Surface Of Hollow Fiber Membrane Research Articles

A comparison of three modification methods for polyvinylidene fluoride membrane grafting

Abstract UV-induced covalent bonding, UV-benzophenone (BP) embedding, and ozone-activated grafting methods were respectively used to graft 2-acrylamido-2-methyl-1-propanesulfonic acid (AMPS) on polyvinylidene fluoride (PVDF) hollow fiber membrane surfaces via orthogonal test. The rejection rate, permeating flux, and pure water flux were chosen as comprehensive evaluation indexes to optimize the modification conditions. The optimal experimental conditions for UV-induced covalent bonding, UV-BP embedding, and ozone-activated grafting methods were obtained. Subsequently, three membranes were prepared by these three methods under their optimal modification conditions to compare their properties. The PVDF-g-AMPS-2 membrane obtained by the UV-BP embedding method exhibited the highest hydrophilicity and lipophobicity, and its water and underwater oil contact angles were respectively 66.0° and 146.6°. Besides, The PVDF-g-AMPS-2 membrane can resist the adhesion of oil with the underwater oil adhesion force of zero. What’s more, the PVDF-g-AMPS-2 membrane possessed the largest pure water flux (544.5 L/(m2·h·bar)), permeation flux (66.5 L/(m2·h·bar)), and recovered flux (205.7 L/(m2·h·bar)). By comparison, UV-BP embedding with simpler procedures can fabricate the AMPS modified PVDF membrane with superior performance, which has better application prospects in industrial scale-up production.

Novel self-cleaning PVDF/MoO3/ZnO/GO dual layer hollow fiber photocatalytic membrane with excellent photocatalytic performance of EDCs removal and energy storage capability

Endocrine-disrupting chemicals (EDCs) have a wide range of detrimental effects on health, particularly on the human endocrine system. Efflux This research study involves the application of - molybdenum trioxide, zinc oxide and graphene oxide (MoO3/ZnO/GO) with polyvinylidene fluoride (PVDF) membrane as photocatalytic dual layer hollow fiber (DLHF) membrane as novel energy storage photocatalytic membrane towards efficient degradation of EDCs under visible light illumination. Ternary MoO3/ZnO/GO was synthesized using hydrothermal method and was embedded on the surface of dual layer hollow fiber membrane by dry-wet spinning method by varying the GO loading at 0.1, 0.25 and 0.5 wt%. The results indicated that the 0.5 PVDF/MoO3/ZnO/GO DLHF photocatalytic membrane exhibited improved wettability, high porosity, good water flux, and exceptional EDCs removal, achieving removal rates of 73.08%, 75.80%, 73.65%, 100%, 95.57%, and 53.50% for 1 mg/L BPA, 1 μg/L BPA, 2 μg/L gabapentin, 1 μg/L diclofenac, 10 μg/L caffeine, and 6 μg/L nonylphenol, respectively after 240 min of light exposure. Besides, energy storage capability achieved 96.07% rejection of 1 mg/L BPA in dark condition while stability and reusability test showed 0.5 PVDF/MoO3/ZnO/GO DLHF achieve 74.02% regeneration efficiency after 3 consecutive cycles. Furthermore, the photocatalytic properties of 0.5 PVDF/MoO3/ZnO/GO DLHF could assure a self-cleaning property and increase its lifetime. The PVDF/MoO3/ZnO/GO DLHF photocatalytic membrane served as a versatile 3-in-1 solution, enhancing photocatalytic degradation and rejection capabilities while also serving as a promising energy storage material with self-cleaning properties for removing EDCs from aquatic environments, regardless with or without the presence of light.

'Dark' CO2 fixation in succinate fermentations enabled by direct CO2 delivery via hollow fiber membrane carbonation.

