Chlorine-resistance of reverse osmosis (RO) polyamide membranes

Nonpreferential Solvent Transport through an Intrinsic Cyclodextrin Pore in a Polyester Film

We performed equilibrium molecular dynamics simulations to study the transport of water and hexane solvents through cyclodextrin(CD)-based membranes (α-/β-/γ-CD/TMC). Although it is known that water and hexane can permeate through the macrocyclic cavity, surprisingly, when it is present in the CD-based membrane (α-/β-/γ-CD/TMC), these solvents are not permeating through the CD cavity. Interactions between membrane functional group atoms with the water and hexane suggest that these solvents primarily permeate through the polar aggregate pores formed via ester-linkage rather than the CD cavity. Our observation reveals that both solvents can permeate through the membrane; however, the hexane flux was one order of magnitude lower than water flux. Our study suggests that further work is needed to confirm the functional significance of the macrocyclic cavity in solvent permeation and the existence of Janus pathways.

Research on Reverse Osmosis (RO)/Nanofiltration (NF) Membranes Based on Thin Film Composite (TFC) Structures: Mechanism, Recent Progress and Application

The global shortage of clean water is a major problem, even in water-rich regions. To solve this problem, low-cost and energy-efficient water treatment methods are needed. Membrane separation technology (MST), as a separation method with low energy consumption, low cost, and good separation effect, has been widely used to deal with seawater desalination, resource recovery, industrial wastewater treatment, and other fields. With the continuous progress of scientific and technological innovation and the increasing demand for use, NF/RO membranes based on the TFC structure are constantly being upgraded. This paper presents the recent research progress of NF and RO membranes based on TFC structures and their applications in different fields, especially the formation mechanism and regulation of selective layer structures and the modification methods of selective layers. Our summary provides fundamental insights into the understanding of NF and RO membrane processes and hopefully triggers further thinking on the development of membrane filtration process optimization.

Nanomaterials-modified reverse osmosis membranes: a comprehensive review

Because of its great efficiency and widespread application, reverse osmosis (RO) is a popular tool for water desalination and purification. However, traditional RO membranes have a short lifespan due to membrane fouling, deterioration, decreased salt rejection rate, and the low water flux with aging. As a result, membrane modification has received a lot of attention recently, with nanomaterials being extensively researched to improve membrane efficacy and lifespan. Herein, we present an in-depth analysis of recent advances of RO membranes modification utilizing nanomaterials. An overview of the various nanomaterials used for membrane modification, including metal oxides, zeolites, and carbon nanomaterials, is provided. The synthesis techniques and methods of integrating these nanomaterials into RO membranes are also discussed. The impacts of nanomaterial change on the performance of RO membranes are addressed. The underlying mechanisms responsible for RO membrane enhancements by nanomaterials, such as improved surface hydrophilicity, reduced membrane fouling via surface repulsion and anti-adhesion properties, and enhanced structural stability, are discussed. Furthermore, the review provides a critical analysis of the challenges and limitations associated with the use of nanomaterials to modify RO membranes. Overall, this review provides valuable insights into the modification of RO membranes with nanomaterials, providing a full grasp of the benefits, challenges, and future prospects of this challenging topic.

More resilient polyester membranes for high-performance reverse osmosis desalination

Thin-film composite reverse osmosis membranes have remained the gold standard technology for desalination and water purification for nearly half a century. Polyamide films offer excellent water permeability and salt rejection but also suffer from poor chlorine resistance, high fouling propensity, and low boron rejection. We addressed these issues by molecularly designing a polyester thin-film composite reverse osmosis membrane using co-solvent-assisted interfacial polymerization to react 3,5-dihydroxy-4-methylbenzoic acid with trimesoyl chloride. This polyester membrane exhibits substantial water permeability, high rejection for sodium chloride and boron, and complete resistance toward chlorine. The ultrasmooth, low-energy surface of the membrane also prevents fouling and mineral scaling compared with polyamide membranes. These membranes could increasingly challenge polyamide membranes by further optimizing water-salt selectivity, offering a path to considerably reducing pretreatment steps in desalination.

