Mitigation of Biofilm Development on Thin-Film Composite Membranes Functionalized with Zwitterionic Polymers and Silver Nanoparticles

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.

Enhanced adsorption of aqueous perfluorooctanoic acid on iron-functionalized biochar: elucidating the roles of inner-sphere complexation

Perfluorooctanoic acid (PFOA) is ubiquitously detected in various water bodies, which raises the urgent need for developing effective and economic remediation methods in response to its health risks. The adsorptive removal of PFOA by biochar (BC) is regarded as a simple, effective, and economical technique. However, engineered BCs, including FeCl3-activated BC, for PFOA removal and adsorption mechanisms have been ill-studied. In this study, a FeCl3-activated dairy manure-derived biochar (Fe@MBC) was prepared via one-step pyrolysis/activation, and its properties and adsorption characteristics were compared with a pristine manure-derived biochar (P-MBC). The FeCl3 activation largely increased the surface area of Fe@MBC and the deposition of FexOy minerals on surface of Fe@MBC while significantly elevating the surface roughness of Fe@MBC. The maximum adsorption capacity of Fe@MBC for PFOA (233 mg·g-1) was five times higher than that of P-MBC (46 mg·g-1). PFOA adsorption was favorable at low solution pH and was independent on ionic strength, which supported the major contribution by inner-sphere complexation rather than out-sphere complexation. This mechanism was further confirmed by the disappearance of FeO peak on Fourier transform infrared spectrum and the blue-shift of Fe binding energies on X-ray photoelectron Fe 2p spectrum of Fe@MBC after PFOA adsorption. Fe@MBC maintained a near 100% adsorption capacity for PFOA after 4 cycles of chemical regeneration. Fe@MBC also exhibited efficient removal for PFOA and other PFAS compounds at trace levels in the lake water and wastewater treatment plant effluent. Thus, this study highlights a promising insight for selectively eliminating PFASs from water.

Innovative temperature-responsive membrane with an elastic interface for biofouling mitigation in industrial circulating cooling water treatment

To address the issues of scaling caused by heat and water evaporation in regard to circulating cooling water (CCW), TFC membrane filtration systems have been increasingly considered for terminal treatment processes because of their excellent separation performance. However, membrane biofouling phenomenon significantly hinders the widespread utilization of TFC membranes. In this study, to harness the thermal phenomenon of CCW and establish a stable and durable multifunctional antibiofouling layer, temperature-responsive Pnipam and the spectral antibacterial agent Ag were organically incorporated into commercially available TFC membranes. Biological experimental findings demonstrated that above the lower critical solution temperature (LCST), the contraction of Pnipam molecular chains facilitated the inactivation of bacteria by the antibacterial agent, resulting in an impressive sterilization efficiency of up to 99 %. XDLVO analysis revealed that below the LCST, the establishment of a hydration layer on the functional interface resulted in the creation of elevated energy barriers, effectively impeding bacterial adhesion to the membrane surface. Consequently, a high bacterial release rate of 98.4 % was achieved on the low-temperature surface. The alterations in the functional membrane surface conformation induced by temperature variations further amplified the separation between the pollutants and the membrane, creating an enhanced "elastic interface." This efficient and straightforward cleaning procedure mitigated the formation of irreversible fouling without compromising the integrity of the membrane surface. This study presents a deliberately engineered thermoresponsive antibiofouling membrane interface to address the issue of membrane fouling in membrane-based CCW treatment systems while shedding new light on the mechanisms of "inactivation" and "defense."

Machine Learning Aided Design and Optimization of Antifouling Surfaces

Antifouling surfaces, renowned for their strong surface resistance to proteins, cells, or tissues in various biological and environmental conditions, have broad applications in implanted devices, antibacterial coatings, biosensors, responsive materials, water treatment, and lab-on-a-chip. While extensive experimental research exists on antifouling surfaces, machine learning studies on this topic are relatively few. This perspective specifically focuses on exploring the complex relationships between the composition, structure, and properties of antifouling surfaces, examining how these factors correlate with surface hydration and protein adsorption. Different machine learning models have been developed to analyze and predict single and multiple protein adsorptions on various types of surfaces, ranging from structureless surfaces to well-ordered and rigid self-assembled monolayers, dynamically ordered polymer brushes, and complex filtration membranes. These models not only identify key descriptors or functional groups critical for antifouling performance (surface hydration, protein adsorption) but also predict the antifouling properties for a specific surface. Recognizing current challenges, this perspective delineates future research directions in the antifouling field. By leveraging and comparing current machine learning approaches, it aims to advance both the design and fundamental understanding of antifouling surfaces, thereby pushing the boundaries of innovation in this critical field.

Emerging strategies for treating medical device and wound-associated biofilm infections

Bacterial infections represent a significant global threat to human health, leading to considerable economic losses through increased healthcare costs and reduced productivity. One major challenge in treating these infections is the presence of biofilms - structured bacterial communities that form protective barriers, making traditional treatments less effective. Additionally, the rise of antibiotic-resistant bacteria has exacerbated treatment difficulties. To address these challenges, researchers are developing and exploring innovative approaches to combat biofilm-related infections. This mini-review highlights recent advancements in the following key areas: surface anti-adhesion technologies, electricity, photo/acoustic-active materials, endogenous mimicking agents, and innovative drug delivery systems. These strategies aim to prevent biofilm formation, disrupt existing biofilms, and enhance the efficacy of antimicrobial treatments. Currently, these approaches show great potential for applications in medical fields such as medical device and wound - associated biofilm infections. By summarizing these developments, this mini-review provides a comprehensive resource for researchers seeking to advance the management and treatment of biofilm-associated infections.

