Hollow Fiber Membrane Research Articles

Electroextraction of Large Volume Samples Using Paper Points Coupled With Hollow Fiber Membranes: Study of Parameters and Strategies to Enhance Analytical Performance.

Electroextraction (EE) encompasses a range of sample preparation methods whose effectiveness, selectivity, and efficiency are significantly influenced by the physical-chemical characteristics of analytes, samples, and instrumental conditions. This article explores, for the first time, various strategies aimed at enhancing the extraction efficiency of a recent approach of EE utilizing a paper point (PP) combined with a hollow fiber (HF) (abbreviated as PP-HF-EE) to extract various cationic and anionic model compounds from water samples. The study also explores, experimentally, the impact of agitation, organic filter composition, PP diameter, and PP brand on extraction performance, and proves that all these factors are quite important, especially when digital image analysis is utilized for determination. Furthermore, this work demonstrates the ease and feasibility of simultaneously extracting cations and anions using PP-HF-EE and proposes a straightforward method to enhance analyte concentration on the vertex of the PP through a base-to-vertex focusing. Lastly, it is demonstrated, using capillary electrophoresis coupled to a UV-Vis detector, that for PP-HF-EE, the extraction efficiency and pre-concentration factor are less dependent on other parameters when multiple PPs per sample are utilized, with signal enhancement values of up to 111 and 339 for nortriptyline and haloperidol, respectively. All the findings and strategies presented herein constitute significant contributions that can facilitate future research in method development, particularly in the utilization of PP-HF-EE and similar EE approaches.

Biogas purification using cellulose nanocrystals/polyvinyl alcohol coated facilitated transport hollow fiber membranes with L‐arginine as CO2 carrier

AbstractThe composition of biogas consists mainly of CH4 (~60%) and CO2 (40%). To be considered a clean fuel, CH4 concentration in biogas must be increased to over 95%. In this study, membranes which were stacked in a chamber were utilized to purify biogas by passing biogas over them. These membranes were composed of polyethersulfone hollow fiber substrate coated with a “selective layer” made of cellulose nanocrystals (CNC‐0–2 wt) in polyvinyl alcohol (PVA) and l‐arginine as a CO2 carrier. Of the different CNC concentrations in PVA‐LA, CNC1/PVA‐LA (1.0 wt% CNC in PVA‐LA) displayed the lowest water contact angle of 17° (corresponding to higher moisture absorbing ability). With further increase in CNC concentration, even though CNC1.5/PVA‐LA showed the higher crystallinity (66%), and water contact angle increased (20°); reducing the chances of facilitated transport of CO2 through it. Biogas separation experiments were conducted at 90% RH and different feed pressures (0.8–1 bar) for various CNC concentrations. Increasing the CNC concentration led to a thicker selective layer, enhancing the CO2 permeability and selectivity up to CNC1/PVA‐LA. However, with the further addition of CNC, both permeability and selectivity decreased. At 90% RH and 1 bar feed pressure, the CNC1/PVA‐LA setup demonstrated a CO2 permeability of 20,522 Barrer and a selectivity of 33, making it suitable for low‐pressure biogas storage systems with lower energy requirements.

Influence of irregular fiber filling on the performance of hollow fiber membrane modules for cold water production

The countercurrent hollow fiber membrane-based evaporative water cooler (MEWC) offers an eco-friendly and compact solution for cold water generation. This study introduces a random sequential addition algorithm to model the real-world irregular fiber filling within the MEWC. Inspired by the honeycomb structure, the developed 3-D numerical model adopts a calculation unit featuring a hexagonal prism comprising multiple fibers. Validation against experimental data reveals an average relative error of 2.81 % concerning outlet water temperature. The effects of fiber filling patterns (regular layout and random layout) on the velocity and temperature fields of the MEWC are investigated. Comparisons of outlet water temperature, cooling efficiency, consumptive electric power ratio, and heat and mass transfer resistance composition between these layouts under various operating conditions are conducted. The results indicate that the random layout fosters severe channeling effect and large flow dead zones, impairing air side heat and moisture transfer. The random layout exhibits over 15.9 % reduction in cooling efficiency and 36.3 % decrease in consumptive electric power ratio compared to the regular layout. Irregular fiber filling leads to a notable 158.6 % increase in air side heat transfer resistance and a 35.9 % rise in mass transfer resistance. Although irregular filling compromises the cooling performance, it demonstrates potential for energy savings under certain conditions. Design schemes should be carefully tailored to meet specific application requirements by considering these trade-offs.

