Organic fouling inhibition on electrically conducting carbon nanotube–polyvinyl alcohol composite ultrafiltration membranes

Localized heating coupling with radical oxidation eliminating antibiotic resistance genes (ARGs) in interfacial photothermal Fenton-like disinfection process

Conventional oxidative disinfection processes are inefficient in eliminating intracellular antibiotic resistance genes (iARGs) due to the barrier of the cell membrane and the competitive reaction of cellular constituents within antibiotic-resistant bacteria (ARB), resulting in the widespread prevalence of ARGs in recycled water. This study presented the first application of localized heating coupling with advanced oxidation to destroy the resistant Escherichia coli cells and improved subsequent iARGs (blaTEM-1) degradation in a novel photothermal Fenton-like disinfection process. The Fe-Mn@CNT microfiltration membrane, comprising carbon nanotubes wrapped with Fe and Mn nanoparticles (Fe-Mn@CNT), was employed as a nanomaterial for photothermal conversion and H2O2 activation. The highly efficient absorption of full-spectrum photons by CNTs enabled the Fe-Mn@CNT membrane to concentrate light to generate localized intense heat, resulting in the destruction of ARB nearby, and the subsequent release of iARGs. Interfacial heat favored Fe-Mn-induced H2O2 activation, leading to the production of more ·OH, which in turn promoted the oxidation for ARG degradation and ARB cell damage. The results of the acetylcysteine quenching experiments indicated that interfacial heating and radical oxidation-induced accumulation of intracellular reactive oxygen species contributed to the elimination of about 1-log iARGs through direct attack. The integrity of the cell membrane, the morphology of ARB and the variation of i/e ARG copy numbers were observed to reveal that the introduction of interfacial heating aggravated the cell lysis and accelerated the iARGs release, resulting in the inactivation of 7.27-log ARB and the elimination of 4.64-log iARGs and 2.23-log eARGs. Localized heating coupling with ·OH oxidation achieved a 143 % increase in iARGs removal compared to the conventional Fenton-like oxidation. The interfacial photothermal Fenton-like disinfection process exhibited remarkable material stability, robust disinfection performance, and effective suppression of horizontal gene transfer, underscoring its immense potential to mitigate the risk of ARG dissemination in reclaimed water systems.

TiO2-PAA-SiO2 pearl chain blend modified polyvinylidene fluoride ultrafiltration membrane with excellent oil-water separation, anti fouling performance and durability

In this work, a new type of composite nanoparticles, 'pearl chain', was developed by linking titanium dioxide and silicon dioxide by polyacrylic acid polymer chains, and the prepared TiO2-PAA-SiO2 composite nanoparticles were analysed by SEM, Fourier transform infrared spectroscopy, x-ray photoelectron spectroscopy and thermogravimetric analysis, zeta potential, x-ray diffraction, etc. The success of this work was verified by the successful linking of TiO2-PAA-SiO2 composite nanoparticles.TiO2-PAA-SiO2 composite nanoparticles were analysed to verify the successful attachment of pearl chains. The obtained TiO2-PAA-SiO2 were subsequently blended in different ratios to prepare polyvinylidene fluoride (PVDF) ultrafiltration membranes. The membrane performance was tested by porosity and water contact angle measurements, scanning electron microscopy, as well as experiments using bovine serum proteins and MTBE interception. The results showed that when a certain amount of TiO2-PAA-SiO2 was added, the surface wettability, porosity and permeability of the prepared modified composite membranes were significantly improved, and the BSA adsorption rate was increased from 71.59% to 80.86%, and the retention rate of MTBE was increased by 77%, in addition to showing a better anti-pollution effect (FRR: 91.07%). It was finally concluded that the prepared membranes embedded with 1.0 wt.% TiO2-PAA-SiO2 nanofillers showed good overall filtration performance, better contamination resistance and remarkable durability. The present work successfully demonstrated the feasibility of using polyacrylic acid chemical chains to connect nanoparticles with different functions to prevent particle loss and substantially enhance membrane performance, which is valuable for bridging connection of composite nanoparticles and exploring the development of high-performance ultrafiltration membranes.

Elucidating the Mechanism of Electro-Adsorption on Electrically Conductive Ultrafiltration Membranes via Modified Poisson-Boltzmann Equation

Electrically conductive membranes (ECMs) were prepared by coating porous ethylenediamine-modified polyacrylonitrile (PAN-EDA) UF membranes with an ultrathin layer of platinum (Pt) nanoparticles through magnetron sputtering. These ECMs were used in electrofiltration to study the removal of brilliant blue dye from an aqueous solution under positive electrical potentials (0-2.5 V). Negative electrical potentials (-1.0--2.5 V) were also investigated to regenerate the membrane by desorbing the dye from the ECM surface. At +0 V, the EC PAN-EDA membrane adsorbed the dye due to its intrinsic positive charge. Application of -2.0 V resulted in a maximum of 39% desorption of the dye. A modified Poisson-Boltzmann (MPB) model showed that -2.0 V created a repulsive force within the first 24 nm of the membrane matrix, which had a minimal effect on dye ions adsorbed deeper within the membrane, thus limiting the electro-desorption efficiency to 39%. Moreover, increasing positive potentials from +0.5 V to +2.5 V led to increased dye electro-adsorption by 9.5 times, from 132 mg/m2 to 1112 mg/m2 at pH 8 (equivalent to the membrane's isoelectric point). The MBP simulations demonstrated that increasing electro-adsorption loadings are related to increasing attractive force, indicating electro-adsorption induced by attractive force is the dominant mechanism and the role of other mechanisms (e.g., electrochemical oxidation) is excluded. At pH 5, electro-adsorption further increased to 1390 mg/m2, likely due to the additional positive charge of the membrane (zeta potential = 9.2 mV) compared to pH 8. At pH 8, complete desorption of the dye from the ECM surface was achieved with a significant repulsive force at -2.0 V. However, as pH decreased from 8 to 5, the desorption efficiency decreased by 3.9% due to the membrane's positive charge. These findings help elucidate the mechanisms of electro-adsorption and desorption on ECMs using dye as a model for organic compounds like humic acids.