High-Performance Nanofiltration Membrane with Dual Resistance to Gypsum Scaling and Biofouling for Enhanced Water Purification

Nanofiltration (NF) technology is pivotal for ensuring a sustainable and reliable supply of clean water. To address the critical need for advanced thin-film composite (TFC) polyamide (PA) membranes with exceptional permselectivity and fouling resistance for emerging contaminant purification, we introduce a novel high-performance NF membrane. This membrane features a selective polypiperazine (PIP) layer functionalized with amino-containing quaternary ammonium compounds (QACs) through an in situ interfacial polycondensation reaction. Our investigation demonstrated that precise QAC functionalization enabled the construction of the selective PA layer with increased surface area, enhanced microporosity, stronger electronegativity, and reduced thickness compared to the control PIP membrane. As a result, the QAC NF membrane exhibited an approximately 51% increase in water permeance compared to the control PIP membrane, while achieving superior retention capabilities for divalent salts (>99%) and emerging organic contaminants (>90%). Furthermore, the incorporation of QACs into the PIP selective layer was proved to be effective in mitigating mineral scaling by allowing selective passage of scale-forming cations, while simultaneously exhibiting strong antimicrobial properties to combat biofouling. The in situ QAC incorporation strategy presented in this study provides valuable guidelines for the fit-for-purpose design of the selective PA layer, which is crucial for the development of high-performance NF membranes for efficient water purification.

Mechanisms and Strategies of Advanced Oxidation Processes for Membrane Fouling Control in MBRs: Membrane-Foulant Removal versus Mixed-Liquor Improvement

Membrane bioreactors (MBRs) are well-established and widely utilized technologies with substantial large-scale plants around the world for municipal and industrial wastewater treatment. Despite their widespread adoption, membrane fouling presents a significant impediment to the broader application of MBRs, necessitating ongoing research and development of effective antifouling strategies. As highly promising, efficient, and environmentally friendly chemical methods for water and wastewater treatment, advanced oxidation processes (AOPs) have demonstrated exceptional competence in the degradation of pollutants and inactivation of bacteria in aqueous environments, exhibiting considerable potential in controlling membrane fouling in MBRs through direct membrane foulant removal (MFR) and indirect mixed-liquor improvement (MLI). Recent proliferation of research on AOPs-based antifouling technologies has catalyzed revolutionary advancements in traditional antifouling methods in MBRs, shedding new light on antifouling mechanisms. To keep pace with the rapid evolution of MBRs, there is an urgent need for a comprehensive summary and discussion of the antifouling advances of AOPs in MBRs, particularly with a focus on understanding the realizing pathways of MFR and MLI. In this critical review, we emphasize the superiority and feasibility of implementing AOPs-based antifouling technologies in MBRs. Moreover, we systematically overview antifouling mechanisms and strategies, such as membrane modification and cleaning for MFR, as well as pretreatment and in-situ treatment for MLI, based on specific AOPs including electrochemical oxidation, photocatalysis, Fenton, and ozonation. Furthermore, we provide recommendations for selecting antifouling strategies (MFR or MLI) in MBRs, along with proposed regulatory measures for specific AOPs-based technologies according to the operational conditions and energy consumption of MBRs. Finally, we highlight future research prospects rooted in the existing application challenges of AOPs in MBRs, including low antifouling efficiency, elevated additional costs, production of metal sludge, and potential damage to polymeric membranes. The fundamental insights presented in this review aim to elevate research interest and ignite innovative thinking regarding the design, improvement, and deployment of AOPs-based antifouling approaches in MBRs, thereby advancing the extensive utilization of membrane-separation technology in the field of wastewater treatment.

Fighting against biofilm: The antifouling and antimicrobial material

Biofilms are groups of microorganisms protected by self-secreted extracellular substances. Biofilm formation on the surface of biomaterial or engineering materials becomes a severe challenge. It has caused significant health, environmental, and societal concerns. It is believed that biofilms lead to life-threatening infection, medical implant failure, foodborne disease, and marine biofouling. To address these issues, tremendous effort has been made to inhibit biofilm formation on materials. Biofilms are extremely difficult to treat once formed, so designing material and coating bearing functional groups that are capable of resisting biofilm formation has attracted increasing attention for the last two decades. Many types of antibiofilm strategies have been designed to target different stages of biofilm formation. Development of the antibiofilm material can be classified into antifouling material, antimicrobial material, fouling release material, and integrated antifouling/antimicrobial material. This review summarizes relevant research utilizing these four approaches and comments on their antibiofilm properties. The feature of each method was compared to reveal the research trend. Antibiofilm strategies in fundamental research and industrial applications were summarized.

Enhancing proton transport in polyvinylidenedifluoride membranes and reducing biofouling for improved hydrogen production in microbial electrolysis cells

Hydrophilic porous membranes, exemplified by polyvinylidene fluoride (PVDF) membranes, have demonstrated significant potential for replacing ion exchange membranes in microbial electrolysis cells (MECs). Membrane fouling remains a major challenge in MECs, impeding proton transport and consequently limiting hydrogen production. This study aims to investigate a synergistic antifouling strategy for PVDF membrane through the incorporation of a coating composed of polydopamine (PDA), polyethyleneimine (PEI), and silver nanoparticles (AgNPs). The PDA-PEI-Ag@PVDF membrane not only effectively mitigates fouling through steric and electrostatic repulsion forces, but also amplifies ion transport by facilitating water diffusion and electromigration. The PDA-PEI-Ag@PVDF membrane exhibited a reduced membrane resistance of 1.01 mΩ m2 and PDA-PEI-Ag modifying PVDF membrane was found to be effective in enhancing the proton transportation of PVDF membrane. Therefore, the enhanced hydrogen production rate of 2.65 ± 0.02 m3/m3/d was achieved in PDA-PEI-Ag@PVDF-MECs.