Impact of drug incorporation into micelle on reduced griseofulvin and meloxicam permeation across a hollow fiber membrane

A hollow fiber membrane (HFM) was previously characterized as a potential permeation component of a dissolution/permeation system. Two objectives were to assess the impact of micellization on drug permeation across HFM and identify a preferred permeation model from three models: permeation from only free drug, permeation from both free drug and micelle-bound drug, and permeation with enhancement from micelle shuttling. HFM studies were conducted under unsaturated drug conditions, using griseofulvin and the more hydrophilic drug meloxicam, with and without surfactant [sodium lauryl sulfate, polysorbate 80, and polyoxyethylene (10) lauryl ether]. Griseofulvin was micelle incorporated to a greater extent than meloxicam, such that griseofulvin flux decreased to a greater extent than for meloxicam. The griseofulvin permeation model from only free drug was rejected, since griseofulvin flux required free drug to be about 5-20 fold higher in HFM flux studies than supported by solubility studies, depending on surfactant. Permeation from both free griseofulvin and micelle-bound griseofulvin successfully accommodated observed flux, where micelle permeability was about 5-fold lower than free drug permeability for HFM with 10KDa MWCO. Permeation with enhancement from micelle shuttling was not the preferred explanation, although the model accommodated flux data and provided aqueous boundary layer thicknesses similar to other setups.

Exploration of Daptomycin Adsorption by Polymethylmethacrylate Hemofilter In Vitro.

Blood purification therapy with cytokine-adsorbing hemofilters has been used to treat sepsis-associated hypercytokinemia. Polymethylmethacrylate (PMMA) hemofilters are frequently used for this purpose; however, adsorption and removal of teicoplanin, a therapeutic agent, have been reported. Similar concerns have been shared regarding daptomycin because its structure resembles that of teicoplanin; nevertheless, there have been no reported effects associated with daptomycin in this context. We studied the adsorption of daptomycin onto a PMMA hemofilter in vitro and investigated its adsorption onto hollow fiber membranes by adding cut PMMA membranes to a daptomycin solution. Additionally, the daptomycin solution was circulated in a dialysis circuit connected to a PMMA hemofilter, and changes in daptomycin content were examined. The daptomycin content decreased immediately after adding the hollow fiber membranes, similar to that observed for teicoplanin. The daptomycin content was lower than that of the standard reagent in the dialysis circuit model, reaching values below the measurement limit after 20 min. These results suggested that daptomycin was adsorbed and removed by the PMMA hemofilter. Encountering this effect during clinical use is plausible; therefore, daptomycin administration via a PMMA hemofilter should be avoided during blood purification therapy.

Three-dimensional CFD modeling for hollow fiber gas separation membrane modules based on a dual porous media model

Mathematical modeling is crucial to optimizing the design of the hollow fiber membrane (HFM) module. A Computational Fluid Dynamics (CFD) model enables efficient three-dimensional (3D) simulations of HFM modules, which integrates a dual porous media approach, significantly reducing computational costs. Validation against alternative simulations and experimental data confirms its prediction capability (<7% deviation). Comparative analyses demonstrate the superior reliability of the 3D approach over one-dimensional simulations. Detailed velocity, pressure, and concentration profiles for the shell and tube sides reveal optimization opportunities such as dead zones within the module. Aerometric studies show significant pressure drops (>30%) for smaller fiber diameters (<100μm) on the permeate side. The model's adaptability suggests broader applications in membrane gas separation processes with modifications. This research highlights the efficacy of CFD modeling in enhancing the design and optimization of HFM modules, highlighting the cost savings of the dual porous media approximation.

