Fouling Problems Research Articles

Ceramic membrane fouling caused by recycling biological activated carbon filter backwash water: Effective backwash with ozone micro-nano bubbles.

The widespread use of ceramic membranes in wastewater recycling is still hampered by membrane fouling problems. Frequent chemical cleaning increases operating and maintenance costs. This work proposes ozone micro-nano-bubble (O3-MNB) backwash as a new backwashing method to control the ceramic membrane fouling. Activated carbon filter backwash water (ACFBW) was used as feed water for the ceramic membrane and the effect of O3-MNB backwash was compared with tap water backwash, air-micro-nano-bubble (Air-MNB) backwash and ozone water backwash. The results of the flux tests showed that the irreversible fouling resistance (RFi) for the O3-MNB backwash was only 4.8 %, 10.0 % and 23.3 % of the RFi for the tap water backwash, Air-MNB backwash and O3 water backwash, respectively. The results of the SEM and CLSM analyses demonstrated that the combination of ozone with MNB for backwashing was an effective method for the removal of viable cells and majority of proteins and polysaccharides from the surface of the ceramic membrane. However, the application of ozone also led to the release of microbial DNA, which increased its binding to Al₂O₃ on the ceramic membrane. Furthermore, the increased ozone concentration transported by the MNB could promote the generation of a large number of hydroxyl radicals (•OH) due to the effect of Al₂O₃, which potentially enhanced the oxidation of macromolecular contaminants in the pores. At the same time, the electrostatic repulsion and hydrophobic action provided by the MNB improved the efficacy of peeling off the filter cake layer when cleaning the membrane pores. Consequently, this study demonstrated the effectiveness of O3-MNB backwash in the long-term operation of ceramic membranes and provided insights into the fundamental mechanism by which this process controlled the membrane fouling.

Exploration of modified Polymers of Intrinsic Microporosity (PIM) for extracorporeal membrane oxygenator (ECMO)

Extracorporeal Membrane Oxygenation (ECMO) is the most important supporting therapy to rescue patients with respiratory distress syndrome (ARDS), for which the membrane oxygenator offers a place for CO2 and O2 exchange. Although Poly (4-methyl-1-pentene) (PMP) has been extensively used as ECMO material, the problems of protein adsorption fouling and the need for anticoagulation remain challenging for clinical applications. Additionally, the challenges associated with the functional modification of PMP material underscore the importance of finding a new material with excellent gas permeability and blood compatibility. On the other hand, Polymers of Intrinsic Microporosity (PIM) has been extensively studied in the field of gas separation due to their unique twisted helical structure and high free volume. However, its hydrophobic nature also raises concerns about its anti-fouling ability and hemocompatibility, which restricts the exploration of PIM in ECMO applications. Herein, we modify the PIM-1 membrane and study the hemocompatibility of PIM-1, carboxylated-PIM-1, and amidoxime-functionalized-PIM-1, and explore their gas permeability by molecular dynamics simulation and experimental verification. The modified PIM membranes exhibit remarkable comprehensive performance, including effective anti-protein adhesion and hemocompatibility, high oxygen permeability, and CO2 removal rate. Blood oxygenation tests also reveal that the modified membranes prepared in this work fully meet practical requirements, exhibiting great application potential.

Remediation of crude oil contaminated oily wastewater using nanostructured ZnO-decorated ceramic membrane: Membrane fouling and their mitigation using photo-catalytic self-cleaning process

In membrane-based oil water separation, the fouling of oil on the membrane pores due to the adsorption of oily feed components (crude oil) is a major disadvantage. In order to address the problem of membrane fouling, in this work, the filtration membrane itself was coated with a photoactive semiconducting material to self-clean the fouled membrane by photo-catalytic degradation. In addition to the self-cleaning, the other major functionality of the coating is to render a favorable surface wettability, conducive for water passing oil water separation. The basic membrane is porous alumina (Al2O3) substrate, on which a layer of crystalline Zinc Oxide (ZnO) thin film was coated by single step RF magnetron sputtering. The fabricated membrane is super-hydrophilic in the air and super-oleophobic underwater, and this contrasting wettability is crucial for the water passing oil water separation. The advantage of preferentially water passing membrane is that the oil clogging on the membrane surface is less than that of the oil passing membrane. However, after prolonged use with crude oil-contaminated feed, the accumulation of organic pollutants on the membrane surface hinders the smooth permeation of water through the membrane. The oil water filtration system involves cross flow through the ZnO-deposited Al2O3 membrane with the application of trans-membrane pressure. The membrane achieved an excellent separation efficiency (99.66 %) of oil and water from the oil emulsified water, and high permeates flux (908.4 L/m2.h.bar) for 200 ppm crude oil contaminated oily feed (surfactant stabilized crude oil-in-water emulsion). After a prolonged use of 540 min, the permeate flux declined due to the accumulation of organic pollutants present in the oily water. The original flux was restored by initiating photocatalytic degradation of organic pollutants by the exposure of UV radiation on the used membrane surface. The ZnO-deposited Al2O3 membrane shows an excellent light induced photocatalytic self-cleaning and antifouling with flux recovery ratio of around 88 %. In addition to this application, this manuscript also presents the morphological, elemental, structural, and topological characterizations of coated membrane.