Membrane modification with carbon nanomaterials for fouling mitigation: A review

This paper provides a comprehensive overview of recent advancements in membrane modification for fouling mitigation in various water treatment processes, employing carbon nanomaterials such as fullerenes, nanodiamonds, carbon quantum dots, carbon nanotubes, and graphene oxide. Currently, using different carbon nanomaterials for polymeric membrane fouling mitigation is at various stages: CNT-modified membranes have been studied for more than ten years and have already been tested in pilot-scale setups; tremendous attention has been paid to utilizing graphene oxide as a modifying agent, while the research on carbon quantum dots' influence on the membrane antifouling properties is in the early stages. Given the intricate nature of fouling as a colloidal phenomenon, the review initially delves into the factors influencing the fouling process and explores strategies to address it. The diverse chemistry and antibacterial properties of carbon nanomaterials make them valuable for mitigating scaling, colloidal, and biofouling. This review covers surface modification of existing membranes using different carbon materials, which can be implemented as a post-treatment procedure during membrane fabrication. Creating mixed-matrix membranes by incorporating carbon nanomaterials into the polymer matrix requires the development of new synthetic procedures. Additionally, it discusses promising strategies to actively suppress fouling through external influences on modified membranes. In the concluding section, the review compares the effectiveness of carbon materials of varying dimensions and identifies key characteristics influencing the antifouling properties of membranes modified with carbon nanomaterials.

Production of Stable Electrically Conductive PVDF Membranes Based on Polydopamine-Polyethyleneimine-Assisted Deposition of Carbon Nanotubes

Electrically conductive membranes (ECMs) have emerged as a multifunctional separation technology that integrates membrane filtration with electrochemical reactions. Physical stability remains a critical challenge for ECMs synthesized by coating polymer membranes with conductive materials. In this article, polydopamine (PDA) and polyethyleneimine (PEI) were used to facilitate the synthesis of significantly more stable ECMs using poly(vinylidene fluoride) (PVDF) ultrafiltration membranes and carbon nanotubes (CNTs). Four different synthesis methods were compared in terms of the final surface stability and separation properties: (1) CNTs deposited on PEI-crosslinked PDA-coated PVDF membranes, (2) PEI-crosslinked CNTs deposited on PDA-coated PVDF, (3) PDA, PEI and CNTs sequentially deposited layer-by-layer on PVDF, and (4) PEI-crosslinked PDA deposited on CNT-coated PVDF. The results revealed that method 1 generated ECMs with the greatest physical stability, highest electrical conductivity (18,518 S/m), and sufficient permeability (395.2 L/(m2·h·bar). In comparison, method 2 resulted in membranes with the highest permeability (2128.5 L/(m2·h·bar), but with low surface conductivity (502 S/m) and poor physical stability (i.e., 53-75% lower peel-off forces compared to other methods). Overall, methods 1, 3, and 4 can be used to make highly conductive membranes with a 97-99% removal of methyl orange by electrochemical degradation at -3 V.

Design and characterization of an electrochemically-modulated membrane chromatography device

Membrane separations offer a compelling alternative to traditional chromatographic methods by overcoming mass transport limitations. We introduce an additional degree of freedom in modulating membrane chromatography by using metalized membranes in a potential-driven process. Investigating the impact of a gold coating on membrane characteristics, the sputtered gold layer enhances the surface conductivity with stable electrochemical behavior. However, this comes at the expense of reduced permeability, wettability, and static binding capacity (∼ 474 µg g-1 of maleic acid). The designed device displayed a homogenous flow distribution, and the membrane electrodes exhibit predominantly capacitive behavior during potential application. Modulating the electrical potential during the adsorption and desorption phase strongly influenced the binding and elution behavior of anion-exchange membranes. Switching potentials between ±1.0 V vs. Ag/AgCl induces desorption, confirming the process principle. Elution efficiency reaches up to 58 % at -1.0 V vs. Ag/AgCl in the desorption phase without any alteration of the mobile phase. Increasing the potential perturbation ranging from +1.0 V to -1.0 V vs. Ag/AgCl resulted in reduced peak width and improved elution behavior, demonstrating the feasibility of electrochemically-modulated membrane chromatography. The developed process has great potential as a gentle and sustainable separation step in the biotechnological and chemical industry.

