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The photocatalytic membranes have been reported to treat textile dye effluents; however, it is challenging to maintain their long-term functionality due to the poor binding stability of nanoparticles on the membrane surface and the low stability of the membrane to UV radiation. To address this, PVDF photocatalytic hollow fiber membranes were prepared by coating with polydopamine (PDA) for 1–4 h, then with titanium dioxide nanoparticles (TiO 2) in the current study. SEM and EDX results showed that TiO 2 adhered firmly to the PDA-pretreated membrane after ultrasonic treatment. The PDA layer protected the membranes from UV irradiation. The PVDF-TiO 2 membrane without PDA pretreatment was destroyed after 24 h of UV irradiation, while after 9 days of continuous irradiation, the membranes treated with PDA for 2 h remained unchanged. Compared with the original membrane, applying PVDF membranes coated with PDA for 2 h and TiO 2 for 1 h increased the Reactive Red 239 rejection and flux recovery rates by 13% and 40%, respectively, achieving 60% COD removal. The permeate flux and dye rejection rate were stable after 5 cycles (20 h of operation). This study demonstrates that the obtained membranes can perform prolonged membrane filtration with high-performance durability for dye wastewater treatment. [Display omitted] • TiO 2 was strongly bonded to the PVDF membrane pretreated with PDA. • Introducing PDA-TiO 2 enhanced the stability of dye permeate flux and dye rejection. • The PVDF-PDA-TiO 2 membranes significantly improved the COD removal efficiency. • PVDF-PDA-2h-TiO 2 -1 h membrane showed excellent resistance to UV and reusability. • Self-protecting/cleaning, hydrophilicity, and durability of membrane all improved. [ABSTRACT FROM AUTHOR]

The focus of whey processing has been changed from waste treatment to the production of valuable products owing to the advancement of membrane technology. Producing high quality whey products at low energy consumption entails novel techniques for whey concentration. This study proposes forward osmosis (FO) as a potential approach to concentrate whey protein solutions, which is superior to the concentration via reverse osmosis (RO), mainly owing to the low hydraulic pressure during FO process. In particular, this work validated the feasibility of FO-based whey concentration using high-performance hollow fiber membranes that were fabricated in-house. The investigation focused on the effects of various operating conditions on the concentration performance. The experimental results reveal that optimal concentration efficiency would be achieved by appropriately choosing the cross-flow velocity, draw solution concentration and the maximum attainable concentration of whey protein solution. Especially, the flux decline behaviour as a function of the whey protein concentration in the feed solution indicated rapid formation of a polarized or gel foulant layer at the membrane surface. The proposed mechanism was supported by the investigation of physical cleaning with water, showing that the post-process cleaning after the concentration cycle was able to recover the membrane performance, whereas the intermediate cleaning during one concentration cycle had little impact on the concentration efficiency enhancement. This study has practical significance for the application of FO in the concentration of dairy streams and other liquid foods. [ABSTRACT FROM AUTHOR]

Abstract: Due to the unique properties of amphiphilic Pluronic block copolymers, they have been blended with other polymers such as PVDF to prepare membranes. Considering the stability issue, the strong pore-forming ability of Pluronic F127, and the mechanical strength of the resultant membranes, Pluronic/LiCl mixed additive consisting of a very low concentration of Pluronic has been used in this study. The effects of spinning conditions on PVDF hollow fiber fabrication have also been studied. It is found that the use of merely 0.2wt% of Pluronic is sufficient to impose significant impacts on the morphology, filtration performance, and mechanical properties of the resultant fibers. Hollow fibers spun using higher coagulant temperature, higher take-up speed, and water as the bore fluid exhibit better mechanical properties and filtration performance. PVDF hollow fiber membranes with PWP of 1180L/m2 hMPa and MWCO of 5kDa were obtained when spun with optimized spinning conditions and using 3wt% of LiCl and 0.2wt% of Pluronic as the mixed additive. The fibers can withstand a pressure of 0.55MPa from the lumen. [Copyright &y& Elsevier]

In a gas–liquid membrane contactor, a larger pore size can result in a lower membrane mass transfer resistance. However, the membrane pore size is usually limited by the concern of pore wetting, e.g. a large pore size means a higher wetting tendency. As a breakthrough, this paper reported a porous polyetherimide (PEI) hollow fiber membrane with high surface porosity and large pore size to minimize the membrane mass transfer resistance by using a triple-orifice spinneret in the hollow fiber spinning process, and followed by a novel approach of fluorinated silica (fSiO2) nanoparticles (NPs) incorporation to make the membrane surface highly hydrophobic and chemical resistant to prevent the membrane from wetting caused by the large pore size on the membrane surface. The newly developed composite hollow fiber membranes showed the advancing contact angle value of 123.3°, receding contact angle value of 107.2°, and contact angle hysteresis of only 15.9°, indicating the high water resistant property. The composite membrane also exhibited a higher rigidity property compared with the original PEI substrate. The CO2 absorption flux of the composite membranes was investigated in both physical and chemical absorptions in a gas–liquid membrane contactor system. The membrane contactor showed a stable performance throughout the 60d long-term operation using a 2M sodium taurinate aqueous solution as the liquid absorbent. The highly hydrophobic composite hollow fiber membrane was able to outperform a conventional polymeric hydrophobic membrane in term of superior gas absorption flux and outstanding long-term stability, suggesting that the formation of organic–inorganic composite membranes is an effective way to enhance the feasibility of membrane contactor processes for practical applications. The results demonstrated the important role of membrane fabrication and modification techniques in facilitating the commercialization of membrane contactor technology. [ABSTRACT FROM AUTHOR]

Abstract: Pressure retarded osmosis (PRO) is a promising membrane process to harvest the vast amount of free energy from the mixing of fresh and salty waters without adverse environmental impacts. A competent membrane for PRO should possess the features of high water permeability to allow water permeation, excellent salt rejection to maintain the osmotic driving force, low structure parameter to minimize the internal concentration polarization (ICP), and robust strength to withstand the required hydraulic pressure. In this work, we have developed a novel hollow fiber membrane by balancing these competing factors based on our prior experience in the thin-film composite (TFC) membranes. The newly developed TFC hollow fiber membrane can achieve a power density of 20.9W/m2 at a pressure of 15bar, using synthetic seawater brine (1.0M NaCl) as the draw solution and synthetic river water (1mM NaCl) as the feed water, respectively. The simultaneous specific reverse salt flux was found to be 0.03mol/L, which is much lower than reported flat-sheet membranes, as the self-supported hollow fiber membrane can eliminate the deformation-enhanced reverse salt diffusion that is typical for flat-sheet membranes. However it was observed that the water permeability and structure parameter of the TFC hollow fiber membrane varied noticeably corresponding to the change in the hydraulic pressure imposed in the fiber lumen. Over a certain range (ΔP<15bar), such variations of increasing A value and decreasing S value proved to have positive impacts, as they facilitate the water permeation and reduce the ICP in the PRO process. [Copyright &y& Elsevier]

Abstract: A novel dual-layer forward osmosis (FO) hollow fiber membrane has been designed and successfully fabricated by using a triple orifice spinneret. The fiber consists of two layers made from polyamide-imide (PAI) polymer for the outer layer and polyethersulfone (PES) polymer for the porous inner layer. Specifically, after obtaining asymmetric microporous PAI/PES dual-layer hollow fibers via non-solvent induced phase inversion, polyethyleneimine (PEI) polyelectrolyte modification on the outer PAI layer was applied to produce a nanofiltration (NF)-like thin layer, while the PES porous inner layer remained intact as PES is inert to PEI. The membrane morphology, structure and surface property were carefully tailored by adjusting polymer dope composition and spinning conditions. These membranes were subsequently characterized by a series of standard protocols in terms of membrane structure, permeability and salt rejection, and were utilized in FO process. It was found that the resultant dual-layer NF hollow fiber membrane can achieve pure water permeability of 15.9lm−2 h−1 bar−1 and a high rejection to divalent cations up to 89%. In FO process, the dual-layer hollow fiber exhibited a water flux of 27.5lm−2 h−1 in the orientation of active layer facing feed water by using 0.5MMgCl2 as draw solution and de-ionized (DI) water as feed at room temperature. The newly developed dual layer hollow fibers outperform all the single layer and dual-layer NF hollow fibers reported in the literature for FO applications. [Copyright &y& Elsevier]

