Nanofiltration Membrane: Pore size above 1nm, generally 1-2nm. It is a functional semi-permeable membrane that allows solvent molecules or certain low molecular weight solutes or low valence ions to pass through. It is a special and promising variety of separation membrane, which is named for its ability to retain substances with a size of approximately nanometers. It is used for removing organic matter and coloration from surface water, removing hardness from groundwater, partially removing dissolved salts, concentrating fruit juices, and separating useful substances from pharmaceuticals.