A large 40, 000 m³/day plant, which has been inaugurated recently at Okinawa, is introduced. The reduction of boron concentration in the permeate of the RO seawater desalination units is discussed. The trend of application of the high pressure RO to a high-recovery seawater and a landfill leachate desalination processes is explained.
The nanofiltration has become an inportant purification process for treating the drinking water sources. However, the commercial membranes are too numerous that it is important to qualify them properly.
The various unique UF and MF modules, developed at the Aqua-renaissance '90 project, are now used for the high-recovery drinking water treatment processes.
The acid and alkali recovery processes, which use ion-exchange membranes, namely, dialysis, electro-dialysis and electrolysis processes, are introduced. The ion-exchange process, where resins are regenerated not by acid or alkali but by using ion-exchange membranes are finally introduced.

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Ion exchange membranes technology for acid and base recovery is reviewed. Diffusion dialysis is advanced for its low investment cost and high recovery of both waste acid and waste base. On the other hand, it has disadvantages of low concentration of recovered liquid and increase of total quantity of liquid. To improve such disadvantage of diffusion dialysis, a combination process of a diffusion dialysis and electrodialysis is proposed. A newly developed hydrogen ion selective membrane enabled an electrodialysis process to recover concentrated acid from acid waste at the same time separating dissolved metal ion from free acid. Regeneration of acid and base with a bipolar membrane electrodialysis is also introduced.

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Nanofiltration (NF) is a pressure driven membrane process which falls between reverse osmosis and ultrafiltration. In the early 1980's, several thin-film composite type of NF membranes were developed. Since then NF technology has been widely applied in a variety of applications including municipal and industrial water treatment and food processing.
NF membrane performance is characterized from its fundamental characteristics such as charge, charge density, molecular-weight cutoff, and pure water permeability coefficient. NF membrane performance can be improved or specialized by adjusting these parameters. Another way to improve membrane processes is to combine NF with any other separation processes which is referred to as hybrid process. In this article the hybrid NF processes are reviewed and their potential benefits are demonstrated in more detail.

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The new RO seawater desalination system for cost and energy saving has been developed. The newly developed “Brine Conversion Two-stage RO Seawater Desalination System” uses less energy than the conventional system to produce the same amount of fresh water. This system produces more fresh water from the concentrated water (salt concentration 5.8%, produced under 6.5 MPa pressure), which was exhausted to the sea in the conventional system.
The new type membrane, which can be operated in conditions of high-pressure (9.0 MPa) and high concentration (5.8%), was developed and its performance of seawater desalination have been proved to be in good conditions.

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Landfill leachate contains highly concentrated inorganic salts and relatively low level of organics measured as BOD or COD, which are reported to have recalcitrant chlorinated carbon such as dioxins. Those feature of leachate are induced from waste dumped mostly composed of incinerated ashes. Conventional leachate treatment system with calcium removal, biological treatment, sedimentation with coagulation, filtration and carbon adsorption cannot remove inorganic salt and persistent organic matters. A landfill leachate treatment test system with reverse osmosis system using DT-Module has been tested and operated at a landfill site in Japan and showed an excellent performance removing highly concentrated salts by 99.4% and chlorinated carbon such as dioxins by 99.6% or more. Recovery rates of reverse osmosis system were 90-95%. By those experiments, it became to be possible to adopt reverse osmosis system for leachate treatment in Japan in combination with proper concentrate treatment.

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In order to prepare a membrane with high ethanol permselectivity, the effects of preparation conditions such as the composition of starting solution, calcination temperature and period on pervaporation performance of silicalite membrane has been investigated in detail.
The silicalite membranes were prepared on porous supports of sintered stainless steel by hydrothermal synthesis at 170°C for 48 h-192h. Then silicalite membrane was calcined at over 250°C for 20h-60h in an ordinal oven. The pervaporation performance of the silicalite membranes was measured at 30-60°C for 5 vol% ethanol aqueous solution as a feed and was evaluated by separation factor α and fluxes.
The silicalite membrane prepared by hydrothermal synthesis at 170°C for 144h using a solution, where H₂O/SiO₂ ratio was 90, and calcined at 375°C for 60h. The silicalite membrane prepared showed a separation factor α (EtOH/H₂O) =120 with a total flux of 0.29kg/m²·for a 5 vol% ethanol aqueous solution at 30°C.

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Our proposal is that over a certain range of the solute concentration of multi-component electrolyte mixtures, it is possible to assume that each ion can transport independently through a membrane without interaction between the ions and between each ion and the membrane charge. In this paper, the results of experiments obtained using a commercial nanofiltration membrane with 8 kinds of underground brackish water are reported; the results are then used to obtain ion permeabilities using transport equations. From these results it is possible to estimate each ion concentration and pH in the permeate. The effect of osmotic pressure can be estimated from the calculated ion concentrations. Finally, it is shown that the mass transfer coefficients obtained can be correlated to the similar equation previously reported for the spiral-wound type module.
Although assumptions made in this paper have a certain limit in application, with this method it is simple to estimate permeate water qualities.

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We have newly developed high ozone resistance microfiltration (MF) module using polyvinylidene-fluoride (PVOF) hollow fiber membrane which has high ozone resistance despite being organic material. A new filtration system using this MF module together with ozone can consistently provide 3 to 4 times higher permeate flux compared against the filtration without ozone for various types of feed water. This is because ozone decomposes or denatures a part of organic materials in the raw water and reduce fouling of the membrane surface.

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