The MF and UF membrane filtrations have been applied to the water purification process since early 1980's. They have an extremely high removal efficiency of suspended particles including bacteria. However, the future development of the membrane filtration in the water purification process needs to solve the following two problems ; how to improve the removal efficency of soluble matters and how to control the membrane fouling. This paper dealt with the removal efficiency of the soluble organics and inorganics such as humic substances, manganese and ammonia nitrogen in a hybrid MF membrane system with circulating the powdered activated carbons, and the removal mechanism of humic substances by the vibratory shear enhanced NF membrane process. The fouling mechanism in UF membrane filtration was discussed using the data obtained in a series of batch membrane filtration of the Chitose river water. The cake resistance was most significant compared to the other resistances, and the increase in the cake resistance with increasing permeate volume was expressed by a modified Ruth cake filtration equation. The effect of the pre-coagulation and air scrubbing on the control of membrane fouling was also discussed.

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We have already developed several kinds of high performance polyamide composite membranes for reverse osmosis (RO). They have replaced cellulose acetate membranes in the field of ultrapure water production, seawater desalination, softening and desalination of brackish water, and recovery of valuable materials. RO membranes are mainly used in ultrapure water production system for semiconductor manufacturing in Japan, and the RO process is already indispensable fundamental technique in it.
Today, as a much lower pressure operation is required from a view point of energy saving, improvement of a water productivity of membrane element is one of the technological trends in the field of low pressure RO membrane elements.
Recently, we have developed a new crosslinked fully aromatic polyamide super ultra low pressure composite RO membrane which can be used at around 0.5 MPa. The new composite RO membrane has approximately 50% higher water flux than UTC-70U keeping the high solute rejection of UTC-70U.

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We have newly developed high ozone resistant microfiltration (MF) module using polyvinylideneflouride hollow fiber membrane which has high ozone resistance despite being organic material. A new filtration system using this MF module together with ozone can provide 3 to 4 times higher permeate flux compared with the filtration without ozone. Moreover, it has been found that when ozone remains on the membrane surface, higher permeate flux achieved.

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Vibratory shear enhanced processing membrane filtration has developed to solve problems of fouling and/or plugging which are occurringin the conventional crossflow system. The high shear rate which is generated by the vigorous vibration acts on the surface of the membrane and this high shear rate prevents fouling on the surface of the membrane and plugging in its flow path. This unique system expands to wide range of applications not only where cross flow system are conventionally used but also as an alternative technologies such as evaporator, centrifuge, and filter press where high concentrations are required. In this paper, summaries of various technology issues and applications of vibratory shear enhanced processing membrane filtration are described.

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The spiral wound RO element for a high recovery seawater desalination system has developed. The RO element has many advantages suitable for high recovery RO seawater desalination. Based on newly developed membrane and unique element structure, this element was specifically developed for high pressure (maximum operating pressure 9 MPa) and high salt rejection on high concentration
A RO desalination plant, using the newly developed RO elements with open-intake seawater, has been operated by Nitto Denko Corporation in Tropical Biosphere Research Center, National University of the Ryukyus at Sesoko, Motobu-cho, Okinawa in Japan.
The plant Uses eighteen 8-inch-elements “NTR-70SWH-S8” with the nominal performance of 99.7% rejection and 16 m³/d permeate flux under the factory test conditions (at a pressure of 9 MPa, and recovery of 12%, with feed solution of 5.8% NaCl, at 25°C). The RO plant produces 210 m³ /d of permeate water. The recovery ratio was maintained at 60% by high operating pressure. The permeate water quality has been kept less than 250 mg/l TDS.

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The glycine and leucine permeability coefficients, P_gly and P_leu, in their mixed solutions through a cation exchange membrane were measured as a function of HCl concentration, C_HCl, from 0 to 10^-1 mol/l for three different interfacial conditions and were compared with the results for P_gly and P_leu, in their single solutions. Generally P_gly increases with an increase in HCl concentration. However, P_gly decreased between C_HCl=10^-2mol/l and C_HCl=10^-1 mol/l for only the case when HCl was added to the amino acid feed side. Compared with P_gly in a single glycine solution, P_gly in a mixed solution was smaller than that in the single solution. However, their profile outlines are similar. P_leu, also increased with an increase in HCl concentration. P_leu, is smaller than that of P_gly, which corresponds with the result in a single solution. P_leu decreased between C_HCl=10^-2 mol/l and C_HCl =10^-1 mol/l for only the case when HCl is added to the amino acid feed side. Compared with the P_leu in the single leucine solution, P_leu in mixed solution is not very different. The transport mechanism was determined to be an interfacial transport phenomenon. However, the effect of the interfacial transport in mixed solution appears to be decreased if compared with the case in a single solution. The reduced results for glycine in mixed solutions imply that the glycine transport is affected by that of leucine. As the solutions are not idealistic, which means that there exists an interaction between glycine and leucine, the permeability coefficient ratios of glycine to leucine, P_gly /P_leu, in the mixed solution did not correspond with that of the single solution. The highest P_gly /P_leu was 6.7 at C_HCl=10^-4mol/l for the case when HCl was added to the amino acid-permeated side and the next one was 6.1 at C_HCl=10^-4 mol/l for the case when HCl was added to both sides of the membrane.

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A newly developed nanofiltration membrane module “CM Series” which is constructed by cross wound hollow fiber, has high permeate flow rate per module volume at low pressure from tap water and uniformly distributed flow inside the module. Therefore this membrane module has 2 to 3 times as high permeate flow rate as compared with spiral wound modules and can be useful at high recovery ratio condition. It was confirmed that nanofiltration system by this membrane module was effective for removal of organic contaminants. It is considered that this membrane module can be used for advanced treatment of drinking water.

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