Fabrication and evaluation of PVDF membranes modified with cellulose and cellulose esters from peanut (Arachis hypogea L.) shell for application in methylene blue filtration

Polyvinylidene fluoride (PVDF) membrane is frequently employed for filtration due to its excellent properties. The hydrophobicity of PVDF membrane causes easy fouling; therefore, hydrophilic polymer materials are required to increase hydrophilicity. This study applies cellulose and cellulose esters as fillers for PVDF membranes to solve the fouling problem. Cellulose esters, such as cellulose acetate (PSCA), cellulose benzoate (PSCB), and cellulose citrate (PSCC), were successfully synthesized from peanut shell cellulose (PSC) using Fischer and non-Fischer reactions. The phase inversion method was successfully used to fabricate PVDF membranes with cellulose or cellulose esters as fillers. The fabricated membranes have been applied for methylene blue (MB) filtration. Adding PSC fillers improved the hydrophilicity and performance of the PVDF membranes up to 23.49 ± 2.40 L m−2 h−1 for water flux and 95.75 ± 0.78 % for rejection of MB. Regarding cellulose esters, cellulose acetate gave the highest value of 77.63 L m−2 h−1 for water flux, and cellulose citrate gave the highest value of 86.88 ± 3.54 % for MB rejection. Hence, cellulose or cellulose esters from peanut shells are suitable fillers for MB filtration in PVDF membranes.

Ultraviolet Grafting of Bismuth Oxide Enhances the Photocatalytic Performance of PVDF Membrane and Improves the Problem of Membrane Fouling.

Photocatalytic membranes are crucial in addressing membrane fouling issues. However, the grafting amount of the catalyst on the membrane often becomes a key factor in restricting the membrane's self-cleaning capability. To address the challenge, this manuscript proposes a method for solving membrane fouling, featuring high grafting rates of bismuth oxide (Bi2O3) and acrylic acid (AA), significant contaminant degradation capability, and reusability. A highly photocatalytic self-cleaning microfiltration membrane made of polyvinylidene fluoride bismuth oxide and acrylic acid (PVDF-g-BA) was prepared by attaching nano Bi2O3 and acrylic acid onto the polyvinylidene fluoride membrane through adsorption/deposition and UV grafting polymerization. Compared with pure membranes and pure acrylic grafted membranes (PVDF-g-AA), the modified membrane grafted with 0.5% bismuth oxide not only improves the grafting rate and filtration performance, but also has higher self-cleaning ability. Furthermore, the degradation effect of this membrane on the organic dye methyl violet 2B under visible light irradiation is very significant, with a degradation rate reaching 90% and almost complete degradation after 12 h. Finally, after repeated filtration and photocatalysis, the membrane can still significantly degrade contaminants and can be reused.

Deep learning-based image analysis for filamentous and floc-forming bacteria in wastewater treatment

In municipal wastewater treatment, effective secondary clarification relies on the balance between floc-forming bacteria and filamentous bacteria. Consequently, comprehensive and real-time monitoring of this balance will enable reliable operation of biological wastewater treatment. This research presents an artificial intelligence (AI)-based approach for the classification of filamentous and floc-forming bacteria in microscopic images using deep learning. To provide ground truth labeling, an automated rule-based segmentation algorithm was developed using color and morphology criteria along with supplementary filtration steps to enhance the precision of filamentous and floc-forming bacteria identification. The segmentation algorithm demonstrated reliable detection and categorization of bacteria across varying background intensities and effectively recognized intricate microbial configurations. Subsequently, the supervised deep learning model was trained on the segmented images and constructed with an encoder/decoder architecture. Machine training with only 68 microscopic images demonstrated successful classification of the filamentous and floc-forming bacteria with a 97.8 % accuracy. In addition, qualitative evaluation demonstrated that the deep learning model could generalize machine understanding across diverse scenarios and discern misclassified filamentous bacteria accurately. The proposed model stands as a promising automated tool for real-time quantification of filamentous and floc-forming bacteria in bioreactors and clarifiers, offering the potential for reliable operation as well as immediate actions for sludge bulking and membrane fouling problems.