Abstract: One of the major barriers that hinder the application of forward osmosis (FO) processes is the lack of optimized membranes that possess high water flux, low salt leakage and good anti-internal concentration polarization (ICP) and anti-fouling/anti-scaling properties during practical FO operations. In this study, novel composite FO hollow fiber membranes with an RO-like selective skin and an NF-like secondary selective skin were successfully developed for the first time. The fabrication procedures involved making ultrafiltration hollow fiber substrate using poly(amide–imide) (PAI) polymer material via phase inversion method, followed by interfacial polymerization (IP) and chemical modification to yield a polyamide RO-like inner skin and a positively charged NF-like outer skin, respectively. It was found that the sequence of conducting IP on the substrate inner surface prior to the chemical modification of the outer skin was preferred in order to achieve better performance for the resultant double-skinned hollow fibers. The newly developed FO hollow fibers exhibited high water permeability of 2.05L/m2 hbar and 85% rejection to NaCl at 1bar pressure as well as superior FO water flux of 41.3L/m2 h and low ratio of salt flux over water flux of 0.126g/L when using DI water and 2.0M NaCl as feed and draw solutions, respectively, in the active layer facing draw solution (AL-DS) orientation. Furthermore, the experimental results showed that the composite FO hollow fiber membrane was able to outperform single-skinned membrane when the feed contains divalent ions or the feed exhibits high scaling tendency to membrane. This suggested that the integration of RO- and NF-like two selective skins in FO membrane is an effective way to minimize the ICP effect, mitigate the membrane scaling and thus enhance the feasibility of FO processes for practical applications. [Copyright &y& Elsevier]

Abstract: A new type of forward osmosis (FO) hollow fiber membranes with an antifouling nanofiltration (NF)-like selective layer has been developed in this work. The fabrication involves a step of porous poly(amide-imide) (PAI) ultrafiltration (UF) hollow fiber spinning via phase inversion, followed by simple polyelectrolyte post-treatments using positively charged polyethyleneimine (PEI) for cross-linking and negatively charged polystyrene sulfonate sodium salt (PSS) for deposition. The membranes are subsequently characterized by a series of standard protocols and evaluated in FO process. The PAI FO membranes possess a pure water permeability of 3.7–4.3Lm−2 h−1 bar−1 and Na2SO4 rejections up to 85% at 1bar. In the FO process, the membranes can achieve water flux of 17 and 12Lm−2 h−1 for active layer facing draw solution (AL-facing-DS) and active layer facing feed water (AL-facing-FW) configurations, respectively, using a 2000ppm Na2SO4 aqueous solution as the feed and 0.5M Na2SO4 as the draw solution. When the feed contained 1000ppm bovine serum albumin (BSA) and 2000ppm Na2SO4, a steady water flux of 11Lm−2 h−1 can be maintained using 0.5M Na2SO4 as the draw solution at ambient temperature of 23°C. The approach of making FO membranes developed in the present study offers the advantages of simple fabrication process, tailorable selective layer and promising membrane performance for protein-contained wastewater treatment by FO process. [Copyright &y& Elsevier]

Abstract: For the first time, a specially designed pressure retarded osmosis (PRO) hollow fiber membrane has been successfully developed and applied in the PRO process to demonstrate its potential for power generation. The membrane fabrication method is similar to that used for making thin-film composite (TFC) forward osmosis hollow fiber membranes, but further optimization and improvement have led to a new type of TFC hollow fiber membranes with much greater mechanical strength in addition to its excellent separation property and high water flux. The TFC PRO hollow fiber membranes have a water permeability (A) of 9.22×10−12 m/(sPa), salt permeability (B) of 3.86×10−8 m/s and structural parameter (S) of 4.6×10−4 m. It can withstand hydrostatic pressure as high as 9bar with its relatively large dimension of 0.98mm lumen diameter. This PRO hollow fiber membrane is superior to all other PRO membranes reported in the open literature in terms of power density. A power density as high as 10.6W/m2 can be achieved using seawater brine (1.0M NaCl) and wastewater brine (40mM NaCl), which suggests that the newly developed PRO hollow fiber membrane has great potential to be applied in PRO processes to harvest salinity gradient energy. A higher pressure is preferred as it allows generation of higher power density (pressures of 12bar may be optimal for seawater as the high salinity stream), and this can be realized by reduced fiber dimension. Further optimization of the membrane structure will be performed. [Copyright &y& Elsevier]

Abstract: Five types of novel hollow fiber module configurations with structured-straight fibers, curly fibers, central-tubing for feeding, spacer-wrapped and spacer-knitted fibers, have been designed and constructed for the direct contact membrane distillation (DCMD) process. Their module performances were evaluated based on permeation flux experiments, fluid dynamics studies, and tracer-response tests for flow distribution as well as process heat transfer analysis. The novel designs showed flux enhancement from 53% to 92% compared to the conventional module, and the spacer-knitted module had the best performance. The fluxes of all the modified configurations, except the structured-straight module, were independent of the feed flow velocity, and the modules with undulating membrane surfaces (curly and spacer-knitted fibers) were able to achieve more than 300% flux improvement in the laminar flow regime. The improved performance was attributed to the improved fiber geometries or arrangements that can provide effective boundary layer surface renewal and more uniform flow distribution, confirmed by the sodium chloride tracer response measurements. The heat transfer analysis underscores the advantage of the module with curly fibers with the least temperature polarization effect (temperature polarization coefficient=0.81–0.65 at T m =303–333K), which is favorable for enhancing permeation flux. [Copyright &y& Elsevier]

Abstract: The outer surface of polyvinylidene-co-hexafluoropropylene (PVDF–HFP) asymmetric microporous hollow fiber membrane prepared by phase inversion process was activated by 10wt.% of NaOH solution, and subsequently modified with the mixture solution of α,ω-triethoxysilane terminated perfluoropolyether or Fluorolink®S 10 (FS10) and tetraethoxysilane (TEOS) in order to enhance the hydrophobicity of the membrane. The chemical and physical changes of the membranes were investigated by attenuated total reflection infrared spectroscopy FTIR-ATR and scanning electron microscope (SEM). The characteristics of the modified membrane were examined in terms of liquid entry pressure of water (LEPw), pore size and pore size distribution, contact angle and mechanical properties. The modified fibers were also used in the membrane contactor system to evaluate their performance for CO2 absorption. FTIR-ATR result showed the enrichment of fluorine and ethoxysilane on the modified PVDF–HFP membranes leading to higher LEPw and contact angle than those of the unmodified membrane by 36% and 33%, respectively. The contact angle increased from 95.5° to 127.8°. Compared to the unmodified PVDF–HFP hollow fiber, the cross-sectional morphology and mechanical properties of the modified membrane changed insignificantly, while the membrane mean pore size was reduced from 32.7nm to 25.2nm. The CO2 physical absorption performance of the modified fibers was better than the unmodified fibers. The membrane mass transfer coefficients of the unmodified and modified PVDF–HFP hollow fiber were 5.69×10−5 and 7.56×10−5 m/s, respectively, indicating that the modified membranes have good potential for application in the gas absorption process. [Copyright &y& Elsevier]