TiO2-embedded dual-layer mullite hollow fiber membranes for efficient removal of Persistent organic pollutants from wastewater

Persistent organic pollutants (POPs) are toxic pollutants that harm the environment and ecosystems. This study presents a novel approach to develop a dual-layer hollow fiber ceramic membrane for phenolic compound removal. A co-extrusion-based phase inversion process and co-sintering techniques were employed to fabricate the membrane, and the effects of TiO2 loadings on the outer layer were investigated. Characterization techniques, including FTIR, SEM, EDX, and zeta potential analysis, were used to analyze the mullite and TiO2 powders and membranes. The membrane’s performance was evaluated through rejection tests of POPs at various concentrations (10, 500, and 1000 ppm) and fouling assessments were conducted. The results showed that the M−MT0.6 membrane, with a mean pore size of 0.0245 μm, effectively rejected benzoic acid (81.45 %), gallic acid (91.45 %), and hydroquinone (74.49 %) from wastewater, achieving the highest permeate flux (1320.50 L/m2·h) for gallic acid at 10 ppm. Additionally, M−MT0.6 exhibited minimal fouling over a 1-h filtration cycle, with the lowest fouling rate (35.1 %) recorded at 1000 ppm for BA, attributed to effective backwashing. However, higher fouling rates were observed at 10 ppm for BA (90.10 %) and HQ (83.50 %). Overall, this study demonstrates the potential of the novel membrane for effective removal of POPs from industrialwastewater.

Time-dependent mechanical behavior analysis using Weibull models of cellulose hollow fiber membranes produced by green solvent

The mechanical behavior of sustainable (“green”), bio-based cellulose hollow fiber membranes (hereafter, hollow fiber) produced using green solvent, which is potential for desalination and solvent-resistant nanofiltration, can be evaluated either in dry or water-conditioned (wet) states. However, the effect of conditioning time on the mechanical behavior of hollow fibers has not been conclusive. In this work, an extensive evaluation involving an experimental campaign and rigorous application of statistical models for cellulose hollow fibers produced using green solvent (1-ethyl-3-methylimidazolium diethyl phosphate or [EMIM][DEP]) via a dry-jet spinning technique is reported. First, we evaluated the microstructures and separation performance (water permeation, solute rejection) of hollow fibers made of different cellulose concentrations (10–15 wt%) in both pristine and conditioned states. Then, the strength, stiffness, and ductility of hollow fiber samples of different gauge lengths (25 and 50 mm) were measured by a standard tensile test device. Here, the effect of conditioning time on mechanical properties was evaluated after the hollow fiber samples were water-immersed at different times (from 30 s to 2 months). The strength distribution of conditioned hollow fibers was modeled and analyzed using two-parameter and three-parameter Weibull models. Our results showed that the cellulose content of 15 wt% in the hollow fibers produced a denser microstructure, providing the lowest molecular weight cut-off (MWCO). The cellulose content and gauge length slightly modified the mechanical properties of hollow fibers when they were evaluated in pristine, dry conditions. The mechanical properties of hollow fibers were drastically reduced after 10 min of water immersion, beyond which their properties were stabilized. Weibull modeling of mechanical reliability showed that two- or three-parameter Weibull could estimate the failure probability of hollow fibers quite well. Nonetheless, the three-parameter Weibull is better than the two-parameter one in terms of accuracy in determining the threshold strength located at the “lower-end tail.” Our analysis provides a rigorous demonstration of Weibull modeling in evaluating the time-dependent mechanical behavior of ductile, cellulose-based hollow fiber membranes, which is essential to support the design and development of future hollow fiber membranes in desalination industries.

