Triple antifouling strategies for reverse osmosis membrane biofouling control

Deciphering membrane biofouling induced by micro-/nano-plastics in nanofiltration: Metagenomic insights and spacer-driven mitigations

Nanofiltration (NF) is an effective process for micro-/nano-plastics (MNPs) interception, but the impact of accumulated MNPs on the microbial community structure and metabolic pathways of biofilms on NF membranes remains unclear. This provides uncertainty with respect to membrane biofouling behavior and the risks to efficient NF operations. In this study, the size-dependent (20 nm-25 μm) and concentration-dependent (0.1-50 mg·L-1) effects of MNPs on the biofouling of a NF membrane treating secondary wastewater effluent were studied. Three MNPs-tolerant, hypermetabolic and polystyrene-degradable genera (i.e., Acinetobacter, Novosphingobium and Asticcacaulis) were detected in biofilms as dominant taxonomic compositions. MNPs led to an increase of 19.3 %-76.7 % in biomass contents and a more rapid decrease in permeate flux, with 0.1 mg·L-1 of 80 nm NPs causing the most severe membrane biofouling. Metagenomic analysis revealed that MNPs upregulated enzymes involved in exopolysaccharide (ExoA/L/M/P/Q/X/Y/Z) and tyrosine (COMT, FeaB and AOC3) biosynthesis and quorum sensing (PhzF and CiaH/R), and suppressed cell motility pathways including flagellar assembly and bacterial chemotaxis. Novel types of perforated column spacer (PCS) enhanced the hydrodynamics of the membrane feed with a lower pressure drop and higher fluid velocity, introduced micro-jets and greater mass transfer inside feed channels, thus eliminating the deposition of MNPs and mitigating membrane biofouling. Overall, a greater understanding of the interaction mechanisms between MNPs and membrane biofouling in secondary effluent filtration will help develop more effective MNPs management strategies and achieve more sustainable NF operations.

Maximizing membrane antifouling potential: The impact of fluoride positioning in multifunctional designs

Fluoropolymers with low surface energy demonstrate outstanding potential for fouling release. However, their limited effectiveness in practical antifouling applications requires integration with other strategies. This study explored the significant impact of fluoropolymers in a multifunctional approach that combines antiadhesion (S), antibacterial (M), and fouling release (H) properties to enhance the performance of thin-film-composite (TFC) membranes for controlling biofouling (The letters S, M and H originate from the initial letters of the corresponding functional monomers). We constructed membrane surface functionalities with fluoropolymers placed in different layers: p(H-M-S), which incorporates fluoropolymers in the innermost layer as a release-antibacterial-antiadhesion membrane; p(M-H-S), where fluoropolymers are in the middle layer as an antibacterial-release-antiadhesion membrane; and p(M-S-H), with fluoropolymers in the outermost layer as an antibacterial-antiadhesion-release membrane. This multifunctional approach resulted in superior membrane transport properties and varying resistance to biofouling. During repeated filtration cycles, the p(H-M-S) membrane showed the most effective biofouling mitigation and long-term durability, achieving an 82 % flux recovery in the third cycle due to the synergistic effects of its three combined functions. The p(M-H-S) membrane displayed strong antiadhesion performance in the early stages but had limited durability over time. In contrast, the p(M-S-H) membrane revealed the weakest fouling resistance, likely because of the hydrophobic nature of the fluorinated components in the outermost layer. Bacterial adhesion assay and protein release tests further demonstrated that the p(M-H-S) membrane reduced bacterial adhesion by 66 % and released 23 % of the protein foulants. This effectiveness is attributed to the antifouling activity provided by the hydrophilic zwitterions and bactericidal quaternary ammonium compounds, as well as the fouling-release capability of fluoropolymers, which facilitates the detachment of foulants under hydraulic forces. Microscopic analysis, coupled with interfacial energy evaluations, confirmed the presence of various multi-defense mechanisms based on the different functional architectures of the membranes. These findings offer valuable insights for designing optimized multifunctional antifouling membranes with improved performance and stability.

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.

