of the traditional method, the effluent remains neutral and no solid waste is generated. This study presents an environmental and effective adsorbent for lithium extraction.

Antifouling Asymmetric Block Copolymer Nanofilms via Freestanding Interfacial Polymerization for Efficient and Sustainable Water Purification

Membrane materials that resist nonspecific or specific adsorption are urgently required in widespread practical applications, such as water purification, food processing, and life sciences. In water purification, inevitable membrane fouling not only limits membrane separation performance, leading to a decline in both permeance and selectivity, but also remarkably increases operation requirements, and augments extra maintenance costs and higher energy consumption. In this work, we report a freestanding interfacial polymerization (IP) fabrication strategy for in situ creation of asymmetric block copolymer (BCP) nanofilms with antifouling properties, greatly outperforming the conventional surface post-modification approaches. The resultant free-standing asymmetric BCP nanofilms with highly-dense, highly-hydrophilic polyethylene glycol (PEG) brushes on one side, can be readily formed via a typical IP process of a well-defined double-hydrophilic BCP composed of a highly-efficient antifouling PEG block and a membrane-forming multiamine block. The asymmetric BCP nanofilms have been applied for efficient and sustainable natural water purification, demonstrating extraordinary antifouling capabilities accompanied with superior separation performance far beyond commercial polyamide nanofiltration membranes. The antifouling behaviors of asymmetric BCP nanofilms derived from the combined effect of the hydration layer, electrostatic repulsion and steric hindrance were further elucidated by water flux and fouling resistance in combination with all-atom molecular dynamics (MD) simulation. This work opens up a new avenue for the large-scale and low-cost creation of broad-spectrum, asymmetric membrane materials with diverse functional "defect-free" surfaces in real-world applications.

A Facile Surface Modification Scheme for Medical-Grade Titanium and Polypropylene Using a Novel Mussel-Inspired Biomimetic Polymer with Cationic Quaternary Ammonium Functionalities for Antibacterial Application

Medical device-associated infection remains a critical problem in the healthcare setting. Different clinical- or device-related methods have been attempted to reduce the infection rate. Among these approaches, creating a surface with bactericidal cationic functionality has been proposed. To do so, a sophisticated multi-step chemical procedure would be needed. Instead, a simple immersion approach was utilized in this investigation to render the titanium and polypropylene surface with the quaternary ammonium functionality by using a mussel-inspired novel lab-synthesized biomimetic catechol-terminated polymer, PQA-C8. The chemical oxidants, CuSO4/H2O2, as well as dopamine, were added into the novel PQA-C8 polymer immersion solution for one-step surface modification. Additionally, a two-step immersion scheme, in which the polypropylene substrate was first immersed in the dopamine solution and then in the PQA-C8 solution, was also attempted. Surface analysis results indicated the surface characteristics of the modified substrates were affected by the immersion solution formulation as well as the procedure utilized. The antibacterial assay has shown the titanium substrates modified by the one-step dopamine + PQA-C8 mixtures with the oxidants added and the polypropylene modified by the two-step scheme exhibited bacterial reduction percentages greater than 90% against both Gram-positive S. aureus and Gram-negative E. coli and these antibacterial substrates were non-cytotoxic.

Title Preparation and Desalination of Semi-Aromatic Polyamide Reverse Osmosis Membranes (ROMs)

Reverse osmosis membrane (ROM) technology has a series of advantages, such as a simple process, no secondary pollution, high efficiency, energy saving, environmental protection, and good separation and purification effects. High-performance semi-aromatic polyamide reverse osmosis membranes (ROMs) were prepared by interfacial polymerization (IP) of novel cyclopentanecarbonyl chloride (CPTC) and m-phenylenediamine (MPD) monomers. The surface morphology, hydrophilicity and charge of the ROMs were characterized by field-emission scanning electron microscopy (SEM), a contact angle tester and a solid-surface zeta potential analyzer. The effects of CPTC concentration, MPD concentration, oil-phase solvent type, IP reaction time and additive concentration on the performance of semi-aromatic polyamide ROMs were studied. SEM morphology characterization showed that the surface of the prepared polyamide ROMs presented a multinodal structure. The performance test showed that when the concentration of MPD in the aqueous phase was 2.5 wt.%, the concentration of sodium dodecylbenzene sulfonate (SDBS) was 0.2%, the residence time in the aqueous phase was 2 min, the concentration of CPTC/cyclohexane in the oil phase was 0.13 wt.%, the IP reaction was 20 s, the NaCl rejection rate of the semi-aromatic polyamide ROM was 98.28% and the flux was 65.38 L/m2·h, showing good desalination performance. Compared with an NF 90 commercial membrane, it has a good anti-BSA pollution ability.

