Nanosegregated liquid crystals such as columnar, smectic, and bicontinuous cubic phases lead to self–organization of nanochannels capable of transporting ions, electrons, and molecules. Liquid–crystalline films with nanochannels have a great potential as solid–phase electrolyte and semiconductor, and separation membranes. The approaches to the development of ions, molecules, and electron conductors based on liquid–crystalline ordered nanostructures are described.

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Seawater desalination with reverse osmosis membrane (SWRO) was developed in the middle of 20th century. In SWRO process, one of the largest problems has been energy consumption, which is mainly due to the osmotic pressure effect and is smaller than that in thermal desalination process. In order to reduce energy consumption, innovative technologies such as large productivity RO membrane elements, high energy recovery units, process optimization with simulation technologies, and highly efficient systems were developed and commercialized. Especially, productivity of SWRO membrane became doubled in the last decade, and the energy recovery efficiency reached more than 95%. These technologies made SWRO systems more reliable and cost effective, and large SWRO plants have been constructed and operated in the world as well as the Middle East since the end of 1990’s when water shortages became more serious. The SWRO technologies are expected to be developed and contribute to secure the water sustainably.

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For the cell harvesting process, membrane filtration has been gaining popularity instead of coagulation–flotation or centrifugation process, because it can easily concentrate the algae cells more than 60 g/L with a low energy consumption. The major drawback of this technology is membrane fouling, which increase the operation cost to a large extent as a result of reduction of membrane permeability. For more efficient use of membrane, we should increase the operation flux to 4.0 m3/m2/day, but it is still difficult to be achieved with the normal membrane and general washing condition. In this study, we prepared the novel hollow fiber membrane having the nominal pore size of 2.0 µ m and optimized the washing condition to achieve the 30–times concentration with operation flux of 4.0 m3/m2/day. As a result of the use of novel membrane and optimal washing condition, we could achieve 30–fold concentration with a flux of 4.0 m3/m2/day. Furthermore, the final trans–membrane pressure was low enough (60 kPa), implying that there was a possibility to be able to set higher operation flux or higher concentration level. Then, we developed novel harvesting process, which includes both membrane filtration and sedimentation process. We optimize the operation condition in lab–scale experiment and applied it to the pilot-scale system. As a result of the pilot-scale experiment, 300–fold concentration and high flux operation of 4.0 m/d was found to be achieved. In addition, we make a tool to predict the operation flux based on the analysis of fouling index and particle size distribution of microalgae.

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This outline introduces the use of a membrane for wastewater treatment that will help to reduce energy consumption as well as possibly generate energy. Membrane bioreactors (MBRs) are a superior method for easily providing high quality effluent; the obstacle, however, is that it requires tremendous energy during aeration. An energy-saving MBR with swing media can hold a large amount of microbes. In this system, the mixed liquor suspended solids (MLSS) of the reactor is low, and thus the viscosity of the aeration tank is also of a low value. Oxygen is, therefore, easily dissolved. The new MBR can reduce energy needed for aeration by approximately 30%. Current incineration facilities evaporate the process wastewater using high temperature effluent gas in order to prevent discharge of the wastewater; this process reduces the efficiency of power generation. We can, however, recover that electricity using an RO membrane system to reduce wastewater by more than 70%. Recently power generation systems using FO membranes have been proposed. However, the performance of FO membranes and draw solutions (DS) remain insufficient. We develop a high flux FO membrane and magnetic particle DS immobilized polyelectrolyte. It has been suggested that a high flux FO membrane and magnetic particle DS may produce approximately 0.3 kWh/m3 of electricity.

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Membrane bioreactors (MBRs) have been widely used for wastewater treatment. MBRs are subject to membrane fouling. To perform chemical cleaning at appropriate timing, fouling must be predicted in the long–term. Fouling prediction corresponds to transmembrane pressure (TMP) prediction under conditions of constant-rate filtration. A reason for difficulty of TMP prediction is TMP jumps, which is rapid increase of TMP after long-term operation of MBRs under constant–rate filtration. Our laboratory therefore have been developing both TMP prediction models and TMP jump prediction models. TMP prediction models can predict future TMP with high accuracy in the longterm. TMP jump prediction models can accurately predict timing of TMP jumps. A schedule of chemical cleaning of membrane can be arranged by using those models. By analyzing TMP jump model, operating conditions such as aeration can be designed for performing energy–saving MBRs. In addition, CFD simulation can provide useful information on optimizing size of bubble and arrangement of membranes in MBR.

