Nanofiltration （NF）

Nanofiltration refers to a specialty-membrane processthat rejects dissolved solutes in the approximate size range of 1 nanometer (10Angstroms) — hence the term “nanofiltration.”

With respect to the size and weight of solutes thatnanofiltration membranes reject, NF operates in the realm between reverse osmosis (RO) and ultrafiltration (UF) : Nanofiltration membranes can effectively reject,among other contaminants:

▸ Dissolved organics.

▸ Endotoxins/pyrogens.

▸ Insecticides/pesticides.

▸ Herbicides.

▸ Antibiotics.

▸ Nitrates.

▸ Sugars.

▸ Latex emulsions.

▸ Metal ions.

It also rejects certain soluble salts. Specifically, NF rejects dissolved saltsin 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 higherrejections of 90 – 98 percent. Transmembrane pressures are typically 50 – 225psi (3.5 – 16 bar).

The ideal nanofiltration membrane has a very high-waterpermeability, but the ideal permeability of solutes might be near zero or somehigher value, depending on the solute and application. For example, an applicationmay require near-zero permeability for pesticides and 50 percent permeabilityfor calcium ions.

Typical applications of nanofiltration membrane systemsinclude:

▸ The removal of color and total organiccarbon (TOC) from surface water.

▸ The removal of hardness or radium from wellwater.

▸ The overall reduction of total dissolvedsolids (TDS).

▸ The separation of organic from inorganicmatter in specialty food* and wastewater applications.