Low-pressure thin-film composite nanofiltration membranes with enhanced selectivity and antifouling property for effective dye/salt separation

For better sustainable resource recovery and elevating the separation efficiency of dye/salt mixture, it is essential to develop an appropriate nanofiltration membrane for the treatment of textile dyeing wastewater containing relatively smaller molecule dyes. In this work, a novel composite polyamide-polyester nanofiltration membrane was fabricated by tailoring amino functionalized quantum dots (NGQDs) and β-cyclodextrin (CD). An in-situ interfacial polymerization occurred between the synthesized NGQDs-CD and trimesoyl chloride (TMC) on the modified multi-carbon nanotubes (MWCNTs) substrate. The incorporation of NGQDs significantly elevated the rejection (increased by ∼ 45.08%) of the resultant membrane for small molecular dye (Methyl orange, MO) compared to the pristine CD membrane at low pressure (1.5 bar). The newly developed NGQDs-CD-MWCNTs membrane exhibited enhanced water permeability without compromising the dye rejection compared to the pure NGQDs membrane. The improved performance of the membrane was primarily attributed to the synergistic effect of functionalized NGQDs and the special hollow-bowl structure of CD. The optimal NGQDs-CD-MWCNTs-5 membrane expressed pure water permeability of 12.35 L m^-2h^-1 bar^-1 at the pressure of 1.5 bar. Noteworthily, the NGQDs-CD-MWCNTs-5 membrane not only showed high rejection for the larger molecular dye of Congo Red (CR, 99.50%) but also for the smaller molecular dye of MO (96.01%) and Brilliant Green (BG, 95.60%) with the permeability of 8.81, 11.40, and 6.37 L m^-2h^-1 bar^-1, respectively at low pressure (1.5 bar). The rejection of inorganic salts by the NGQDs-CD-MWCNTs-5 membrane was 17.20% for sodium chloride (NaCl), 14.30% for magnesium chloride (MgCl₂), 24.63% for magnesium sulfate (MgSO₄), and 54.58% for sodium sulfate (Na₂SO₄), respectively. The great rejection of dyes remained in the dye/salt binary mixed system (higher than 99% for BG and CR, <21% for NaCl). Importantly, the NGQDs-CD-MWCNTs-5 membrane exhibited favorable antifouling performance and potential good operation stability performance. Consequently, the fabricated NGQDs-CD-MWCNTs-5 membrane suggested a prospective application for the reuse of salts and water in textile wastewater treatment owing to the effective selective separation performance.

Construction and Chlorine Resistance of Thiophene-Poly(ethyleneimine)-Based Dual-Functional Nanofiltration Membranes

The demand to improve the chlorine resistance of polyamide (PA) membranes is escalated with greater amounts of chlorine-containing disinfectant being used in global water treatment during the COVID-19 pandemic. In this work, we designed thiophene-functionalized poly(ethyleneimine) (TPEI) materials first and grafted them onto a conventional PA membrane to develop novel nanofiltration membranes (PEI-M, TPEI-1-M, TPEI-2-M). These membranes have dual-functionalized selective surfaces covered by hydrophilic amino groups and electron-rich thiophene moieties, which endow these membranes with superior chlorine resistance and improved separation performance. The modified membranes increase the rejection of MgCl2 from 86.5% of the nascent PA membrane (PA-M) to higher than 93.0% without sacrificing the membrane water permeability. More stable separation performance is achieved with all of the as-prepared membranes than PA-M after exposure to a 2000 ppm sodium hypochlorite solution. TPEI-2-M outperforms other membranes after being treated in a chlorination intensity of 16,000 ppm·h with the smallest flux loss and the highest MgCl2 rejection. This is mainly ascribed to the highest amount of amino and thiophene moieties on the TPEI-2-M surface. This study provides an effective protocol for developing novel PA-based nanofiltration membranes while demonstrating its superiority over current technologies with exceptional separation performance and antichlorine ability.