Abstract: Membrane wetting is a major concern for the application of membrane contactors. In order to develop a novel hydrophobic membrane that can be used in membrane contactors, a hydrophobic surface modification method for Torlon® polyamide-imide (PAI) membrane was explored, which has not been reported previously. Asymmetric microporous hollow fiber membranes were fabricated using PAI material followed by a simple surface modification using a silane coupling agent, 3-aminopropyltrimethoxysilane (APTMS), and a perfluro-compound (Fluorolink S10) to produce PAI hollow fiber membranes with a hydrophobic surface. The reactions between PAI and the modification reagents have been confirmed by experiments. Optimal modification conditions were investigated by varying the modification parameters, such as APTMS treatment temperature, APTMS concentration, APTMS treatment time, and Fluorolink S10 treatment time. The modified PAI membranes were, subsequently, characterized by a series of standard protocols in terms of membrane morphology, chemical structure, contact angle, porosity and critical water entry pressure. A preliminary study of using the modified membranes in a membrane contactor for CO2 absorption was also carried out. The newly developed PAI hollow fiber membranes showed much higher hydrophobicity, the contact angle was improved from 76° to 108–117° and the critical water entry pressure was improved from 0.7–0.8bar to 2.1–4.0bar. Moreover, the modified PAI hollow fiber membranes showed reasonably high CO2 flux by using water as a physical absorption liquid. The results indicate that the modified PAI membranes have great potential to be used in membrane contactor applications. [Copyright &y& Elsevier]

Abstract: The amphiphilic Pluronic triblock copolymers of poly(ethylene oxide) (PEO) and poly(propylene oxide) (PPO) have received much attention recently as both the surface modifier and pore former in membrane fabrication. In this study, a systematical study has been carried out to investigate the effect of Pluronics with different molecular architectures and contents as a pore-forming additive on the fabrication of polyethersulfone (PES) ultrafiltration (UF) hollow fibers, and to identify the most preferential features of Pluronic for making high performance membranes. The as-spun hollow fibers were characterized in terms of cross-sectional membrane morphology, membrane surface chemistry, mechanical properties, pure water permeation (PWP), molecular weight cut-off (MWCO), and pore size distribution. It was observed that the PWP and MWCO of the as-spun hollow fibers are dependent on the structure of additives. Among all the membranes spun with 5wt% additives, the hollow fibers spun using Pluronic F127 and F108 as the additives possess the highest PWP, the lowest MWCO, and the narrowest pore size distribution. It is possible that the PEO brush layer formed on the internal pore surface by Pluronic F127 and F108 might reduce the apparent pore size and hence improved the solute rejection of the resultant membranes. A comparison between Pluronic and poly(ethylene glycol) (PEG) as additives also confirmed the importance of the presence of PPO chain in Pluronic in the formation of high-performance membranes. When Pluronic F127 concentration was 10wt%, the as-spun hollow fiber exhibited the highest PWP of 113.8L/m2 hbar and the lowest MWCO of 9kDa. [Copyright &y& Elsevier]

Abstract: Hollow fiber membranes with a positively charged nanofiltration (NF)-like selective layer have been successfully fabricated by utilizing asymmetric microporous hollow fibers made of Torlon® polyamide–imide (PAI) material as the porous substrate followed by polyelectrolyte post-treatment using polyethyleneimine (PEI), which has not been reported previously. The reaction between PAI and PEI has been confirmed by experiments. The membrane structure and surface property are carefully tailored by adjusting polymer dope composition, spinning conditions and the post-treatment parameters. These membranes are, subsequently, characterized by a series of standard protocols in terms of membrane morphology, structure, permeability and salt rejection, and are applied in forward osmosis (FO) processes. The newly developed PAI hollow fiber membranes show a pure water permeability of 2.19–2.25L/m2 hbar and reasonable NaCl and MgCl2 rejections of 49% and 94% at 1bar, respectively. It is also found that in FO processes, when using 0.5M MgCl2 as a draw solution and DI water as the feed in the active layer facing feed water (AL-facing-FW) configuration at 23°C, the water fluxes of two PAI FO hollow fiber membranes are 8.36 and 9.74L/m2 h, respectively, and the J S /J V of the two membranes is smaller than 0.4g/L, which is lower than the data of 0.85g/L for commercial FO membrane from Hydration Technologies Inc. (HTI). Different from a neutral membrane, the positively charged FO membrane provides double electric repulsions to the salt transfer through the membrane in the AL-facing-FW configuration, leading to a reduction of salt penetration, while in the active layer facing draw solution (AL-facing-DS) configuration, the positive charges facilitate salt transportation. This study provides a simple and effective approach to make hollow fibers suitable for FO applications. [Copyright &y& Elsevier]

Abstract: Polyvinylidene fluoride-co-hexafluropropylene (PVDF-HFP) has received much attention recently as a promising membrane material for membrane contactor application. A systematic study has been carried out to investigate the effects of polyethylene glycol (PEG) with different molecular weights and different loadings as an additive on the fabrication of PVDF-HFP asymmetric microporous hollow fiber membranes. Moreover, the synergetic effects of coagulation temperature and the second additive (lithium chloride: LiCl) with PEG are also evaluated. Experiments revealed that the addition of PEG into the PVDF-HFP/NMP solution resulted in the system thermodynamically less stable in reaction with water, promoting rapid phase demixing in the phase inversion process. When the same 3wt% PEG was added into the dope solution, the dimension of finger-like macrovoids of the resultant membrane increased in parallel with the increase of PEG molecular weight from 200 to 600 and 6000kDa, and pure water permeability (PWP) also increased accordingly. An increase in PWP was also observed when PEG-200 loading in the dope solution was increased from 3 to 5 and 10wt%, corresponding to the morphology change of resultant membranes. As a synergetic effect of coagulation temperature with PEG, the finger-like pores occurred in the membrane at room temperature expanded to much larger macrovoids using 10°C water as the coagulant, and the big finger-like pores almost disappeared when the coagulation bath temperature was increased to 40°C because of delayed phase demixing. The big macrovoid size can also be suppressed by adding the second small molecule additive, LiCl, due to its strong interactions with NMP and PVDF-HFP to delay the dope precipitation. The irregular inner contour of the membrane can be eliminated by the increase of coagulation bath temperature to 40°C. The hollow fiber membrane made by a dope of PVDF-HFP/PEG-6000/LiCl/NMP (15/3/3/79 in weight) using 40°C water as the coagulant exhibited a high PWP of 117L/m2 hatm and reasonably good MWCO of 150kDa. An improvement has been made in the current work as compared to previous PVDF-HFP hollow fiber membranes reported in literatures. [Copyright &y& Elsevier]

Abstract: The performance of membrane distillation depends on both membrane and module characteristics. This paper describes strategies to improve the performance of hollow fiber membrane modules used in direct contact membrane distillation (DCMD). Three different types of hydrophobic polyvinylidene fluoride (PVDF) hollow fiber membrane (unmodified, plasma modified and chemically modified) were used in this study of direct contact membrane distillation (DCMD). Compared to the unmodified PVDF hollow fiber membrane, both modified membranes showed greater hydrophobicity and mechanical strength, smaller maximum pore sizes and narrower pore size distributions, leading to more sustainable fluxes and higher water quality (distillate conductiviy<1μscm−1) over a one month test using synthetic seawater (3.5wt% sodium chloride solutions). Comparing the plasma and chemical modification the latter has marginally better performance and provides potentially more homogeneous modification. MD modules based on shell and tube configuration were tested to identify the effects of shell and lumen side flow rates, fiber length and packing density. The MD flux increased to an asymptotic value when shell-side Re f was larger than 2500, while the permeate/lumen side reached an asymptotic value at much lower Re p (>300). By comparing the performance of small and larger modules, it was found that it is important to utilize a higher shell-side Re in the operation to maintain a better mixing near the membrane surface in a larger module. Single fiber tests in combination with heat transfer analysis, verified that a critical fiber length existed that is the required length to assure sufficient driving force along the fiber to maintain adequate MD performance. In addition, for multi-fiber modules the overall MD coefficient decreased with increasing packing density, possibly due to flow maldistribution. This study shows that more hydrophobic membranes with a small maximum pore size and higher liquid entry pressure are attainable and favorable for MD applications. In order to enhance MD performance various factors need to be considered to optimize fluid dynamics and module configurations, such as fiber length, packing density and the effect of module diameter and flow rates. [Copyright &y& Elsevier]