Polyphenol mediated α-FeOOH/g-C3N4 heterojunction membrane for fast purification of surfactant-stabilized O/W emulsions with super-wetting and Photo-Fenton self-cleaning functions

In the practical purification of oily wastewater, the application of polymer-based membrane is greatly restricted due to the oil adhesion and complicated fouling problems. Herein, to conquer the aforementioned challenges, we prepared the polyphenol mediated Photo-Fenton self-cleaning and superhydrophilic/underwater superoleophobic α-FeOOH/g-C3N4@PVDF composite membrane via simple vacuum-assisted self-assembly technology. The g-C3N4 nanosheets modified by tannic acid were introduced into the surface of PVDF ultrafiltration membrane, in which the intercalation structure was regulated by the random interpenetration of α-FeOOH nanorods. The abundant hydroxyl and amino groups and the rough micro-nano structure formed by intercalation structure were favorable for the superhydrophilic feature (WCA = 0°, UOCA>150°), thus resulting in ultra-low oil adhesion. Specially, the intercalation structure improved the water permeation channel, further promoting the water/oil separation flux. Therefore, the composite membrane exhibited superior separation flux (452.35–650.21 L m−2 h−1) and separation efficiency (>99.06 %) for various surfactant-stabilized emulsions. Moreover, thanks to the Photo-Fenton reaction, the composite membrane showed excellent degradation efficiency on simulated pollutants (various dyes) within 60 min (MeB: 95.55 %, CR: 90.83 %, MO: 98.90 %, CV: 95.11 %), showing satisfactory photocatalytic self-cleaning performance. This work provides a strategy for the potential application of polymer-based membranes in the treatment of complex surfactant-stabilized emulsion wastewater from petrochemical industry.

Integration of membrane bioreactor with a weak electric field: Mitigating membrane fouling and improving effluent quality targeting low energy consumption

The electrical assisted MBR (EMBR) has been employed to improve the water quality and solve the fouling problem. However, advanced material-based electrodes or high operation voltage bring difficulties for the practical application of EMBR. Herein, a weak electric field generated by titanium electrodes was employed to establish an EMBR and the fouling mechanism was investigated in detail. The results showed that introduction of a weak electric field at voltage of 0.1 V/cm and current density of 7 μA/cm2 efficiently decreased the extracellular polymeric substances (EPS) content by over 40 % as such extended the service time of MBR by more than 20 %. Specifically, the weak electric field reduced the relative abundance of Bacteroidetes, known for secreting proteinaceous EPS, by 38.61 %, and increased relative abundance of Patescibacteria with EPS decomposition by 6.73 times, thus effectively reducing the EPS concentration. Further KEGG pathway analysis revealed that electric field accelerated enzymatic reactions and promoted microbial metabolism of carbohydrate and amino acid. Furthermore, this weak field reduced the sludge deposition on membrane by increase of the electrostatic repulsion and the irreversible fouling was mediated. According to the composition of the fouling layer, a corresponding cleaning scheme was applied. This EMBR consistently produced high-quality effluent in all cycles, with 99.31 % COD, 98.73 % NH4+-N, 85.87 % TP and 92.66 % TN removals. In conclusion, the weak electric field endow EMBR exceptional anti-fouling ability and superior effluent quality under lower energy consumption.

Full-length 16S rRNA gene sequencing reveals the operating mode and chlorination-aggravated SWRO biofouling at a nuclear power plant.

