Nano filtration also known as membrane separation process is essentially a liquid phase one, as it separates various inorganic and organic substances from solution in a liquid mainly, but by no means entirely, water. It is done by diffusion through a membrane, under different pressure that is considerably less than that for reverse osmosis but still greater than that for ultra-filtration. The development of a thin film composite membrane gave real impetus to nano-filtration as a recognized process. The unique ability of nano filtration to separate & fractionate ionic well as relatively low molecular weight organic species has resulted in its popularity lately.
NF membranes are also useful in removing natural organic matter (especially color, taste, odor) from water and in removal of trace herbicides from large water flows. These plants can be used for separating residual quantities of disinfectants from drinking water.