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A synthetic hormone, 17α-ethynylestradiol (EE2), has received much attention due to its widespread occurrence and adverse effects on aquatic animals. The removal of EE2 from water has been very challenging mostly because of its low concentration in environmental waters. Here we report a simple and novel approach for concentrating EE2 through adsorption and elution using microporous polyethersulfone (PES) hollow fiber membrane in a cross-flow filtration system, which can be easily scalable for practical applications. Our results showed that microporous PES hollow fiber membrane has a high EE2 adsorption capability (∼100% from water containing 20 μg/L of EE2) and the adsorbed EE2 could be eluted using a small volume of 10% ethanol solution to achieve a recovery efficiency of 75.9 ± 8.5%. We further demonstrated that the PES hollow fiber membrane maintained ∼100% removal of EE2 throughout five cycles of adsorption and elution. Our results from molecular simulation suggest that the strong affinity between PES and EE2 is mainly attributed to the π- π interaction and the hydrogen bonding. This proof-of-concept demonstrates for the first time that PES hollow fiber membrane system can remove EE2 at low concentrations, and elute EE2 solutions at a much higher concentration over multiple cycles in a sustainable and environmentally-benign condition. [ABSTRACT FROM AUTHOR]

This study investigated the fouling behavior and chemical cleaning of forward osmosis (FO) membranes for treating produced/process water (PPW) from a real gas field using thin-film composite FO hollow fiber membranes. Experiments revealed that membrane fouling occurred during the PPW treatment, which hindered the water and solute transport through the membrane. The water permeability and FO reference water flux of the membrane decreased by 22.9% and 24.8%, respectively, after fouling. Membrane surface characterization was carried out, and the results indicated the deposition and entrapment of organic species on the membrane after the PPW treatment. The efficiencies of various cleaning agents, including sodium dodecyl sulfate (SDS), ethylenediaminetetraacetic (EDTA) and NaOH, were evaluated. It was found that cleaning with SDS for 15 min is the most effective method for restoring water flux, and very stable FO performance can be obtained during batch treatment of PPW. The FO membrane can reduce the PPW volume by 50% at a relatively high average water flux of 15.6 L·m − 2 ·h − 1 in the active layer facing feed solution orientation using 1 M NaCl as draw solution (equivalent to the draw solution available in the field). This study demonstrates the great potential of FO technology for produced/process water treatment. [ABSTRACT FROM AUTHOR]

[Display omitted] • Microfiltration PTFE hollow fibres were transformed into durable, high value OSN membranes. • A PEI/PIP based polyamide thin film was successfully synthesized on PTFE hollow fibre substrates. • A two-time interfacial polymerization was conducted to obtain a defect-free polyamide layer. • The resultant membranes could withstand strong aprotic solvents like DMF and DMSO. • The membranes had high solute rejections, of up to 95 % methyl orange (327 Da) rejection in DMF. Polymeric membranes have been extensively studied for organic solvent nanofiltration (OSN) but many fail to show sufficient chemical resistance in strong solvents like dimethylformamide (DMF) and dimethyl sulfoxide (DMSO). This study focuses on harnessing the outstanding chemical resistance of polytetrafluoroethylene (PTFE), to develop polyamide-PTFE thin film composite (TFC) membranes that are resistant to such aprotic solvents. A defect-free polyamide thin film layer was successfully synthesized on the microfiltration PTFE hollow fibre substrates, overcoming challenges such as large and uneven pore size, and hydrophobicity of the PTFE substrates. A simple polydopamine (PDA) coating was carried out to improve the substrate's hydrophilicity prior to the polyamide synthesis via interfacial polymerization (IP). Polyethyleneimine (PEI) and trimesoyl chloride (TMC) were used as the monomers and a two-time IP method was employed to obtain a defect-free polyamide coating. The synthesized membranes showed high acetonitrile (ACN) and DMF permeabilities of 7.94 and 3.70 lm−2h−1bar−1, respectively, with acid fuchsin (585 Da) rejections of > 90 %. The molecular weight cut-off (MWCO) of the membranes could be further reduced to ∼300 Da by the addition of piperazine (PIP) monomers. The membranes also showed excellent stability and performance in a 72-hour OSN test performed in DMF indicating their great potential in effective molecular separation in harsh solvents. This study demonstrates how a simple modification and coating technique can transform commercially available microfiltration PTFE hollow fibres into durable and high value OSN membranes. [ABSTRACT FROM AUTHOR]

Pressure retarded osmosis (PRO) is a promising energy harvesting technique. However, when polymeric hollow fiber membrane is used for the PRO process, the mechanical strength of the membrane is a big concern. As hollow fiber membrane is self-supported and due to its polymeric nature, it may gradually deform over time under high pressure loading, or membrane “creeping” will occur. Current work is the first attempt to analyze the membrane creeping phenomenon of a novel thin film composite (TFC) hollow fiber. The membrane creeping was evaluated via nanoindentation by using atomic force microscope (AFM). A non-stop 200-hour PRO test and integrity check, which have not been reported previously, were carried out to investigate the membrane performance under various operating pressures. The results show that the membrane is able to produce a stable power density output of 19.2 W/m 2 at 15.0 bar, using 1.0 M NaCl as the draw solution and DI water as the feed water. Membrane creeping was observed when the applied pressure exceeded the safe operation limit (or the flux turning point, where the membrane flux started to increase with increasing applied pressure in the PRO mode), which caused an irreversible damage to the membranes. This study identified safe and optimum operation conditions of the laboratory-made PRO hollow fiber membrane to achieve the most favorable PRO performance. It provides guidance for practical applications of polymeric hollow fiber membranes in PRO process. [ABSTRACT FROM AUTHOR]