Designing sustainable membrane-based water treatment via fouling control through membrane interface engineering and process developments

Membrane-based water treatment processes have been established as a powerful approach for clean water production. However, despite the significant advances made in terms of rejection and flux, provision of sustainable and energy-efficient water production is restricted by the inevitable issue of membrane fouling, known to be the major contributor to the elevated operating costs due to frequent chemical cleaning, increased transmembrane resistance, and deterioration of permeate flux. This review provides an overview of fouling control strategies in different membrane processes, such as microfiltration, ultrafiltration, membrane bioreactors, and desalination via reverse osmosis and forward osmosis. Insights into the recent advancements are discussed and efforts made in terms of membrane development, modules arrangement, process optimization, feed pretreatment, and fouling monitoring are highlighted to evaluate their overall impact in energy- and cost-effective water treatment. Major findings in four key aspects are presented, including membrane surface modification, modules design, process integration, and fouling monitoring. Among the above mentioned anti-fouling strategies, a large part of research has been focused on membrane surface modifications using a number of anti-fouling materials whereas much less research has been devoted to membrane module advancements and in-situ fouling monitoring and control. At the end, a critical analysis is provided for each anti-fouling strategy and a rationale framework is provided for design of efficient membranes and process for water treatment.

An Overview of the Modification Strategies in Developing Antifouling Nanofiltration Membranes

Freshwater deficiency has become a significant issue affecting many nations' social and economic development because of the fast-growing demand for water resources. Nanofiltration (NF) is one of the promising technologies for water reclamation application, particularly in desalination, water, and wastewater treatment fields. Nevertheless, membrane fouling remains a significant concern since it can reduce the NF membrane performance and increase operating expenses. Consequently, numerous studies have focused on improving the NF membrane's resistance to fouling. This review highlights the recent progress in NF modification strategies using three types of antifouling modifiers, i.e., nanoparticles, polymers, and composite polymer/nanoparticles. The correlation between antifouling performance and membrane properties such as hydrophilicity, surface chemistry, surface charge, and morphology are discussed. The challenges and perspectives regarding antifouling modifiers and modification strategies conclude this review.

High Flux Nanofiltration Membranes with Double-Walled Carbon Nanotube (DWCNT) as the Interlayer

Nanofiltration (NF) membranes with a high permeability and rejection are of great interest in desalination, separation and purification. However, how to improve the permeation and separation performance still poses a great challenge in the preparation of NF membranes. Herein, the novel composite NF membrane was prepared through the interfacial polymerization of M-phenylenediamine (MPD) and trimesoyl chloride (TMC) on a double-walled carbon nanotube (DWCNT) interlayer supported by PES substrate. The DWCNT interlayer had a great impact on the polyamide layer formation. With the increase of the DWCNT dosage, the XPS results revealed an increase in the number of carboxyl groups, which decreased the crosslinking degree of the polyamide layer. Additionally, the AFM results showed that the surface roughness and specific surface area increased gradually. The water flux of the prepared membrane increased from 25.4 L/(m²·h) and 26.6 L/(m²·h) to 109 L/(m²·h) and 104.3 L/(m²·h) with 2000 ppm Na₂SO₄ and NaCl solution, respectively, under 0.5 MPa. Meanwhile, the rejection of Na₂SO₄ and NaCl decreased from 99.88% and 99.38% to 96.48% and 60.47%. The proposed method provides a novel insight into the rational design of the multifunctional interlayer, which shows great potential in the preparation of high-performance membranes.

A sacrificial protective layer as fouling control strategy for nanofiltration in water treatment

High-performance nanofiltration (NF) membrane with super antifouling capability as well as reusability is highly desired in water treatment. A new antifouling strategy by a coating-decoating-recoating cycle was investigated for effective removal of fouling and restoring the original membrane performance. The functional membrane surface was fabricated by in-situ coating a 'green' and biodegradable carboxymethyl chitosan (CMCS) layer as physical barrier. The CMCS layer can be decoated and re-coated by simple procedures. Results showed that (i) the CMCS layer enhanced surface hydrophilicity, surface smoothness and fouling resistance of NF membrane, (ii) both the unfouled and fouled CMCS layer were easily decoated by the strong acid solution, (iii) the CMCS layer was easily re-coated by facile recoating and (iv) the water flux recovery ratio of membrane with coating layer was maintained more than 88.8% during fouling testing by natural organic matter (NOM) after four sequential cycles of coating, decoating and recoating process. The re-coated membrane exhibited stable, improved membrane operational and antifouling performance. The coating-decoating-recoating approach is proven to be low-cost and eco-friendly strategy for NOM fouling control on NF membrane in water treatment applications.