Maintenance-free antifouling polymeric membrane potentiometric sensors based on self-polishing coatings

Polymeric membrane ion-selective electrodes (ISEs) have been widely used in environmental monitoring. However, in complicated marine environments, marine biofouling usually becomes a sticky problem for these electrodes. Herein, for the first time, a novel maintenance-free antifouling potentiometric marine sensor based on a self-polishing coating (SPC) is proposed. The SPC is synthesized by using the seeded emulsion polymerization method based on the triisopropylsilyl methacrylate monomer as the regulator of the self-renewal rate. This coating can be simply modified onto the electrode surface by drop-casting. The silyl acrylate side groups of the obtained SPC on the sensor surface can be hydrolyzed in the marine alkaline medium. The shear movement of seawater driven by sea waves, wind, gravity, or vibration removes the leftover (fouled) brittle polymer backbone and thus the fouling marine microorganisms. As a proof-of-concept experiment, a polymeric membrane Ca2+-ISE is chosen as a model. Compared to the unmodified electrode, the SPC-coated Ca2+-ISE exhibits remarkable improved antifouling properties in terms of superior anti-adhesive abilities towards marine microorganisms, such as bacterial cells and algae and excellent long-term stability even in the presence of high levels of marine microorganisms. Since no additional manual maintenance is required for maintaining the antifouling abilities of the sensor, the proposed self-polishing sensor may lay an important foundation for construction of unattended long-term potentiometric monitoring systems in real marine environments.

Inhibition of biofouling by in-situ grown zwitterionic hydrogel nanolayer on membrane surface in ultralow-pressurized ultrafiltration process

Ultralow-pressurized ultrafiltration membrane process with low energy consumption is promising in surface water purification. However, membrane fouling and low selectivity are significant barriers for the wide application of this process. Herein, an ultrathin zwitterionic hydrogel nanolayer was in-situ grown on polysulfone ultrafiltration membrane surface through interfacially-initiated free radical polymerization. The hydrogel-modified membrane possessed improved biological fouling resistance during the dynamic filtration process (bovine serum albumin, Escherichia coli and Staphylococcus aureus), comparing with commercial polysulfone membrane. The enhanced biofouling resistance ability of zwitterionic hydrogel nanolayer was derived from the foulant repulsion of hydration shell and the bactericidal effect of quaternary ammonium, according to the results of foulant-membrane interaction energy analyses and antibacterial performances. In surface water treatment, the zwitterionic hydrogel layer inhibited biofouling and resulted in the formation of a loose and thin biofilm. In addition, the hydrogel-modified membrane possessed 22% improvement in dissolved organic carbon (DOC) removal and 134% increasement in stable water flux, compared to commercial polysulfone membrane. The in-situ grown zwitterionic hydrogel nanolayer on membrane surface offers a prospectively alternative for biofouling control in ultralow-pressurized membrane process.

Functionalization of seawater reverse osmosis membrane with quorum sensing inhibitor to regulate microbial community and mitigate membrane biofouling

Membrane biofouling is a challenge to be solved for the stable operation of the seawater reverse osmosis (SWRO) membrane. This study explored the regulation mechanism of quorum sensing (QS) inhibition on microbial community composition and population-level behaviors in seawater desalination membrane biofouling. A novel antibiofouling SWRO membrane (MA_m) by incorporating one of quorum sensing inhibitors (QSIs), methyl anthranilate (MA) was prepared. It exhibited enhanced anti-biofouling performance than the exogenous addition of QSIs, showing long-term stability and alleviating 22 % decrease in membrane flux compared with the virgin membrane. The results observed that dominant bacteria Epsilon- and Gamma-proteobacteria (Shewanella, Olleya, Colwellia, and Arcobacter), which are significantly related to (P ≤ 0.01) the metabolic products (i.e., polysaccharides, proteins and eDNA), are reduced by over 80 % on the MA_m membrane. Additionally, the introduction of MA has a more significant impact on the QS signal-sensing pathway through binding to the active site of the transmembrane sensor receptor. It effectively reduces the abundance of genes encoding QS and extracellular polymeric substance (EPS) (exopolysaccharides (i.e., galE and nagB) and amino acids (i.e., ilvE, metH, phhA, and serB)) by up to 50 % and 30 %, respectively, resulting in a reduction of EPS by more than 50 %, thereby limiting the biofilm formation on the QSI-modified membrane. This study provides novel insights into the potential of QSIs to control consortial biofilm formation in practical SWRO applications.

Surface modification of FeⅢ-juglone coating on nanofiltration membranes for efficient biofouling mitigation

Nanofiltration membranes have increasingly played a vital role in the purification of surface water and the recycling of wastewater. However, the problem of membrane biofouling, which leads to shortened service life and increased energy consumption, has hindered the widespread application of nanofiltration membranes. In this study, we developed functionalized nanofiltration membranes with anti-adhesive and anti-biofouling properties by coordinating FeIII and juglone onto commercial nanofiltration membranes in a facile and viable manner. Due to the hydrophilic nature of the FeⅢ-juglone coating as well as its ultra-thin thickness and minimal impact on the membrane pores, the permeance of the optimally modified membrane even increased slightly (14 %). The outstanding anti-adhesive property of the FeⅢ-juglone coating was demonstrated by a significant reduction in the adsorption of proteins and bacteria. Furthermore, the modified membranes exhibited lower flux decline amplitude and reduced biofilm deposition during dynamic fouling experiment, further supporting the outstanding anti-biofouling performance of the nanofiltration membrane after the modification with FeⅢ-juglone coating. This study presents a novel and feasible approach for simultaneously improving the water permeance, anti-adhesive property and anti-biofouling property of commercial nanofiltration membranes.