Interfacial polymerization is an effective technique to synthesize high performance polyamide thin film membranes. However, it is still very challenging to apply this technique on ceramic hollow fibres or tubular membranes, especially when the substrate pore size is in the microfiltration range. In this study, we demonstrated that thin polyamide layer can be synthesized directly on microfiltration ceramic tubular membranes with a surface pore size of 0.1–0.2 μm via interfacial polymerization without an intermediate layer. A thin polyamide layer with a thickness 30–40 nm was coated on the inner surface of the ceramic substrate by circulating the monomers of branched polyethyleneimine (PEI), piperazine (PIP), and trimesoyl chloride (TMC) through the membrane lumen. The thin film layer showed good integration with the ceramic substrate and could withstand high pressure of at least 10 bar. The mechanical property of the polyamide layer was examined using AFM and the modulus was measured. The thin film composite membranes demonstrated excellent nanofiltration performance with a pure water permeability of 16–18 LMH bar−1 and a molecular weight cut-off of ∼250 Da. The membranes also showed good salt rejections (>90%) to CaCl 2 , MgCl 2 and MgSO 4 , and still maintained high rejections of MgCl 2 and sucrose at elevated temperature of 80 °C. The use of highly inert ceramic substrates has enabled the application of polyamide membranes under more challenging conditions. Image 1 • PEI-based polyamide thin film was synthesized on microfiltration ceramic tubular membranes without an intermediate layer. • The membranes demonstrated excellent nanofiltration performance with a PWP of 16–18 LMH bar−1 and a MWCO of ∼250 Da. • The membranes also showed good divalent salt rejections for CaCl 2 , MgCl 2 and MgSO 4. • The rejections of MgCl 2 and sucrose remained high at elevated temperature of 80 °C. • The mechanical property of the polyamide film was studied using the AFM pinpoint mode and the modulus was measured. [ABSTRACT FROM AUTHOR]

This report demonstrates the fabrication of a composite hollow fiber membrane that efficiently recovers dissolved methane (dCH 4) from anaerobic wastewater treatment effluents via membrane contactor (MC) process. We first fabricated highly porous hollow fiber membranes (∼85% porosity) using polyvinylidene difluoride (PVDF). Then, we coated the whole structure (bulk), or lumen side of PVDF supports with polydimethylsiloxane (PDMS), a hydrophobic polymer possessing high gas permeability. The adjustment of the concentration of PDMS precursor mix could effectively serve for tuning the performance characteristics of MC membranes and helped suppress membrane wetting, a major performance-reducing factor. Despite their denser skin layers, the lumen-modified membranes demonstrated superior dCH 4 recovery flux. Mass transfer analyses have confirmed the importance of preserving bulk porosity while coating the membrane surfaces. The long-term performance tests performed using actual anaerobic effluents suggested that the PDMS coating did not accelerate fouling, such that the lumen-modified MC membranes showed an almost steady flux for 8 days with an anaerobic membrane bioreactor effluent. A high-strength effluent, obtained from an up-flow anaerobic sludge blanket reactor, induced faster fouling. However, we observed only a ∼20% flux decline in a 10-day operation. Thus, we propose that the designed PDMS-PVDF composite membranes are promising for industrial practices. Image 1 • We prepared PDMS-coated PVDF porous hollow fiber membranes for membrane contacting. • Both lumen- and bulk-modified PVDF membranes were successful in methane recovery. • Lumen-modified PDMS-PVDF membrane outperformed commercial PP and PDMS membranes. • Lumen-modified PVDF achieved long-term performance with actual anaerobic effluents. [ABSTRACT FROM AUTHOR]

Tailoring the hydrophobic properties of membranes is an important requirement in gas-liquid membrane contactor processes because the membrane can be wetted by liquid. This paper describes the hydrophobic modification of the chemical surface of a polyvinylidene fluoride hollow-fiber membrane using a commercial perfluoropolyether, Fluorolink S10. The contact angle of the modified membrane was influenced by the modification parameters, and hence parameter optimization was required to obtain a highly hydrophobic membrane. The sodium hydroxide concentration (pH 8, 10 and 12), dehydrofluorination time (30, 60 and 90 min), and chemical solution grafting time (30, 60 and 90 min) were identified as the control parameters of this modification and were optimized using the Taguchi approach. The optimized membrane was then applied to recover methane from anaerobic membrane bioreactor effluent and benchmarked with a commercial polypropylene membrane manufactured for degasification of water. The contact angle of the polyvinylidene fluoride membrane was improved by 32% after the surface modification (under the optimal modification condition indicated by the Taguchi method). The membrane mass transfer coefficient was measured as 1.53 × 10 −4 m/s. Our membrane showed better methane recovery performance than the commercial polypropylene membrane and a very stable flux without pore wetting during 10 days of operation with synthetic effluent (made by saturating a 60:40 methane/carbon dioxide mixture into tap water). In addition, the membrane prepared in this study could be operated without significant fouling (7% flux drop during 8 days of operation) with real anaerobic membrane bioreactor effluent. [ABSTRACT FROM AUTHOR]

In this study, the glutaraldehyde (GA) crosslinking was adopted in combination of layer-by-layer (LBL) polyelectrolyte deposition to develop a novel hollow fiber NF membrane with low-pressure water softening capability for synthesized hard water containing divalent counterion SO 4 2− . The challenges for the new membrane include (a) the presence of SO 4 2− in the feed water, which tends to deteriorate positively charged NF membrane retention to divalent ions; (b) high salinity feed water up to 10,000 ppm total dissolved salt (TDS); (c) 2 bar operating pressure that requires the membrane to have a good Mg 2+ /Na + selectivity and less mass transfer resistance in the substrate; and (d) better separation performance as compared with the state-of-the-art and commercial NF membranes. Based on the membrane characterization results, the possible structure of the deposited layers and the effect of GA crosslink was proposed. It was found that the crosslinking could tighten the membrane surface pores with increased hydrophilicity while the membrane surface charge was reduced. Therefore, mainly based on the size exclusion, the crosslinked LBL*1.5C membrane showed more than 10 LMH/bar permeability with above 95% rejection to each of 1000 ppm MgCl 2 , MgSO 4 and Na 2 SO 4 solution under 2 bar pressure. It was also proved to be more suitable for the low-pressure water softening application at 2 bar in all tested feed water with the presence of SO 4 2− and TDS up to 10,000 ppm in terms of both permeability and hardness removal efficiency when compared with commercial NF 270 and NF 90 membranes. [ABSTRACT FROM AUTHOR]