Anaerobic succinate fermentations can achieve high-titer, high-yield performance while fixing CO2 through the reductive branch of the tricarboxylic acid cycle. To provide the needed CO2, conventional media is supplemented with significant (up to 60g/L) bicarbonate (HCO3-), and/or carbonate (CO32-) salts. However, producing these salts from CO2 and natural ores is thermodynamically unfavorable and, thus, energetically costly, which reduces the overall sustainability of the process. Here, a series of composite hollow fiber membranes (HFMs) were first fabricated, after which comprehensive CO2 mass transfer measurements were performed under cell-free conditions using a novel, constant-pH method. Lumen pressure and total HFM surface area were found to be linearly correlated with the flux and volumetric rate of CO2 delivery, respectively. Novel HFM bioreactors were then constructed and used to comprehensively investigate the effects of modulating the CO2 delivery rate on succinate fermentations by engineered Escherichia coli. Through appropriate tuning of the design and operating conditions, it was ultimately possible to produce up to 64.5g/L succinate at a glucose yield of 0.68g/g; performance approaching that of control fermentations with directly added HCO3-/CO32- salts and on par with prior studies. HFMs were further found to demonstrate a high potential for repeated reuse. Overall, HFM-based CO2 delivery represents a viable alternative to the addition of HCO3-/CO32- salts to succinate fermentations, and likely other 'dark' CO2-fixing fermentations.

A simple and effective method to adjust the size of micropores on the inner surface of Polyvinylidene fluoride hollow fiber membranes

AbstractPore‐forming agents affect phase thermodynamics of solution‐case membranes, hence influencing the structure and properties of the membrane. Polyvinylidene fluoride (PVDF) membrane has many advantages, but more in‐depth research is needed regarding directional control of membrane pore size. To solve this problem, a simple and efficient method is proposed. By adjusting the percentage of polyvinylpyrrolidone (PVP) in the casting solution, pore diameter is controlled between 0.01 and 10 μm. The number density and diameter of the inner surface increased significantly with increasing PVP content. The relevance of this study lies in the modulation of the inner surface micropore size of PVDF hollow fiber membranes in a simple and efficient procedure.Highlights Adjusting the size of micropores on the inner surface. The size range of the inner surface is controlled between 0.01 and 10 μm. It is possible to regulate the pore structure by limiting PVP concentration. Significant increase in the number and size of pore on the inner surface. A simple method for regulating the size of micropores.

Advanced (bio)fouling resistant surface modification of PTFE hollow-fiber membranes for water treatment

Membrane surface treatment to modify anti-(bio)fouling resistivity plays a key role in membrane technology. This paper reports on the successful use of air-stimulated surface polymerization of dopamine hydrochloride incorporated ZnO nanoparticles (ZnO NPs) for impeding the intrinsic hydrophobicity and low anti-(bio)fouling resistivity of polytetrafluoroethylene (PTFE) hollow-fiber membranes (HFMs). The study involved the use of pristine and polydopamine (Pdopa) coated PTFE HFMs, both with and without the presence of an air supply and added ZnO NPs. Zeta potential measurements were performed to evaluate the dispersion stability of ZnO NPs prior to immobilization, while morphological characterization and time-dependency of the Pdopa growth layer were illustrated through scanning electron microscopy. Pdopa surface polymerization and ZnO NPs immobilization were confirmed using FT-IR and EDX spectroscopy. Transformation of the PTFE HFM surface features to superhydrophilic was demonstrated through water contact angle analysis and the stability of immobilized ZnO NPs assessed by ICP analysis. Anti-fouling criteria and (bio)fouling resistivity performance of the surface-modified membranes were assessed through flux recovery determination of bovine serum albumin in dead-end filtration as well as dynamic-contact-condition microbial evaluation against Staphylococcus spp. and Escherichia coli, respectively. The filtration recovery ratio and antimicrobial results suggested promising surface modification impacts on the anti-fouling properties of PTFE HFM. As such, the method represents the first successful use of air-stimulated Pdopa coating incorporating ZnO NPs to induce superhydrophilic PTFE HFM surface modification. Such a method can be extended to the other membranes associated with water treatment processes.

A Study of the Phosphorylcholine Polymer Coating of a Polymethylpentene Hollow Fiber Membrane.