Conductive nanofiltration membranes via in situ PEDOT-polymerization for electro-assisted membrane fouling mitigation

Nanofiltration (NF) membranes play a pivotal role in water treatment; however, the persistent challenge of membrane fouling hampers their stable application. This study introduces a novel approach to address this issue through the creation of a poly(3,4-ethylenedioxythiophene) (PEDOT)-based conductive membrane, achieved by synergistically coupling interfacial polymerization (IP) with in situ self-polymerization of EDOT. During the IP reaction, the concurrent generation of HCl triggers the protonation of EDOT, activating its self-polymerization into PEDOT. This interwoven structure integrates with the polyamide network to establish a stable selective layer, yielding a remarkable 90 % increase in permeability to 20.4 L m-2 h-1 bar-1. Leveraging the conductivity conferred by PEDOT doping, an electro-assisted cleaning strategy is devised, rapidly restoring the flux to 98.3 % within 5 min, outperforming the 30-minute pure water cleaning approach. Through simulations in an 8040 spiral-wound module and the utilization of the permeated salt solution for cleaning, the electro-assisted cleaning strategy emerges as an eco-friendly solution, significantly reducing water consumption and incurring only a marginal electricity cost of 0.055 $ per day. This work presents an innovative avenue for constructing conductive membranes and introduces an efficient and cost-effective electro-assisted cleaning strategy to effectively combat membrane fouling.

Advances in Membrane Separation for Biomaterial Dewatering

Biomaterials often contain large quantities of water (50-98%), and with the current transition to a more biobased economy, drying these materials will become increasingly important. Contrary to the standard, thermodynamically inefficient chemical and thermal drying methods, dewatering by membrane separation will provide a sustainable and efficient alternative. However, biomaterials can easily foul membrane surfaces, which is detrimental to the performance of current membrane separations. Improving the antifouling properties of such membranes is a key challenge. Other recent research has been dedicated to enhancing the permeate flux and selectivity. In this review, we present a comprehensive overview of the design requirements for and recent advances in dewatering of biomaterials using membranes. These recent developments offer a viable solution to the challenges of fouling and suboptimal performances. We focus on two emerging development strategies, which are the use of electric-field-assisted dewatering and surface functionalizations, in particular with hydrogels. Our overview concludes with a critical mention of the remaining challenges and possible research directions within these subfields.

Optimizing electroactive membrane performance for microalgae harvesting: A response surface methodology study of membrane formulation and operating parameters for electro filtration

Developing electroactive membranes for filtration has gained importance owing to their effectiveness in mitigating the long-lasting issue of fouling faced with traditional membranes. Here, we developed thin electroactive metallic films on to stainless steel mesh (SSM) using electrodeposition method and evaluated their performance for microalgae harvesting via electro filtration. The effect of electrodeposition parameters on membrane formulation and operating parameters for electro filtration, both in continuous and intermittent modes, were evaluated and optimum values were obtained using response surface methodology (RSM). The optimal combination of electrodeposition parameters is 1000 μA/cm2 and 5 min for deposition current density and time, respectively. Whereas the electric field strength of 20 V/mm with an application time of 1 min is suggested to be the optimal combination of electro filtration parameters for maximized flux recovery and corresponding experimental rejection efficiency of more than 90%. Overall, this research contributes to a better understanding of the parameters governing electro-filtration and offers insights for improving the performance of membrane-based microalgae harvesting systems.

Electrothermal interfacial evaporation through carbon-nanostructured composite membranes

High energy demand required in membrane distillation (MD) process to heat feed water and maintain the necessary temperature gradient across the membrane presents a challenge to widespread adoption of MD. In response to this challenge, surface heating membrane distillation (SHMD) has emerged as a promising solution. SHMD can employ solar or electrical energy to directly heat the membrane and feed, eliminating the need for an external heat source to heat feed water. In this study, we explore electrothermally-driven interfacial evaporation using a multi-walled carbon nanotube (MWCNT)-based composite membrane and further envision its utilization for high-efficient SHMD. Upon application of voltage, the resistance of the MWCNT leads to the conversion of electrical energy into heat, which is then uniformly transferred to feeds. The MWCNT-based composite membrane exhibited an evaporative water flux of up to 2.34 kg m-2h-1 with an associated energy efficiency of 61% and demonstrated outstanding localized surface heating performance. The employed membranes exhibited no significant variations in either resistance or surface temperature, regardless of the direction of the applied electric field. Energy parameters from the electrothermal membranes showed quantitative agreement with values reported for various electrothermal MD systems, suggesting the potential of the composite membranes in energy-efficient and cost-effective localized heating MD applications.

Facile Synthesis of Electrically Conductive Membranes

A facile and effective strategy that can be used to fabricate electrically conductive membranes (ECMs) of diverse filtration performance (i.e., water productivity and solute rejection) is not available yet. Herein, we report a facile method that enables the fabrication of ECMs of a broad performance range. The method is based on the use of polyethylenimine (PEI), glutaraldehyde, and any of a diverse set of conductive materials to cast an electrically conductive layer atop any of a diverse set of substrates (i.e., from microfiltration to reverse osmosis membranes). We developed the reported ECM fabrication method using graphite as the conductive material and PVDF membranes as substrates. We demonstrate that graphite-PVDF ECMs were stable and electrically conductive and could be successfully used for solute filtration and electrochemical degradation. We also confirmed that the PEI/glutaraldehyde-based ECM fabrication method is suitable for conductive materials other than graphite, including carbon nanotubes, reduced graphene oxide, activated charcoal, and silver nanoparticles. Compared with the substrates used for their fabrication, ECMs showed low electrical sheet resistances that varied with conductive material, increased solute rejection, and reduced water permeance. Taken together, this work presents a promising general strategy for the fabrication of ECMs for environmental applications from diverse substrates and conductive materials.