Due to its toxicity to ecosystem, phenol removal from industrial wastewater before discharge is a priority concern. Extractive membrane bioreactor (EMBR), a novel wastewater treatment process combining aqueous–aqueous extractive membrane process and biodegradation, has shown potential in treating phenol in wastewater. In this paper, composite hollow fiber membranes with different levels of poly(dimethylsiloxane) (PDMS) intrusion were prepared by coating a layer of PDMS on a Polyetherimide (PEI) hollow fiber substrate. Their applicability to EMBR for phenol removal was studied. The prepared membranes were characterized by microscopy and gas permeation test, and their performances were evaluated in aqueous–aqueous extractive membrane processes and EMBR process. The overall mass transfer coefficient for phenol, or k 0 , was found to be significantly affected by the level of PDMS intrusion in the composite membranes. This is because the penetration of PDMS into the porous substrate results in a denser membrane structure, which consequently increases the membrane resistance. A slight penetration of PDMS into the substrate was found to be necessary for the composite membranes to achieve high k 0 while maintaining low inorganic flux across the membranes. Wilson-plot analysis suggests that membrane resistance dominated over liquid boundary layer resistances. After more than 250 h of EMBR operation, significant biofilm growth was observed on the composite membranes and the k 0 was dropped but stabilized at around 7.5×10 −7 m/s. This k 0 was 7.5 times higher than commercial PDMS tubular membranes (without biofilm development) reported in previous studies, confirming the superiority of thin film composite membranes prepared in this work. It was also found that process optimization to control biofilm thickness is important in order to enhance phenol removal rate in EMBR. [ABSTRACT FROM AUTHOR]

Novel composite forward osmosis (FO) hollow fiber membranes with two selective skin layers were developed in the present work. The polyethersulfone (PES) hollow fiber substrate was firstly fabricated by a phase inversion method. The RO-like polyamide skin layer was then prepared on the inner surface of the hollow fiber substrate via interfacial polymerization (IP), while the NF-like outer skin layer was prepared via polyelectrolyte layer-by-layer (LBL) assembly. Three double-skinned membranes with negative (DS#1.5), positive (DS#2.0) and minimal (DS#2.5) outer surface charges under neutral pH environment were evaluated for their capabilities against organic fouling in the FO process. The newly developed double-skinned membranes possess water permeability greater than 2 l/m 2 h bar and NaCl rejection higher than 95% under 2 bar pressure, and have superior water flux and less salt leakage than the commercial HTI FO membranes as well as all the reported double-skinned FO membranes with RO-like selective layers. Most importantly, the double-skinned DS#2.5 hollow fiber membrane exhibits exciting organic fouling resistance because of its highly hydrophilic NF-like secondary layer with minimal surface charge and tightened surface structure to mitigate possible substrate pore clogging and fouling layer formation. A stable water flux of around 25 l/m 2 h was attained for DS#2.5 membrane using <0.5 M NaCl as the draw solution and a water containing 200 ppm dextran (DEX) or Aldrich humic acid (AHA), or lysozyme (LYS) and 10 mM NaCl as the model feed in the active layer against the draw solution (AL-DS) configuration, suggesting its great potential for practical FO applications. [ABSTRACT FROM AUTHOR]

In this study, the self-assembly of rare-earth Anderson polyoxometalates (POMs) on the surfaces of imide polymeric hollow fiber membranes was designed for fabrication of novel POMs-functionalized interfacial composite membranes. The rare-earth Anderson POM ([Gd(H 2 O) 7 Cr(OH) 6 Mo 6 O 18 ] n ) nanoparticles with controllable size and distribution were successfully constructed. Experimental results revealed that the self-assembly was a surface-induced growth process. The silanol groups on the membrane surfaces generated by the (3-aminopropyl)trimethoxysilane pretreatment were essential for the self-assembly process because of the potential hydrogen bonding ( OH⋯POMs) and coordination bonding ( OH Gd) interactions. This work provided a simple but practical method not only for the fabrication of novel POMs-functionalized membranes, but also for the synthesis of POMs nanoarchitectures. In addition, the potential application of the as-prepared POMs-functionalized hollow fiber membranes in degradation of organic pollutant has also been explored. The idea of interfacial membrane contactor has been utilized for the catalytic wet air oxidation of phenol under mild conditions. A three-phase (gas/catalyst/liquid) interface was successfully built up, which enhanced the catalytic efficiency. It is anticipated that these novel POMs-functionalized membranes can promisingly be used as catalytic membrane contactors for wastewater treatment under mild conditions. [ABSTRACT FROM AUTHOR]

