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The structure parameter of the forward osmosis membrane has been defined as the characteristics of the support membrane, not related to the separation layer. Therefore, studies for improving the performance of the forward osmosis (FO) membranes have been focused on the optimization of the support structure. This study demonstrates that the separation thin-film polyamide (PA) layer has a strong impact on the performance of the FO membrane thus the structure parameters (S). We intentionally utilized a polyethersulfone hollow fiber substrate and two types of active separation skin were prepared at the inner surface: the first MPD/TMC and the second by adding triethylamine (TEA) into the aqueous phase during the interfacial polymerization (IP). By adding TEA, a rough PA layer with a leaf-like structure and a high crosslinking degree was obtained followed with high FO flux and low reverse salt flux attributed to the increased effective filtration area and crosslinking degree. The structure parameter of the FO membrane was reduced from 0.78 mm (for MPD/TMC system) to 0.45 mm (for MPD-TEA/TMC system). The result indicated that for the same substrate, lower structure parameter corresponded to the skin layer with higher permeance and rejection. This study confirmed that the structure parameter is more an inherent property of the entire TFC FO membrane than the character of the porous substrate. Future design for FO membranes needs to regulate the substrate, but more importantly to optimize the separation layer. • An approaching ratio (α) was designed as a simple guideline for control the structure parameter of FO membranes. • Diethylene glycol was used as the nonsolvent to control the approaching ratio. • Lowest structure parameter and highest FO performance were obtained at α = 50 %. • The optimized TFC membrane is of practical interest for lithium concentration. [ABSTRACT FROM AUTHOR]

Vanadium is an important rare element and has been widely used in metallurgical industry, aerospace industry and chemical industry due to its special physical and chemical properties. In this work we explored the feasibility of using forward osmosis (FO) to concentrate the vanadium leaching solution (VLS) using saturated sodium chloride as the draw solution. The effluent draw solution can be directly reused as a raw material in the vanadium production process without the need for regeneration. The VLS concentration performance was evaluated using commercial thin film composite (TFC) and cellulose triacetate (CTA) FO membranes. It was found that the FO water flux decline was due to the coupled effects of VLS concentration and fouling. TFC membrane exhibited higher initial water flux but also experienced more severe fouling and faster flux decline. Importantly, this study observed an existence of a critical concentration factor (CF) during VLS concentration. Below the critical CF, membrane fouling was mainly caused by surface crystallization and flux decline was relatively milder; above the critical CF, severe bulk crystallization occurred in the feed VLS, which caused significant membrane scaling and dramatical flux decline. The critical CF concept was further used to guide the FO operation for VLS concentration in this study. While severe membrane fouling at a CF above the critical value could be removed by a brief water rinse, operating the FO below the critical CF is preferred for which cyclic VLS concentration process was demonstrated to be feasible without the need for periodic membrane cleaning. Overall, the results suggest that the FO can be a promising solution for highly efficient and low-energy VLS concentration. Image 1 • FO was used for energy-efficient concentration of vanadium leaching solution (VLS). • The existence of a critical concentration factor (CF) was observed for VLS concentration by FO. • Below the critical CF membrane fouling was caused by surface crystallization and flux decline was mild. • Above the critical CF membrane was severely fouled due to bulk crystallization and flux decline was dramatic. • Operating the FO concentration processes below the critical CF is preferred. [ABSTRACT FROM AUTHOR]

Preparation of dialysate for hemodialysis (or dialysis) requires dilution of the dialysis concentrate with purified water. Present practice contains two steps: first to purify water, and then water is transported to clinic to mix with the dialysate concentrate before treatment. As a new forward osmosis dialysis hybrid process, based on osmotic dilution, is evaluated for decentralized health care systems. A commercial cellulose triacetate (CTA) and a tailor-made thin film composite (TFC) polyamide FO membranes were examined. The rejection of salts in tap water by the FO membranes was investigated, and the real rejections of various ions as a function of permeate flux were well described by using a irreversible thermodynamic model. The hollow fiber TFC FO membrane showed higher water flux and lower reverse salt flux than the CTA membrane in diluting process. Both steric hindrance and electrostatic repulsion explained the rejection behavior of the membranes to the ions. Higher rejections of anions were obtained than cations, which was attributed to the anions selection characteristics of the membranes. No obvious foulings or scalings were observed in a relatively long time osmotic dilution process over 5 repeated cycles. The stable, high efficient osmotic dilution process in hemodialysis holds a strong promise in reducing the consumption of purified water or even eliminating the water purification step. This work provides a potentially new platform hemodialysis which can be portable and implementable away from major hospitals and major clinics. Image 1 • Tap water was used to dilute dialysis concentrate based on forward osmosis. • Ion rejections versus flux were fit well using irreversible thermodynamic model. • Low reverse diffusion of components in dialysis concentrate was found. • Very light fouling after long time osmotic dilution could be cleaned by rinsing with caustic. [ABSTRACT FROM AUTHOR]