Modification of poly (vinylidene fluoride-co-hexafluoropropylene) membranes by sulfonated poly (ether ether keton) coating for membrane distillation of textile wastewater

The textile and related industries can produce a large amount of wastewater with organic dyes pollutants which can cause uncertain environmental impacts. In this study, the improved poly (vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) hollow fiber membranes were used in a continuous air gap membrane distillation (AGMD) operation for wastewater treatment of the Hamadan textile factory, Iran. The porous membranes were fabricated by a phase-inversion process and the inner surface was coated by a thin layer of sulfonated poly (ether ether keton) (SPEEK). After SPEEK coating, the water contact angle of the membrane decreased from about 93° to 57°. The SPEEK coated membrane presented mean pore size and overall porosity of 10 nm and 82.2%, respectively. For the wastewater treatment, the improved membrane presented the water flux and color rejection of 24.7 kg/m2 h and 99.8% during 72 h of the AGMD operation, respectively. Additionally, the treated wastewater reduced to the turbidity of ∼2 NTU, total dissolved solid (TDS) of 16 mg/L and chemical oxygen demand (COD) of 10 mg/L. The coated membrane presented a reasonable anti-fouling property with a flux recovery ratio (FRR) of 91.7% after 72 h of the operation. Hence, the improved PVDF-HFP membrane can be a potential alternative for the removal of organic dyes from wastewater via a membrane distillation process.

From single tube to multi-channel configuration: Constructing nanofiltration membranes with superior adhesion strength on the ceramic support by interfacial polymerization

Ceramic membranes with multi-channel configurations exhibit superior mechanical strength, high packing density, and high separation efficiency, making them more suitable for industrial applications than single tube and hollow fiber membranes. However, the preparation of thin-film composite (TFC) membranes on multi-channel ceramic supports remains a challenge because of the poor compatibility between organic and inorganic materials and their special configuration. In this study, nanofiltration membranes with a stabilized structure supported by 19-channel ceramic membranes were successfully prepared with improved adhesion strength and dynamic interfacial polymerization. TFC membranes with different channels exhibited uniform microstructure and stable performance. Specifically, polyethyleneimine, which served as a polymerization reactant, can be tightly wound on the surface of ceramic membranes via hydrogen bonding and van der Waals forces during interfacial polymerization. Owing to the enhanced cross-linked network interactions between the support and separation layers, the adhesion strength was significantly improved. Consequently, the optimized membranes maintained excellent rejection to MgCl2 of ∼94 % after the back-flush test under the pressure of 4 bar. Additionally, the multi-channel TFC membranes exhibited stable performance, with a pure water permeance of ∼14.9 LMH/bar and a molecular weight cut-off of 450 Da. When filtering sunset yellow for 10 h, the prepared membranes exhibited stable permeance and excellent rejection performance.

Enhanced gravity-driven membrane filtration for purifying roof rainwater using multi-walled carbon nanotubes tuned PVDF hollow fiber membranes

The collection and reuse of roof rainwater can alleviate water shortage for daily life. In this study, polyvinylidene fluoride hollow fiber membranes tuned with three multi-walled carbon nanotubes (pure MWCNTs, MWCNTs-COOH, and MWCNTs-OH) were prepared using a non-solvent induced phase separation method for gravity-driven membrane filtration to purify roof rainwater. The results showed that the MWCNTs were distributed on the membrane surface and throughout the porous structure of the cross-section, which changed the pore structure parameters and hydrophilicity. The pure water flux of the MWCNTs tuned membranes increased by 152.5 % at 1.0 bar, and the rejection rates of humic acid and bovine serum albumin increased from 97.4 % and 75.7 % to 98.9 % and 96.3 %, respectively. The extended Derjaguin, Landau, Verwey, and Overbeek (xDLVO) theory states that the presence of MWCNTs leads to changes in the physicochemical properties of the membrane surface, resulting in membranes with different anti-fouling behaviors. A gravity-driven membrane filtration test was continuously operated for 100 days, and all membranes removed 25.0–26.7 %, 49.5–53.0 %, and 89.0–93.3 % of total dissolved solids, dissolved organic carbon, and turbidity from roof rainwater, respectively. However, the pure MWCNTs modified membrane with relatively hydrophobic properties showed a 12.4 % increase in flux over the unmodified membrane. Importantly, the presence of the MWCNTs in the membrane changed the microbial diversity in the biofilter cake layer.