Antimicrobial Nanoparticles Mediated Prevention and Control of Membrane Biofouling in Water and Wastewater Treatment: Current Trends and Future Perspectives

Global water scarcity and water pollution necessitate wastewater reclamation for further use. As an alternative to conventional techniques, membrane technology is extensively used as an advanced method for water purification and wastewater treatment due to its selectivity, permeability, and efficient removal of pollutants. However, microbial biofouling is a major threat that deteriorates membrane performance and imparts operational challenges. It is a natural phenomenon caused by the undesirable colonization of microbes on membrane surfaces. The economic penalties associated with this menace are enormous. The traditional preventive measures are dominated by biocides, toxic chemicals, cleaners and antifouling surfaces, which are costly and often cause secondary pollution. Recent focus is thus being directed to promote inputs from nanotechnology to control and mitigate this major threat. Different anti-microbial nanomaterials can be effectively used to prevent the adhesion of microbes onto the membrane surfaces and eliminate microbial biofilms, to provide an economical and eco-friendly solution to biofouling. This review addresses the formation of microbial biofilms and biofouling in membrane operations. The potential of nanocomposite membranes in alleviating this problem and the challenges in commercialization are discussed. The antifouling mechanisms are also highlighted, which are not widely elucidated.

In Situ Formation of Silver Nanoparticles Induced by Cl-Doped Carbon Quantum Dots for Enhanced Separation and Antibacterial Performance of Nanofiltration Membrane

Polyamide (PA) nanofiltration (NF) membranes suffer from biofouling, which will deteriorate their separation performance. In this study, we proposed a strategy to incorporate silver nanoparticles (Ag NPs) into PA NF membranes in situ, in order to simultaneously enhance water permeability and antibacterial performance. The chloride-doped carbon quantum dots (Cl-CQDs) with photocatalytic performance were pre-embedded in the PA selective layer. Under visible light irradiation, the photogenerated charge carriers generated by Cl-CQDs rapidly transported to silver ions (Ag+ ions), resulting in the in situ formation of Ag NPs. The proposed strategy avoided the problem of aggregating Ag NPs, and the amount of Ag NPs on the membrane surfaces could be easily tuned by changing silver nitrate (AgNO3) concentrations and immersion times. These uniformly dispersed Ag NPs increased membrane hydrophilicity. Thus, the obtained thin film nanocomposite Ag NPs (TFN-Ag) membrane exhibited an improved water flux (31.74 L m-2 h-1), which was ~2.98 times that of the pristine PA membrane; meanwhile, the sodium sulfate (Na2SO4) rejection rate was 96.11%. The sterilization rates of the TFN-Ag membrane against Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus) were 99.55% and 99.52%, respectively. Thus, this facile strategy simultaneously improved the permeability and antibacterial property of PA NF membranes.

Bacterial Biofilm Formation on Biomaterials and Approaches to Its Treatment and Prevention

Bacterial biofilms can cause widespread infection. In addition to causing urinary tract infections and pulmonary infections in patients with cystic fibrosis, biofilms can help microorganisms adhere to the surfaces of various medical devices, causing biofilm-associated infections on the surfaces of biomaterials such as venous ducts, joint prostheses, mechanical heart valves, and catheters. Biofilms provide a protective barrier for bacteria and provide resistance to antimicrobial agents, which increases the morbidity and mortality of patients. This review summarizes biofilm formation processes and resistance mechanisms, as well as the main features of clinically persistent infections caused by biofilms. Considering the various infections caused by clinical medical devices, we introduce two main methods to prevent and treat biomaterial-related biofilm infection: antibacterial coatings and the surface modification of biomaterials. Antibacterial coatings depend on the covalent immobilization of antimicrobial agents on the coating surface and drug release to prevent and combat infection, while the surface modification of biomaterials affects the adhesion behavior of cells on the surfaces of implants and the subsequent biofilm formation process by altering the physical and chemical properties of the implant material surface. The advantages of each strategy in terms of their antibacterial effect, biocompatibility, limitations, and application prospects are analyzed, providing ideas and research directions for the development of novel biofilm infection strategies related to therapeutic materials.

Self-forming electroactive dynamic membrane for enhancing the decolorization of methyl orange by weak electrical stimulation

An electroactive dynamic membrane (EADM), which enabled simultaneous solid-liquid separation and contaminants removal, has been developed by electrostimulation using domestic wastewater as inoculum. Results showed that both the control dynamic membrane (CDM), without electrical stimulation, and the EADM systems exhibited stable removal performance with chemical oxygen demand (COD), and a robustness in responding to a fluctuating organic load. With the introduction of a weak electrical field, the EADM transmembrane pressure (TMP) was significantly reduced (0.02 kPa/d) compared with the control (0.20 kPa/d). In the treatment of methyl orange (MO), the EADM system achieved a decolorization efficiency of 85.87 %, much higher than the control dynamic membrane (CDM) system (58.84 %), which can be attributed to electrical stimulation and H₂ production on cathode. Microbial analysis has established that electrostimulation enriched the electroactive bacteria in the dynamic biofilm, and shaped the microbial structure, with improved contaminant removal. The results of this study highlight the potential of regulating the microbial community and creating a beneficial biofilm as a dynamic layer to facilitate contaminant removal.