Aquaporins are water channel proteins with high permeability and solute rejection, making them ideal components for the preparation of desalination biomimetic membranes. In one strategy, E. coli aquaporin Z (AqpZ) proteoliposomes are immobilized in a polyamide layer formed by interfacial polymerization at the inner surface of hollow fibers. However, once polymerization occurs, the system is almost a black box where it is difficult to disentangle the relative contribution to performance of (i) water permeation through AqpZ channels and (ii) the possible modification of the properties or structure of the polymer layer by the mere presence of protein and lipid. Indeed, the fate of protein and lipid once the polymer is formed, and how much of it is actually used, is under debate. Also, the performance of these modules has been reported to be stable over several months. This is intriguing because of the expected degradation of functional AqpZ and lipid with time. Herein, we used lipid and AqpZ, both fluorescently labeled, to unequivocally localize both components only at the inner surface of the hollow fibers. To characterize module performance, we tested about 30 half-inch modules containing five hollow fibers each. Those reconstituted with wild type AqpZ produced higher permeability (∼8.5 ± 0.9 LMH/bar) than those reconstituted with AqpZ mutant (R189A) (∼5.6 ± 1.7 LMH/bar) or lipid-only liposomes (3.7 ± 1.1 LMH/bar). However, while these differences are significant, they are smaller than expected from the comparison of relative permeabilities of membranes incorporating wild-type AqpZ, R189A mutant and only-lipid. In addition, we show that in a five-month long experiment, performance of two of these modules showed only minor deterioration, if any, which is not consistent with the observed rapid degradation of proteoliposomes at room temperature. Overall, these data obtained in this set-up suggests that although both AqpZ and lipid are localized at the inner of the hollow fibers, they mainly behave as additives that modify the properties of the robust polyamide layer. A small contribution of AqpZ channel activity to module performance is possible, but to be significant it would require full coverage and a higher protein density in the proteoliposomes, which at present cannot be achieved in the current protocol. [Display omitted] • Thirty half-inch modules (5 hollow fibers each) were tested. • Fluorescent lipid and AqpZ are only found co-localized with the IP layer. • Modules perform better with wild type AqpZ than with R189A inactive mutant. • Module performance does not directly correlate with proteoliposome permeability. • Long-term module performance is inconsistent with degradation of proteoliposomes. [ABSTRACT FROM AUTHOR]

The ultra-permeable membranes (UPMs) are expected to reduce the specific energy consumption (SEC) of desalination, but the potential of UPMs in hollow fiber configuration has not been well quantified. Herein, we analyse the SEC and footprints of UPM modules in three feed salinities: seawater reverse osmosis (SWRO), brackish water RO (BWRO) and low-pressure RO (LPRO). Through the modelling the fluid dynamics and mass transport of RO systems, we find that a tripling in spiral-wound SWRO membrane permeability (based on the current value of 1 L m−2 h−1 bar−1; LMH/bar) could result in 16% decrease in SEC. Contrastingly, the quadrupling of hollow fiber SWRO membrane permeability (based on the current value of 0.25 LMH/bar) could reduce the SEC by 23%. According to our analysis, hollow fiber and spiral-wound SWRO membranes with permeabilities up to 1 LMH/bar and 3 LMH/bar, respectively, can reduce the SEC of seawater desalination. On the other hand, membranes with permeabilities up to 9 LMH/bar and 12 LMH/bar can lead to SEC savings in BWRO and LPRO desalination, respectively. This study provides a general guidance to RO membrane researchers on the permeability upper-limit of which UPMs could bring about SEC and footprint savings at a system level. [Display omitted] • Energy savings achievable by high permeability RO membranes were quantified. • Modelling was performed by simulating fluid dynamics in various RO configurations. • Hollow fiber SWRO membranes (up to 1 LMH/bar) could reduce energy consumption. • Spiral-wound SWRO membranes (up to 3 LMH/bar) could reduce energy consumption. • High permeability RO membranes could bring about greater benefits in BWRO/LPRO. [ABSTRACT FROM AUTHOR]

The use of nanotechnology in water separation membranes is a promising approach to alleviate the global water crisis. Graphene oxide (GO) with its unique water transport property has exhibited high potential for application in the water treatment processes. In this study, we have designed and fabricated a novel nanofiltration (NF)-like GO surface deposited poly(amide-imide)–polyethyleneimine (PAI–PEI) hollow fiber membrane. The PAI hollow fiber substrate was prepared by phase inversion and modified with PEI to obtain a positively charged membrane surface. The negatively charged GO nanosheets were then electrostatically immobilized onto the membrane surface via an instant dip-coating to form the NF-like selective layer. Our results have shown that the GO nanosheets serve as effective selective barriers and can achieve higher water permeability up to 86% without compromising membrane selectivity when used to substitute part of the PEI cross-linked selective layer. This is attributed to the smaller hydrodynamic resistance of GO nanosheets and their ability to effectively narrow the pore size distribution. Moreover, shortening of the membrane modification time and better mechanical properties of the GO modified membrane can be attained by avoiding excessive PEI cross-linking. The GO deposition also exhibits good stability when subjected to a backwashing pressure of 100,000 Pa and a cross-flow rate of 600 mL/min, which corresponds to a velocity of 14 cm/s and a Reynolds number of ~870. These results have demonstrated a high potential of using this GO modified hollow fiber membrane for large scale water softening applications. [ABSTRACT FROM AUTHOR]

The layer-by-layer (LbL) self-assembly is a common method for fabricating nanofiltration (NF) membranes. However, most multilayers are usually too thick and lack the necessary attributes to endow NF membranes with good permselectivity. In this study, we present a polyelectrolyte multilayered method by integrating dopamine as a "bio-glue". A three-step deposition was applied to the negatively charged PES substrate surface, following an alternate sequence of poly(allylamine hydrochloride) (PAH), dopamine (DA) and poly(sodium 4-styrenesulfonate) (PSS). The dopamine molecules were intercalated between the PAH and PSS layers to achieve a thinner thickness, higher hydrophilicity, smaller surface roughness and narrower pore size distribution. The resultant flat sheet (PAH/DA/PSS)4 polyelectrolyte multilayered (PEM) membranes exhibited enhanced water permeability (more than 60% increment from 13.5 to 21.9 LMH/bar) and higher rejection toward divalent ions (increasing MgCl 2 rejection from 91.0% to 94.8%) as compared with the control (PAH/PSS)4 NF membrane. Furthermore, the developed LbL method was applied on hollow fiber membrane modules and was able to achieve a higher Li+/Mg2+ selectivity from 15.6 to 37.8 and Na+/Mg2+selectivity from 11.0 to 19.1 using different simulated brines as feed solutions. On the whole, this polyelectrolyte multilayered method shows great potential for practical applications, including groundwater softening, seawater pretreatment and lithium extraction. [Display omitted] • A novel three-step LbL self-assembly method was proposed by integrating dopamine. • Dopamine intercalated selective layer exhibited a thinner and smoother surface. • The NF (PAH/DA/PSS)4 membrane showed better water permeability and higher divalent ion rejection. • Higher Na+/Mg2+ and Li+/Mg2+ selectivity was achieved due to the smaller pore size distribution. [ABSTRACT FROM AUTHOR]