Abstract: Among four membrane distillation (MD) configurations, direct contact MD (DCMD) and vacuum MD (VMD) exhibit attractive characteristics from different perspectives and have great potential in treating reverse osmosis (RO) brine. Aiming at establishing a quick approach to predict the key output parameters associated with MD module performance and process efficiency, Aspen plus was employed to conduct systematic evaluation for both DCMD and VMD. Due to the lack of built-in MD operation models in Aspen Plus, one dimensional transport models were developed and complied as user customized units to simulate the hollow fiber-based DCMD and VMD modules. The corresponding programming was coded in FORTRAN language. The mathematical models for DCMD and VMD were verified by comparing the simulations results with the experimental and literature data, respectively. By incorporating the boundary-layer effect into the newly-established transport models, steady-state simulations of the respective DCMD and VMD flowsheets were carried out. The results showed that the DCMD presented much lower process efficiency than VMD in terms of permeation flux and specific energy consumption per kg distillate generated, even though it is considered as the simplest and most commonly employed configuration. With the same module specifications and operating conditions at equivalent energy cost, the VMD system demonstrated a minimal 2.5-fold higher average vapor flux (e.g., water recovery capacity) when compared to DCMD. The fundamental difference between the two configurations was revealed through MD mass- and heat-transfer analysis. Based on simulated temperature profiles, it was found that the VMD configuration presented a much higher driving force (transmembrane temperature difference) and negligible conductive heat loss to the membrane, which is a promising feature for achieving high thermal efficiency. [Copyright &y& Elsevier]

Abstract: In this study, three types of micro-structured alumina hollow fibre membranes, i.e. Membranes I, II, and III, have been developed and characterised for potential use in wastewater treatments. They consist of two basic structures: finger-like micro-channels for reduced transmembrane resistance, and sponge-like layer(s) for micro-filtration (MF). They have been fabricated via a combined phase-inversion and sintering technique, whereby the viscous fingering phenomenon that takes place concurrent to phase inversion leads to the formation of a plurality of finger-like voids or micro-channels within the membranes. The three internal coagulants used were hexane, DMSO and tap water with air gaps of 0 or 30cm. Mechanical strength and water permeation flux were found to be sensitive to changes in membrane morphology, while pore size distribution of the separation layer(s) were less affected and were all in the microfiltration range. Membrane II, with just one very thin separation layer, exhibited the highest water permeation flux of 1874L/(m2 h) at 0.1MPa. Effects of sintering temperature on pore size distribution, mechanical property and water permeation of the three membranes, in particular Membrane II, were systematically investigated. Sintering temperatures between 1300°C and 1350°C are suggested for Membrane II, taking into consideration of the reduced water permeation at higher sintering temperatures and the lowered mechanical strength at lower sintering temperatures. [Copyright &y& Elsevier]

Abstract: Composite nanofiltration (NF) hollow fiber membranes desirable for water softening under low operating pressure (<2bar) were successfully developed in the current study. The thin-film selective layer of the composite hollow fiber was formed through interfacial polymerization on the inner surface of a polyethersulfone (PES) ultrafiltration (UF) membrane substrate with branched polyethyleneimine (PEI) and trymesoyl chloride (TMC) employed as the monomers in aqueous and organic phases, respectively. It is found that a proper molecular weight of PEI and the presence of sodium dodecyl sulfate (SDS) in the aqueous phase are important for a successful interfacial polymerization reaction. The resulting membrane prepared with optimized preparation parameters possesses a positively charged thin-film selective layer with pure water permeability (PWP) of about 17l/m2 hbar and a molecular weight cut-off (MWCO) of around 500Da, which translates into the effective pore diameter of about 1.29nm. With combined separation mechanisms of Donnan exclusion and steric hindrance, it was possible to achieve MgCl2 and MgSO4 rejection of 96.7% and 80.6%, respectively, when tested for 1000ppm feed solutions at 2bar operating pressure. In addition, for a 3000ppm TDS feed stream containing salt mixtures, the membrane rejections for Mg2+ and Ca2+ ions were found to be around 90% while the water flux was about 20l/m2 h at 2bar pressure, suggesting the potential of the newly developed composite hollow fibers for effective water softening application. [Copyright &y& Elsevier]

Abstract: This study explores the potential of microstructured hollow fiber designs to enhance process performance in a direct contact membrane distillation (DCMD) system. Hollow fibers with 10 different geometries (wavy- and gear-shaped cross sections) were evaluated. A series of three-dimensional computational fluid dynamic (CFD) simulations were carried out to investigate their capability in terms of depolarizing the buildup of liquid boundary layers, thus improving water productivity. Analyses of heat and mass transfer as well as the flow-field distribution in respective MD modules were obtained. It was found that the enhancement of the heat-transfer coefficients, h f , was up to 4.5-fold for a module with a wavy fiber design 07 and an approximate 5.5-fold h p increase for a gear-shaped fiber design. The average temperature polarization coefficient and mass flux N m of the gear-shaped fiber module showed an improvement of 57% and 66%, respectively, over the original straight fiber design, followed by the wavy designs 07 and 08. The enhanced module performance was attributed to the improved hydrodynamics through the flow channels of various fiber geometries, which was confirmed by the visualization of flow-field and temperature profiles in CFD. Investigations of the fiber-length effect showed that the gear-shaped fiber modules exhibited the highest flux enhancement of 57–65% with the same length, compared to the modules with original straight and wavy fibers. In addition, the gear-shaped fiber module is very sensitive to feed velocity changes. Therefore, employing a smart microstructured design on the membrane surface would bring in a significant improvement under adverse flow conditions. Moreover, the computed water production and hydraulic energy consumption (HEC) among the modules with various fiber geometries were compared. With 1.9-fold surface area increase per unit volume, the gear-shaped fiber configuration had the highest water production but the lowest HEC, followed by wavy designs 07 and 08. [Copyright &y& Elsevier]

Abstract: As an extended exploration of process enhancing strategies, nine modified hollow fiber modules with various turbulence promoters were designed and modeled using a two dimensional computational fluid dynamic (CFD) heat-transfer model to investigate their potential in improving heat transfer and module performance for a shell-side feed direct contact membrane distillation (DCMD) system. With the aids of turbulence promoters, the feed heat-transfer coefficient h f of the modified modules generally showed much slower decreasing trends along the fiber length compared to the original (unmodified) module. A 6-fold h f enhancement could be achieved by a modified module with annular baffles and floating round spacers. Consistently, the temperature polarization coefficient (TPC) and mass flux distribution curves of these modified modules presented increasing trends and gained an optimal improvement of 57% and 74%, respectively. With the local flow fields and temperature profiles visualized in CFD simulations, it was confirmed that an appropriate selection of turbulence promoters could promote intense secondary flows and radial mixing to improve the shell-side hydrodynamics and enhance heat transfer. Moreover, an increase of flow velocity was used and compared as a conventional approach to improve hydrodynamics. It was found that a well-designed module could bring more significant enhancement for a liquid-boundary layer dominant heat-transfer process. Finally, the hydraulic energy consumption (HEC) caused by the insertion of turbulence promoters or the increase of circulating velocity was compared. Configurations with attached quad spacers or floating round spacers achieved a good compromise between enhanced permeation fluxes and modest HECs. Overall, the TPC decreases with increasing MD coefficient (C) values and operating temperatures; while the thermal efficiency increases dramatically with increasing C and operating temperatures in a MD system. [Copyright &y& Elsevier]