Optimization of vacuum membrane distillation and advanced design of compact solar water heaters with heat recovery

With the escalating global population, freshwater scarcity has become a pressing challenge. To address this issue, this paper presents a novel compact solar water heater (CSWHT) system incorporating heat recovery and submerged-membrane filtration. The research aims to develop an efficient desalination method that reduces water production costs and maximizes output. The system comprises a feed storage tank, a vacuum membrane distillation (VMD) system positioned atop the submerged CSWHT, a liquid ring vacuum pump (LRVP) utilizing waste heat from the outlet to preheat the feed, and hollow fiber membranes.Three critical parameters, namely the mass of the feed in the storage tank, the number of hollow fiber membrane rows, and the feed volumetric flow rate, were optimized using a multi-objective non-dominated sorting genetic algorithm II (NSGA II) to minimize water production cost (WPC) while maximizing water production. Subsequently, the Technique for Order of Preference by Similarity to Ideal Solution (TOPSIS) was employed to identify the optimal scenario from among the selected best solutions.For Mediterranean seawater and a 6 m2 solar collector area, the multi-objective NSGA II algorithm identified 20 membrane rows per collector, 334.4 kg feed mass in the storage tank, and 0.027 kg.s−1 feed mass flow rate as the optimal system parameters. Under these optimized conditions, the system exhibited a daily production capacity of 92.5 kg water, 4.6 kg chloride, and 0.03 g bromide, while achieving a production cost of 12.2 USD.m−3 and a gain output ratio (GOR) of 1.6. These results highlight the system's remarkable potential for desalination with high efficiency and low cost. Future research should focus on scaling up the system and exploring its applicability in various geographical locations.

Polypropylene membrane with gradient-distributed covalent organic framework for highly efficient blood oxygenation

Hollow fiber membrane (HFM) is widely used for extracorporeal membrane oxygenator (ECMO) because of large membrane area, high packing density, self-supporting structure and good flexibility. However, polymeric HFMs often suffer from a trade-off between gas permeability and anti-plasma leakage performance. In this study, HFMs with gradient structure were prepared by introducing COF-42 as fillers into the polypropylene (PP) matrix through surface segregation. The enriched COF-42 near the upper surface endowed the membrane a gradient structure to reduce the plasma leakage and improve gas permeability. Compared with PP membranes, PP/COF-42 oxygenation membranes retained good blood compatibility and higher mechanical properties. The PP/COF-42–0.5 HFMs exhibited O2 exchange rate of ∼ 342.6 ml min−1 m−2 and CO2 exchange rate of ∼ 989.6 ml min−1 m−2, which was about 218.7 % and 15.4 % larger than that of the PP HFMs, respectively. Moreover, the simulated plasma leakage time could reach 124 h, which was about 21 times longer than that of PP HFMs. The membranes exhibited excellent blood oxygenation performance and anti-plasma leakage performance, which had great potential in ECMO.