A scaled-up hollow fibre thin-film composite (TFC) module was successfully developed for organic solvent forward osmosis (OSFO) application in the pharmaceutical industry. The membrane consists of cross-linked P84 polyimide substrate with a polyamide selective layer, formed via interfacial polymerisation. The performance of the lab-scale module was compared to the scaled-up module in reverse osmosis and forward osmosis modes. The results from both tests revealed that the solvent permeability of the scaled-up module decreased while its selectivity increased slightly. This might be caused by the uneven distribution of liquids during interfacial polymerisation, leading to varied membrane performance. The scaled-up module was further tested for OSFO performance using a range of PEG-400 concentrations (0.5–2 M) in acetone and isopropanol as draw solutions. At 2 M PEG-400 concentration, the module demonstrated high isopropanol and acetone permeability of 0.63 LMH and 13.9 LMH, respectively. Moreover, the reverse solute flux of PEG-400 in acetone and isopropanol were relatively low at 0.188 g/l and 0.153 g/l, respectively. The module was further tested for OSFO application in the pharmaceutical industry by concentrating levofloxacin in acetone, using 2 M PEG-400 as draw solution. The process was able to concentrate levofloxacin from 1000 ppm to 16,000 ppm with very low reverse solute flux of 0.178 g/l. Therefore, this work presents a scalable TFC membrane for OSFO application in the pharmaceutical industry. [Display omitted] • Scaled-up module (0.4 m2) of TFC hollow fibre membrane for organic solvent forward osmosis process was successfully fabricated. • High porosity (79%) and low structural parameter (217 μm) for membrane substrate was achieved. • Membrane exhibited excellent acetone and IPA solvent flux of 13.9 LMH and 0.63 LMH, respectively, using a 2 M PEG-400 draw solution. • A pharmaceutical stream was concentrated to a factor of 16 with low specific reverse solute flux [ABSTRACT FROM AUTHOR]

A scaled-up hollow fibre thin-film composite (TFC) module was successfully developed for organic solvent forward osmosis (OSFO) application in the pharmaceutical industry. The membrane consists of cross-linked P84 polyimide substrate with a polyamide selective layer, formed via interfacial polymerisation. The performance of the lab-scale module was compared to the scaled-up module in reverse osmosis and forward osmosis modes. The results from both tests revealed that the solvent permeability of the scaled-up module decreased while its selectivity increased slightly. This might be caused by the uneven distribution of liquids during interfacial polymerisation, leading to varied membrane performance. The scaled-up module was further tested for OSFO performance using a range of PEG-400 concentrations (0.5–2 M) in acetone and isopropanol as draw solutions. At 2 M PEG-400 concentration, the module demonstrated high isopropanol and acetone permeability of 0.63 LMH and 13.9 LMH, respectively. Moreover, the reverse solute flux of PEG-400 in acetone and isopropanol were relatively low at 0.188 g/l and 0.153 g/l, respectively. The module was further tested for OSFO application in the pharmaceutical industry by concentrating levofloxacin in acetone, using 2 M PEG-400 as draw solution. The process was able to concentrate levofloxacin from 1000 ppm to 16,000 ppm with very low reverse solute flux of 0.178 g/l. Therefore, this work presents a scalable TFC membrane for OSFO application in the pharmaceutical industry. [Display omitted] • Scaled-up module (0.4 m2) of TFC hollow fibre membrane for organic solvent forward osmosis process was successfully fabricated. • High porosity (79%) and low structural parameter (217 μm) for membrane substrate was achieved. • Membrane exhibited excellent acetone and IPA solvent flux of 13.9 LMH and 0.63 LMH, respectively, using a 2 M PEG-400 draw solution. • A pharmaceutical stream was concentrated to a factor of 16 with low specific reverse solute flux [ABSTRACT FROM AUTHOR]

Abstract: The layer-by-layer (LBL) polyelectrolyte deposition was applied on polyethersulfone (PES) hollow fiber ultrafiltration membrane to prepare nanofiltration (NF) membrane for low pressure water softening application for the first time. The effects of polyelectrolyte type and molecular weight (MW), deposited bilayer number, polyelectrolyte solution pH and supporting electrolyte concentration on the performance of resultant membranes were studied thoroughly. Experiments revealed that the pH of the polyelectrolyte solution and supporting electrolyte concentration presented the most notable effects. For weak poly-cations, Poly(ethylenimine) (PEI) and Poly(allylamine hydrochloride) (PAH), the solution pH affected the membrane performance significantly, and high water permeability and divalent cation rejection were obtained at optimum pH values. Using a low concentration of supporting electrolyte at underneath layers was proved to be an effective way to increase water permeability while maintaining high salt rejection. A salt water flux (SWP) of 12LMH/bar and 94% Mg2+ rejection was obtained by depositing only two bilayers of PSS/PAH polyelectrolytes on the PES substrate, while for the 3000ppm mixed salt solution, the water permeability was 11LMH/bar with Mg2+ and Ca2+ rejection as high as 90%. These promising results demonstrate that LBL technique is potentially applicable for preparing low-pressure water softening hollow fiber membranes. [Copyright &y& Elsevier]