Reverse osmosis (RO) membrane fouling and biological contamination problems faced by seawater desalination systems are microbiologically related. We used full-length 16S rRNA gene sequencing to assess the bacterial community structure and chlorine-resistant bacteria (CRB) associated with biofilm growth in different treatment processes under the winter mode of a chlorinated seawater desalination system in China. At the outset of the winter mode, certain CRB, such as Acinetobacter, Pseudomonas, and Bacillus held sway over the bacterial community structure, playing a pivotal role in biofouling. At the mode's end, Deinococcus and Paracoccus predominated, with Pseudomonas and Roseovarius following suit, while certain CRB genera still maintained their dominance. RO and chlorination are pivotal factors in shaping the bacterial community structure and diversity, and increases in total heterotrophic bacterial counts and community diversity in safety filters may adversely affect the effectiveness of subsequent RO systems. Besides, the bacterial diversity and culturable biomass in the water produced by the RO system remain high, and some conditionally pathogenic CRBs pose a certain microbial risk as a source of drinking water. Targeted removal of these CRBs will be an important area of research for advancing control over membrane clogging and ensuring water quality safety in the future.

Super-slippery silicone-based gel coating with a regenerative oil layer for long-term prevention of surface contamination

Polymer-based gel-type coatings, in which oil molecules are absorbed within polymer networks, have drawn attention as functional coatings to address fouling problems. However, surface drought caused by lubricant depletion limits the longevity of conventional gel-type coatings. In this study, a super-slippery long-chain entangled polydimethylsiloxane (LEP) gel that can self-regenerate a low-viscosity oil layer is proposed to enhance its long-term anti-fouling performance in both indoor and marine habitats. The proposed LEP gel coating can effectively prevent contamination from numerous liquids and protect aluminum surfaces from corrosion in seawater. Even when it was incubated with Porphyridium purpureum, marine red algae that readily stick to the surface, no biofilm was formed on the coated samples for 37 weeks. In field tests, no biological adhesion was observed on the coating surface which was applied to port structures and left for two summer months. This enhanced anti-contamination performance is mainly attributed to the dual protective barrier comprising the underlying polymer layer and regenerative oil layer. Due to special property of continuous self-regeneration of oil layer, the proposed LEP gel surface demonstrates much enhanced sustainability, compared to conventional gel-type coatings. Consequently, the long-term anti-contamination performance of the super-slippery LEP gel coating would pave the way for novel approach to its practical applications.

Experimental study of fouling characteristics of CaCO3 precipitated crystal scale mixed with different particles in an alternating magnetic field environment

This paper is to study the effect of CaCO3 precipitated crystal scale mixed with different particles on the scaling characteristics under the action of electromagnetic field. The simulation of industrial field experiments, based on the electromagnetic water treatment dynamic experimental bench, change the type of particles, concentration, magnetic field strength, according to the experimental results of the thermal resistance and scale inhibition rate curve under different working conditions, through the scanning electron microscope microscopy analysis of the fouling samples, to study the effect of CaCO3 fouling mixed with different particles in the role of the magnetic field on the effect of the law on the deposition characteristics.The results show that: electromagnetic field on MgO particles dirt and CaCO3 dirt deposition have inhibition effect; CaCO3 and different concentrations of CaCO3 crystalline particles mixed, CaCO3 particles, the more the electromagnetic field on the formation of CaCO3 precipitation scale inhibition effect is not obvious; CaCO3 precipitation scale and MgO particles mixed in the magnetic field can significantly enhance the effect of the field of the inhibition of the scale, magnetic field Under the action of the magnetic field, as the content of MgO particles increases, the scale inhibition effect on the dirt is first enhanced and then weakened until it tends to be about 0. Scanning electron microscopy analyses showed that the morphology and degree of aggregation of calcium carbonate fouling crystals were influenced by MgO particles under the action of electromagnetic fields, and CaCO3 fouling was transformed from regular ortho-hexahedra to acicular aragonite and amorphous CaCO3, which made the stripping phenomenon more significant.Comprehensive experimental results and scanning electron microscopy analyses of fouling samples show that the mixture of CaCO3 solution with a small amount of MgO particles can be an effective means to inhibit the precipitation of crystalline fouling under the environment of alternating electromagnetic field. This study provides theoretical guidance for the application of alternating magnetic field in the future, and provides new ideas and methods for solving the problem of crystalline fouling in industry.