A phosphorylcholine polymer (poly(MPC-co-BMA-co-TSMA), PMBT) was prepared by free radical polymerization and coated on the surface of the polymethylpentene hollow fiber membrane (PMP-HFM). ATR-FTIR and SEM analyses showed that the PMBT polymer containing phosphorylcholine groups was uniformly coated on the surface of the PMP-HFM. Thermogravimetric analysis showed that the PMBT had the best stability when the molar percentage of MPC monomer in the polymer was 35%. The swelling test and static contact angle test indicated that the coating had excellent hydrophilic properties. The fluorescence test results showed that the coating could resist dissolution with 90% (v/v%) ethanol solution and 1% (w/v%) SDS solution. The PMBT coating was shown to be able to decrease platelet adherence to the surface of the hollow fiber membrane, and lower the risk of blood clotting; it had good blood compatibility in tests of whole blood contact and platelet adhesion. These results show that the PMBT polymer may be coated on the surface of the PMP-HFM, and is helpful for improving the blood compatibility of membrane oxygenation.

Graphene oxide hollow fiber membranes for solvent dehydration by nanofiltration

Traditional technologies for solvent/water separation such as distillation and chromatography remain energy intensive. State-of-the-art organic solvent nanofiltration (OSN) membranes exhibit high solvent-solute selectivity, but their ability to discriminate between solvents is limited. Graphene oxide (GO) with homogeneous and tunable 2D nanochannels is a promising solution for this purpose, benefiting from its exceptional transport properties. Here, a one-step pressure-assisted cross-linking strategy was applied to coat GO on the inner surface of hollow fiber membranes. The direction of the external driving force during the assembly of the GO selective layers displays an important influence on the microstructure of the nanochannel and the separation performance. The covalent bonding formed at the GO/polyimide (PI) interface and PI substrate endows the membrane with significantly improved stability in solvent environments. The tunable morphology and hydrophilicity characteristic of the GO layer leads to the rapid transport of acetonitrile while impeding the penetration of water molecules. What's more, the migration route of acetonitrile is shorter than that of water in the cross-linked GO nanochannels. In particular, the cross-linked GO hollow fiber (CGHF) membrane exhibits a high acetonitrile permeance of 145.3 L m−2h−1 bar−1, and the dilute acetonitrile solution could be concentrated from 10 wt% to 92.4 ± 3.0 wt%. This means that the elaborately designed nanochannels offer a high energy-efficient prospect for solvent dehydration and OSN.

MoS2-TiO2 coated PVDF-based hollow fiber membranes for permeate flux enhancement in membrane distillation

In this work, the surface of a PVDF-based hollow fiber membrane was modified by coating MoS2-TiO2 to improve the performance of membrane distillation (MD). The MoS2-TiO2 was first synthesized at different ratios using a one-step hydrothermal process. Then, the PVDF-based hollow fiber membrane was spun at various air gaps and PES was also added as an additive. As 5M5T (50 wt% MoS2 and 50 wt% TiO2) possessed better physicochemical properties and narrow band gap, the 5M5T was mixed with trichloro(octadecyl)silane in (OTS) at various loading to form a dip-coating solution. The PP20 membrane (PVDF + PES) spun at a 20 cm air gap was used as a support for MD due to its high porosity and low membrane thickness. It was observed that the contact angle of the MoS2-TiO2/PP20 membrane increased significantly to 136.8 ± 2.33° when the membrane was coated with 0.2% of 5M5T MoS2-TiO2. The MD performances were investigated via an in-house MD system. The results revealed that the performances of MoS2-TiO2/PP20 membranes were much higher than previously reported membranes due to their enhanced hydrophobicity and porosity properties. It was observed that a higher operating temperature could elevate the permeate flux up to 23.3 kg·m−2·h−1, but less than 0.1% changes in the rejection rate. The results obtained in this work suggest that the MoS2-TiO2 coated on the PVDF-based membrane can overcomes the typical permeability/rejection rate trade-off effect, which can play a significant role in enhancing MD performances.