Electroactive membrane with the electroactive layer beneath the separation layer to eliminate the interference of humic acid in the oxidation of antibiotics

Removing harmful antibiotics is essential to reclaiming water from municipal secondary effluent. Electroactive membranes are effective in the removal of antibiotics but challenged by the abundant coexisting macromolecular organic pollutants in municipal secondary effluent. To eliminate the interference of macromolecular organic pollutants in the removal of antibiotics, we propose a novel electroactive membrane with a top polyacrylonitrile (PAN) ultrafiltration layer and a bottom electroactive layer composed of carbon nanotubes (CNTs) and polyaniline (PANi). When filtering the mixture of tetracycline (TC, a typical antibiotic) and humic acid (HA, a typical macromolecular organic pollutant), the PAN-CNT/PANi membrane performed sequential removal. It retained HA at the PAN layer (by ∼96%) and allowed TC to reach the electroactive layer where it was electrochemically oxidized (e.g., by ∼92% at 1.5 V). The TC removal of the PAN-CNT/PANi membrane was marginally affected by HA, unlike that of the control membrane with the electroactive layer on the top that showed decreased TC removal after the addition of HA (e.g., decreased by 13.2% at 1 V). The decreased TC removal of the control membrane was attributed to the attachment (but not competitive oxidation) of HA on the electroactive layer that impaired the electrochemical reactivity. The HA removal prior to TC degradation realized by the PAN-CNT/PANi membrane avoided the attachment of HA and guaranteed TC removal on the electroactive layer. Long-term filtration for 9 h revealed the stability of the PAN-CNT/PANi membrane, and its advantageous structural design was conformed in the context of real secondary effluents.

A novel reduced graphene oxide/polypyrrole conductive ceramic membrane enhanced electric field membrane bioreactor: Mariculture wastewater treatment performance and membrane fouling mitigation

A novel electric field membrane bioreactor (EMBR) for mariculture wastewater treatment utilizing reduced graphene oxide/polypyrrole ceramic membrane (rGO/PPy CM) was constructed and compared with MBRs using CM support and rGO/PPy CM. EMBR (rGO/PPy) obtained the highest pollutant removal rates (84.99% for TOC, 85.98% for NH₄⁺-N), the lowest average membrane fouling rate (2.42 kPa/d) and pollutant adhesion performance by characterization. Meanwhile, the specific fluxes of characteristic foulants in EMBR were enhanced, and the total resistances were reduced by 8.12% to 62.46%. The underlying mechanisms included reduced attraction energy and improved electrostatic repulsion between contaminants in EMBR and membrane by the extended Derjaguin-Landau-Verwey-Overbeek (XDLVO) theory, DLVO model and force analysis. Therefore, this study complemented the understanding of antifouling effect and mechanism in EMBR by interaction energy and force analysis of characteristic pollutants. These findings also provided new insights into the application of EMBR for mariculture wastewater treatment.

Enhanced Antifouling in Flat-Sheet Polyphenylsulfone Membranes Incorporating Graphene Oxide-Tungsten Oxide for Ultrafiltration Applications

In this study tungsten oxide and graphene oxide (GO-WO_2.89) were successfully combined using the ultra-sonication method and embedded with polyphenylsulfone (PPSU) to prepare novel low-fouling membranes for ultrafiltration applications. The properties of the modified membranes and performance were investigated using Fourier-transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), contact angle (CA), water permeation flux, and bovine serum albumin (BSA) rejection. It was found that the modified PPSU membrane fabricated from 0.1 wt.% of GO-WO_2.89 possessed the best characteristics, with a 40.82° contact angle and 92.94% porosity. The permeation flux of the best membrane was the highest. The pure water permeation flux of the best membrane showcased 636.01 L·m^-2·h^-1 with 82.86% BSA rejection. Moreover, the membranes (MR-2 and MR-P2) manifested a higher flux recovery ratio (FRR %) of 92.66 and 87.06%, respectively, and were less prone to BSA solution fouling. The antibacterial performance of the GO-WO_2.89 composite was very positive with three different concentrations, observed via the bacteria count method. These results significantly overtake those observed by neat PPSU membranes and offer a promising potential of GO-WO_2.89 on activity membrane performance.

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.

Electroactive Ultrafiltration Membrane for Simultaneous Removal of Antibiotic, Antibiotic Resistant Bacteria, and Antibiotic Resistance Genes from Wastewater Effluent

To combat the spread of antibiotic resistance into the environment, we should adequately manage wastewater effluent treatment to achieve simultaneous removal of antibiotics, antibiotic resistant bacteria (ARB), and antibiotic resistance genes (ARGs). Herein, we fabricate a multifunctional electroactive poly(vinylidene fluoride) ultrafiltration membrane (C/PVDF) by phase inversion on conductive carbon cloth. The membrane possesses not only excellent retention toward ARB and ARGs but also exhibits high oxidation capacity as an electrode. Notably, sulfamethoxazole degradation involving hydroxylation and hydrolysis by the anode membrane is predominant, and the degradation efficiency is up to 81.5% at +4 V. Both electro-filtration processes exhibit significant ARB inactivation, anode filtration is superior to cathode filtration. Moreover, the degradation of intracellular ARGs (iARGs) located in the genome is more efficient than those located in the plasmid, and these degradation efficiencies at -2 V are higher than +2 V. The degradation efficiencies of extracellular ARGs (eARGs) are opposite and are lower than iARGs. Compared with regular filtration, the normalized flux of electroactive ultrafiltration membrane is improved by 18.0% at -2 V, 15.9% at +2 V, and 30.4% at +4 V during treating wastewater effluent, confirming its antifouling properties and feasibility for practical application.