Unraveling the intricate fouling behaviors of landfill leachate components during membrane distillation concentration toward zero liquid discharge

Membrane distillation (MD) holds promise for cost-effectively concentrating wastewater toward zero liquid discharge (ZLD), while membrane fouling problems still hinder its practical application, especially for high-strength wastewater containing complex constituents. This study investigated the effects of different foulant components in actual landfill leachate (LFL) on MD deep concentration performances. The fouling behaviors of LFL components were revealed by comprehensively characterizing and analyzing the physicochemical properties of the fouling layers and membrane-foulant interactions. Results illustrated that suspended solids (SS) and macromolecular organics (MO) played significant yet distinct roles in fouling layer formation. SS (>0.45 μm, ∼24 % TOC) possessed strong adhesion energies with membrane surfaces and constructed the main skeleton of the fouling layer at the preliminary concentration stage; while MO (>20 kDa, 0.36 % TOC) deposition resulted in a densely packed fouling layer, influencing the salt crystallization potential and interfering with water and ammonia transport. In contrast, the low-molecular organics with the highest content (<20 kDa, ∼75 % TOC) were mainly electron-donor monopolar substances weakly adsorbed on the nonpolar membrane surface. Removing SS and MO from LFL notably prevented fouling layer formation and maintained high membrane efficacies (water flux decline mitigated from ∼50 % to ∼15 % and ammonia rejection increased from 71 % to 88 %), even as water recovery increased to 95 %. The findings of this work imply conventional anti-fouling strategies (e.g., complete removal or degradation of organic components) may have gone beyond what is necessary, and will inspire the development of simpler and greener methods to maintain membrane efficacy during high-strength wastewater treatment toward ZLD.

A wastes-based hierarchically structured cellulose membrane: Adsorption performance and adsorption mechanism

It was imperative to expeditiously investigate novel avenues for the valorization of agricultural waste biomass crop straws. The straws represented promising substrates to design eco-friendly adsorbents for the effective treatment of complex dyeing wastewater owing to their widespread availability, low cost, easy production, and environmental friendliness. Despite the advantages, developing adsorbents with versatile uses, antibacterial properties, and strong mechanical qualities remained a challenge. Herein, a sustainable waste treatment strategy is put forward by developing multifunctional adsorbents derived from agricultural waste. The adsorbents are designed to synchronously adsorb the typical contaminants such as organic molecule (methylene blue, MB) and heavy metal ions (cadmium ion, Cd2+) in dyeing wastewater. Through the assembly of cellulose fibers, multiscale cellulose membrane (MCM) substrates with enhanced two-dimensional (2D) structure were simply fabricated from biomass crop straws. Coating functional copper phosphate (CP) nanoflakes on the MCM substrate effectively constructed the hierarchical structure to achieve the synchronous adsorption. The synergistic effects of electrostatic attraction, hydrogen bonding and coordination greatly prompted the adsorption process. Furthermore, the multifunctional adsorbents were imparted with satisfactory antibacterial properties, thereby expected to solve the problem of membrane fouling in wastewater. Hierarchically structured copper phosphate @ cellulose antibacterial adsorbents (CP@MCM) exhibit huge application potential in the resource utilization of agricultural waste and effective treatments for dyeing wastewater.

Enhancing Solar-Driven Water Purification by Multiscale Biomimetic Evaporators Featuring Lamellar MoS2/GO Heterojunctions.

Solar-powered steam generation holds a strong sustainability in facing the global water crisis, while the production efficiency and antifouling performance remain challenges. Inspired by river moss, a multiscale biomimetic evaporator is designed, where the key photothermal conversion film composed of lamellar MoS2/graphene oxides (GO) can significantly enhance the evaporation efficiency and solve the problem of fouling. First-level leaf-like MoS2/GO nanosheets, obtained by a modified hydrothermal synthesis with an assisted magnetic-field rotation stirring, are self-assembled into a second-level nanoporous film, which achieves an evaporation rate (ER) of 1.69 kg m-2 h-1 under 1 sun illumination and an excellent self-cleaning ability. The tertiary-bionic evaporator with a macroscopic crownlike shape further enhances the ER to 3.20 kg m-2 h-1, 189% above that of planar film, yielding 20.25 kg m2 of freshwater from seawater during a daytime exposure of 6 h. The exceptional outcomes originate from the macroscopic biomimetic design and the microscopic integration of heterojunction interfaces between the MoS2 and GO interlayers and the nanoporous surface. The biomimetic evaporator indicates a potential direction through surface/interface regulation of photothermal nanomaterials for water desalination.

