Nano filtration Membrane (NF) is a membrane liquid-separation technology sharing many characteristics with reverse osmosis (RO). Unlike RO, which has high rejection of virtually all dissolved solutes, NF provides high rejection of multivalent ions, such as calcium, and low rejection of monovalent ions, such as chloride.
As the globally recognized leader in liquid-separation innovations and solutions, we help customers across industries and markets solve their toughest water-treatment challenges with our experience, expertise, and FilmTec™ portfolio of reverse osmosis and nanofiltration membrane technology.
Between reverse osmosis and ultrafiltration
Nanofiltration refers to a specialty-membrane process that rejects dissolved solutes in the approximate size range of 1 nanometer (10 Angstroms) — hence the term “nanofiltration.”
With respect to the size and weight of solutes that nanofiltration membranes reject, NF operates in the realm between reverse osmosis (RO) and ultrafiltration (UF) : Organic molecules with molecular weights greater than 200 – 400 are rejected. Nanofiltration membranes can effectively reject, among other contaminants:
- Dissolved organics.
- Latex emulsions.
- Metal ions.
It also rejects certain soluble salts. Specifically, NF rejects dissolved salts in the range of 20 – 98 percent. Salts which have monovalent anions (e.g., sodium chloride or calcium chloride) have rejections of 20 – 80 percent, whereas salts with divalent anions (e.g., magnesium sulfate) have higher rejections of 90 – 98 percent. Transmembrane pressures are typically 50 – 225 psi (3.5 – 16 bar).
The ideal nanofiltration membrane has a very high water permeability, but the ideal permeability of solutes might be near zero or some higher value, depending on the solute and application. For example, an application may require near-zero permeability for pesticides and 50 percent permeability for calcium ions.
Typical applications of nanofiltration membrane systems include:
- The removal of color and total organic carbon (TOC) from surface water.
- The removal of hardness or radium from well water.
- The overall reduction of total dissolved solids (TDS).
- The separation of organic from inorganic matter in specialty food* and wastewater applications.