Abstract: A comprehensive analysis on the dominant effects for heat and mass transfer in the direct contact membrane distillation (DCMD) process has been performed with the aid of computational fluid dynamics (CFD) simulations for hollow fiber modules without and with annular baffles attached to the shell wall. Potential enhancement strategies under different circumstances have been investigated. Numerical simulations were carried out to investigate the effect of the MD intrinsic mass-transfer coefficient of the membrane (C) on the performance enhancement for both non-baffled and baffled modules. It was found that the temperature polarization coefficient (TPC) decreases significantly with increasing C value regardless of the existence of baffles, signifying a loss of overall driving force. However, the higher C compensated for this and the mass flux showed an increasing trend. A membrane with a lower C value was found to be less vulnerable to the TP effect. In this case, the introduction of turbulence aids such as baffles did not show substantial effect to improve system performance. In contrast, introducing baffles into the module can greatly enhance the mass flux and the TPC for a membrane with a high C value, where the main heat-transfer resistance is determined by the fluid side boundary layers. The effect of operating temperature on heat and mass transfer in the MD process was also studied with a membrane of a lower C value (2.0×10−7 kgm−2 s−1 Pa−1). Although the TPC generally decreased with increasing operating temperatures, the mass flux N m increased significantly when operating temperature increased. A baffled module showed a more significant improvement than a non-baffle module at a higher temperature. Moreover, it was confirmed that higher operating temperatures are preferable for a substantial improvement in the heat/mass transfer as well as MD thermal efficiency, even with a relatively small transmembrane temperature difference of 10K. [Copyright &y& Elsevier]

Abstract: The heat and mass transfer processes in direct contact membrane distillation (MD) under laminar flow conditions have been analyzed by computational fluid dynamics (CFD). A two-dimensional heat transfer model was developed by coupling the latent heat, which is generated during the MD process, into the energy conservation equation. In combination with the Navies–Stokes equations, the thermal boundary layer build-up, membrane wall temperatures, temperature polarization coefficient (TPC), local heat transfer coefficients, local mass fluxes as well as the thermal efficiency, etc. were predicted under counter-current flow conditions. The overall performance predicted by the model, in terms of fluxes and temperatures, was verified by single hollow fiber experiments with feed in the shell and permeate in the lumen. Simulations using the model provide insights into counter-current direct contact MD. Based on the predicted temperature profiles, the local heat fluxes are found to increase and then decrease along the fiber length. The deviation of the membrane wall temperature from the fluid bulk phase on the feed and the permeate sides predicts the temperature polarization (TP) effect. The TP coefficient decreases initially and then increase along the fiber length. It is also found that the local Nusselt numbers (Nu) present the highest values at the entrances of the feed/permeate sides. Under the assumed operating conditions, the feed side heat transfer coefficients h f are typically half the h p in the permeate side, suggesting that the shell-side hydrodynamics play an important role in improving the heat transfer in this MD configuration. The model also shows how the mass transfer rate and the thermal efficiency are affected by the operating conditions. Operating the module at higher feed/permeate circulation velocities enhances transmembrane flux; however, the thermal efficiency decreases due to the greater heat loss at a higher permeate velocity. The current study suggests that the CFD simulations can provide qualitative predictions on the influences of various factors on MD performance, which can guide future work on the hollow fiber module design, module scale-up and process optimization to facilitate MD commercialization. [Copyright &y& Elsevier]

Anaerobic wastewater treatment processes are becoming increasingly widespread due to their advantages in sludge management and net energy consumption. One major reason behind the energy benefit of the mainstream anaerobic processes is methane (CH 4) production. Nevertheless, over one-third of the produced CH 4 typically remains in effluent streams in dissolved form. To recover the dissolved CH 4 (dCH 4) from anaerobic effluents, the membrane contactor (MC) process enabled by porous membranes offers a promising way. However, membrane wetting and fouling issues hinder the practical implementation of the concept. Here we report a wetting- and fouling-resistant hollow fiber membrane that can operate with realistic anaerobic effluents. Coating of a highly porous (~85%) hollow fiber support with a conformal layer of polydimethylsiloxane (PDMS) provides resistance to wetting, but fouling persists. To tackle the fouling issue, we post-treated the uncured PDMS-coatings with PDMS-based amphiphilic copolymers with short (147 Da) or long (~1570 Da) side chains. Both types of post-treated membranes exhibited an improved performance when tested against effluent samples taken not only from an anaerobic membrane bioreactor but also from an upflow anaerobic sludge blanket (UASB) reactor. The membrane treated with the short-side-chain copolymer could sustain 7 days of continuous operation with UASB effluent with a performance loss of only ~10%. We observed that the fouling layers were much richer in proteins rather than subtances similar to humic and fulvic acids and microbial byproducts. Besides, we calculated that our wetting/fouling-resistant membranes provide a net energy benefit for the MC process (when the recovered CH 4 is retrofitted to the process as fuel). Thus, our results suggest that the MC-based dCH 4 recovery process is a viable alternative for industrial practices in case the demonstrated custom-designed membranes are employed. Image 1 • PDMS coating provides antiwetting property to PVDF-based hollow fiber membranes. • Hydrophilization of PDMS-coated composite membranes provides fouling resistance. • We recovered >50% of dissolved CH4 from anaerobic effluents via contactor process. • A performance loss of only ~10% took place for UASB effluents at a 7-day operation. • Contactor process may enhance net energy output of anaerobic wastewater treatments. [ABSTRACT FROM AUTHOR]

A membrane contactor has been considered as one of the most effective tools for biomethane (CH 4) recovery from anaerobic effluents owing to its several strengths. However, without thoroughly understanding various factors ranging from operating parameters (e.g., liquid or gas flow rate) to membrane characteristics (e.g., porosity, pore size, hydrophobicity, inner diameter, membrane area, and fiber length), a membrane contactor could just break even, or even worse, may be operated at a loss before turning a profit. Much of the groundwork is required to make sure to gain net benefits while avoiding those sorts of pitfalls. Herein, we attempted to screen several factors ranging from operation-to membrane-related parameters to ensure whether they meet essential criteria. To be specific, this study covers the following aspects: i) the optimal gas-liquid flow rate (G / L) ratio to minimize both the gas-phase resistance and the dilution of the final sweep gas, ii) the combined effects of G / L ratio and mass transfer area (A M) on the energy recovery performance, iii) the influences of an inner diameter (d i) and A M on the CH 4 recovery (RE CH4) and the net energy production, iv) the influences of the L , porous structure, A M , and hydrophobicity on the RE CH4 and the energy output from the microturbine, v) the minimum criterion for the d i to minimize the energy required for the liquid pump, and vi) correlation between the pore structure and pore clogging. Through the thorough studies, we drew nine useful and meaningful conclusions including the best G / L ratio (0.0425 at the A M of 1 m2), necessary requisites (porous structure, larger A M , and more hydrophobicity) for higher RE CH4 , the lower limit of a d i (190 μm) to minimize the energy required for the liquid pump, and so on. We expect that this comprehensive study can help researchers and engineers opt for operation- and membrane-related parameters leading to the desirable performance of a membrane contactor for energy recovery from anaerobic effluents. Image 1 • The influences of membrane contactor operation parameters on the net energy production were systematically examined. • The influences of membrane characteristics on the energy production were also delineated. • Both theoretical and empirical studies were comprehensively carried out. • The criteria for the two parameters were provided to maximize the net energy production. [ABSTRACT FROM AUTHOR]

Several factors affect the performance of membrane-contacting systems for recovering dissolved methane (CH 4) from anaerobic effluents, from membrane- to operations-related parameters. However, the conditions necessary to achieve high-efficiency CH 4 recovery remain unclear. To improve our understanding of these dynamics, we systematically investigated the effects of membranes' physicochemical characteristics and operating parameters in a membrane-contacting system. We not only explored theoretical approaches to weigh the influence of diverse parameters but also evaluated the performance of four types of membranes with distinct morphological and chemical characteristics at various liquid velocities. According to our theoretical calculations, enlarging the mass transfer area (A M) decreases CH 4 flux while a higher liquid flow rate (L) results in a reduction in CH 4 recovery. Meanwhile, increasing the membrane's inner diameter (d i) has a negative influence on both CH 4 flux and recovery. However, a larger A M and a higher L are required to achieve higher recovery and flux, respectively. Our experimental results demonstrate that the capillary pressure imposed by the module inlet, pore wetting, and membrane resistance can also significantly affect the overall mass transfer resistance, thereby having a profound effect on CH 4 flux. We clarify the underlying mechanisms to explain how each parameter influences CH 4 flux and recovery, which leads to a system optimization to achieve the greatest CH 4 recovery efficiency. Image 1 • The influence of membrane characteristics on methane (CH 4) recovery in a membrane contactor was investigated. • The influence of operating parameters on CH 4 recovery was also evaluated. • Both theoretical and experimental analyses were conducted for a comprehensive understanding. • The requirements to obtain the optimum CH 4 recovery efficiency were provided. [ABSTRACT FROM AUTHOR]

