Nanoflltration is a pressure driven membrane process between reverse osmosis and ultrafiltration. The rejection is low for salts with monovalent anion and nonionized organics with molecular weight below 150 while high for salts with di-and multivalent anions and organics with molecular weight above 300. Examples of applications are removal of color and TOC from Florida surface water, removal of hardness, radium, and sulfate from well water, removal of sulfate from seawater and simultaneous removal of sodium chloride and concentration of organics with molecular weight 300-1 000 in the food and pharmaceutical industries. The investment cost for a nanofiltration plant is about the same as for a brackish water reverse osmosis plant, but the energy savings can be considerable by using nanoflltration instead of reverse osmosis.

The effects of temperature on the performance of four thin-film composite, aromatic polyamide commercial membranes (FilmTec, FT30 membranes) have been investigated experimentally. The operating conditions cover a temperature range of 5-60 °C and a pressure range of 350-7000 kPa, and the feed solution used is a 2000 ppm aqueous solution of sodium chloride. In general, it has been found that separation is independent of temperature at higher pressures. However, for lower pressures, separation decreases, passes through a minimum, and increases with increasing temperature. The permeation flux increases significantly with temperature. The compaction of the membranes causes the pure water permeability coefficient, A, to vary over the entire pressure range. Compaction is more pronounced as the temperature is increased. The A values, extrapolated to zero pressure, varied with temperature and were well represented by an Arrhenius plot. The apparent activation energies for water flux were found to vary with membrane type and temperature range but were * To whom correspondence should be addressed.

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