Nano filtration (NF) is a technology ranging somewhere in between Ultrafiltration (UF) and Reverse Osmosis (RO) having a pore size of about one nanometer. However in case of NF the membrane is rated by molecular weight cut-off rather than pore size. The operating pressure of a NF system is much lower than that of a RO one.
A special feature of the NF-membrane is its ion selectivity: monovalent ions pass the membrane a lot easier than multivalent ions like sulfate or carbonate. This may be used to reclaim unconsumed acids coming from an etching or cleaning process. However its typical area of operation is the separation of fluids, the removal of ions and the mechanical filtration with extremely small pores.