Polyester Nanofiltration Membranes for Efficient Cations Separation

Polyester nanofiltration membranes highlight beneficial chlorine resistance, but their loose structures and negative charge result in poor cations retention precluding advanced use in cations separation. This work designs a new monomer (TET) containing "hydroxyl-ammonium" entities that confer dense structures and positive charge to polyester nanofiltration membranes. The TET monomer undergoes efficient interfacial polymerization with the trimesoyl chloride (TMC) monomer, and the resultant TET-TMC membranes feature one of the lowest molecular weight cut-offs (389 Da) and the highest zeta potential (4 mv, pH: 7) among all polyester nanofiltration membranes. The MgCl2 rejection of the TET-TMC membrane is 95.5%, significantly higher than state-of-the-art polyester nanofiltration membranes (<50%). The Li+ /Mg2+ separation performance of TET-TMC membrane is on par with cutting-edge polyamide membranes, while additionally, the membrane is stable against NaClO though polyamide membranes readily degrade. Thus the TET-TMC is the first polyester nanofiltration membrane for efficient cations separation.

Sustainability in Membrane Technology: Membrane Recycling and Fabrication Using Recycled Waste

Membrane technology has shown a promising role in combating water scarcity, a globally faced challenge. However, the disposal of end-of-life membrane modules is problematic as the current practices include incineration and landfills as their final fate. In addition, the increase in population and lifestyle advancement have significantly enhanced waste generation, thus overwhelming landfills and exacerbating environmental repercussions and resource scarcity. These practices are neither economically nor environmentally sustainable. Recycling membranes and utilizing recycled material for their manufacturing is seen as a potential approach to address the aforementioned challenges. Depending on physiochemical conditions, the end-of-life membrane could be reutilized for similar, upgraded, and downgraded operations, thus extending the membrane lifespan while mitigating the environmental impact that occurred due to their disposal and new membrane preparation for similar purposes. Likewise, using recycled waste such as polystyrene, polyethylene terephthalate, polyvinyl chloride, tire rubber, keratin, and cellulose and their derivates for fabricating the membranes can significantly enhance environmental sustainability. This study advocates for and supports the integration of sustainability concepts into membrane technology by presenting the research carried out in this area and rigorously assessing the achieved progress. The membranes' recycling and their fabrication utilizing recycled waste materials are of special interest in this work. Furthermore, this study offers guidance for future research endeavors aimed at promoting environmental sustainability.

An economical and simple method for preparing highly permeable and chlorine-resistant reverse osmosis membranes with potential commercial applications

The improvement in the overall efficiency of thin-film composite (TFC) reverse osmosis (RO) membranes is limited by their low permeability and sensitivity to degradation by chlorine. In the present study, polypiperazine (PIP), the commonly used amine monomer in preparing commercial TFC nanofiltration (NF) membranes, was used to regulate the m-phenylenediamine (MPD) based interfacial polymerization (IP) process. The results showed that addition of PIP optimized the micro-structure and surface properties of the polyamide (PA) layer. When the MPD and PIP mass ratio was 1 : 1, the TFCW-1:1 membrane exhibited 70% flux enhancement compared to pure MPD-based TFCW-1:0 membranes. Besides, the TFCW-1:1 membrane exhibited better chlorine-resistant performance since the NaCl rejection declined to just 3.8% while it was 11.3% for TFCW-1:0 membranes after immersion in 500 ppm NaClO solution for 48 h. Such improvement can be attributed to the increased number of unreacted amine groups and the thickness of the PA layer that PIP brought, which provided a sacrificial protective layer to consume the active chlorine, and thus maintain the integrity of the inner rejection layer. In all, the novelty and purpose of the present work is to find a more simple and scalable method to fabricate high-performance TFC RO membranes by using commonly, cheaply and frequently used materials.

