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Abstract: Delamination-free ultrafiltration (UF) dual layer hollow fibers have been successfully fabricated by dry jet-wet spinning technique. Two different polymers of poly(amide-imide) (PAI) and polyethersulfone (PES) were utilized as the selective layer on the outer side and the porous support layer on the inner side, respectively. The dual layer substrates were subsequently modified to develop a nanofiltration (NF)-like skin on the outer layer by polyethyleneimine (PEI) cross-linking followed by multilayer polyelectrolyte depositions. These membranes were characterized by a series of standard protocols in terms of membrane structure, permeability and salt rejection, and were applied in FO process. Experiments reveal that the dual-layer NF hollow fiber modified by polyelectrolyte cross-linking and depositions can achieve pure water permeability of 4.1l/m2.h.bar and a high rejection to MgCl2 up to 97%. In FO process, the dual-layer hollow fibers exhibited a water flux of 39 and 21lm−2 h−1 in the orientations of active layer facing draw solution and feed water, respectively, by using 0.5M MgCl2 as draw solution and de-ionized (DI) water as feed at room temperature. It suggests that the combined treatment of polyelectrolyte cross-linking and deposition is an effective way to form a NF-like selective layer for FO dual-layer hollow fiber membranes. [Copyright &y& Elsevier]

Abstract: A direct contact membrane distillation system (DCMD) was simulated by using Aspen Plus for the purpose of energy efficiency and economic analyses. A cross-flow membrane module was firstly modeled and then incorporated into the flowsheet for system simulation. Detailed investigations have been conducted to understand the relationships of the water flux/production, the gain output ratio (GOR) and the water production cost (WPC) with respect to various design and operation parameters of the DCMD system. Simulation results revealed that in the DCMD studied here, a critical membrane area existed, below which, significant increases of water production and the GOR were observed with increasing membrane area, leading to a significant drop in the WPC. Increasing feed temperature imposes positive impacts on water flux and the GOR. For the higher feed and permeate velocities, there were increases in water flux, water production and the GOR. However for the WPC there were optimum fluid velocities beyond which the penalty of more energy input in the form of electricity consumption for pumping was significant. It was also found that when the temperature difference in the heat exchanger was increased to 6°C, the WPC can be reduced considerably by cutting down the heat exchanger cost. [Copyright &y& Elsevier]

Abstract: This study incorporates gas bubbling into direct contact membrane distillation (DCMD) and examines its effect on the MD performance especially at elevated salt concentrations in the feed steam. Process optimization in the bubbling assisted DCMD process was carried out which involved varying operating conditions and module configurations. Also, observations were performed for the scaling status on the membrane surface with operating time in different modules to further understand the role of gas bubbling in affecting the behavior of crystal deposition when the salt concentration has reached super-saturation. Due to intensified local mixing and physical flow disturbance in the liquid boundary layer on the feed side, a higher flux enhancement could be achieved in a bubbling system with either a higher feed operating temperature, lower feed and permeate flow velocities, inclined module orientation, shorter fiber length or lower packing density. It was also found that gas bubbling not only enhanced the permeation flux by average 26% when concentrating feed solution from 18% salt concentration to saturation, but also delayed the occurrence of major flux decline due to crystal deposition when compared to the module with spacers. These results were confirmed by membrane surface autopsy at different operating stages using SEM. [Copyright &y& Elsevier]

Abstract: High performance flat sheet forward osmosis (FO) membranes have been successfully fabricated using Torlon® polyamide-imide (PAI) materials via phase inversion followed by polyelectrolyte polyethyleneimine (PEI) post-treatment to form a nanofiltration (NF)-like rejection layer with positive charges. The structure and charge property of the FO membranes were carefully tailored by optimizing casting conditions and selecting different immersing methods for the post-treatment. Especially, when the PAI micro-porous substrate was embedded with a woven fabric, the enhanced mechanical strength of the membrane made it possible to reduce the thickness of the substrate to 55μm, which is in favor of high water flux. The resultant membranes can reach a water flux of 29.65Lm−2 h−1 with a ratio of salt flux to water flux (J s /J v ) of <0.8gL−1 in the active layer facing draw solution (AL-facing-DS) configuration, or the water flux of 19.2Lm−2 h−1 and the J s /J v of <0.5gL−1 in the active layer facing feed water (AL-facing-FW) configuration using 0.5M MgCl2 as the draw solution and de-ionized water as the feed water at room temperature. [Copyright &y& Elsevier]

Abstract: There has been a resurgence of interest in forward osmosis (FO) as a potential means of desalination, dewatering and in pressure retarded osmosis, which Sidney Loeb was advocating over 3decades ago. This paper describes the characteristics and potential applications of a newly developed FO hollow fiber membrane, which was fabricated by interfacial polymerization on the inner surface of a polyethersulfone (PES) hollow fiber. This FO membrane presents excellent intrinsic separation properties, with a water flux of 42.6L/m2 h using 0.5M NaCl as the draw solution and DI water as the feed with the active layer facing the draw solution orientation at 23°C. The corresponding ratio of salt flux to water flux was only 0.094g/L, which is superior to all other FO membranes reported in the open literature. To evaluate different application scenarios, various NaCl solutions (500ppm (8.6mM), 1wt.% (0.17M) and 3.5wt.% (0.59M)) were used as the feed water to test the performance of the FO membrane. The membrane can achieve a water flux of 12.4L/m2 h with 3.5wt.% NaCl solution as the feed and 2M NaCl as the draw solution, suggesting it has good potential for seawater desalination. [ABSTRACT FROM AUTHOR]

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

Abstract: Forward osmosis (FO) has attracted wide interest for its many potential applications. Recent developments suggest that double-skinned FO membranes may perform superiorly over conventional single-skinned ones. In this design, a dense rejection skin facing the draw solution is responsible for the separation, while a second skin facing the feed solution is designed to prevent foulants entering into the porous support layer sandwiched between the two skins. For the first time, an analytical model is developed for double-skinned FO membranes and is verified experimentally. Model simulations suggest that an optimal double-skinned membrane shall have a feed skin similar to that of a low rejection nanofiltration membrane to minimize the overall hydraulic resistant and to reduce internal concentration polarization. On the other hand, the optimization of the draw skin calls for a compromise between its water permeability and solute rejection. FO water flux is greater for support layers with higher mass transfer coefficients. In addition, it decreases with decreasing draw solution concentration and increasing feed solution concentration. While membrane orientation plays an important role for applications with low feed solution concentrations (with the denser skin preferentially facing the draw solution), this effect becomes negligible at high feed solution concentrations. [Copyright &y& Elsevier]

Abstract: There has been an increasing interest in the novel integration of forward osmosis (FO) and biological process known as the osmotic membrane bioreactor (OMBR). However, little operating experience is available to adequately assess the feasibility of the technology for larger scale application. The goal of this study is to provide fundamental information on the technology. In this study, an OMBR system was continuously operated for 73days. It was found that the high retention property of the FO membrane and salt transmission from the draw solution resulted in increasing mixed liquor salinity until a stable state was reached. In spite of the elevated salinity, the water flux was relatively stable at around 3Lm−2 h−1. Post-experiment analyses indicated mild membrane fouling, and its effect on water permeability was insignificant. An ion analysis check indicated that scaling did not occur. The SEM examination detected a thin gel-like secondary layer on the membrane surface. It was deduced that this secondary layer could have an influencing role on salt transmission during the experiment, and moderated salt concentration in the bioreactor. [Copyright &y& Elsevier]