Japan has started water reuse projects since 1980 to promote effective utilization of water resources by the national and local governments. However, 1% of total discharge of municipal sewage treatment plants is reused outside of the plants at the present. There are many challenges such as safety evaluation, lowering energy consumption and cost, and public acceptance to overcome in promotion of water reuse. Therefore, we carried out JST CREST project “Development and Evaluation of Water Reuse Technologies for the Establishment of 21st Century Type Water Cycle System.” We also performed demonstration project to verify wastewater reclamation system by MLIT B–DASH Project in Itoman City, Okinawa based on our research achievement of the JST CREST project. Okinawa Prefecture Government and Itoman City also performed investigations to install the water reuse projects for multipurpose applications. These recent situation is described in this article.

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This review article presents trends and prospects of membrane separation processed using ion–exchange membranes in water treatment and energy conversion processes. Cation–exchange membranes (CEMs) and anion–exchange membranes (AEMs) have permselectivity for counter–ions; hence, electrodialysis (ED) process using the membranes has been applied to desalination/concentration processes of salty water. A bipolar membrane composed of a cation– and an anion–exchange layer generates protons and hydroxyl ions in a case of applying voltage across the membrane, and has applied to acid regeneration etc. A charged mosaic membrane consisting of cation– and anion–exchange domains passing through the membrane has permselectivity for electrolytes; hence, it can be applied to desalination process using a piezo–dialysis system. A reverse electrodialysis system having the same structure as ED converts salinity gradient energy between two salt solutions to electric power, and is expected as a renewable energy with a high operating rate and a small footprint.

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Ion exchange membranes have been used in various industrial fields for desalination and concentration applications. Also, by using a bipolar membrane, it is possible to produce acids and alkalis from several salts. In recent years, such a bipolar electrodialysis method, that can reduce the volume of waste has been attracting attention even in the recovery of lithium, which is a material of a secondary battery. In this report, we will introduce our efforts to produce lithium hydroxide from lithium sulfate or lithium carbonate.

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Cation– and anion– exchange membranes, used for the concentration of seawater, were prepared by an electronbeam– induced graft polymerization method (EB method). An ultra high molecular weight polyethylene (UHMWPE) film, which is a commercially available polymeric film, was selected for use as the base film. The EB method consists of three main phases. The first involves electron beam irradiation. The second involves graft polymerization. The third involves the introduction of an ion–exchange group. We found that the concentration performance of the ion– exchange membrane prepared by the electron–beam–induced graft polymerization method was better than that of a commercially available membrane. To provide a method for producing our membrane industrially, we manufactured producing apparatus. The concentrating performance of the ion exchange membranes producing used by our apparatus was better than that of a commercially available membrane and maintained for 140 days.

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A large amount of organic solvents were used in chemical processes, and most of the discharged solvents were incinerated, resulting in CO2 discharge in the atmosphere. In order to reduce the discharge amount of CO2 gas, the used organic solvents are desirable to be refined and reused in chemical plants. Nowadays, the organic solvents were mainly refined by distillation method because this method can be applicable to many liquid mixtures. In this article, purification methods of typical organic solvents, widely used in industry are firstly explained. Then, applicability of membrane system to the purification process of the organic solvents is discussed briefly.

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Separation of organic solvent by membrane is an emerging technology for the purification or separation of organic solvents. In this study, game changing OHF (Organic solvent Hyper Filtration) membranes and their applications are under development to realize the replacement from energy–consuming distillation to energy–efficient membrane process. Nano filtration (NF)–type hollow fiber OHF membrane was developed by TIPS (Thermally–Induced Phase Separation) method using solvent–resistant polymers such as nylon 6. The prepared membranes showed methanol (MeOH) permeability of > 2 LMH (L･m–2･h–1) with molecular weight cut–off (MWCO) of about 1,000 and stability for >1 month. Reverse osmosis (RO)–type organic composite OHF membrane was developed by the interfacial polymerization method. A highly cross-linked polyamide layer was prepared on a solvent resistant support membrane. The membrane showed selectivity for MeOH against toluene (TOL) in separation test using MeOH/TOL mixture. Membrane performance was Rej.＝ 65% Flux ＝ 16 LMH at 40 bar. The stability was > 2 weeks. NF–type TiO2/ZrO2 ceramic composite OHF membrane was developed using organic chelating ligands (OCL) as a pore size–fixing spacer. The membrane showed high permeability for organic solvents such as hexane (26 LMH) and MeOH (25 LMH) at 6 bar with MWCO of about 1,000 and stability of > 1 week. NF–type inorganic nanosheet OHF membrane was developed by laminating nanosheets of niobate and/or graphene oxide onto solvent resistant support membrane using chemical binders. The membrane showed relatively high MeOH permeability (11 LMH at 2 bar) and good rejection against organic dyes such as Evans blue (Mw : 960.8) with 87%.