Robust In Situ Fouling Control toward Thin-Film Composite Reverse Osmosis Membrane via One-Step Deposition of a Ternary Homogeneous Metal-Organic Hybrid Layer

Membrane fouling is one of the persistent headaches for water desalination because of the significant detriment to membrane performance and operating cost control. It is a great challenge to overcome such crisis in a facile and robust manner. This work was dedicated to customizing an antifouling thin-film composite (TFC) reverse osmosis (RO) membrane with a polydopamine (PDA)/β-alanine (βAla)/Cu²⁺ ternary homogeneous metal-organic hybrid coating. The metal ions were evenly distributed in a continuous organic network via polydentate coordination. The incorporation of βAla enabled a substantial promotion of the Cu²⁺ loading capacity on the membrane surface. The involved one-step codeposition protocol made the surface engineering practically accessible. The deposition time was optimized to afford an uncompromising permselectivity of the membrane. This novel trinity was a smart blend of anti-adhesive and bactericidal factors, and each component in the all-in-one layer performed its own function. The hydrophilic PDA/βAla phase induced weak deposition propensity of organic foulant and bacteria onto the modified membrane, as elucidated by water flux variation, foulants adhesion profile, and interfacial interaction energy. Meanwhile, the Cu²⁺-loaded surface strongly inactivated the attached bacteria to further alleviate biofouling. Excellent sustainability and stability implied the reliable performance of such trinity-coated membrane in practical service. Given the simplicity and robustness, this work opened a promising avenue for in situ fouling control of TFC RO membranes during water desalination.

Designing a MOF-based slippery lubricant-infused porous surface with dual functional anti-fouling strategy

Material that resists biofouling adhesion is needed in a complex marine environment, but few of them can combine ultra-low fouling and environmental friendliness. Slippery lubricant-infused porous surface (SLIPS) is such a material, but it lacks the contact-killing ability, which limits its stability and anti-fouling efficiency. Here, we report a metal organic framework (MOF-based) Slippery ionic liquid-infused surface with excellent antifouling performance via synergistic release and contact-killing defense strategy. The dense needle-like MIL-110 array, grown in situ on the aluminum surface, is conducive to the stable storage of quaternary ammonium salt (QAS) ionic liquid. Compared to the control group with mature biofilm formed on the surface, SLIPS showed non-fouling performance in a 10-day test and another 21-day test under more challenging conditions. The adsorption amount of lipopolysaccharide (LPS) on SLIPS was 50% lower than that on the aluminum sheet and the aluminum sheet with MIL-110 grown on the surface as the control groups within three hours. The relationship between bacterial adhesion and LPS adsorption indicated that the anti-adhesion performance of SLIPS was mediated by the weak adhesion and easy release property of its surface to extracellular fouling molecules. This study provides the possibility to systematically reveal the antifouling mechanism of SLIPS on bacterial adhesion.

Separation, anti-fouling, and chlorine resistance of the polyamide reverse osmosis membrane: From mechanisms to mitigation strategies

Membrane technology has been widely used in the wastewater treatment and seawater desalination. In recent years, the reverse osmosis (RO) membrane represented by polyamide (PA) has made great progress because of its excellent properties. However, the conventional PA RO membranes still have some scientific problems, such as membrane fouling, easy degradation after chlorination, and unclear mechanisms of salt retention and water flux, which seriously impede the widespread use of RO membrane technology. This paper reviews the progress in the research and development of the RO membrane, with key focus on the mechanisms and strategies of the contemporary separation, anti-fouling and chlorine resistance of the PA RO membrane. This review seeks to provide state-of-the-art insights into the mitigation strategies and basic mechanisms for some of the key challenges. Under the guidance of the fundamental understanding of each mechanism, operation and modification strategies are discussed, and reasonable analysis is carried out, which can address some key technical challenges. The last section of the review focuses on the technical issues, challenges, and future perspective of these mechanisms and strategies. Advances in synergistic mechanisms and strategies of the PA RO membranes have been rarely reviewed; thus, this review can serve as a guide for new entrants to the field of membrane water treatment and established researchers.