Simultaneous and Sensitive Detection of Three Pesticides Using a Functional Poly(Sulfobetaine Methacrylate)-Coated Paper-Based Colorimetric Sensor

Chlorpyrifos (CHL), profenofos (PRO) and cypermethrin (CYP) are widely used in combination to increase crop yields. However, these three pesticides can cause serious harm to human health and do not easily degrade. In this study, a novel visible paper sensor has been prepared successfully and different colorimetric reactions were utilized to detect the three pesticides simultaneously. The sensor was constructed by grafting a zwitterionic polymer onto a cellulose filter (CF) and placing it on a glass surface modified with PDMS. The branch shape was designed to form multiple detection areas, which were modified with specific pesticides and corresponding chromogenic reagents. The as-prepared colorimetric platform exhibited high sensitivity, a short detection time, a good linear response and a low detection limit (LOD) for the three pesticides (chlorpyrifos: y = 46.801 - 1.939x, R² = 0.983, LOD = 0.235 mg/L; profenofos: y = 40.068 + 42.5x, R² = 0.988, LOD = 4.891 mg/L; cypermethrin: y = 51.993 + 1.474x, R² = 0.993, LOD = 4.053 mg/L). The comparison of the results obtained by the proposed paper sensor and those obtained by spectrophotometry further revealed the stability and reliability of the paper sensor. In particular, the color intensity of the interaction between the pesticides and coloring agents could be directly observed by the human eye. The consistency of the colorimetric/optical assay was proven in real target pesticide samples. Thus, this sensing strategy provides a portable, cost-effective, accurate and visualized paper platform, which could be suitable for application in the fruit and vegetable industry for monitoring CHL, PRO and CYP in parallel.

Nanomaterials and Coatings for Managing Antibiotic-Resistant Biofilms

Biofilms are a global health concern responsible for 65 to 80% of the total number of acute and persistent nosocomial infections, which lead to prolonged hospitalization and a huge economic burden to the healthcare systems. Biofilms are organized assemblages of surface-bound cells, which are enclosed in a self-produced extracellular polymer matrix (EPM) of polysaccharides, nucleic acids, lipids, and proteins. The EPM holds the pathogens together and provides a functional environment, enabling adhesion to living and non-living surfaces, mechanical stability, next to enhanced tolerance to host immune responses and conventional antibiotics compared to free-floating cells. Furthermore, the close proximity of cells in biofilms facilitates the horizontal transfer of genes, which is responsible for the development of antibiotic resistance. Given the growing number and impact of resistant bacteria, there is an urgent need to design novel strategies in order to outsmart bacterial evolutionary mechanisms. Antibiotic-free approaches that attenuate virulence through interruption of quorum sensing, prevent adhesion via EPM degradation, or kill pathogens by novel mechanisms that are less likely to cause resistance have gained considerable attention in the war against biofilm infections. Thereby, nanoformulation offers significant advantages due to the enhanced antibacterial efficacy and better penetration into the biofilm compared to bulk therapeutics of the same composition. This review highlights the latest developments in the field of nanoformulated quorum-quenching actives, antiadhesives, and bactericides, and their use as colloid suspensions and coatings on medical devices to reduce the incidence of biofilm-related infections.

Maintaining Antibacterial Activity against Biofouling Using a Quaternary Ammonium Membrane Coupling with Electrorepulsion

Antibacterial modification is a chemical-free method to mitigate biofouling, but surface accumulation of bacteria shields antibacterial groups and presents a significant challenge in persistently preventing membrane biofouling. Herein, a great synergistic effect of electrorepulsion and quaternary ammonium (QA) inactivation on maintaining antibacterial activity against biofouling has been investigated using an electrically conductive QA membrane (eQAM), which was fabricated by polymerization of pyrrole with QA compounds. The electrokinetic force between negatively charged Escherichia coli and cathodic eQAM prevented E. coli cells from reaching the membrane surface. More importantly, cathodic eQAM accelerated the detachment of cells from the eQAM surface, particularly for dead cells whose adhesion capacity was impaired by inactivation. The number of dead cells on the eQAM surface was declined by 81.2% while the number of live cells only decreased by 49.9%. Characterization of bacteria accumulation onto the membrane surface using an electrochemical quartz crystal microbalance revealed that the electrorepulsion accounted for the cell detachment rather than inactivation. In addition, QA inactivation mainly contributed to minimizing the cell adhesion capacity. Consequently, the membrane fouling was significantly declined, and the final normalized water flux was promoted higher than 20% with the synergistic effect of electrorepulsion and QA inactivation. This work provides a unique long-lasting strategy to mitigate membrane biofouling.

Antibiofouling Characteristics and Mechanisms in an Anammox Membrane Bioreactor Based on an Optimized Photocatalytic Technology─Photocatalytic Optical Fibers

As an ecofriendly photocatalytic antifouling technology for membrane bioreactors (MBRs), photocatalytic optical fibers (POFs) can decrease the replacement cost of modified membranes and prevent the proliferation of photosynthetic bacteria caused by direct light illumination. Here, POFs were applied in situ in an anaerobic ammonium oxidation (anammox) MBR for membrane biofouling control. Compared with the control MBR without POFs treatment, the average fouling cycle of the POFs-loaded MBR was extended by 137%, and the energy consumption caused by membrane fouling was saved by 18%. In the antibiofouling process, ^•OH was the key photocatalytic reactive species. On the fouled POFs-loaded membranes, the membrane-adhered foulant was significantly decreased by photocatalytic degradation of the proteins, polysaccharides and humic substances in the microbial metabolites. The membrane-attached bacteria were inactivated by the POFs by the mechanisms of cell-membrane destruction and cell-membrane permeabilization, which caused bacterial necrosis and apoptosis, respectively. Moreover, the total nitrogen-removal efficiencies of the two MBRs were maintained at 85.3-90.4%, and the abundance of anammox bacteria increased from 21.3% to 46.2% during the 202 days of operation, indicating an efficient anammox process with excellent nitrogen-removal performance, biomass retention, and anammox bacteria enrichment. The systematic insights into the antibiofouling performance and mechanisms of POFs in anammox MBRs will promote application and development of membrane-filtration technology in wastewater treatment using environmentally friendly and energy-efficient antifouling strategies.