A critical review on classifications, characteristics, and applications of electrically conductive membranes for toxic pollutant removal from water: Comparison between composite and inorganic electrically conductive membranes

Research efforts have recently been directed at developing electrically conductive membranes (EMs) for pressure-driven membrane separation processes to remove effectively the highly toxic pollutants from water. EMs serve as both the filter and the electrode during filtration. With the assistance of a power supply, EMs can considerably improve the toxic pollutant removal efficiency and even realize chemical degradation to reduce their toxicity. Organic-inorganic composite EMs and inorganic EMs show remarkable differences in characteristics, removal mechanisms, and application situations. Understanding their differences is highly important to guide the future design of EMs for specific pollutant removal from water. However, reviews concerning the differences between composite and inorganic EMs are still lacking. In this review, we summarize the classifications, fabrication techniques, and characteristics of composite and inorganic EMs. We also elaborate on the removal mechanisms and performances of EMs toward recalcitrant organic pollutants and toxic inorganic ions in water. The comparison between composite and inorganic EMs is emphasized particularly in terms of the membrane characteristics (pore size, permeability, and electrical conductivity), application situations, and underlying removal mechanisms. Finally, the energy consumption and durability of EMs are evaluated, and future perspectives are presented.

Membrane fouling mitigation by coagulation and electrostatic repulsion using an electro-AnMBR in kitchen wastewater treatment

Anaerobic membrane bioreactor (AnMBR) is considered an efficient technique for kitchen wastewater treatment; however, membrane fouling restricts their applicability. In this study, a novel AnMBR with an Fe anode and Ti membrane cathode (electro-AnMBR) was constructed. The reactor exhibited good performance in pollutant removal and antifouling in kitchen wastewater treatment. Compared with the traditional AnMBR, the electro-AnMBR increased phosphate removal by approximately 55% and reduced transmembrane pressure (TMP) by 50%. Coagulation from the Fe²⁺/Fe³⁺ released by the sacrificial anode increased the sludge floc size and porosity, significantly reducing the membrane fouling potential. In addition, the lower amounts of extracellular polymeric substances (EPS) in the electro-AnMBR, due to an increased Methanosarcina abundance, facilitated membrane-fouling mitigation. Almost no TMP difference was observed between the AnMBRs with Ti, ceramic, and polyvinylidene fluoride (PVDF) membranes. Quantitative analysis using an electrochemical quartz crystal microbalance with dissipation monitoring indicated that the electrostatic repulsion between EPS and cathodic membrane was positively correlated with the applied voltage. In addition, proteins in EPS had a higher membrane fouling potential than polysaccharides, and Fe³⁺ coagulation reduced adhesion capacity and alleviated membrane fouling. This study provides a perspective viewpoint for AnMBR membrane fouling mitigation and reactor design.

Porous polyvinyl alcohol/graphene oxide composite film for strain sensing and energy-storage applications

In this study, a flexible porous polyvinyl alcohol (PVA)/graphene oxide (GO) composite film was developed and tested for flexible strain sensing and energy-storage applications. Morphology and mechanical properties were studied; tensile strength and Young's modulus increased by 225% and 86.88%, respectively, at 0.5 wt% GO. The PVA/GO film possesses exceptional sensing ability to various mechanical strains, such as tension, compression, bending, and torsion. For example, the gauge factor of the PVA/GO film as a tensile-strain sensor was measured as 2.46 (246%). Under compression loads, the PVA/GO composite film showed piezoresistive and capacitive strain-sensing characteristics. Under 5 kPa of compression load, the relative resistance increased by 81% with a 100 msec response time; the relative capacitance increased by 160% with a 120 msec response time. The PVA/GO strain sensor exhibited high durability and reliability over 20 × 10³cycles of tensile strain and bending at 3.33 Hz. Moreover, the PVA/GO composite film showed good electrochemical properties due to its porous structure; the maximum capacitance was 124.7 F g^-1at 0.5 wt% GO. After 20 × 10³charging-discharging cycles, the capacitance retention rate was 94.45%, representing high stable capacitance performance. The results show that electrically conductive porous PVA nanocomposite films are promising candidates for strain sensing and energy-storage devices.

Electro-Enhanced Separation of Microsized Oil-in-Water Emulsions via Metallic Membranes: Performance and Mechanistic Insights

Conventional separation membranes suffer from evitable fouling and flux decrease for water treatment applications. Herein, a novel protocol of electro-enhanced membrane separation is proposed for the efficient treatment of microsized emulsions (∼1 μm) by rationally designing robust electroresponsive copper metallic membranes, which could mitigate oil fouling and coenhance permeance (from ∼1026 to ∼2516 L·m^-2·h^-1·bar^-1) and rejection (from ∼87 to ∼98%). High-flux Cu membranes exhibit superior ductility and electrical conductivity, enabling promising electroactivity. Separation performance and the fouling mechanism were studied under different electrical potentials and ionic strengths. Application of negative polarization into a large-pore (∼2.1 μm) Cu membrane is favorable to not only almost completely reject smaller-sized oil droplets (∼1 μm) but also achieve antifouling and anticorrosion functions. Moreover, surfactants around oil droplets might be redistributed due to electrostatic repulsion, which effectively enhances the steric hindrance effect between neighboring oil droplets, mitigating oil coalescence and consequently membrane fouling. Furthermore, due to the screening effect of surfactants, the presence of low-concentration salts increases the adsorption of surfactants at the oil-water interface, thus preventing oil coalescence via decreasing oil-water interfacial tension. However, under high ionic strengths, the fouling mechanism converts from cake filtration to a complete blocking model due to the reduced electrostatic repulsion between the Cu membrane and oil droplets. This work would provide mechanistic insights into electro-enhanced antifouling for not only oil emulsion separation but also more water treatment applications using rationally designed novel electroresponsive membranes.