A new class of thin film nanocomposite (TFN) hollow fiber (HF) membrane of polydopamine (PDA) modified HKUST-1 (mHKUST-1) incorporated in polyamide (PA) matrix supported by polyethersulfone (PES) substrate was constructed via interfacial polymerization method for brackish water desalination in low-pressure reverse osmosis (RO) process. The PDA modification facilitated the HKUST-1 even dispersion, thus resulting in better compatibility between the inorganic nanofillers and the organic matrix. The impact of HKUST-1 loadings on the overall performances of the resultant HKUST-1@PA/PES membranes was investigated. Introducing the mHKUST-1 nanofillers not only enhanced surface hydrophilicity and negative surface charges for the selective layer, which improved membrane's fouling resistance to humic acid (HA), but also led to nearly doubled water permeance when comparing with the pristine PA membrane (increasing from 3.51 to 6.94 Lm−2h-1bar−1), without obvious salt rejection deterioration (~98.2% at 2 bar and 97.4% rejections at 4 bar for 500/2000 ppm NaCl solutions, respectively). The integrity of the HKUST-1@PA/PES membrane was examined and verified after 30-days operation. Overall, the results achieved in this work demonstrate promising potential of the metal organic framework (MOF)-based TFN membranes used for desalination in low-pressure RO process. To sum up, this work has exhibited a facile method to incorporate the metal organic framework (MOF) into the PA layer, and the resultant MOF-based TFN membrane indicates its great potential for desalination in low-pressure RO process. • A thin film nanocomposite hollow fiber membrane was constructed via interfacial polymerization. • Polydopamine (PDA) modified HKUST-1 was incorporated in polyamide matrix supported by polyethersulfone substrate. • The PDA modification facilitated the HKUST-1 even dispersion in PA matrix, without the formation of defects. • A water permeability of 6.94 Lm−2h-1bar−1 and 97.4% rejections at 4 bar for 2000 ppm NaCl solution were achieved. • The long-term stability test verified the good integrity of the HKUST-1@PA/PES membranes after 30-days operation. [ABSTRACT FROM AUTHOR]

Gas-liquid membrane contactor (GLMC) has been regarded as a promising alternative to conventional contacting processes for CO 2 absorption. In this work, a composite hollow fiber (HF) membrane with an aminosilane-modified zeolitic imidazolate framework-8 (mZIF-8) based dense skin layer was designed and synthesized for high-efficiency biogas upgrading in the GLMC process, by dispersing mZIF-8 nanocrystals into poly(dimethylsiloxane) matrix and then depositing on a porous polyvinylidene fluoride (PVDF) substrate. (3-aminopropyl)triethoxysilane was introduced to modify the ZIF-8 nanocrystals, thereby enabling the chemical bonding with PDMS chains for avoiding interfacial voids and further enhancing hydrophobicity. Compared with the control membrane, the newly developed mZIF-8 based composite membrane with a dense skin exhibited competitive hydrophobicity with a contact angle of 130°, ensuring its anti-wetting ability. It exhibited an enhanced biogas upgrading performance with the absorption fluxes of 2.3 and 3.8 × 10−3 mol m−2·s−1 using water and 1 M monoethanolamine (MEA) as absorbents, respectively (liquid velocity = 0.25 m s−1). In particular, a comparable selectivity of CO 2 /CH 4 with the value of ∼20 was achieved by using MEA as absorbent in the GLMC process. A robust long-term stability of the mZIF-8 based composite HF membrane was also achieved in a 15-day operation. This work offers a new perspective for promoting CO 2 mass transfer with mZIF-8 based composite HF membranes, thereby improving the biogas upgrading performance in GLMC applications. • A composite hollow fiber membrane with a ZIF-8 based dense skin layer was designed and synthesized. • The ZIF-8 nanocrystals were modified to cross-link with PDMS chains for further hydrophobicity enhancement. • The newly developed membrane exhibited competitive hydrophobicity, ensuring its anti-wetting ability. • An enhanced biogas upgrading performance was achieved in gas-liquid membrane contact applications. [ABSTRACT FROM AUTHOR]

In this work, a positively charged hollow fiber nanofiltration (NF) membrane based on twice interfacial polymerization (IP) reactions was developed for water soften and heavy metal ions removal. The first IP reaction was conducted on the polyethersulfone (PES) hollow fiber substrate using a mixture of branched polyethyleneimine (PEI) and piperazine (PIP) as the aqueous phase monomers in the aqueous phase reacting with trimesoyl chloride (TMC) in the cyclohexane solution. Then, a secondary IP reaction was performed between tris(2-aminoethyl) amine (TAEA) solution and the residual acyl chloride groups on the membrane to increase the positive charge density on the membrane surface. Consequently, a NF membrane with intensified positive surface charge density was successfully fabricated. The optimized membranes achieved a high rejection of MgCl 2 of 97.6% while maintaining a pure water permeability (PWP) of 16.0 L m−2 h−1 bar−1. Meanwhile, the membranes exhibit high rejection values of 99.8% to Cu2+ and 99.7% to Zn2+, respectively. In conclusion, this work provides a facile way to prepare a positively charged membrane for efficient water softening and metal ions removal. [Display omitted] • A novel polyamide NF hollow fiber membrane via a secondary IP reaction had been successfully fabricated. • The secondary IP reaction between TAEA and the residual acyl chloride groups effectively enhances the positive change density on membrane surface. • This modification method has no influence on membrane structure. • The optimum membrane shows more than 90% rejection of Mg2+ and Ca2+ and 99% rejection of heavy metals. [ABSTRACT FROM AUTHOR]

How the membrane support affects the performance of thin-film composite (TFC) membranes has long been under debate. Our present study experimentally establishes that the support pore number density (number per unit area) as well as its surface porosity play pivotal roles in affecting the characteristics and permselectivity of TFC membranes. The structure of hollow fiber supports was finely tuned and characterized via a series of techniques, which provided a link to the physicochemical properties of the interfacially polymerized polyamide films. During the spinning process, decreasing the content of N -methyl-2-pyrrolidone in the bore fluid drastically reduced the pore size and surface porosity of the support. The resultant TFC membranes showed a lower water permeability (tested under 1 bar using 500 ppm NaCl). Adding lithium chloride to the polymer dope also led to a support with smaller pores and lower porosity, but increased surface pore number density. The resulting TFC membranes had a substantially higher water permeability and slightly higher salt rejection. In both arrays of membranes, all membranes shared similar thickness of polyamide leaf but a more crumpled film was found on a less porous support, suggesting that the surface porosity of the support affected the effective surface area of films. However, the TFC membrane with a higher effective surface area did not necessarily possess a higher permeability. Rather, a TFC membrane having a support with a higher surface porosity or a higher pore number density exhibited a higher water permeability, demonstrating that the lateral transport path of water through films had a significant impact on the water permeability of TFC membranes. Interestingly, in both cases, the selectivity of the TFC membranes was maintained when the water permeability increased. This study clarifies longstanding misunderstandings concerning the effects of the support on TFC membrane performance and provides insight into fabricating highly permeable and selective TFC membranes. • A base film embedded in the polyamide layer determines performance of TFC membranes. • Enlarging surface porosity of supports could enhance permeability of TFC membranes. • Increasing pore density of supports could enhance permeability of TFC membranes. • Supports affect lateral diffusion of water through films and thereby permeability. • Rejection was maintained while the permeability of TFC was drastically enhanced. [ABSTRACT FROM AUTHOR]

