Nanofiltration is a pressure driven separation process. The filtration process takes place on a selective separation layer formed by an organic semi-permeable membrane. The driving force of the separation process is the pressure difference between the feed and the filtrate (permeate) side at the separation layer of the membrane.
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.