Principles of nanofiltration membrane processes

Nanofiltration (NF) membrane is a class of pressure-driven membrane, which is an intermediate of ultrafiltration membrane and reverse osmosis (RO). With the pore size ranging from 0.1 to 1 nm (equivalent to molecular weight cut-off of 200–1000 Da), the NF membrane has a high removal rate for multivalent salt ions and organic solutes which have a molecular weight larger than 200 Da. Hence, the NF membrane is suitable to be used to remove hardness, heavy metals, and large organic matter such as dyes. However, it has a low rejection of monovalent ions and neutral solutes with a molecular weight below 200, which can be removed only through RO membranes.