Birefringence of Thin Uniaxial Polymer Films Estimated Using the Light Polarization Ellipse

A simple method for determining the linear birefringence of the thin layers based on the determination of the orientation of the polarization ellipse of totally polarized light is proposed and it is applied to PVA thin foils. Theoretical notions and the experimental procedure are described. The linear birefringence of polymer thin foils with different degrees of stretching is determined and the applicability of the method is discussed.

Conductive polyethersulfone membrane facilely prepared by simultaneous phase inversion method for enhanced anti-fouling and separation under low driven-pressure

Electrically conductive membranes have been regarded as a new alternative to overcome the crucial drawbacks of membranes, including permeability-selectivity trade-off and fouling. It is still challenging to prepare conductive membranes with good mechanical strength, high conductivity and stable separation performance by reliable materials and methods. This work developed a facile method of simultaneous phase inversion to prepare electrically conductive polyethersulfone (PES) membranes with carboxylic multiwalled carbon nanotubes (MWCNT) and graphene (Gr). The resultant MWCNT/Gr/PES nanocomposite membranes are composed of the upper MWCNT/Gr layer with good conductivity and the base PES layer providing mechanical support. MWCNT as nanofillers effectively turns the insulting PES layers to be electrically conductive. With the dispersing and bridging functions of Gr, the MWCNT/Gr layer shows an enhanced electric conductivity of 0.10 S/cm. This MWCNT/Gr/PES membrane in an electro-filtration cell achieves excellent retention of Cu(II) ions up to 98 % and a high flux of 94.5 L m^-2∙h^-1∙bar^-1 under a low driven-pressure of 0.1 MPa. The conductive membrane also shows improved anti-fouling capability during protein filtration, due mainly to the electrostatic repulsion and hydrogen evolution reaction on the electrode. This facile strategy has excellent potential in electro-assistant membrane filtration for fouling control and effective separation.

Removal of As(III) by Electrically Conducting Ultrafiltration Membranes

As(III) species are the predominant form of arsenic found in groundwater. However, nanofiltration (NF) and reverse osmosis (RO) membranes are often unable to effectively reject As(III). In this study, we fabricate highly conducting ultrafiltration (UF) membranes for effective As(III) rejection. These membranes consist of a hydrophilic nickel-carbon nanotubes layer deposited on a UF support, and used as cathodes. Applying cathodic potentials significantly increased As(III) rejection in synthetic/real tap water, a result of locally elevated pH that is brought upon through water electrolysis at the membrane/water interface. The elevated pH conditions convert H₃ASO₃ to H₂AsO₃^-/HAsO₃^2- that are rejected by the negatively charged membranes. In addition, it was found that Mg(OH)₂ that precipitates on the membrane can further trap arsenic. Importantly, almost all As(III) passing through the membranes is oxidized to As(V) by hydrogen peroxide produced on the cathode, which significantly decreased its overall toxicity and mobility. Although the high pH along the membrane surface led to mineral scaling, this scale could be partially removed by backwashing the membrane. To the best of our knowledge, this is the first report of effective As(III) removal using low-pressure membranes, with As(III) rejection higher than that achieved by NF and RO, and high water permeance.

Preparation and Characterization of MWCNTs/PVDF Conductive Membrane with Cross-Linked Polymer PVA and Study on Its Anti-Fouling Performance

Based on carboxylated multi-walled carbon nanotubes (MWCNTs-COOH), a MWCNTs/PVDF conductive membrane was prepared by a vacuum filtration cross-linking method. The surface compositions and morphology of conductive membranes were studied by X-ray photoelectron spectroscopy and high-resolution field emission scanning electron microscopy, respectively. The effects of cross-linked polymeric polyvinyl alcohol (PVA) on the conductive membrane properties such as the porosity, pore size distribution, pure water flux, conductivity, hydrophilicity, stability and antifouling properties were investigated. Results showed that the addition of PVA to the MWCNTs/PVDF conductive membrane decreased the pure water flux, porosity and the conductivity. However, the hydrophilicity of the modified MWCNTs/PVDF conductive membrane was greatly improved, and the contact angle of pure water was reduced from 70.18° to 25.48° with the addition of PVA contents from 0 wt% to 0.05 wt%. Meanwhile, the conductive membranes with higher content had a relatively higher stability. It was found that the conductive functional layer of the conductive membrane had an average mass loss rate of 1.22% in the 30 min ultrasonic oscillation experiment. The tensile intensity and break elongation ratio of the conductive membrane are improved by the addition of PVA, and the durability of the conductive membrane with PVA was superior to that without PVA added. The electric assisted anti-fouling experiments of modified conductive membrane indicated that compared with the condition without electric field, the average flux attenuation of the conductive membrane was reduced by 11.2%, and the membrane flux recovery rate reached 97.05%. Moreover, the addition of PVA could accelerate the clean of the conductive membranes.