Pressure-driven distillation using air-trapping membranes for fast and selective water purification

Membrane technologies that enable the efficient purification of impaired water sources are needed to address growing water scarcity. However, state-of-the-art engineered membranes are constrained by a universal, deleterious trade-off where membranes with high water permeability lack selectivity. Current membranes also poorly remove low-molecular weight neutral solutes and are vulnerable to degradation from oxidants used in water treatment. We report a water desalination technology that uses applied pressure to drive vapor transport through membranes with an entrapped air layer. Since separation occurs due to a gas-liquid phase change, near-complete rejection of dissolved solutes including sodium chloride, boron, urea, and N-nitrosodimethylamine is observed. Membranes fabricated with sub-200-nm-thick air layers showed water permeabilities that exceed those of commercial membranes without sacrificing salt rejection. We also find the air-trapping membranes tolerate exposure to chlorine and ozone oxidants. The results advance our understanding of evaporation behavior and facilitate high-throughput ultraselective separations.

Ultrasound-assisted synthesis of MSNs/PS nanocomposite membranes for effective removal of Cd2+ and Pb2+ ions from aqueous solutions

Contamination of heavy metal (Cd²⁺ & Pb²⁺) ions in drinking water is producing major impacts on the environment and public health and is considered one of the greatest dangers to humanity. Membrane technology has been chosen over other processing methods due to its simplicity and high capacity for more effective removal of hazardous heavy metals. In the current study, amine, thiol, and bi-thiol functional groups were used to functionalize mesoporous silica nanoparticles (MSNs) to improve the efficiency of the silica nanoparticle. The morphology of the MSNs as well as the existence of amine and thiol on the surface of MSNs was demonstrated by a variety of characterization techniques, including FTIR, TEM, and SEM examination. The impact of surface-modified MSNs on the morphology, properties, and performance of polysulfone (PS) nanofiltration (NF) membranes was also evaluated. The membrane that incorporated amine with thiol-based MSNs (DiMP-MSNs/PS-NF membrane) had the highest pure water permeability (6.7 LMH bar^-1). As a result of the functional groups, the surface-modified MSNs/PS nanofiltration are extremely effective at removing heavy metal ions from aqueous solutions. The surface-modified MSNs/PS nano-filtration membranes exhibit unprecedented Cd²⁺ and Pb²⁺ removal rates of approximately 82% and 99%, respectively. This research indicates the possible application of the surface-modified MSNs/PS nanofiltration membrane as a promising platform to remove heavy metal ions from polluted water.

Separation Performance of Membranes Containing Ultrathin Surface Coating of Metal-Polyphenol Network

Metal-polyphenol networks (MPNs) are being used as versatile coatings for regulating membrane surface chemistry and for the formation of thin separation layers. The intrinsic nature of plant polyphenols and their coordination with transition metal ions provide a green synthesis procedure of thin films, which enhance membrane hydrophilicity and fouling resistance. MPNs have been used to fabricate tailorable coating layers for high-performance membranes desirable for a wide range of applications. Here, we present the recent progress of the use of MPNs in membrane materials and processes with a special focus on the important roles of tannic acid-metal ion (TA-Mⁿ⁺) coordination for thin film formation. This review introduces the most recent advances in the fabrication techniques and the application areas of TA-Mⁿ⁺ containing membranes. In addition, this paper outlines the latest research progress of the TA-metal ion containing membranes and summarizes the role of MPNs in membrane performance. The impact of fabrication parameters, as well as the stability of the synthesized films, is discussed. Finally, the remaining challenges that the field still faces and potential future opportunities are illustrated.

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.