Highlights: [•] Effect of intrinsic properties of foulants on FO membrane performance was studied. [•] Diffusivity governs hollow fiber membrane performance in FO mode. [•] Flat sheet membrane performance in PRO mode was controlled by combined mechanisms. [•] The mechanisms include diffusivity, size exclusion and electrostatic interactions. [ABSTRACT FROM AUTHOR]

Abstract: A novel functionalized multi-walled carbon nanotube (MWCNT) immobilized polyethyleneimine–poly(amide–imide) (PEI–PAI) hollow fiber membrane was designed and fabricated using an easily scalable method. PAI hollow fiber was spun via phase inversion, followed by functionalized MWCNTs immobilization via vacuum filtration before a chemical post-treatment using PEI was applied to obtain a positively charged selective layer. The resulting membranes were evaluated in the forward osmosis (FO) process. The membrane prepared using a 0.62mg/L of MWCNTs solution shows a pure water permeability of 4.48L/m2hbar with a MgCl2 rejection of 87.8% at 1bar. This is a 44% enhancement in water permeability without significant compromise on the salt permeability when compared to membranes without MWCNTs. In addition, FO water flux of membranes prepared using 0.31 and 1.25mg/L of MWCNTs solutions have also been enhanced up to 29% without compromising the solute flux in the active layer facing feed water orientation using 0.5M MgCl2 solution as the draw solution and deionized water as the feed water. These encouraging results suggest that hollow fiber membranes immobilized with commercial MWCNTs exhibit good potential to be further developed for applications in the FO process. [Copyright &y& Elsevier]

Thin-film composite (TFC) membranes are generally preferred over integrally skinned asymmetric (ISA) membranes in pressure retarded osmosis (PRO) process due to their much higher water permeability, but they cannot operate in the active layer facing feed solution (AL-FS) orientation because of potential delamination of the rejection layer under the high applied pressure. However, operating under AL-FS orientation is preferred as a strategy for better fouling control. Hence, in this study, three ISA hollow fiber membranes were fabricated using a dry-jet wet-spinning method, followed by chemical cross-linking to obtain membranes for PRO application. The best-performing membrane was subjected to fouling test in two orientations. Our results demonstrate that the AL-FS orientation is better for a sustainable long-term PRO operation, given the stable performance throughout the two-day testing. Also, the current use of power density per membrane area as a performance benchmark may not be practical for large-scale PRO operation, and the volumetric power density per module is more relevant. In terms of volumetric power density for a hypothetical 5-in. module, our best-performing membrane is predicted to generate a 3.6 to 10 times better power density than commercial modules, rendering our ISA hollow fiber membranes promising for scaling-up to bigger modules. [Display omitted] • Operating under AL-FS orientation is preferred as a strategy for better fouling control. • Integrally skinned asymmetric hollow fiber membranes were developed for AL-FS orientation in PRO. • The membranes achieved sustainable power production when wastewater was employed. • The volumetric power density was predicted to yield promising solution for practical application. [ABSTRACT FROM AUTHOR]

Thin-film composite (TFC) membranes are generally preferred over integrally skinned asymmetric (ISA) membranes in pressure retarded osmosis (PRO) process due to their much higher water permeability, but they cannot operate in the active layer facing feed solution (AL-FS) orientation because of potential delamination of the rejection layer under the high applied pressure. However, operating under AL-FS orientation is preferred as a strategy for better fouling control. Hence, in this study, three ISA hollow fiber membranes were fabricated using a dry-jet wet-spinning method, followed by chemical cross-linking to obtain membranes for PRO application. The best-performing membrane was subjected to fouling test in two orientations. Our results demonstrate that the AL-FS orientation is better for a sustainable long-term PRO operation, given the stable performance throughout the two-day testing. Also, the current use of power density per membrane area as a performance benchmark may not be practical for large-scale PRO operation, and the volumetric power density per module is more relevant. In terms of volumetric power density for a hypothetical 5-in. module, our best-performing membrane is predicted to generate a 3.6 to 10 times better power density than commercial modules, rendering our ISA hollow fiber membranes promising for scaling-up to bigger modules. [Display omitted] • Operating under AL-FS orientation is preferred as a strategy for better fouling control. • Integrally skinned asymmetric hollow fiber membranes were developed for AL-FS orientation in PRO. • The membranes achieved sustainable power production when wastewater was employed. • The volumetric power density was predicted to yield promising solution for practical application. [ABSTRACT FROM AUTHOR]

Municipal solid waste (MSW) gasification is an attractive waste-to-energy (WTE) technology with promise for future solid waste management, owing to the production of syngas which can be used as an alternative energy resource. However, quality of produced syngas is not meeting expectation. One promising solution is to use oxygen-enriched gas (OEG) to elevate produced syngas quality but producing OEG is costly. Herein, we demonstrated an asymmetric defect-free hollow fiber membrane made up of Matrimid® 5218 polyimide for scaling-up to 2-inch membrane modules. Our modules have an effective surface area up to 2.6 m2 with a packing density of up to 44% to produce OEG of 45% O 2 purity. The 2-inch membrane module was integrated into a lab-scale gasification process to produce syngas using refuse derived fuel (RDF) generated from MSWs collected from the university campus. Prior to this, the lab-scale gasification was first optimized by tuning the gasification temperature, O 2 purity and equivalence ratio (ER). Then, MSW gasification using membrane-based OEG was carried out, and compared against air gasification and synthetic OEG of the same O 2 purity. Our results showed that, at O 2 purity of 45%, gasification temperature of 900 °C and ER of 0.15, the quality of produced syngas was elevated with a lower heating value (LHV) of 9.15 MJ/m3 and H 2 /CO ratio of 1.43, which was substantially higher than air gasification with LHV and H 2 /CO ratio reported at 5.38 MJ/m3 and 0.81, respectively. Gasification results for membrane-based OEG and synthetic OEG were also comparable, while process simulation evidence suggested that membrane-based separation was at least 2-fold less energy-intensive than cryogenic distillation and pressure swing adsorption. Overall, this proof-of-concept successfully demonstrates the viability and competitiveness of membrane process for producing OEG at medium O 2 purity (i.e. , 40–50%) to support MSW gasification for WTE conversion. [Display omitted] • Hollow fiber membrane modules with up to 2.6 m2 surface area were developed. • OEG with O 2 purity of c.a. 45% can be produced at close to 2 L/min flow rate. • Membrane-based OEG gasification produces syngas with 70% higher LHV as that of air gasification. • Membrane-based OEG produces syngas with comparable LHV as that of synthetic OEG. • Simulation shows that membrane separation is less energy-intensive for producing OEG of medium purity. [ABSTRACT FROM AUTHOR]