A novel glue attachment approach for precise anchoring of hydrophilic EGCG to enhance the separation performance and antifouling properties of PVDF membranes

A novel glue attachment approach was proposed to form a durable hydration layer on a hydrophobic PVDF hollow fiber membrane (PVDF HFM) surface to improve its hydrophilicity and antifouling ability during wastewater filtration. The functional glue was synthesized from reclaimed styrene butadiene rubber (SBR) and a hydroxyl group was created with an epoxidation reaction (ESBR). The hydrophilic epigallocatechin-s-gallate (EGCG) was then precisely anchored via hydrogen bonding with multiple phenolic hydroxyl groups in the ESBR without penetrating into the inner matrix of the PVDF to prevent flux decline. The hydrophilicity of the PVDF membrane increased drastically and the water contact angle decreased from 62.7° to 45.1° with only a 25% decline in the pure water flux. Furthermore, due to precise anchoring of the EGCG, the modified EGCG-ESBR/PVDF membrane showed a higher pure water flux (110.6 L m−2h−1) and much higher BSA and oil (kerosene) rejection rates (approximately 94.5% and 99.5%, respectively) compared to membranes directly coated with EGCG (EGCG-PVDF). Moreover, the modified membrane also showed higher water flux recovery after multiple filtration cycles. This promising and efficient hydrophilic modification suggests great potential for application of the eco-friendly material in wastewater treatment.

Using Tannic-Acid-Based Complex to Modify Polyacrylonitrile Hollow Fiber Membrane for Efficient Oil-In-Water Separation

Separating oil from water allows us to reuse both fluids for various applications, leading to a more economical process. Membrane separation has been evidenced as a cost-effective process for wastewater treatment. A hollow fiber membrane made of polyacrylonitrile (PAN) is an excellent choice for separating oil from water because of its superior chemical resistance. Its low antifouling ability, however, reduces the effectiveness of its separation. Hence, in this study, we used tannic acid (TA) and FeIII complex to modify the surface of the PAN hollow fiber membrane. To improve membrane performance, different reaction times were investigated. The results demonstrate that even when the TA-FeIII covered the pores of the PAN membrane, the water flux remained constant. However, when an emulsion was fed to the feed solution, the flux increased from 50 to 66 LMH, indicating low oil adhesion on the surface of the modified membrane. When compared to the pristine membrane, the modified membrane had superior antifouling and reusability. As a result, the hydrophilic TA-FeIII complex on PAN surface improves overall membrane performance.

Improved Spherical Particle Preparation of Ceftriaxone Sodium via Membrane-Assisted Spherical Crystallization

Spherical drug particles prepared by the spherical crystallization technique can simultaneously improve the mobility of particles, mechanical properties, drug solubility and bioavailability, etc. However, high-efficient mixing of a solution and the formation of uniform bridging liquid droplets were crucial for accurate control of spherical crystallization processes. Herein, a novel membrane-assisted spherical crystallization (MASC) technology was proposed to produce monodisperse spherical agglomerates of ceftriaxone sodium. The poor solvent permeation rate of MASC was stabilized by adjusting the liquid flow velocity in the shell side and tube side. Uniform bridging liquid droplets constructed by a polytetrafluoroethylene hollow fiber membrane were observed in real time. A stable flow field and crystallization microenvironment were provided on the hollow fiber membrane surface. The crystal size distribution and the coefficient of variation of ceftriaxone sodium products were improved compared with those of conventional spherical crystallization (CSC) under the same stirring rate. The impurities of CSC products did not meet the requirements due to the degradation after 14 days’ acceleration experiment, while the one of MASC products still met the pharmacopoeia requirements after 30 days. This study provides a potential membrane-based technology for the enhancement of spherical crystallization of related drugs.

Cobalt-free SrFe1−xMoxO3-δ perovskite hollow fiber membranes for oxygen separation

SrFe0.95Mo0.05O3-δ (SFM5) perovskite hollow fiber (HF) membranes with a finger-like structure were fabricated by a phase inversion technique. The oxygen flux through SFM5 hollow fiber membrane was evaluated and reached 0.64 μmol/cm2 *s at T = 880 °C, which is 5 times higher than that of a disk SFM5 membrane (0.12 μmol/cm2 *s). A further increase in oxygen fluxes was attained by Ag deposition on the inner surface of SFM5 hollow fiber membrane. The oxygen flux of SFM5 HF membranes is governed by surface-exchange reactions on the permeate side. The equilibrium "3 − δ − lg pO2 − T" diagrams showed that doping of SF by molybdenum leads to a broadening of the cubic perovskite phase stability region.