Cation-π Interactions Contribute to Hydrophobic Humic Acid Removal for the Control of Hydraulically Irreversible Membrane Fouling

Hydraulically irreversible membrane fouling is a major problem encountered during membrane-based water purification. Membrane foulants present large hydrophobic fractions, with humic acid (HA) being a prevalent example of hydrophobic natural organic matter. Furthermore, HA contains numerous aromatic rings (π electrons), and its hydrophobic interactions are a major cause of irreversible membrane fouling. To address this issue, in this study, we used the cation-π interaction, which is a strong noncovalent, competitive interaction present in water. Because the strength of cation-π interactions depends on the combination of cations and π molecules, utilizing the appropriate cations will effectively remove irreversible fouling caused by hydrophobic HA. We performed macroscale experiments to determine the cleaning potential of the test cations, nanomechanically analyzed the changes in HA cohesion caused by the test cations using a surface force apparatus and an atomic force microscope, and used molecular dynamics simulations to elucidate the HA removal mechanism of test studied cations. We found that the addition of 1-ethyl-3-methylimidazolium, an imidazolium cation with an aromatic moiety, effectively removed the HA layer by weakening its cohesion, and the size, hydrophobicity, and polarity of the HA layer synergistically affected the HA removal mechanism based on the cation-π interactions.

Recent advances in structural engineering of photocatalysts for environmental remediation

Photocatalysis appears to be an appealing approach for environmental remediation including pollutants degradation in water, air, and/or soil, due to the utilization of renewable and sustainable source of energy, i.e., solar energy. However, their broad applications remain lagging due to the challenges in pollutant degradation efficiency, large-scale catalyst production, and stability. In recent decades, massive efforts have been devoted to advance the photocatalysis technology for improved environmental remediation. In this review, the latest progress in this aspect is overviewed, particularly, the strategies for improved light sensitivity, charge separation, and hybrid approaches. We also emphasize the low efficiency and poor stability issues with the current photocatalytic systems. Finally, we provide future suggestions to further enhance the photocatalyst performance and lower its large-scale production cost. This review aims to provide valuable insights into the fundamental science and technical engineering of photocatalysis in environmental remediation.

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.

Toward a universal framework for evaluating transport resistances and driving forces in membrane-based desalination processes

Desalination technologies using salt-rejecting membranes are a highly efficient tool to provide fresh water and augment existing water supplies. In recent years, numerous studies have worked to advance a variety of membrane processes with different membrane types and driving forces, but direct quantitative comparisons of these different technologies have led to confusing and contradictory conclusions in the literature. In this Review, we critically assess different membrane-based desalination technologies and provide a universal framework for comparing various driving forces and membrane types. To accomplish this, we first quantify the thermodynamic driving forces resulting from pressure, concentration, and temperature gradients. We then examine the resistances experienced by water molecules as they traverse liquid- and air-filled membranes. Last, we quantify water fluxes in each process for differing desalination scenarios. We conclude by synthesizing results from the literature and our quantitative analyses to compare desalination processes, identifying specific scenarios where each process has fundamental advantages.

Graphene Quantum Dot-Added Thin-Film Composite Membrane with Advanced Nanofibrous Support for Forward Osmosis

Forward osmosis (FO) technology for desalination has been extensively studied due to its immense benefits over conventionally used reverse osmosis. However, there are some challenges in this process such as a high reverse solute flux (RSF), low water flux, and poor chlorine resistance that must be properly addressed. These challenges in the FO process can be resolved through proper membrane design. This study describes the fabrication of thin-film composite (TFC) membranes with polyethersulfone solution blown-spun (SBS) nanofiber support and an incorporated selective layer of graphene quantum dots (GQDs). This is the first study to sustainably develop GQDs from banyan tree leaves for water treatment and to examine the chlorine resistance of a TFC FO membrane with SBS nanofiber support. Successful GQD formation was confirmed with different characterizations. The performance of the GQD-TFC-FO membrane was studied in terms of flux, long-term stability, and chlorine resistance. It was observed that the membrane with 0.05 wt.% of B-GQDs exhibited increased surface smoothness, hydrophilicity, water flux, salt rejection, and chlorine resistance, along with a low RSF and reduced solute flux compared with that of neat TFC membranes. The improvement can be attributed to the presence of GQDs in the polyamide layer and the utilization of SBS nanofibrous support in the TFC membrane. A simulation study was also carried out to validate the experimental data. The developed membrane has great potential in desalination and water treatment applications.

