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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: 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: Forward osmosis (FO) has received intensive studies recently for a range of potential applications such as wastewater treatment, water purification and seawater desalination. One of the major challenges to be overcome is the lack of an optimized FO membrane that can produce a high water flux comparable to commercial RO membranes. Two types of thin-film composite FO hollow fibers with an ultra-thin polyamide-based RO-like skin layer (300–600nm) on either the outer surface (#A-FO) or inner surface (#B-FO) of a porous hollow fiber substrate have been successfully fabricated. These novel composite FO hollow fibers have been characterized by a series of standard protocols and benchmarked against commercially available FO flat sheet membranes and reported NF hollow fibers used for the FO process. The characterization reveals that the FO hollow fiber membranes possess a large lumen. The substrates are highly porous with a narrow pore size distribution. The active layers present excellent intrinsic separation properties with a hydrophilic rejection layer and good mechanical strength. The #B-FO hollow fiber membrane can achieve a high FO water flux of 32.2L/m2 h using a 0.5M NaCl draw solution in the active rejection layer facing draw solution (AL-facing-DS) configuration at 23°C. The corresponding salt flux is only 3.7g/m2 h. To the best of our knowledge, the performance of the #B-FO hollow fiber is superior to all FO membranes reported in the open literature. The current study suggests that the optimal FO membrane structure would possess a very small portion of sponge-like layer in a thin and highly porous substrate, which suggests a way for further improvement. [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]

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]

Extractive membrane bioreactors (EMBRs) are promising wastewater treatment processes combining an aqueous-aqueous extractive membrane process and biodegradation. The target contaminants diffuse through an extractive membrane and are metabolized by the active biofilm attached on the downstream membrane surface and microorganisms in the bioreactor. The benefit of EMBRs is that the biomass is not exposed to the potentially hostile feed conditions (high salinity, pH extremes etc.). The physicochemical properties of membrane surfaces on the receiving side facing the bioreactor are critical in controlling the extent and nature of the membrane-attached biofilm. In this work, novel nanofibrous composite membranes with a superhydrophobic surface (coded as NC) or a superhydrophilic surface (coded as M-NC) on the receiving side have been designed, developed and evaluated in EMBRs. Compared to commercial polydimethysiloxane (PDMS) tubular membranes, both NC and M-NC possessed 10 times higher phenol extraction efficiency in an aqueous-aqueous extractive membrane process. The uncontrolled biofilm growth on the membrane surface after 12 days of cross flow EMBR (CF-EMBR) operation resulted in 62% reductions of overall mass transfer coefficients ( k 0 ) of both NC and M-NC. However, both membranes exhibited better performance in a submerged EMBR (S-EMBR) configuration due to the presence of air bubbles scouring on the membrane surface. Moreover, the fouling-releasing fluoro-polymeric surface of the hydrophobic NC was able to attenuate the tendency of microbial attachment and encourage biofilm scouring from the membrane surface in the S-EMBR. In contrast, more polysaccharides were present in the biofilm on the poly (ethylene glycol) (PEG)-modified M-NC surface, which acted as adhesives to tightly immobilize the biofilm on the membrane surface. Lastly, the NC which exhibited a higher stable k 0 of 5.7 × 10 −7 m/s in 12 days of S-EMBR operation, has been tested in a pilot S-EMBR to treat actual industrial wastewater. It showed a stable and competitive k 0 of 6.5 × 10 −7 m/s in 31 days operation, demonstrating its feasibility for hostile industrial wastewater treatment. [ABSTRACT FROM AUTHOR]