Abstract: Great efforts from the membrane community have been devoted in developing suitable membranes for forward osmosis (FO) applications in recent years. In the current study, the layer-by-layer (LBL) polyelectrolyte assembly technique has been successfully applied onto a microporous polyethersulfone (PES) hollow fiber substrate to make novel LBL hollow fiber membranes suitable for FO process for the first time. The FO performance of the LBL hollow fibers with different numbers of deposited layers has been evaluated using deionized (DI) water as the feed and MgCl2 solution of various concentrations as the draw solution in both orientations. With 6 layers deposited and in the active layer facing draw solution (AL-facing-DS) orientation, the membrane showed high water fluxes of 14.6, 25.9 and 40.5L/m2 h with corresponding salt to water flux, J s /J v, ratio of 0.034, 0.066 and 0.201g/L using 0.05, 0.1 and 0.5M draw solution, respectively. These promising results demonstrate the potential application of the LBL hollow fibers in FO process using low concentration draw solutions, which can substantially reduce the draw solution replenishment, and the energy consumption for draw solution regeneration and separation. [Copyright &y& Elsevier]

Abstract: Dual layer hollow fiber membranes have become increasingly attractive due to their many benefits made possible by one-step fabrication using the non-solvent induced phase inversion method. Obtaining a good lamination between the two layers as well as a regular morphology are critical to make a usable hollow fiber membrane. This study aims to explore the mechanism of the lamination/delamination phenomenon and regular/irregular morphology that can occur in the fabrication of dual layer hollow fiber membrane. Simultaneous extrusion of poly(amide-imide) and polyethersulfone (PES) dope solutions was carried out by using a triple orifice spinneret. Thermodynamic properties and phase separation kinetics of the polymer dopes as well as various spinning parameters were carefully tailored in order to investigate the evolution of the membrane morphology and structure. A series of experiments have confirmed that when the external coagulant, water, has a higher diffusion rate in the outer layer than in the inner layer, the outer layer tends to expand to form large macrovoids and to hold more water at the interface. As a result, the accumulated water probably impedes the adhesion of the two layers, leading to a delamination of two layers. On the other hand, if water has a slower penetration rate through the outer layer dope than the inner layer dope, a good adhesion between these two layers is expected. Under this scenario, since macrovoids formed in the inner layer may lead to the expansion of the inner layer, a distortion of the finger-like structure/macrovoids in the inner and an irregularity of the inner contour may occur. This study provides a solid foundation to develop superior dual layer hollow fiber membranes with an inter-penetrating dual layer structure. [Copyright &y& Elsevier]

Abstract: This research focused on combined organic–inorganic fouling and cleaning studies of forward osmosis (FO) membranes. Various organic/inorganic model foulants such as sodium alginate, bovine serum albumin (BSA) and silica nanoparticles were applied to polyamide-polyethersulfone FO hollow fiber membranes fabricated in our laboratory. In order to understand all possible interactions, experiments were performed with a single foulant as well as combinations of foulants. Experimental results suggested that the degree of FO membrane fouling could be promoted by synergistic effect of organic foulants, the presence of divalent cations, low cross-flow velocity and high permeation drag force. The water flux of fouled FO hollow fibers could be fully restored by simple physical cleaning. It was also found that hydrodynamic regime played an important role in combined organic–inorganic fouling of FO membranes. [Copyright &y& Elsevier]

Abstract: Forward osmosis (FO) process as an alternative to conventional desalination techniques has attracted much attention in recent years. Since mineral salt scaling is one of the major limitations for seawater desalination, the current study focused on the behaviors of thin film composite (TFC) FO hollow fibers, which were fabricated in our laboratory, under the circumstance of calcium sulfate (CaSO4) scaling with sodium chloride as draw solution. The performance of FO hollow fiber membranes was compared with commercially available FO flat sheet membranes. Several cleaning strategies were also explored. Depending on the membrane orientation, experimental results suggested that the scaling of the FO hollow fibers was dominated by cake layer formation along with pore blocking in the orientation of active layer facing draw solution (AL-DS). The pore blocking could be a result of the penetration of crystals from the feed solution into the support matrix of the membrane, or the formation of crystals inside the porous support layer. At the same driving force, the water flux of the FO hollow fibers in the orientation of active layer facing feed solution (AL-FS) was twice higher than the water flux of the flat sheet membrane in both orientations. The water flux of scaled FO hollow fibers and flat sheet membranes in the AL-DS orientation could be successfully restored by hydraulic backwash procedure. To the best of our knowledge, this is the first study to examine the inorganic scaling of FO membranes in the AL-DS orientation. [Copyright &y& Elsevier]