Inner‐coated highly selective thin film nanocomposite hollow fiber membranes for the mixture gas separation

AbstractPolyamide‐based thin film nanocomposite (TFN) membranes were prepared by incorporating nanoparticles in an aqueous phase containing m‐phenylenediamine (MPD) and an organic phase containing trimesoyl chloride (TMC) by interfacial polymerization (IP) method. The 3‐aminopropyltrimethoxy silane grafted mesoporous synthetic hectorite (APTMSH) was synthesized and added in an aqueous monomer solution while the IP. In this work, the TFN layer interfacial compatibility has been enhanced by building the covalent bond between APTMSH and other two monomers by IP method. The coating of the TFN selective layer was done on the inner surface of polysulfone hollow fiber membranes. The interesting results were obtained for the binary mixture gas separation containing water vapor/N2 and CO2/CH4. Improved gas permeance and selectivity have been obtained using APTMSH‐incorporated TFN membranes. The developed TFN membranes have been characterized using several physicochemical methods. The results show that with the addition of APTMSH in MPD solution up to 0.5 w/w% the best water vapor permeance 2485 GPU and CO2 permeance 22.3 GPU were obtained along with water vapor/N2 selectivity 725.5 and CO2/CH4 selectivity 26.68 respectively through APTMSH@TFN‐3 membrane.

Simulation of novel jellyfish type of process for bioremediation application

A bioinspired device was fabricated as a sustainable remedial method and its performance as a membrane-enzyme reactor with cyclic ultrafiltration was investigated. The body of the jellyfish-like device was composed of two parts: 1) Jellyfish arms: Mono and co-axial electrospinning have been utilized to synthesize the flexible parts (e.g., multilayer membrane PS-PVDF/PAN/PS-PVDF) used for immobilization of aliphatic degrading enzymes, and 2) Jellyfish tentacles: Hollow fiber membranes were selected for physical immobilization of polycyclic aromatic hydrocarbon (PAH) degrading enzymes. To study the behavior of the membrane/enzyme reactor, the hollow fiber enzyme reactor with pulsation was operated by recycling an enzyme solution to assess ultrafiltration efficiency. A mathematical model was suggested to describe the experimental data obtained in this study to predict the effectiveness of the reactor for PAH removal. When testing the performance of the jellyfish-like device, those equipped with nanofibers with an oil sorption capacity of (10. ±0.7gdilbit/gfiber) were more effective at removing oil particles before they touched the hollow fiber membrane surface. Moreover, the reaction rate measured in a free soluble enzyme and a recirculating immobilized enzyme solution exhibited a slight difference in the kinetic parameter, Km (0.03 and 0.021 mM) due to the internal diffusional resistance. Based on biodegradation studies, a synergistic effect between membrane adsorption, enzymatic degradation, and ultrafiltration was proposed for the removal of anthracene from the column of water.

High efficiency and flexible construction of hydrophilic polymer brushes on polyether ether ketone hollow-fiber membrane surface for improving permeability separation, and anti-fouling performances

Polyether ether ketone (PEEK) is a high-performance thermoplastic used as a separation membrane for wastewater treatment, purification, and recycling, especially in harsh environments. However, the applications of PEEK membranes are limited by their processing difficulty, low permeability, and membrane fouling. Herein, a PEEK hollow fibre membrane (PHFM) was fabricated by melt-spinning of polyetherimide (PEI)/PEEK blends and extracting PEI. Thereafter, a hydration layer consisting of 2-hydroxylethyl acrylate (HEA) chains was constructed on the PHFM surface based on the surface-initiated atom transfer radical polymerisation method. The grafting density and grafting length of the HEA chains were modulated by varying the bromination time and ATRP reaction time, and the hydrophilicity of the resulting PHFM surface was enhanced significantly without deteriorating its original porous structure. The controllable pores and hydrated layers on the PHFM surface simultaneously improved the permeability, separation performance, and anti-fouling properties of the membrane. Under a bromination time of 6 h and an ATRP reaction time of 8 h, the water flux of the modified PHFM was enhanced by 364 %. The rejection rate of bovine serum albumin (BSA) by the modified membrane exceeded 90 %. According to the extended Derjaguin–Landau–Verwey–Overbeek theory, the improved anti-fouling performance was related to the weakened acid–base attraction between the foulants and membrane with the hydration layer. After multiple separation-washing cycles, the total fouling and irreversible fouling of the modified PHFM were reduced. The normalised water flux and BSA rejection ratio of the modified anti-fouling PHFM remained 216 % and 90 %, respectively.