Development of an antimicrobial and antifouling PES membrane with ZnO/poly(hexamethylene biguanide) nanocomposites incorporation

Although polyethersulfone (PES) membranes are extensively utilized in water and wastewater treatment, they typically encounter serious bio/organic fouling problems. In this work, an antimicrobial and antifouling PES membrane was developed through incorporating novel ZnO/PHMB (zinc oxide/ polyhexamethylene biguanide hydrochloride) nanocomposites on the surface of a commercial PES membrane, with PDA (polydopamine) serving as an intermediate connection layer. XPS, along with synchrotron-based XRF and ATR-FTIR results confirmed the successful synthesis of the ZnO/PHMB nanocomposites and ZnO/PHMB membranes. The ZnO/PHMB nanocomposites exhibited an impressive antimicrobial rate of 99.99 % with a minimal amount of PHMB addition (wtZnO:wtPHMB = 1:0.01). The concentration of the ZnO/PHMB nanocomposites had the most significant impact on the antimicrobial performance of the ZnO/PHMB membrane. The 600ZP membrane (i.e., the PES membrane modified with 600 mg/L ZnO/PHMB nanocomposites) emerged as the optimal choice, as evidenced by its commendable antimicrobial performance (92.80 %), water flux (249.02 LMH), RB (Rose Bengal sodium salt) rejection (93.96 %), and cost-benefit considerations. Compared to the pristine PES membrane, the 600ZP membrane showed 5.32 %, 15.76 %, and 7.62 % increased hydrophilicity, water flux, and RB rejection rate, respectively. Additionally, the 600ZP membrane possessed a bactericidal rate of 92.80 % and a flux recovery rate of 89.24 % after three cycles of SA (sodium alginate) filtration, indicating enhanced antimicrobial and antifouling capacities. The 600ZP membrane exhibited a remarkable 91.05 % higher water flux following prolonged (72 h) treatment of secondary effluent, compared to the PES membrane. Attribute to the increased hydrophilicity, outstanding antimicrobial activity, as well as excellent stability and durability, the as-prepared ZnO/PHMB membrane shows great potential for wastewater treatment.

Investigation of Slagging Condition in a Zhundong Coal-Fired Boiler via In Situ Optical Measurement of Gaseous Sodium.

In this study, a portable spectral analysis instrument based on spontaneous emission spectroscopy (SES) was developed for the in situ, non-intrusive, and quantitative measurement of gaseous Na inside ZD coal-fired boilers, which is mainly applied for predicting slagging in furnaces. This technology is needed urgently because the problem of fouling and slagging caused by high alkali metals in ZD coal restricts the rational utilization of this coal. The relative extended uncertainty for the measurement of gaseous Na concentration is Urel = 10%, k = 2, which indicates that measurement data are reliable under working conditions. It was found that there is a clear linear relationship between the concentration of gaseous Na and fouling in high-alkali coal boilers. Therefore, a fast and efficient method for predicting the slagging and fouling of high-alkali coal boilers can be established by using this in situ online real-time optical measurement.

Optimum content of incorporated nanomaterials: Characterizations and performance of mixed matrix membranes a review

Environmental concerns about chemical and biological pollution of water are of alarming proportions. Therefore, various polymeric membranes with improved mechanical and physico-chemical qualities for water treatment were developed using mixed matrix membranes (MMMs) or nanoparticles (NPs) embedded with the membranes. However, the problem of fouling and consequent higher operating and membrane replacement costs are barriers to the use of membrane technology. Therefore, a deeper comprehension of membrane fouling is not only essential for finding solutions but also a crucial factor in the development of membrane technology. The conventional blending modification would result in a large number of nanoparticles in the polymer matrix. In reality, the aggregation of nanoparticles in composite membranes is a considerable issue and would result in unfavorable changes to the features of the membrane (e.g. decreased water flux, weakened mechanical strength). In this review, it was looked into the effect of an optimal concentration of the hydrophilic nanoparticle additions to avoid the aggregation of nanoparticles in composite membranes and the reduced of using high amounts of valuable and costly nanoparticles in the membranes production and to obtain better results. The influence of the additives, such as (carbon nanotubes (CNTs), silica (SiO2), titanium dioxide (TiO2), zinc oxide (ZnO), aluminum oxide (Al2O3), and graphene oxide (GO), etc.) was investigated.

Coupling pretreatment of ultraviolet/ferrate (UV/Fe(vi)) for improving the ultrafiltration of natural surface water.

