Nanofiltration (NF) is a rapidly advancing membrane separation technique for water and wastewater treatment. NF can be defined as a pressure driven process wherein the pore size of the membrane (0.5 - 1 nm) as well as the trans-membrane pressure (5 - 21 atm) lies between reverse osmosis and ultra filtration.
Due to the lower operating pressure and higher flow rates, nano-filtration is inexpensive when compared to reverse osmosis. NF membranes allow partial permeation of monovalent salts such as sodium chloride while rejecting bivalent salts and hardness to a greater extent from aqueous solutions. NF can lower TDS and hardness, reduce color and odor, and remove heavy metal ions from ground water. Nanofiltration is used as an independent system to treat water, or as a pre-treatment to reverse osmosis, thereby, reducing the load on RO.