Regeneration of CO2 from CO2-rich absorbents using hollow fiber membrane contactors in liquid–liquid extraction mode

This study explores the use of hollow fiber membrane contactors (HFMCs) to efficiently regenerate CO2 from CO2-rich absorbents and convert it into calcium carbonate (CaCO3) via a novel liquid–liquid extraction process. CO2 is absorbed into a potassium carbonate (K2CO3) solution and then desorbed directly into a calcium chloride (CaCl2) solution through a porous polypropylene (PP) hollow fiber membrane. This single-step process significantly reduces the energy costs associated with traditional CO2 chemical capture methods, such as reboilers and gas compression. Key operational parameters, including stripping liquid chemistry (Ca2+ concentration and pH), feed liquid temperature, and HFMC stages, were optimized. CO2 regeneration peaked at pH 11.0 with a Ca2+ concentration of 108.00 mmol/L, achieving a 37 % efficiency at 80 ℃ in a single-stage HFMC. A three-stage HFMC in parallel mode increased CO2 regeneration efficiency to 49 %, though with a lower Ca2+ carbonation efficiency of 2.92 %. The open-loop configuration, which facilitates continuous CO2 absorption from flue gas, demonstrated practical application potential, regenerating approximately 30 % CO2 at a feed flow rate of 0.3 cm/s.

Synergistic tuning of microstructure and morphology in carbon molecular sieve hollow fibers for propylene/propane separation

Asymmetric carbon molecular sieve (CMS) hollow fiber membranes with tunable micro‐ and macro‐structural morphologies for energy efficient propylene‐propane separation are reported here. A sub‐glass transition temperature (sub‐Tg) thermal oxidative crosslinking strategy enables simultaneous optimization of the intrinsic molecular sieving properties while also reducing the thickness of the CMS “skin” derived from the 6FDA:BPDA/DAM polyimide precursors. Such synergistic tuning of CMS microstructure and macroscopic morphology of CMS hollow fibers enables significantly increased propylene permeance (reaching 186.5 GPU) while maintaining an appealing propylene/propane selectivity of 13.3 for 50/50 propylene/propane mixed gas feeds. Our findings reveal a more refined and versatile tool than available with previous O2‐doping pretreatments. The advanced approach here should be broadly useful to other polyimide precursors and diverse gas pairs.

Facile fabrication of robust and tight PIMs-based TFC hollow fiber membranes with a semi-interpenetrating polymer network via liquid phase cross-linking for organic solvent nanofiltration

Resource recovery and reuse are essential for sustainable development, particularly for high-value resources such as homogeneous (photo)catalysts, active pharmaceutical ingredients, and high-value natural compounds, which can offer economic benefits. Recently, organic solvent nanofiltration (OSN) for resource recovery has gained significant attention owing to its advantages including low energy consumption and seamless integration with other processes. Polymers of intrinsic microporosity (PIMs) have great potential as membrane materials for OSN, owing to their excellent pore properties and solution processability. However, swelling and dissolution of PIMs in organic solvents can impede the filtration performance of PIMs-based OSN membranes. In this study, we fabricated thin-film composite hollow fiber membranes for OSN based on PIMs with improved organic solvent stability using a semi-interpenetrating polymer network (semi-IPN) formed by cross-linking Matrimid with 1,6-hexanediamine within the PIMs through the liquid phase cross-linking method. Semi-IPNs mitigate swelling and tighten the pores of PIMs-based membranes, enabling excellent filtration and molecular separation performance. Furthermore, the fabricated PIMs with a semi-IPN membrane exhibited excellent rejection performance (>96 %) for homogeneous photocatalysts, allowing successful concentration and recovery via OSN. Therefore, PIMs-based membranes with a semi-IPN hold great promise as OSN membranes for the recovery of valuable resources.

Synergistic tuning of microstructure and morphology in carbon molecular sieve hollow fibers for propylene/propane separation.

Asymmetric carbon molecular sieve (CMS) hollow fiber membranes with tunable micro- and macro-structural morphologies for energy efficient propylene-propane separation are reported here. A sub-glass transition temperature (sub-Tg) thermal oxidative crosslinking strategy enables simultaneous optimization of the intrinsic molecular sieving properties while also reducing the thickness of the CMS "skin" derived from the 6FDA:BPDA/DAM polyimide precursors. Such synergistic tuning of CMS microstructure and macroscopic morphology of CMS hollow fibers enables significantly increased propylene permeance (reaching 186.5 GPU) while maintaining an appealing propylene/propane selectivity of 13.3 for 50/50 propylene/propane mixed gas feeds. Our findings reveal a more refined and versatile tool than available with previous O2-doping pretreatments. The advanced approach here should be broadly useful to other polyimide precursors and diverse gas pairs.