Polymeric Membrane Marine Sensors with a Regenerable Antibiofouling Coating Based on Surface Modification of a Dual-Functionalized Magnetic Composite

Environmentally compatible polymeric membrane marine sensors with excellent antiadhesive and antibacterial properties have recently been developed. However, the regeneration abilities of these sensors after fouling have rarely been investigated. Herein, a novel strategy for preparation of a regenerable antibiofouling coating via surface modification of a dual-functionalized magnetic composite is proposed. A zwitterionic polymer (i.e., poly(sulfobetaine methacrylate)) and a quaternary ammonium compound (i.e., 3-trimethoxysilylpropyl octadecyldimethyl ammonium chloride) are coated on the surface of Fe₃O₄ microspheres for antiadhesion and bacterial inactivation, respectively. The antifouling magnetic composite can readily be modified on the sensor's surface via the magnetically assisted self-assembly technology. Using a polymeric membrane calcium ion-selective electrode as a model sensor, the protection layer-coated electrode shows the markedly improved antibiofouling activities as compared to the unmodified sensor. More importantly, by altering the direction of the external magnetic field, the antifouling coating can easily be removed after fouling along with the removal of the adsorbed bacterial cells from the electrode's surface, which is followed by re-modifying a fresh coating for regeneration of the antifouling electrode. The proposed methodology for fabrication of a regenerable antibiofouling coating is promising to improve the durability of a marine sensor.

Low-Fouling Gold Nanorod Theranostic Agents Enabled by a Sulfoxide Polymer Coating

Gold nanorods (GNRs) are widely used in various biomedical applications such as disease imaging and therapy due to their unique plasmonic properties. To improve their bioavailability, GNRs often need to be coated with hydrophilic polymers so as to impart stealth properties. Poly(ethylene glycol) (PEG) has been long used as such a coating material for GNRs. However, there is increasing acknowledgement that the amphiphilic nature of PEG facilitates its interaction with protein molecules, leading to immune recognition and consequent side effects. This has motivated the search for new classes of low-fouling polymers with high hydrophilicity as alternative low-fouling surface coating materials for GNRs. Herein, we report the synthesis, characterization, and application of GNRs coated with highly hydrophilic sulfoxide-containing polymers. We investigated the effect of the sulfoxide polymer coating on the cellular uptake and in vivo circulation time of the GNRs and compared these properties with pegylated GNR counterparts. The photothermal effect and photoacoustic imaging of these polymer-coated GNRs were also explored, and the results show that these GNRs are promising as nanotheranostic particles for the treatment of cancer.

Recent progress in nanomaterial-functionalized membranes for removal of pollutants

Membrane technology has gained tremendous attention for removing pollutants from wastewater, mainly due to their affordable capital cost, miniature equipment size, low energy consumption, and high efficiency even for the pollutants present in lower concentrations. In this paper, we review the literature to summarize the progress of nanomaterial-modified membranes for wastewater treatment applications. Introduction of nanomaterial in the polymeric matrix influences membrane properties such as surface roughness, hydrophobicity, porosity, and fouling resistance. This review also covers the importance of functionalization strategies to prepare thin-film nanocomposite hybrid membranes and their effect on eliminating pollutants. Systematic discussion regarding the impact of the nanomaterials incorporated within membrane, toward the recovery of various pollutants such as metal ions, organic compounds, dyes, and microbes. Successful examples are provided to show the potential of nanomaterial-functionalized membranes for regeneration of wastewater. In the end, future prospects are discussed to develop nanomaterial-based membrane technology.

Effects of Ethyl Lauroyl Arginate (LAE) on Biofilm Detachment: Shear Rate, Concentration, and Dosing Time

Biofilm formation is one of the main obstacles in membrane treatment. The non-oxidizing biocide ethyl lauroyl arginate (LAE) is promising for mitigating biofilm development on membrane surfaces. However, the operating conditions of LAE and their impact on biofilm detachment are not comprehensively understood. In this study, a real-time in vitro flow cell system was utilized to observe biofilm dispersal caused by the shear rate, concentration, and treatment time of LAE. This confirmed that the biofilm was significantly reduced to 68.2% at a shear rate of 3.42 s−1 due to the increased physical lifting force. LAE exhibited two different mechanisms for bacterial inactivation and biofilm dispersal. Biofilms treated with LAE at sub-growth inhibitory concentrations for a longer time could effectively detach the biofilm formed on the surface of the glass slides, which can be attributed to the increased motility of microorganisms. However, a high concentration (i.e., bactericidal concentration) of LAE should be seriously considered because of the inactivated sessile bacteria and their residual debris remaining on the surface. This study sheds light on the effect of LAE on biofilm detachment and provides insights into biofouling mitigation during the membrane process.