Ultrafiltration (UF) is a high-potential technology for purifying natural surface water; however, the problem of membrane fouling has limited its widespread application. Herein, ultraviolet (UV)-activated ferrate (Fe(vi)) was used to purify natural surface water and improve the performance of the UF membrane. The combination of UV and Fe(vi) could generate active species (Fe(v), Fe(iv), ˙OH and O2˙-) to degrade pollutants, while the in situ produced Fe(iii) had the effect of coagulation. With the above action, pollutants were removed, and the pollution load of natural surface water was reduced. After treatment with the UV/Fe(vi) system, dissolved organic carbon was reduced by 49.38%, while UV254 was reduced by 45.00%. The removal rate was further increased to 54.88% and 51.67% after UF treatment. In addition, the fluorescent organics were reduced by 44.22%, and the molecular weight of the organics became smaller. In the stage of UF, the terminal J/J0 was increased from 0.61 to 0.92, and the membrane fouling resistance was decreased by 85.94%. The analysis of the membrane fouling mechanism indicates that the role of cake filtration was weakened among all the mechanisms. Fourier transform infrared spectroscopy showed that less pollutants were accumulated on the membrane surface, and scanning electron microscopy revealed that the membrane pore blockage was relieved. In summary, the UV/Fe(vi) co-treatment process proposed in this study can significantly improve the purification efficiency of the UF systems in natural surface water treatment.

Slippery hydrogel surface on PTFE hollow fiber membranes for sustainable emulsion separation.

Establishing an efficient and sustainable membrane module is of great significance for practical oil/water emulsion separation. Superwetting membranes have been extensively studied but cannot meet long lasting separation owing to inevitable membrane fouling. Herein, we constructed a hydrogel-mediated slippery surface on polytetrafluoroethylene (PTFE) hollow fibers and then designed a flexible and swing hollow fiber membrane module inspired by fish gill respiration, which achieved sustainable emulsion separation. A vinyl silane-crosslinked polyvinylpyrrolidone (PVP) hydrogel was interpenetrated with nano-fibrils of the PTFE hollow fibers, thus facilitating fast water permeance while resisting oil intrusion. Liquid-like polydimethylsiloxane (PDMS) brushes were then grafted to promote oil aggregation-release from the membrane surface. Owing to the heterogeneous surface and gill-like structure, the designed PTFE hollow fiber membrane module could separate emulsion in a long-term filtration process, maintaining a high water permeability of 500 L m-2 h-1 bar-1 with a separation efficiency of over 99.9% for 5000 min. This novel technique shows its great potential to realize practical emulsion separation by solving the persistent problem of membrane fouling and permeance decay.

High performance photodegradation resistant PVA@TiO2/carboxyl-PES self-healing reactive ultrafiltration membrane

The occurrence of ultrafiltration (UF) membrane fouling frequently hampers the sustainable advancement of UF technology. Reactive self-cleaning UF membranes can effectively alleviate the problem of membrane fouling. Nevertheless, the self-cleaning process may accelerate membrane aging. Addressing these concerns, we present an innovative design concept for composite self-healing materials based on self-cleaning UF membranes. To begin, TiO2 nanoparticles were incorporated into the polymer molecular structure via molecular design, resulting in the synthesis of TiO2/carboxyl-polyether sulfone (PES) hybrid materials. Subsequently, the nonsolvent-induced phase inversion technique was employed to prepare a novel of UF membrane. Lastly, a polyvinyl alcohol (PVA) hydrogel coating was applied to the hybrid UF membrane surface to create PVA@TiO2/carboxyl-PES self-healing reactive UF membranes. By establishing a covalent bond, the TiO2 nanoparticles were effectively and uniformly dispersed within the UF membrane, leading to exceptional self-cleaning properties. Furthermore, the water-absorbing and swelling properties of PVA hydrogel, along with its capacity to form hydrogen bonds with water molecules, resulted in UF membranes with improved hydrophilicity and active self-healing abilities. The results demonstrated that the water contact angle of PVA@5%TiO2/carboxyl-PES UF membrane was 43.1°. Following a 1-h exposure to simulated solar exposure, the water flux recovery ratio increased from 48.16% to 81.03%. Moreover, even after undergoing five cycles of 12-h simulated sunlight exposure, the UF membranes exhibited a consistent retention rate of over 97%, thus fully demonstrating their exceptional self-cleaning, antifouling, and self-healing capabilities. We anticipate that the self-healing reactive UF membrane system will serve as a pioneering and comprehensive solution for the self-cleaning antifouling challenges encountered in UF membranes while also effectively mitigating the aging effects of reactive UF membranes.