Green preparation of PVDF hollow fiber membranes with multiple pore structure via melt spinning method for oil/water separation

Poly(vinylidene fluoride) (PVDF) is one of the most widely used membrane forming polymers with good processability, outstanding mechanical properties, excellent thermal and chemical stability. In this work, PVDF hollow fiber membranes were prepared through the melt spinning method with CaCl2 and PEG as the composite pore forming agents. The influence of different contents of CaCl2 and PEG on the membrane’s structure and properties were studied based on the pore size distribution, porosity, permeation flux, and oil/water separation test etc. There was no obvious dense layer on the PVDF hollow fiber membrane surface, which exhibited multiple pore structure. With the increase of PEG contents, the pore size, the porosity and oil flux improved effectively, correspondingly, the water contact angle and liquid entry pressure decreased. The permeation fluxes of kerosene also increased obviously with the increase of PEG contents, and the maximum flux of M-3 reached as high as 398.4 L·m-2·h-1. Applied to oil/water separation test, M-3 exhibited good oil/water separation performance, and its separation efficiency for water-in-kerosene emulsion can still reach more than 95 % after ten cycles. In particular, there were not any solvents and diluents used in the preparation process, which was a relatively green preparation process.

A novel method to immobilize zwitterionic copolymers onto PVDF hollow fiber membrane surface to obtain antifouling membranes

Zwitterionic materials are considered to be a promising new-generation non- or low-fouling materials. However, stable, and straightforward introduction of zwitterions into membranes for commercial production remains as a big challenge yet. Herein for the first time we propose a simple approach to immobilize zwitterionic copolymers on poly(vinylidene fluoride) (PVDF) hollow fiber membrane (HFM) surfaces with considerably high stability via surface entrapment and subsequent simple reactions. First, a commercial amphiphilic copolymer, viz. styrene–maleic anhydride (PSMA), was entrapped on the outer surface of PVDF membranes using co-extrusion by a triple orifice spinneret. PSMA exhibited excellent stability on the PVDF membrane, and its reactive anhydride (MA) group was stabilized on the outer membrane surface. Next, the commercially available zwitterionic copolymer poly(2-methacryloyloxyethyl phosphorylcholine-co-2-aminoethyl methacrylate hydrochloride) (P(MPC-AEMA)) was immobilized on the PVDF/PSMA membrane surface by a simple reaction between the MA groups of PSMA and the amine groups of P(MPC-AEMA). The P(MPC-AEMA) reacted membrane exhibited noticeable bovine serum albumin (BSA) antifouling and antibacterial properties during both static adsorption and dynamic filtration. The flux recovery ratio (FRR) of the membrane exceeded 80% after seven cycles of BSA filtration. The modified membrane showed an even higher FRR (∼95%) during bacterial filtration, and such excellent performance was attributed to its super hydrophilicity. Our novel, advanced and straightforward modification method lights on a spotlight for a new pathway to make immobilization of zwitterions on polymeric membrane without needing complicated reactions or procedures.

MO272: Effect of the Hollow Fiber Diameter and Membrane Surface Area of the Polymethyl Methacrylate Membrane Filter Used in Continuous Renal Replacement Therapy on the Lifetime of the Filter

