Nanofiltration is a separation process characterized by organic, thin-film composite membranes with a pore size adequate to remove divalent & Multi Valent Molecules. Unlike reverse osmosis (RO) membranes, which reject all solutes, NF membranes can operate at lower pressures and offer selective solute rejection based on both size and charge.

It is also a thin film composite membrane designed to reject multi-valent ions such as various salts, sugars, proteins, polysaccharides, etc. With a pore size positioned between RO & UF the nano-filtration membrane becomes ideal for concentrating or demineralising in the dairy industry and removal of organic matter, hardness removal, sulphate removal, desalting etc. for wastewater recovery.

Nanofiltration removes divalent ions, which make water hard, so nanofiltration is often used to soften hard water. Nanofiltration refers to a speciality membrane process which rejects particles in the approximate size range of 1 nanometer (10 Angstroms), hence the term “nanofiltration.” NF operates in the realm between UF and reverse osmosis. Organic molecules with molecular weights greater than 200 – 400 are rejected. Also, dissolved salts are rejected in the range of 20 – 98%.

Salts which have monovalent anions (e.g., sodium chloride or calcium chloride) have rejections of 20 – 80%, whereas salts with divalent anions (e.g., magnesium sulfate) have higher rejections of 90 – 98%. Typical applications include removal of colour and total organic carbon (TOC) from surface water, removal of hardness or radium from well water, overall reduction of total dissolved solids (TDS), and the separation of organic from inorganic matter in specialty food and wastewater applications. Transmembrane pressures are typically 50 – 225 psi (3.5 – 16 bar).