Electrochemical advanced oxidation processes coupled with membrane filtration for degrading antibiotic residues: A review on its potential applications, advances, and challenges

Antibiotic pollution is mainly caused by aquaculture wastewater and pharmaceuticals, which are frequently used by humans. Due to limited treatment efficiency or improper selection of treatment methods, these antibiotic residues may be very harmful in human drinking water and aquatic environments. The EAOPs coupling membrane technology (EAOPs-membrane) can play their own advantages, which can significantly improve the degradation efficiency and alleviate membrane pollution (electrochemical manners). In this context, this review mainly collecting researches and information on EAOPs-membrane treatment of antibiotic pollution published between 2012 and 2020. Discussed the different combinations of these two technologies, the mechanism of them in the system to improve the processing efficiency, prolong the working time, and stabilize the system structure. Mainly due to the synergistic effect of electrochemical behavior such as electric repulsion and in-situ oxidation, the membrane fouling in the system is alleviated. In this review it was summarized that the selection of different membrane electrode materials and their modifications. The paper also elaborates the existing challenges facing the EAOPs-membrane methods for antibiotic pollution treatment, and their prospects.

Linking the Tuneability and Defouling of Electrically Conductive Polyaniline/Exfoliated Graphite Composite Membranes

Stimuli responsive membranes, which are able to respond to environmental stimuli, are attracting ever-increasing interests. In this study, we blended exfoliated graphite (EG) into the polyaniline (PANI) and developed PANI/EG composite membranes. The properties of the new generated membranes, especially the stimuli response properties (e.g., electrical tuneability, deformation), were studied. The fouling removal ability of the membrane under applied electrical potential was also investigated by using bovine serum albumin (BSA) as a model foulant. A flat membrane with defect-free surface and good adhesion to the support layer was formed by non-solvent induced phase separation method. The electrical conductivity of the formed PANI/EG composite membrane was (5.10 ± 0.27) ×10^-4 S cm^-1. The dynamic droplet penetration rate through the membranes showed an increase under applied electrical potential, which gives a preliminary quantitative indication of the electrical tuneability of the membranes. The membrane deformation appeared at a fast response under applied potential and recovered to its original position immediately when removing the applied potential. The application of electrical potential led to the removal of BSA foulant from the membrane surface as indicated by the increase in permeance of the fouled membrane on cleaning with 46.2% flux recovery ratio and increased BSA concentration in the wash solution. The electrically conductive PANI/EG composite membranes are able to respond to electrical stimuli, enabling a new range of potential applications including externally tuneability and in situ removal and control of fouling.

Influence of oil droplet behavior in electrochemical micromembrane cells on treating oil/water emulsions with low-salt concentrations

Although flow-through electrode has demonstrated its potential in treating oily wastewater, few studies noted influence of oil droplet behavior on treating oil/water emulsions. In order to explore the influence of oil droplet behavior in a flow-through electrode cell on treating oil/water emulsions with low-salt concentrations, an electrochemical micromembrane cell was applied to treat oil/water emulsions with 0-0.8 g/L NaCl. High chemical oxygen demand (COD) reduction (80-90%) was obtained in treating Sodium dodecylbenzene sulfonate (SDBS) or Tween 80 emulsion by flow-through electrode, while the later had the higher permeate flux (900 mL/min around). The low salt concentration (0.5 g/L NaCl) achieved high COD reduction (87%) and good permeate flux (600 mL/min). Observations using optical microscopy revealed severe deformation of the shape of the charged oil droplet at the flow-through electrode interface. The wetting of oil droplets at the electrode interface occurred when the membrane acted as an anode, which resulted in flow-through electrode fouling, and subsequently, the reduction in permeate flux and treatment efficiency. The results of this study offer an attractive option when using flow-through electrode to treat oil-in-water emulsions under low-salinity conditions.

Electrosorptive removal of organic water constituents by positively charged electrically conductive UF membranes

Negatively charged electrically conductive ultrafiltration (UF) membranes have been intensively investigated for fouling mitigation and rejection enhancement in recent years. This study reports the novel approach of applying positive charge (+2.5 V cell potential) to a conductive membrane to induce electrosorption of negatively charged substances onto the membrane. Subsequently, desorption of negatively charged substances is achieved by changing the potential periodically (e.g., after 30 min) to negative charge (-2.5 V cell potential). For this purpose, sputter deposition of ultra-thin gold layers (40 nm) is used to generate electrically conductive gold-polymer-gold flat sheet membranes by coating the active and the support layer of two commercial polymer UF membranes (polyethersulfone UP150, polyamide M5). When M5 membrane was charged positively during filtration (+2.5 V), Suwannee River NOM, Hohloh lake NOM, humic acid and Brilliant Blue ionic dye showed removal rates of 70 %, 75% and 93% and 99%, respectively. Whereas, when no potential was applied (0 V) removal rates were only 1 - 5 %. When a positive potential was applied to the active membrane layer and a negative potential was applied to the support layer (cell potential 2.5 V), a significant increase of flux with 25 L/(m² h) was observed due to the induction of electro-osmosis. Electrosorption was only observed for M5 membrane (ζ: +13 mV, pH 7) and not with UP150 membrane (ζ: -29 mV, pH 7). Due to a low current density of 1.1 A/m² at a flux of 100 L/(m² h), the additional energy consumption of electrosorption and desorption process was low with 0.03 kWh per m³ of permeate. This study delivered the proof of concept for the novel process of electrosorptive UF with energy consumption between microfiltration and ultrafiltration but NOM removal rates of nanofiltration membranes.