Nano-enhanced sulfonated poly(arylene ether sulfone) composite membranes and their characterization

Chlorine is a widely used oxidizing agent in desalination to control bacteria that cause biofouling. The lack of chlorine resistance in commercial desalination membranes urged the development of an alternate polymer material. In this study, commercially available copolymer (SES0005, AquafoneTM), resistant to dissolved chlorine in water, has theoretical IEC of 2.08 meq.g-1 is blended with 0.5-15 %(w/w) TiO2 nanoparticles of <25 nm diameter and 45-55 m2.g-1 surface area by using ball milling device. SEM-EDS (Scanning Electron Microscope-Energy Dispersive Spectroscopy) result supports TiO2 content and uniform distribution. The chlorine stability of membranes was evaluated in sodium hypochlorite solution from 100 to 2000 ppm (pH 9). TGA and FT-IR analysis were performed for these membranes. The 1.5 %(w/w) TiO2 nano-enhanced membrane water retention is 23 % which is ∼53 % higher than that of pristine (15 %) membrane. Tensile strength of pristine and 0.5 %(w/w) TiO2 nano-enhanced membrane is 23, and 44 MPa, respectively. TiO2 nanoparticle addition improved dimensional and mechanical properties. This study attempts to correlate the SES polymer-TiO2 interactions with the characterization techniques.

Spontaneous Salt-Preventing Solar-Thermal Water Evaporator with a High Evaporation Efficiency through Dual-Mode Water Transfer

Benefiting from the abundant solar energy and the emergence of photothermal conversion equipment, solar-driven water evaporation has shown great potential in seawater desalination. One common problem for solar-thermal evaporation is that the salt crystallized on the surface of solar absorbers during the seawater evaporation process will significantly deteriorate the continuity and efficiency of the evaporation process. In most reports, efforts have been made to transfer the accumulated salts, while the studies on preventing salt crystallization, which leads to better continuity of the production, are limited. Herein, a spontaneous salt-preventing solar-thermal water evaporator was designed, utilizing a dual-mode water transfer structure consisting of in-plane diffusion and in-tube migration. The dual-mode structural system gave rise to uniform and continuous water transfer, efficiently suppressing the salt concentration in the evaporator. As a result, salt crystallization was scarcely found on the surface of the evaporator under 1 sun irradiation for an ultralong time (200 h), demonstrating its high efficiency in inhibiting salt crystallization. In addition, the small contact area between the water and the evaporator could reduce the heat loss during the solar-thermal evaporation process, which further improved the water evaporation rate (1.64 kg m^-2 h^-1).

Treatment of reverse osmosis membrane by sodium hypochlorite and alcohols for enhanced performance using the swelling-fastening effect

Chemicals soaking is generally acknowledged as a convenient and efficient method to improve the performance of reverse osmosis (RO) membranes. The conventional soaking of RO membranes in alkaline sodium hypochlorite (NaClO) usually promotes extensive hydrolysis and cleavage amide bonds, resulting in improved water flux but declined salt rejection. Here, alcohols were added into the NaClO solution to regulate the chlorination processes using their "swelling-fastening" effect. The alcohols could interact with polyamide chains, and thus swell the polyamide network. Due to this interaction, the NaClO has less probability of attacking the polyamide chains. Hence, the chlorine-promoted hydrolysis was partly eased, which could weaken the decrease of salt rejection. Besides, after removing alcohols as well as the dissolved small oligomers and fragments of polyamide, the network was compacted and the loosened sites were healed, which is also beneficial to increase the difficulty of salt penetration. The treatment of RO membrane by the NaClO and alcohols could produce a hydrophilic surface with increased water flux and high salt rejection. The membrane chloridized at 2000 ppm NaClO exhibited a water flux improvement of 20.28% and a salt rejection declination of 0.95%. When treated with 2000 ppm NaClO associated with 5% methanol, the water flux improved 20.13% with little declination in salt rejection.