Abstract: The performance of a forward osmosis (FO) system may be characterised by the assessment parameters: FO–RO flux ratio (J w/J w(RO)), apparent FO water permeability (J w/(π ds − π ml)), and the newly developed flux efficiency factor (J w,ob/J w,re). The former two parameters offer information on extent of internal concentration polarisation and driving force utilisation, respectively. The J w,ob/J w,re factor has practical relevance, and reveals the inevitable trade-off between flux and recovery (φ) for a FO system. The derived J w,ob/J w,re factors corresponded well to experimental observations. High water permeability, low salt-to-water permeability ratio, and large mass transfer coefficient improve the performance of a FO system, but these may also be influenced by operational and fouling effects, such as draw solute transmission, fouling resistance and cake-enhanced concentration polarisation. It was shown that membrane properties also play a significant role in fouling behaviour. Fouling amelioration factors include aeration and osmotic backwash. A thin-film composite membrane showed potential for FO application with favourable intrinsic transport parameters. It was demonstrated that a FO system could achieve stable water production with both relatively high flux efficiency (J w,ob/J w,re =0.8) and high recovery (φ =95.8%), which attested to the technology potential. [Copyright &y& Elsevier]

Abstract: Forward osmosis (FO) is an emerging osmotically driven membrane process, and its applications are becoming diversified. As one important membrane configuration, hollow fiber modules have been applied to some innovative FO processes, e.g., osmotic membrane bioreactor (OMBR). Aside from the inherent concentration polarization (CP) phenomena, new challenges are posed by the coupled concentrating and dilution effects in the design of FO hollow fiber modules. In this paper, a mathematical model is therefore developed to account for the evolution of the local performances within the FO hollow fiber module and to evaluate the global performances of interest. Then, this model is employed to theoretically investigate the filtration behaviors of the FO hollow fiber module by using the well-defined dimensionless groups, which indicates the complex interplay among a variety of design parameters. Particularly, the optimization objectives are focused on enhancing the module-averaged FO efficiency and avoiding the severe concentration variations in the module channels. In terms of the simulation results, some criteria are obtained for optimizing the operating conditions (flow configuration, inlet concentration level, inlet flow rate), the hollow fiber characteristics (fiber length), and the FO membrane properties (active layer selectivity, support layer transport resistance). This work provides deep insights into the design of the FO hollow fiber module, and could be readily modified to accommodate more complicated cases. [Copyright &y& Elsevier]

A 100-piece hollow fibre thin-film composite membrane module was successfully developed for pharmaceutical concentration and solvent recovery. To increase its packing density, thinner P84 polyimide hollow fibre substrates were spun using a smaller spinneret. The substrates were subsequently cross-linked with hexamethylene diamine to achieve organic solvent resistance. An MPD-based thin-film composite was synthesized through interfacial polymerisation to increase selectivity for solutes of less than 300 Da. The thin-film composite was then solvent-activated using N , N -dimethylformamide to increase its solvent permeability. The resulting membrane exhibited excellent performance with 24.2 l m−2 h−1 bar−1 acetone permeability and 90.1% methyl red (269 Da) rejection. In addition, the solvent-activated membrane maintained its performance for prolonged period, demonstrating the scalability of the thin-film composite fabrication process and stability of solvent-activated membranes. The membrane was also able to concentrate levofloxacin (361 Da) from 500 ppm to 20,000 ppm in acetone using a batch process, showing promising results for pharmaceutical applications. Image 1 • 100-piece thin-film composite OSN membrane was successfully fabricated. • 7-day filtration test showed stable organic solvent nanofiltration (OSN) performance. • High acetone permeability of 24.2 l m−2 h−1 bar−1 and 90.1% methyl red rejection. • Active pharmaceutical ingredient was concentrated to 2 wt%. [ABSTRACT FROM AUTHOR]

The use of amphiphilic copolymer Pluronic F127 as an additive has shown effectiveness in fabricating polyethersulfone (PES) membranes with excellent antifouling properties due to its roles in enhancing pore structure and surface hydrophilicity. However, F127 was found to be unstable in polyvinylidene fluoride (PVDF) membranes as its hydrophilic modifying function was deactivated over time. In present work, we developed a novel approach to immobilize F127 in PVDF hollow fiber membranes using polytetrafluoroethylene (PTFE) particles as a binding agent through the combined nonsolvent and thermally induced phase separation (N-TIPS) method. The results suggest that the hydrophobic segment of F127 could adsorb firmly onto PTFE with the hydrophilic segments protruding outwards. The dual-functions of F127 were observed in pore formation and surface hydrophilization for PVDF membranes. The water contact angle of PVDF/PTFE/F127 membranes decreased from 102 ± 4° to 76 ± 3° compared with membranes without additives. The resultant membranes possess a pure water permeability (PWP) of 869 ± 39 L m−2h−1bar−1 with a mean pore size of 0.09 ± 0.01 μm and an outstanding tensile strength of 7.0 ± 0.3 MPa, suggesting the potential of N-TIPS method for tuning the membrane pore structure and hydrophilicity by using multifunctional additives. Image 1 • PTFE or Pluronic-F127 could effectively help tailor bulk and surface properties of PVDF membranes through N-TIPS method. • The instability of F127 in PVDF membranes was significantly relieved in the presence of PTFE. • The mediating effect of PTFE allowed F127 to be a pore-former and surface hydrophilic modifier for PVDF membranes. • The prepared PVDF/PTFE/F127 membranes possess a narrower pore size distribution. • The membrane has improved porosity, tensile strength, hydrophilicity and antifouling property. [ABSTRACT FROM AUTHOR]