Abstract The combination of nonsolvent and thermally induced phase separation (N-TIPS) method has shown promising ability in harvesting the features from the nonsolvent induced phase separation (NIPS) and thermally induced phase separation (TIPS) processes for developing membranes with a tailorable surface pore structure. However, previous approaches have been subjected to either the formation of macrovoids or dense layer due to the dominant NIPS effect, or required sophisticated instruments and operation skills. In this work, a facile attempt was carried out to fabricate novel polyvinylidene fluoride (PVDF) hollow fiber membranes with tunable surface pore structure while maintaining the narrow pore size distribution and mechanical strength. A modified N-TIPS method was developed by using mixed diluents: dimethyl phthalate (DMP) as a water-immiscible poor solvent for TIPS process, and triethyl phosphate (TEP) as a water-miscible neutral solvent to bridge the TIPS and NIPS processes. To further control the membrane formation especially near the membrane surface, an amphiphilic additive Pluronic F127 was also added as a potential pore-former and surface hydrophilicity modifier. PVDF hollow fiber membranes with a highly porous structure and a narrow pore size distribution were successfully synthesized by using TEP and Pluronic F127 in the N-TIPS process. The mechanism of N-TIPS process was thoroughly discussed. The water permeability of the membrane increased significantly from 389 ± 30–922 ± 36 L m–2 h–1 bar–1, with overall porosity improved from 50 ± 2.2–69 ± 2.9%, and a mean pore size of ~ 0.18 µm. The membranes produced by N-TIPS method also exhibited a good tensile strength ranging from 5.6 ± 0.1–6.5 ± 0.2 MPa, showing a great potential for a broad range of water applications after further modifications. Besides, the formation of piezoelectric β-phase crystals of the PVDF membrane was observed when the mixed diluent was used, which sheds light on the possible applications of resultant membranes in electrochemical separation process. Highlights • PVDF hollow fiber membranes were developed via a modified N-TIPS method using mixed diluents together with Pluronic F127. • The NIPS effect could be induced at the outer surface with the co-occurrence of TIPS process along the bulk of membrane. • The surface pore structure of membrane could be tailored without the formation of mechanically weak macrovoids. • The prepared membranes possess a hydrophobic surface with good porosity, permeability and mechanical strength. [ABSTRACT FROM AUTHOR]

An inorganic-organic fluorinated titania-silica (fTiO 2 -SiO 2 )/polyvinylidene fluoride (PVDF) composite membrane was fabricated, via facile in-situ vapor-induced hydrolyzation method followed by hydrophobic modification. This low mass-transfer-resistance membrane, composing of a mesoporous layer deposited onto macroporous substrate, was designed for biogas upgrading in gas-liquid membrane contactor (GLMC) application. The surface hydroxylation was introduced to facilitate the bridging of TiO 2 -SiO 2 nanoparticles and PVDF substrate, which resulted in a more coherent deposition of the fTiO 2 -SiO 2 layer onto the substrate. The surface microstructure was fine-tuned by controlling the amount of doped Si precursor, forming an integrated mesoporous fTiO 2 -SiO 2 layer. The resultant fTiO 2 -SiO 2 /PVDF composite hollow fiber membrane exhibited a tighter pore size of ~25 nm and a desired water contact angle of ~124°, which effectively prevented membrane wetting. The CO 2 absorption fluxes of 8.0 and 5.6 × 10 −3 mol m −2 s −1 were achieved due to the lower mass transfer resistance, by using 1 M of monoethanolamine (MEA) and sodium taurinate as absorbents with a liquid velocity of 0.25 m s −1 , respectively. The long-term stability test showed a good integrity between the fTiO 2 -SiO 2 layer and the PVDF substrate after 31-days of GLMC operation. The main benefit is the robust fluorinated inorganic layer which exhibited strong chemical resistance and high hydrophobicity, thus preventing membrane damage and pore wetting. Overall, this work provides an insight into the preparation of high–performance inorganic/organic composite hollow fiber membranes for carbon dioxide (CO 2 ) removal in GLMC application. [ABSTRACT FROM AUTHOR]

Pressure retarded osmosis (PRO) is an innovative technique to yield osmotic energy. Nevertheless, the PRO performance is exacerbated by the severe membrane fouling occurring within the porous support. It is a potential alternative for sustainable power harvesting to change the membrane orientation from active layer facing draw solution (AL−DS) or PRO mode to active layer facing feed solution (AL−FS) or FO mode for a low-fouling propensity. A novel integral PRO hollow fiber membrane was developed in this work by phase inversion and followed with a facile cross-linking post-treatment. The structure and properties of the resultant membrane were systematically investigated using a series of characterization protocols. The PRO performance of the membrane was studied under various hydraulic pressures at the AL−FS orientation. The results reveal that the substrate with sponge-like structure and relatively dense inner surface can better withstand high pressure in PRO process. Two steps of cross-linking endowed the membrane with a smaller pore size on the outer surface that exhibits high rejection against various inorganic salts. The novel integral membrane can achieve a stable power density output around 4.3 W m −2 at 12 ~ 13 bar hydraulic pressure, using a real wastewater reverse osmosis (RO) retentate and 1.0 M sodium chloride as the feed and draw stream, correspondingly. This result demonstrates that the PRO operation in the AL−FS orientation (FO mode) offers a significant advantage over the AL−DS orientation (PRO mode) by eliminating the pretreatment of the feed water or/and other measures associated with membrane fouling control in the PRO mode. To implement the PRO operation with the AL−FS orientation, developing a robust membrane with an integral structure is critical. The newly developed integral hollow fiber membrane via chemical cross-linking presents the potential for PRO operation in the AL−FS orientation. [ABSTRACT FROM AUTHOR]

A significant amount of methane (CH 4 ) produced from anaerobic digestions of wastewater is dissolved in liquid effluent and discharged. The recovery of dissolved CH 4 is therefore essential in ensuring an enhanced energy production of the anaerobic processes, and minimizing environmental impacts of the greenhouse gas. In this work, a membrane contactor is employed as a mass transfer equipment for the CH 4 recovery. A mathematical model considering simultaneous desorption of CH 4 and carbon dioxide (CO 2 ) is developed using a resistance-in-series model to calculate the overall mass transfer coefficients. The simulations were validated with experimental results obtained using an in-house fabricated hollow fiber membrane as well as a real effluent from Anaerobic Membrane Bioreactor (AnMBR) and synthetic effluent made of water saturated with biogas. Results showed that the CO 2 fluxes were higher than those of CH 4 fluxes due to its higher concentration in liquid phase. A decrease of liquid phase mass transfer resistance by an increase in liquid velocity significantly enhanced both CH 4 and CO 2 fluxes. While, an increase in gas velocity slightly affected the CH 4 flux but enhanced the CO 2 flux considerably. It was also found that the CO 2 desorption increased the CH 4 recovery rate. The desorbed CO 2 helped to increase the mass transfer driving force by reducing the partial pressure of CH 4 in the gas side, and enhancing the gas phase mass transfer coefficient to facilitate CH 4 desorption. The increase of liquid velocity increased mole fraction of CH 4 in the gas outlet but decreased the rate of CH 4 recovery. On the other hand, applying vacuum conditions to decrease gas pressure enhanced the rate of CH 4 recovery but lower the CH 4 mole fraction in the product gas. [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]

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 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: 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]

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: 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: 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]