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Inorganic membranes are promising to be used in separation in organic solvents due to their inherent stability under various types of organic solvents and the mechanical strength. In this article, organic solvent nanofiltration (OSN) and organic solvent reverse osmosis (OSRO) are reviewed from the viewpoints of membrane materials and their applications. The trend to develop high performance OSN and OSRO membranes are described. At present, very few OSRO membranes have been reported, while a variety of OSN ceramic membranes were reported and some of them are commercially available. In addition, the principle of energy–saving by OSN and OSRO is also discussed.

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Membrane separation technology has become popular in recent years as an energy–saving technology in various industrial fields. However, there are almost no membranes that can be used in organic solvents. In this study, we succeeded to fabricate organic solvent resistant microfiltration (MF) and ultrafiltration (UF) membranes by the combined use of thermally induced phase separation (TIPS) method and non–solvent induced phase separation (NIPS) method. Membrane modules made by the prepared membranes were also resistant to many organic solvents, and they could be used in long–term membrane separation test for organic solvent systems such as polystyrene / toluene and Vitamin B12 / methanol.

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Biliary lipids consist of a mixture of bile salts, phospholipids and cholesterol. Monomers and simple micelles of bile salts have potent detergent properties and deleterious effects on cell membranes, which coexist with mixed micelles and vesicles of biliary lipid in a dynamic equilibrium in bile. In the presence of bile salts monomers, ABCB4, belonging to the ATP–binding cassette (ABC) transporter family, secretes the biliary phospholipids, preferentially phosphatidylcholine (PC). The formation of bile salts/PC mixed micelles protects hepatocytes from bile salts cytotoxicity by decreasing the cell association of bile salt molecules. On the other hand, cholesterol inhibits the interaction between bile salts and PC, and hence attenuates the cytoprotective effects of PC against bile salts. The ABCB4– mediated PC efflux is significantly increased by taurohyodeoxycholate, which has high mixed micelle formation ability with PC. These findings will help to develop new therapeutic agents for cholestatic liver diseases.

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Artificial lipid membrane systems (e.g., liposome) have been developed to understand the fundamental behavior of lipids and their biological roles. Membrane surface–enhanced Raman spectroscopy (MSERS) is a powerful method to analyze the lipid membrane due to its high sensitivity. In this study, silver nanoparticles (AgNPs) were coated by the unsaturated phospholipids (1,2–dioleoyl–sn–glycero–3–phosphocholine) for analyzing their behaviors in the membranes. Raman enhancements were observed, in measurements with excitation by green laser (532 nm) and by red laser (785 nm). The enhancement factor analyses revealed that AgNP@lipid systems specifically enhanced the Raman peak at 1668 cm–1 (C ＝ C), thus the MSERS method using AgNPs can be an alternative analysis of biological membrane properties and functions.

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Although forward osmosis (FO) membranes have shown great promise for many applications,there are few studies attempting to create a systematization of the testing conditions at a pilot scale for FO membrane modules. Aquaporin has developed FO (HFFO) modules and providing widely. To address this issue, hollow fiber HFFO membrane modules with different performances (water flux and salt rejection) have been investigated at different operating conditions by Victroria Sanada–Embuena 1). They also investigated FO rejections for caffeine, niacin and urea compared to the RO rejections. I introduced these results and mentioned possibility of applying HFFO membrane.

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