Nanofiltration Membranes Formed through Interfacial Polymerization Involving Cycloalkane Amine Monomer and Trimesoyl Chloride Showing Some Tolerance to Chlorine during Dye Desalination

Wastewater effluents containing high concentrations of dyes are highly toxic to the environment and aquatic organisms. Recycle and reuse of both water and dye in textile industries can save energy and costs. Thus, new materials are being explored to fabricate highly efficient nanofiltration membranes for fulfilling industrial needs. In this work, three diamines, 1,4-cyclohexanediamine (CHD), ethylenediamine (EDA), and p-phenylenediamine (PPD), are reacted with TMC separately to fabricate a thin film composite polyamide membrane for dye desalination. Their chemical structures are different, with the difference located in the middle of two terminal amines. The surface morphology, roughness, and thickness of the polyamide layer are dependent on the reactivity of the diamines with TMC. EDA has a short linear alkane chain, which can easily react with TMC, forming a very dense selective layer. CHD has a cyclohexane ring, making it more sterically hindered than EDA. As such, CHD's reaction with TMC is slower than EDA's, leading to a thinner polyamide layer. PPD has a benzene ring, which should make it the most sterically hindered structure; however, its benzene ring has a pi-pi interaction with TMC that can facilitate a faster reaction between PPD and TMC, leading to a thicker polyamide layer. Among the TFC membranes, TFCCHD exhibited the highest separation efficiency (pure water flux = 192.13 ± 7.11 L∙m-2∙h-1, dye rejection = 99.92 ± 0.10%, and NaCl rejection = 15.46 ± 1.68% at 6 bar and 1000 ppm salt or 50 ppm of dye solution). After exposure at 12,000 ppm∙h of active chlorine, the flux of TFCCHD was enhanced with maintained high dye rejection. Therefore, the TFCCHD membrane has a potential application for dye desalination process.

Advancing Strategies of Biofouling Control in Water-Treated Polymeric Membranes

Polymeric membranes, such as polyamide thin film composite membranes, have gained increasing popularity in wastewater treatment, seawater desalination, as well as the purification and concentration of chemicals for their high salt-rejection and water flux properties. Membrane biofouling originates from the attachment or deposition of organic macromolecules/microorganisms and leads to an increased operating pressure and shortened service life and has greatly limited the application of polymeric membranes. Over the past few years, numerous strategies and materials were developed with the aim to control membrane biofouling. In this review, the formation process, influence factors, and consequences of membrane biofouling are systematically summarized. Additionally, the specific strategies for mitigating membrane biofouling including anchoring of hydrophilic monomers, the incorporation of inorganic antimicrobial nanoparticles, coating/grafting of cationic bactericidal polymers, and the design of multifunctional material integrated multiple anti-biofouling mechanisms, are highlighted. Finally, perspectives on the challenges and opportunities in anti-biofouling polymeric membranes are shared, shedding light on the development of even better anti-biofouling materials in near future.

Review of New Approaches for Fouling Mitigation in Membrane Separation Processes in Water Treatment Applications

This review investigates antifouling agents used in the process of membrane separation (MS), in reverse osmosis (RO), ultrafiltration (UF), nanofiltration (NF), microfiltration (MF), membrane distillation (MD), and membrane bioreactors (MBR), and clarifies the fouling mechanism. Membrane fouling is an incomplete substance formed on the membrane surface, which will quickly reduce the permeation flux and damage the membrane. Foulant is colloidal matter: organic matter (humic acid, protein, carbohydrate, nano/microplastics), inorganic matter (clay such as potassium montmorillonite, silica salt, metal oxide, etc.), and biological matter (viruses, bacteria and microorganisms adhering to the surface of the membrane in the case of nutrients) The stability and performance of the tested nanometric membranes, as well as the mitigation of pollution assisted by electricity and the cleaning and repair of membranes, are reported. Physical, chemical, physico-chemical, and biological methods for cleaning membranes. Biologically induced biofilm dispersion effectively controls fouling. Dynamic changes in membrane foulants during long-term operation are critical to the development and implementation of fouling control methods. Membrane fouling control strategies show that improving membrane performance is not only the end goal, but new ideas and new technologies for membrane cleaning and repair need to be explored and developed in order to develop future applications.