Abstract BACKGROUND AND AIMS When polymethyl methacrylate (PMMA) membranes are used in renal replacement therapy, inflammatory cytokines and other substances are removed by adsorption. However, these filters are also prone to clogging and the filter lifetimes are likely to be short. In the present study, we investigated the effects of the hollow fiber inner diameter and membrane area of PMMA membranes on the filter lifetime and protein removal performance using an in vitro continuous hemofiltration (CHF) experimental model with porcine blood. METHOD Three filters with different hollow fiber inner diameters and membrane areas were used: CH-1.0N (membrane area, 1.0 m2; hollow fiber inner diameter, 200 µm), CH-1.0W (prototype: 1.0 m2; 240 µm), and CH-1.8W (1.8 m2; 240 µm). Blood samples from one pig were divided into three portions, and in vitro CHF experiments for each filter were performed at QB = 100 mL/min and QS = QF = 10 mL/min. The pressure changes, total protein concentration in the blood, and total protein amount in the filtrate were measured during the experiments. From the results of the pressure changes, the time for the TMP to reach 200 mmHg (corresponding to the time when the membrane pores were clogged) and the time for the pressure drop through the filter to reach 200 mmHg (corresponding to the time when the hollow fibers were clogged) were calculated as the filter lifetime for comparative evaluation. RESULTS The time for the TMP to reach 200 mmHg was significantly longer with CH-1.8W than that with CH-1.0N or CH-1.0W (Friedman test, P < .05, n = 15). The time for the pressure drop through the filter to reach 200 mmHg was significantly longer with CH-1.8W than that with CH-1.0N or CH-1.0W (Friedman test, P < 0.05, n = 15). The results suggest that an increased membrane surface area is an essential factor for extending the filter lifetime. The total protein adsorption was significantly higher for the CH-1.0W and CH-1.8W filters than for the CH-1.0N filter (two-way ANOVA and post hoc Tukey test, P < 0.01, n = 15). Thus, the membranes with larger hollow fiber inner diameters (CH-1.8W and CH-1.0W) adsorbed more protein. CONCLUSION A larger membrane area contributes to a longer filter lifetime, whereas increase in the hollow fiber inner diameter does not. On the other hand, the protein removal performance, especially the adsorption performance, was higher for membranes with larger hollow fiber inner diameters.

The effect of aeration mode on the operational effectiveness and membrane bioreactors for greywater treatment and membrane fouling

This study aims to investigated the effect of aeration mode on membrane bioreactors (MBRs) using a self-designed integrated hollow fiber MBR and flat sheet organic MBR for rural greywater treatment. The pollutant removal efficiency, characteristics of activated sludge and mixed liquor, and mechanisms of membrane fouling were systematically analyzed under intermittent aeration and continuous modes. The results indicate that the permeability of MBRs in intermittent aeration mode is higher than that in the continuous aeration mode when operating at the same aeration rate. Due to the higher extracellular polymeric substance (EPS) and soluble microbial product (SMP) concentrations. The removal rates of TN and TP by both MBRs at the intermittent aeration mode were higher than those in the continuous aeration mode due to the difference in the aeration environment. Compared to the flat-sheet organic membrane, the hollow-fiber membrane surface was more likely to form biofilms, which cause biological fouling.The relative abundance of Thermomonas showed a positive correlation with the EPS concentration, indicating that Thermomonas participates in EPS synthesis. This study provides a theoretical basis for evaluating the influence of aeration modes on MBRs,and would be a useful guide for the better control of membrane fouling and treatment of rural greywater.

Fabrication of hollow fiber nanofiltration separation layer with highly positively charged surface for heavy metal ion removal

Efficient concentration and separation of heavy metal ions from wastewater are crucial for environmental protection and resource recovery. In this research, a double highly positively charged nanofiltration (NF) separation layer was constructed on the outer surface of hollow fiber membranes for the first time via surface grafting and iodomethane (CH3I) quaternization. The separating properties for Ni2+, Cu2+ and Cr3+ were measured at different concentrations and pressures, and the long-term stability and anti-fouling property of the membrane were investigated. The relationship between the positively charged degree of surface, pore size, and rejection of heavy metal ions were interpreted by comparing the discrepancies in microstructures and separating properties of membranes. The membrane can efficaciously remove Ni2+ (99.4%), Cu2+ (99.6%), and Cr3+ (99.9%) while maintaining a high permeability (30.9, 29.6 and 28.5 L m−2 h−1 bar−1). The high permeability (about 27.9 L m−2 h−1 bar−1) and rejection (>99%) were retained even after 72 h of operation. Moreover, the membrane exhibited a good anti-fouling property for heavy metal ions. This study offers the reference for preparing hollow fiber NF membrane with stable microstructure, highly positively charged surface and high efficiency for the removal of heavy metal ions.