Fouling control in reverse osmosis for water desalination & reuse: Current practices & emerging environment-friendly technologies

Reverse Osmosis (RO) is becoming increasingly popular for seawater desalination and wastewater reclamation. However, fouling of the membranes adversely impacts the overall process efficiency and economics. To date, several strategies and approaches have been used in RO plants and investigated at the laboratory-scale for their effectiveness in the control of different fouling types. Amid growing concerns and stringent regulations for the conservation of environment, there is an increasing trend to identify technologies that are effective in fouling mitigation as well as friendly to the environment. The present review elaborates on the different types of environment-friendly technologies for membrane fouling control that are currently being used or under investigation. It commences with a brief introduction to the global water crisis and the potential of membrane-based processes in overcoming this problem. This is followed by a section on membrane fouling that briefly describes the major fouling types and their impact on the membrane performance. Section 3 discusses the predominant fouling control/prevention strategies including feedwater pretreatment, membrane and spacer surface modification and membrane cleaning. The currently employed techniques are discussed together with their drawbacks, with some light being shed on the emerging technologies that have the ability to overcome the current limitations. The penultimate section provides a detailed discussion on a variety of eco-friendly/chemical free techniques investigated to control different fouling types. These include both control and prevention strategies, for example, bioflocculation and electromagnetic fields, as well as remediation techniques such as osmotic backwashing and gas purging. In addition, quorum sensing has been specifically discussed for biofouling remediation. The promising findings from different studies are presented followed by a discussion on their drawbacks and limitations. The review concludes with a need for carrying out fundamental studies to develop better understanding of the eco-friendly processes discussed in the penultimate section and their optimization for possible integration into the RO plants.

Antifouling Nanofiltration Membrane Fabrication via Surface Assembling Light-Responsive and Regenerable Functional Layer

Membrane fouling, caused by aggregation of organics and microorganisms from filtrate on the membrane surface, seriously reduces the service life of a nanofiltration (NF) membrane. Developing facile and renewable antifouling modification methods without sacrificing separation properties of the membrane remain an imperative requirement. Herein, a thin-film composite (TFC) NF membrane with a light-responsive and regenerable functional layer (P-TFC) was fabricated via host-guest interactions between the azobenzene (guest) labeled functional polymers and the β-cyclodextrin (host) bonded membrane surface (H-TFC). The P-TFC-3 not only showed outstanding antifouling ability and high flux recovery ratio (FRR > 90% at the fourth antiadhesive test) but also exhibited enhanced water permeability (17.9 L m^-2 h^-1 bar^-1) and high selectivity (α_MgSO4^NaCl = 33.4 and fast antibiotics enrichment capacity) compared with the pristine membrane. Furthermore, when the functional layer was contaminated, it can be removed by ultraviolet light irradiation and a new functional layer can be rebuilt by adding fresh azobenzene labeled functional polymers. After several regeneration processes, the membranes still showed constant separation properties and high flux recovery ability (FRR > 90%). This work proposes an easy-to-assemble and regenerable surface modification strategy to endow TFC NF membranes with excellent fouling resistance and sustainable utilization ability while maintaining high separation properties.

Tailor-made high-performance reverse osmosis membranes by surface fixation of hydrophilic macromolecules for wastewater treatment

Polyamide aromatic (PA) reverse osmosis (RO) membranes are currently the most important materials in the seawater desalination and wastewater treatment industry. This study used hydrophilic macromolecular polyvinylpyrrolidone (PVP) in a PA selective layer to develop a new polyamide thin-film composite (TFC), namely PA-g-PVP RO, which will be used for water treatment. The TFC is prepared via an interfacial polymerisation process, and TFC-based PVP can be transplanted on a PA surface by radiation. PA-g-PVP RO was characterised by ATR-FTIR, SEM, XPS, AFM and contact angle test and then evaluated by determining its permeability, salt retention and antifouling performance, among other properties. Results show that the chemical composition and surface morphology of the polyamide film significantly changed. A PVP brush grafted on an RO membrane surface significantly enhanced the hydrophilicity and antifouling performance of the membrane. When the PVP concentration was increased in an aqueous solution to 2%, the water contact angle of the sacrificial layer of the modified membrane decreased to 24.3°, the fouling recovery ratio to 93.4% and the salt retention increased to 99.5% at a small flux change. This combined technology can also be used for other macromolecules to modify the membrane and study the preparation and modification of ultra-filtration and nano-filtration membranes.

Polyamide aromatic (PA) reverse osmosis (RO) membranes are currently the most important materials in the seawater desalination and wastewater treatment industry.

Biguanidine functional chitooligosaccharide modified reverse osmosis membrane with improved anti-biofouling property

The COSG-modified RO membrane with excellent anti-adhesive and antimicrobial properties was successfully fabricated by second interfacial polymerization.