Modification of ultrafiltration membrane with antibacterial agent intercalated layered nanosheets: Toward superior antibiofouling performance for water treatment

Membrane fouling, especially biofouling induced by biofilm formation on membranes, can result in frequent cleaning or even replacement of membranes. Fabrication of membrane with excellent antibiofouling property is quite attractive due to its effectiveness and low-impact on the operation of membrane-based process. Herein, a cationic antibacterial agent, quaternary ammonium compound (QAC), was intercalated into the interlayer spaces of the MgAl layered double hydroxide (QAC/LDH) by self-assembly. The QAC/LDH composite was incorporated into polyethersulfone (PES) ultrafiltration (UF) membrane (PES-QLDH). The QAC/LDH enhanced the hydrophilicity, water flux, and resistance to organic fouling for the PES-QLDH membrane. The PES-QLDH membrane exhibited superior antibiofouling performance than the control PES membrane, with deposition of a thinner biofilm layer consisted of almost dead cells. The superior antibacterial activity inhibits the adhesion and growth of bacteria on the membrane surface, effectively retarding the formation of biofilms. Importantly, the synergistic effect of QAC and LDH in the PES-QLDH membrane resulted in a high biocidal activity based on both direct and indirect killing mechanisms. The PES-QLDH membrane maintained a stable and high antibacterial activity after several fouling-cleaning cycles. These results imply that the PES-QLDH membrane provides an effective and promising strategy for its long-term application in wastewater treatment.

Phenotypic and transcriptional study of the antimicrobial activity of silver and zinc oxide nanoparticles on a wastewater biofilm-forming Pseudomonas aeruginosa strain

The extensive use of nanoparticles (NPs) in industrial processes makes their potential release into the environment an issue of concern. Ag and ZnO NPs are among the most frequently used NPs, potentially reaching concentrations of 1-4 and 64 mg/kg, respectively, in Wastewater Treatment Plants (WWTPs), with unknown effects over microbial populations. Thus, we examined, in depth, the effect of such NPs on a P. aeruginosa strain isolated from a WWTP. We evaluated the growth, ROS production and biofilm formation, in addition to the transcriptomic response in presence of Ag and ZnO NPs at concentrations potentially found in sewage sludge. The transcriptomic and phenotypic patterns of P. aeruginosa in presence of Ag NPs were, in general, similar to the control treatment, with some specific transcriptional impacts affecting processes involved in biofilm formation and iron homeostasis. The biofilms formed under Ag NPs treatment were, on average, thinner and more homogeneous. ZnO NPs also alters the biofilm formation and iron homeostasis in P. aeruginosa, however, the higher and more toxic concentrations utilized caused an increase in cell death and eDNA release. Thus, the biofilm development was characterized by EPS production, via eDNA release. The number of differentially expressed genes in presence of ZnO NPs was higher compared to Ag NPs treatment. Even though the responses of P. aeruginosa to the presence of the studied metallic NPs was at some extent similar, the higher and more toxic concentrations of ZnO NPs produced greater changes concerning cell viability and ROS production, causing disruption in biofilm development.

Electroless deposition of copper nanoparticles integrates polydopamine coating on reverse osmosis membranes for efficient biofouling mitigation

In this study, highly antimicrobial CuNPs were integrated into a hydrophilic polydopamine (PDA) coating and immobilized on a RO TFC membrane via a mild and facile reduction approach to form a stable and durable dual-functional layer. Based on the XDLVO analysis, the introduction of PDA increased the membrane-foulant total interaction energy (ΔG_mwf) to 14.13 mJ/m², resulting in improved anti-adhesive properties as demonstrated by a 37% decrease in BSA adsorption for the modified membranes. The well dispersed and high loadings of CuNPs induced by PDA conferred strong bacterial toxicity to the modified membranes, reducing the viability of E. coli by 76%. Furthermore, the presence of catechol groups on PDA favors the formation of covalent bond with CuNPs, thus prolonging the durability of the copper-based anti-biofouling membranes. The combination of PDA coating and CuNPs functionalization imparts the membrane with simultaneous anti-adhesive and anti-microbial properties, leading to a substantial reduction in biofouling propensity in dynamic biofouling experiments. Specifically, the flux decline due to biofouling observed for the modified membranes significantly decreased from 65% to 39%, and biofilm thickness and TOC biomass were 58%, and 55% lower, respectively. This study provides a facile and versatile strategy to construct high performance RO membranes with excellent anti-biofouling functionality.

Iron carriers promote biofilm formation and p-nitrophenol degradation

Vertical baffled biofilm reactors (VBBR) equipped with Plastic-carriers and Fe-carriers were employed to explore the effect of biofilm carriers on biofilm formation and p-nitrophenol (PNP) degradation. The results showed that Fe-carriers enhanced biofilm formation and PNP degradation. The maximum thickness of biofilm grown on the Fe-carriers was 1.5-fold higher than that on the Plastic-carriers. The Fe-VBBR reached a maximum rate of PNP removal at 13.02 μM L^-1 h^-1 with less sodium acetate addition (3 mM), while the maximum rate of PNP removal was 11.53 μM L^-1 h^-1 with more sodium acetate addition (6 mM) in the Plastic-based VBBR. High-throughput sequencing suggested that the Fe-VBBR had a higher biodiversity of the bacterial community in evenness, and the Achromobacter genus and Xanthobacteraceae family were as main PNP degraders. Kyoto Encyclopedia of Genes and Genomes (KEGG) Orthology analysis suggested more abundances of iron uptake genes were expressed to transport iron into the cytoplasm under an iron-limited condition in two VBBRs, and the metabolic pathway of PNP degradation went through 4-nitrocatechol and 1,2,4-benzenetriol. Our results provide a new insight for iron enhancing biofilm formation and PNP degradation.