Ultraselective carbon hollow fiber membrane for H2 extraction from blended natural gas

Blending hydrogen into natural gas (H2NG) pipelines is a feasible solution for low-cost hydrogen delivery while purifying H2 at end-use remains challenging due to its high pressure and low H2 concentration. Herein, biomass-derived carbon hollow fiber membranes (CHFMs) with ultrahigh H2/CH4 separation factor of 4149.0 under a simulated H2NG (10 mol% H2/90 mol% CH4) at 30 bar were reported, and the separation performance maintained within 150 h in a dynamic durability test. Furthermore, the CHFMs showed good stability under fluctuating temperature feeds (up to 100 °C). To evaluate the feasibility of the CHFMs for H2 extraction from H2NG, a three-stage membrane system was designed based on the mixed gas separation performances. It suggested that 99.99 mol% H2 can be achieved with a 90 % recovery, and the specific H2 purification cost was 0.245 $/Nm3 for a 1.8 × 105 Nm3/h production scale, which provides the possibility of hydrogen extraction from H2NG pipelines.

Enhanced water purification performance of composite PVA–ZnO–Al2O3 hollow fiber membrane: A breakthrough approach for high-temperature stability, low-pressure water separation

This work describes the development of a composite Al2O3 hollow fiber combined with multiple-layer ZnO nanoparticles and PVA polymer as the active side for low-pressure saltwater purification. The composite membrane was evaluated with an active layer-facing salt solution, and slight suction condition was applied to the permeate inside the membrane lumen. Results show that varying nanoparticle layers to tune the porosity of the composite membrane influenced its morphology, porosity, and hydrophilicity. The effect of porosity tuning on the membrane characteristics and desalination performance was investigated. A salt rejection rate of >90 % was recorded for all 5 % PVA–ZnO–Al2O3 hollow fiber membranes with the highest salt rejection of 96.34 % and the water flux of 15.49 kg·m−2·h−1. The membrane was further tested with untreated natural seawater to demonstrate its ability to withstand continuous operation. The membrane has acceptable chemical stability when exposed to untreated natural seawater. The optimal PVA–ZnO–Al2O3 hollow fiber membrane exhibited efficient water phase change transfer and high salt rejection, making it a promising candidate for seawater purification.

Spatial variability of cake layer in membrane fouling of full-scale MBR: New insights and implications

The spatial variability of the cake layer formed on the hollow fiber membranes during the operation of a full-scale membrane bioreactor (MBR) has been thoroughly investigated, samples from the bulk phase of the reactor and cakes formed on the membrane surface with different locations (i.e., inner layer of the cake (Cake-I), central layer of the cake (Cake-C), and outer layer of the cake (Cake-O)) were collected. The results showed that the viscous nature of proteins, the main component of extracellular polymeric substances (EPS),as well as the hydrophobicity of the protein secondary structure, were factors that led to variations in particle size (Cake-I = 566 μm > Cake-C = 283 μm > Cake-O = 92.2 μm > Bulk sludge = 59.7 μm) and total interaction energy (Cake-I = −216.39 × 104 KT > Cake-C = −68.35 × 104 KT > Cake-O = −30.42 × 104 KT > Bulk sludge = −30.08 × 104 KT) between the spatially varying cake layers. Numerous filamentous bacteria were found in the MBR, and genes related to membrane plugging processes (such as polysaccharide synthesis, surface attachment, and amino acid degradation) of the microbial community composition were regulated within the cake layers. These new insights could be beneficial to developing fouling control and membrane cleaning strategies.