Biocatalytic nanofiltration (NF) membranes incorporated with enzymes show high capacity for micropollutants (MPs) removal. However, there remains significant challenges such as the lack of molecular-level tailoring for skin layer design and effective strategy for enzyme immobilization. In this work, layer-by-layer (LBL) assembly based biocatalytic NF membranes were fabricated for bisphenol (BPA) removal by immobilizing laccase into the skin layer during the LBL polyelectrolytes assembly with controlled crosslinking and immobilization. This strategy enables simultaneous enzyme immobilization and NF skin layer formation. Three laccase immobilization strategies (i.e. , post immobilization, post crosslinking, and post crosslinking and immobilization) on skin layer were explored to prepare NF membrane for evaluating BPA removal efficiency. The post immobilization was identified as the optimal strategy, which endowed the biocatalytic NF membrane with a pure water permeability of 10.9 ± 0.4 LMH/bar and MgCl 2 rejection of 97.2 ± 0.3% under 2 bar pressure, alongside competitive laccase loading (238.8 ± 3.5 μg/cm2) and laccase activity (0.6 U/cm2). The optimal biocatalytic NF membrane exhibited an improvement in BPA removal of 79.5% under an incubation mode and 92.5% under a full recycling mode. The removal efficiencies were ~240% higher than that of the unmodified LBL membrane and clearly comparable to other reported biocatalytic membranes. This performance was attributed to the synergistic effect of membrane rejection, adsorption and laccase catalysis. The optimal biocatalytic NF membrane was found to be robust after six cycles within 14 days, while maintaining a relatively high BPA removal efficiency and salt rejection. Overall, our results open up a new avenue for enzyme immobilization into the skin layer of membranes for designing high-efficient biocatalytic NF membranes for MPs removal. Image 1 • Laccase-decorated LBL skin layer is prepared on lumen side of hollow fiber membrane. • Effects of different laccase immobilization strategies on BPA removal are explored. • Post immobilization strategy endows the membrane with a competitive NF performance. • Desired BPA removal efficiency is achieved with optimal biocatalytic membrane. • The long-term reusability and stability for BPA removal are confirmed. [ABSTRACT FROM AUTHOR]

External concentration polarization (ECP) remains a pervasive challenge for submerged forward osmosis (FO) systems, as it critically reduces the water flux of membranes. In this study, we propose to use transverse vibration on hollow fiber membranes to effectively reduce the ECP and increase the FO water flux performance. The effects of different vibrating amplitude and frequency were investigated. Also, the vibration effect was evaluated under different draw solution concentrations, membrane orientations and draw solute types. Our results show increased water flux with increasing vibrating intensity (i.e., amplitude and frequency) while maintaining a constant specific reverse solute flux (J s /J w). At the highest amplitude (1.2 cm) and frequency (3 Hz) used, the mass transfer coefficient is increased from 0.7 × 10−5 m s−1 (at no vibration) to 1.8 × 10−5 m s−1, which falls within the optimal flux range as determined from our FO modelling results. The increment in mass transfer coefficient is found to be closely related to the improved hydrodynamic conditions due to vibration, and less dependent on the membrane orientation and draw solution concentration. In addition, both modelling and experimental results show that maintaining a reasonably high mass transfer coefficient is especially important for FO process with severe ECP conditions, such as when dilutive ECP is present (i.e., active-layer-facing-feed-solution orientation) or when a high water flux is applied (usually in the active-layer-facing-draw-solution orientation). However, the severe ECP arising from large draw solutes (e.g., larger sized polymer with low diffusivity and high viscosity) might not gain greater benefits from the vibration or improved hydrodynamic conditions. Image 1 • Transverse vibration can mitigate ECP and improve flux in submerged FO processes. • Increasing vibration intensity increases mass transfer coefficient at membrane surface. • Maintaining a high mass transfer coefficient is important for severe ECP conditions. • Severe ECP resulting from large draw solutes cannot gain more benefits from vibration. [ABSTRACT FROM AUTHOR]

Polyamide thin film membranes have shown outstanding performance in organic solvent nanofiltration (OSN). However, it is still challenging to produce polyamide hollow fibres for OSN, mainly due to limited solvent resistance of hollow fibre substrates and the difficulty to synthesize polyamide thin film on the surface of hollow fibre substrates. In this study, polyamide-based hollow fibre composite members for low pressure OSN were successfully developed. Solvent resistant polyimide hollow fibre substrates were first prepared through a non-solvent induced phase separation process, followed by chemical cross-linking with hexamethylene diamine. A polyamide thin film layer was then synthesized via interfacial polymerization, by circulating the reactant monomers including polyethyleneimine (PEI), piperazine (PIP) and trimesoyl chloride (TMC) through the hollow fibre lumen. The polyamide thin film with a thickness of ~60 nm was formed on the inner surface of the hollow fibre substrates. The membranes exhibited excellent nanofiltration (NF) performance under 2 bar operating pressure. The permeability of water, acetone and isopropanol was 6.8, 11.6 and 4.5 l m−2 h−1 bar−1, respectively. The membranes also achieved 99.9% and 91.8% rejection to rose bengal (1017 Da) and acid fuchsin (585 Da), respectively, in acetone. Furthermore, a 72-h filtration test was conducted and the membrane showed steady performance throughout the testing period. This study demonstrates the possibility of fabricating polyamide hollow fibre membranes for organic solvent nanofiltration at low pressure, which is desirable for practical applications. • Solvent resistant polyimide hollow fibre membranes were fabricated through chemical cross-linking. • Polyamide-based (PEI/PIP) layer was formed onto polyimide substrate to obtain a relatively loose selective layer. • Membranes achieved 11.6 and 4.5 l m−2 h−1 bar−1 permeability in acetone and isopropanol at 2 bar respectively. • Membranes maintained more than 90% rejection for acid fuchsin in 72-h filtration test, showing stable OSN performance. [ABSTRACT FROM AUTHOR]