Fouling Prevention in Polymeric Membranes by Radiation Induced Graft Copolymerization

The application of membrane processes in various fields has now undergone accelerated developments, despite the presence of some hurdles impacting the process efficiency. Fouling is arguably the main hindrance for a wider implementation of polymeric membranes, particularly in pressure-driven membrane processes, causing higher costs of energy, operation, and maintenance. Radiation induced graft copolymerization (RIGC) is a powerful versatile technique for covalently imparting selected chemical functionalities to membranes' surfaces, providing a potential solution to fouling problems. This article aims to systematically review the progress in modifications of polymeric membranes by RIGC of polar monomers onto membranes using various low- and high-energy radiation sources (UV, plasma, γ-rays, and electron beam) for fouling prevention. The feasibility of the modification method with respect to physico-chemical and antifouling properties of the membrane is discussed. Furthermore, the major challenges to the modified membranes in terms of sustainability are outlined and the future research directions are also highlighted. It is expected that this review would attract the attention of membrane developers, users, researchers, and scientists to appreciate the merits of using RIGC for modifying polymeric membranes to mitigate the fouling issue, increase membrane lifespan, and enhance the membrane system efficiency.

The effects of several operative parameters on the grafting of selected grafting agents on a polyamide six (PA6) fiber surface

The previous research showed the anti-biofouling improvement of the polyamide six (PA6) fiber when grafted by 2-hydroxyethyl methacrylate (HEMA) individually, and in combination with acrylic acid (AA) known as dual monomers system. The effects of several operative parameters, including vessel reaction temperature and time, ultra violet (UV) pre-irradiation time, and also HEMA-AA mole ratios (for dual system) on the surface grafting of a PA6 fiber by HEMA and also, dual HEMA-AA system were studied. The studied grafting parameters were grafting degree (D), grafting efficiency (E), formed homo and or co-polymer (Y), reaction extent (K), and reaction ratio (R). A pre-UV irradiation technique (PUVA) used for irradiation of the fibers. The results showed efficient polymerization and grafting reactions for the selected operative parameters. The increasing reaction temperature reduced the grafting of the HEMA and AA on the fiber surface. Instead, it accelerated the homo and or co-polymerization of the HEMA and AA monomers. The reaction time had the lowest effect on the homo and co-polymer formation of the used monomers in the studied dual HEMA-AA system. The increasing pre-UV irradiation time was beneficial for the grafting of the studied monomers on the PA6 fiber. The reason referred to increasing the number and concentration of the active sites on the fiber surface.

Surface Design of Liquid Separation Membrane through Graft Polymerization: A State of the Art Review

Surface modification of membranes is an effective approach for imparting unique characteristics and additional functionalities to the membranes. Chemical grafting is a commonly used membrane modification technique due to its versatility in tailoring and optimizing the membrane surface with desired functionalities. Various types of polymers can be precisely grafted onto the membrane surface and the operating conditions of grafting can be tailored to further fine-tune the membrane surface properties. This review focuses on the recent strategies in improving the surface design of liquid separation membranes through grafting-from technique, also known as graft polymerization, to improve membrane performance in wastewater treatment and desalination applications. An overview on membrane technology processes such as pressure-driven and osmotically driven membrane processes are first briefly presented. Grafting-from surface chemical modification approaches including chemical initiated, plasma initiated and UV initiated approaches are discussed in terms of their features, advantages and limitations. The innovations in membrane surface modification techniques based on grafting-from techniques are comprehensively reviewed followed by some highlights on the current challenges in this field. It is concluded that grafting-from is a versatile and effective technique to introduce various functional groups to enhance the surface properties and separation performances of liquid separation membranes.

Osmium Nanoparticles-Polypropylene Hollow Fiber Membranes Applied in Redox Processes

Composite membranes play a very important role in the separation, concentration, and purification processes, but especially in membrane reactors and membrane bioreactors. The development of composite membranes has gained momentum especially through the involvement of various nanoparticles, polymeric, oxide, or metal, that have contributed to increasing their reactivity and selectivity. This paper presents the preparation and characterization of an active metal nanoparticle-support polymer type composite membrane, based on osmium nanoparticles obtained in situ on a polypropylene hollow fiber membrane. Osmium nanoparticles are generated from a solution of osmium tetroxide in tert-butyl alcohol by reduction with molecular hydrogen in a contactor with a polypropylene membrane. The composite osmium-polypropylene hollow fiber obtained membranes (Os-PPM) were characterized from the morphological and structural points of view: scanning electron microscopy (SEM), high resolution SEM (HR-SEM), energy dispersive spectroscopy analysis (EDAX), X-ray diffraction analysis (XRD), Fourier transform Infrared (FTIR) spectroscopy, thermal gravimetric analysis, and differential scanning calorimetry (TGA, DSC). The process performance was tested in a redox process of p-nitrophenol and 10-undecylenic (10-undecenoic) acid, as a target substance of biological or biomedical interest, in solutions of lower aliphatic alcohols in a membrane contactor with a prepared composite membrane. The characteristics of osmium nanoparticles-polypropylene hollow fiber membranes open the way to biological and biotechnological applications. These membranes do not contaminate the working environment, operate at relatively low temperatures, provide a large contact area between reactants, allow successive oxidation and reduction operations in the same module, and help to recover the reaction mass by ultrafiltration. The results obtained show that the osmium-polypropylene composite membrane allows the reduction of p-nitrophenol or the oxidation of 10-undecylenic acid, the conversion depending on the concentration in the lower aliphatic alcohol, the nature of the lower aliphatic alcohol, and the oxidant or reducing flow through the membrane contactor.