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Technological needs for gas separation is being increased to date because of the environment and energy crisis of the current world. Porous coordination compounds (PCCs) or metal organic frameworks (MOFs) have recently attracted significant attention due to their potential in gas capture/separation applications. Their porous structures (e.g. pore and window sizes) as well as affinities to the gas molecules can be designed by the selection of chemical constituents (organic ligands and metal ions), which allow a variety of PCCs used for separations of various molecules in gas or liquid phase. In gas separation applications, PCCs have been used not only as adsorbents but also as solid membranes. Recently, PCC/polymer hybrid is emerging as a new strategy to realize PCC–based membranes with a sort of flexibility and processability. In this review, we highlight gas separation technique using PCCs and introduce emerging approaches towards PCC–based flexible membranes.

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ZIF–8 is a flexible zeolitic imidazole-based metal organic framework (MOF) whose narrow pore apertures swing open by reorientation of imidazolate linkers and expand when probed with guest molecules. An interesting feature of the ZIF–8 MOF is that its crystal size can be varied over a wide range of values (typically from approximately 50 nm to 100 µ m), something that is very hard to achieve with classical porous aluminosilicates. Such crystal size engineering might be exploited to tune the adsorptive and diffusion properties of the material for molecular separation processes. Our studies have aimed at carefully preparing ZIF–8 samples of different crystal size with identical structural and chemical properties to allow an accurate analysis of the effect of crystal size on adsorption and diffusion of guest molecules into the ZIF–8 MOF. Additionally, a simple, facile, and convenient route for in situ aqueous synthesis of well-intergrown ZIF–8 membranes has been developed. This review provides an overview of the aqueous synthesis of ZIF–8 MOF with emphasis on the morphology control and discusses recent progress in ZIF membranes and the challenges and opportunities for future membrane separation technology using MOF.

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A UiO–66 membrane was synthesized on a porous Al2O3 support using an in–situ solvothermal method with a coordination modulation technique. The prepared UiO–66 membrane exhibited the CO2/N2 ideal separation factor of 5.5, which distinctly differ from the values of 0.80 in Knudsen diffusion. In pervaporation tests, the UiO–66 membrane showed the organic selectivity. The separation factor in 10 wt% EtOH/H2O and Acetone/H2O were 4.9 and 12.2, respectively. Additionally, we demonstrated the stable pervaporation perfomance of UiO–66 membrane in an ethanol/water mixture.

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Metal-organic frameworks (MOFs) have been recognized as a new candidate material for gas separation membranes based on their characteristic pore size and adsorption properties. Recently, pure–MOF membranes have been reported using the in–situ growth method and the secondary growth method, which prepare the pure MOF separation layer. Another preparation method is the counter–diffusion method, which supply the solution of the metal salt and the organic ligand from both sides of the porous support. Among several varieties of MOFs, ZIF–8 is one of the most focused materials for separation membranes, which is effective for propylene/propane separation based on their small difference in molecular size. As an example, we prepared the ZIF–8 membrane using the counter–diffusion method with selective ZIF–8 layer prepared within the porous support. The contribution of diffusive separation for propylene/propane was clarified from the analysis of diffusivity and solubility. In this review, the preparation and the characterization of ZIF–8 membranes for propylene/propane separation are presented.

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Sol–gel derived amorphous silica membranes are reviewed in terms of control of network structure for the development of highly permeable gas separation membranes. Metal doping such as palladium and fluorine, as well as spacer method utilizing bridged alkoxide with organic groups between 2 Si atoms, are introduced. Gas permeation properties for amorphous silica membranes were quantitatively evaluated by modified gas translation (GT) model. Pore size determination with the temperature dependence of gas permeances was also introduced, and quantitatively discussed the effect of Si precursor on silica network size and small gas permeation properties.

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The high performance submerged membrane module using flat sheet membrane was introduced and employed in the waste water treatment by MBR. The flat sheet membrane has the characteristics of ultrafiltration with the pore size of 0.04 µ m and thin thickness of 2 mm so as to obtain the high quality of treated water and to save the space of the module installation. In order to reduce the energy consumption of MBR, we introduced the effective membrane cleaning process, the so–called mechanical cleaning process, MCP. The effectiveness of MCP is examined and verified by using the pilot–scale testing equipment. We estimated that the energy consumption per treated water of MBR can achieve the value of less than 0.4 kWh/m3 by using MCP with the high performance submerged flat sheet membrane module.

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