Nanostructured Surface Finishing and Coatings: Functional Properties and Applications

This review presents current literature on different nanocomposite coatings and surface finishing for textiles, and in particular this study has focused on smart materials, drug-delivery systems, industrial, antifouling and nano/ultrafiltration membrane coatings. Each of these nanostructured coatings shows interesting properties for different fields of application. In this review, particular attention is paid to the synthesis and the consequent physico-chemical characteristics of each coating and, therefore, to the different parameters that influence the substrate deposition process. Several techniques used in the characterization of these surface finishing coatings were also described. In this review the sol-gel method for preparing stimuli-responsive coatings as smart sensor materials is described; polymers and nanoparticles sensitive to pH, temperature, phase, light and biomolecules are also treated; nanomaterials based on phosphorus, borates, hydroxy carbonates and silicones are used and described as flame-retardant coatings; organic/inorganic hybrid sol-gel coatings for industrial applications are illustrated; carbon nanotubes, metallic oxides and polymers are employed for nano/ultrafiltration membranes and antifouling coatings. Research institutes and industries have collaborated in the advancement of nanotechnology by optimizing conversion processes of conventional materials into coatings with new functionalities for intelligent applications.

Facile fabrication of a conductive polypyrrole membrane for anti-fouling enhancement by electrical repulsion and in situ oxidation

Conductive membranes provide a promising method to alleviate membrane fouling, but their cost-effective fabrication, which is urgently needed, is still a challenge. This paper describes the facile fabrication of an ultrafiltration conductive polypyrrole (PPy)-modified membrane (PMM) by in situ chemical polymerization of FeCl₃ and monomer pyrrole vapor on a commercial membrane surface. The resulting membrane had a high electrical conductivity and an outstanding water flux of 2766.55 L m^-2 h^-1 bar^-1. The preparation cost of the PPy deposition was $2.22/m², which was ∼8% of the commercial ultrafiltration membrane cost. Once the PMM was charged at -1 V as a membrane electrode, the normalized water flux was maintained at 92.48 ± 1.14% after fouling by bovine serum albumin (BSA) solutions, which was 18.82% higher than that when the PMM was not charged. The reduced membrane fouling was ascribed to the electrical repulsion between the negatively charged BSA and the PMM cathode. In addition, hydroxyl and sulfate radicals were generated by peroxymonosulfate (PMS) activation on the PMM surface through electron transfer by PPy, which facilitated foulant oxidation. The PPy on the PMM surface was oxidized after catalysis and electrochemically reduced when the PMM was charged as a cathode, exhibiting continuous catalytic ability for PMS activation. These findings provide an alternative method for the facile fabrication of cost-effective conductive membranes to mitigate membrane fouling.

Highly Conductive and Permeable Nanocomposite Ultrafiltration Membranes Using Laser-Reduced Graphene Oxide

Electrically conductive membranes are a promising avenue to reduce water treatment costs due to their ability to minimize the detrimental impact of fouling, to degrade contaminants, and to provide other additional benefits during filtration. Here, we demonstrate the facile and low-cost fabrication of electrically conductive membranes using laser-reduced graphene oxide (GO). In this method, GO is filtered onto a poly(ether sulfone) membrane support before being pyrolyzed via laser into a conductive film. Laser-reduced GO composite membranes are shown to be equally as permeable to water as the underlying membrane support and possess sheet resistances as low as 209 Ω/□. Application of the laser-reduced GO membranes is demonstrated through greater than 97% removal of a surrogate water contaminant, 25 μM methyl orange dye, with an 8 V applied potential. Furthermore, we show that laser-reduced GO membranes can be further tuned with the addition of p-phenylenediamine binding molecules to decrease the sheet resistance to 54 Ω/□.

Reactive electrically conducting membranes for phosphorus recovery from livestock wastewater effluents

We present a novel 'proof-of-concept' electrochemically based membrane filtration process for the recovery of nitrogen and phosphorus from livestock wastewater following an anaerobic digestion step. Reactive electrically conducting membranes are shown to precipitate and separate struvite, an eco-friendly fertilizer from synthetic livestock wastewater, resulting in the production of a solid fertilizer and a high-quality water stream, fit for irrigation. The recovery process is based on electrochemical hydrolysis and control of local pH in proximity to the surface of the membrane, and therefore, does not require chemical additives for pH adjustment. The system was assessed at varying concentrations of nitrogen and phosphorus corresponding to diluted and concentrated livestock wastewater (up to 1000 mg/L of N and P). Experimental results show up to 65% removal of phosphorus and nitrogen in the first 30 min of electrochemical filtration, and the precipitates were analytically confirmed to be struvite. In addition, the recovery process was shown efficient as it resulted in limited membrane fouling and flux reduction. Fouling and precipitation results were explained by a mathematical model describing the concentration of N, P, Mg ions in the presence of an external electric field. Accordingly, precipitation takes place in proximity to the membrane's surface but not directly on it, thus, limiting surface fouling. The electrochemical filtration system does not require chemical additives for pH adjustment, and the cost associated with electrochemical membrane-based struvite recovery was calculated to be $158 per ton of dry struvite, which is about 1.4 times lower in comparison to conventional recovery approaches. Overall, the electrochemical filtration system may be a promising alternative for nutrient recovery from livestock wastewater in terms of operational costs, recovery efficiency, and fouling mitigation.