High Flux and Antifouling Nanofiltration Membrane Modified by Ag@UiO-66-NH2 and Its Application for Biphenol A Removal

Owing to the specific porous structure which could provide additional passage channel for some molecules, metal organic frameworks are attractive candidates for enhancing permeability and selectivity of membranes in pervaporation, reverse osmosis, and gas separation. In this experiment, Ag@UiO-66-NH2 was introduced into polyamide separation layer by interfacial polymerization of triethylenetetramine and 1,3,5-benzenetricarboxylic acid chloride for nanofiltration. The results indicated that Ag@UiO-66-NH2 nanoparticles did endow the membranes with rapid diffusion pathways for water molecules. When the content of Ag@UiO-66-NH2 was 0.03 g, the prepared membrane (NF-Ag-3) showed high flux about 47.3 L·m-2·h-1 at 0.6 MPa, which is about 2-fold higher than that of polyamide membrane without Ag@UiO-66-NH2, while the MgSO4 rejection rate remained about 87.4%. The membrane also showed excellent antifouling properties, and the water flux recovery ratio was 95.6% after filtration BSA solution. When it was applied for 50 mg/L bisphenol A removal, the rejection rate reached 94.6%, and the flux is about 49.1 L·m-2·h-1. Moreover, Ag particles on UiO-66-NH2 rendered the membrane with good inhibition for Escherichia coli. The antibacterial rate of the membranes is above 95% when the loading of Ag@UiO-66-NH2 is more than 0.03 g.

Construction of antifouling zwitterionic membranes by facile multi-step integration method

Membrane fouling during the use of separation membrane has always been the main reason for the degradation of membrane performance. The traditional solution is complicated and inefficient, so we proposed multi-step integration method to prepare antifouling zwitterionic poly(aryl ether sulfone) (PAES-Z-x) ultrafiltration (UF) membrane with higher efficiency. We designed and synthesized a bisphenol precursor containing tertiary amine groups, which could provide reactive sites for grafting zwitterionic group. Afterwards, the zwitterionic modified UF membrane was prepared by graft copolymerization and non-solvent-induced phase separation (NIPS). The morphology, hydrophilicity, water flux and rejection of the PAES-Z-x membrane could be optimized by tuning zwitterion content. The hydration layer formed by zwitterions effectively reduced the adsorption of proteins and endowed the membrane good antifouling properties. The resulting membrane showed the pure water flux increased (up to 311 L m^-2h^-1 bar^-1), high bovine serum albumin (BSA) rejection (97%) and good water flux recovery ratio (FRR) (82.8%). Zwitterionic antifouling PAES UF membrane prepared by a simple and effective method provided a new direction for improving PAES UF membrane's antifouling performance.

New insights into effect of alkaline cleaning on fouling behavior of polyamide nanofiltration membrane for wastewater treatment

Membrane fouling is an intractable issue in wastewater treatment by nanofiltration (NF) membrane, and alkaline cleaning is the most effective approach to remove organic fouling on NF membrane. However, it was found that pore swelling of NF membrane induced by alkaline cleaning might reduce cleaning efficiency, and it is never quantified and its effect on membrane fouling behavior is still mysterious. In this work, membrane pore swelling effect (~9.7%, increment of effective pore size) induced by alkaline cleaning (pH 11) is confirmed and its effect on fouling behavior of the polyamide NF membrane is investigated based on experimental and modelling results. It is found that the alkali-induced pore swelling phenomenon would disappear after water filtration at neutral pH for 30 min, and if such cleaned membrane is faced by the small foulants during this pore shrinkage period, the concentration polarization and membrane fouling would be severer, and the subsequent alkaline cleaning is less effective because more foulants enter the enlarged pores and are tightly embedded in the membrane. Thus, the irreversible fouling of the NF membrane increases from 20% to 40% while its permeability recovery declines from 100% to 67% after six fouling/cleaning cycles. When an anionic surfactant sodium dodecyl sulfate (SDS, 10 mM) is added in the alkaline cleaning solution, the adsorption of SDS in/on the membrane can not only improve its hydrophilicity and negative charge, but also quickly eliminate the alkali-induced pore swelling effect and avoid the accumulation of foulants in the pores, thereby enhancing the antifouling performance of the NF membrane. Using the alkaline SDS cleaning, the irreversible fouling of the NF membrane maintains below 10% while its permeability recovery keeps above 100% in six continuous fouling/cleaning cycles.