What is nanofiltration?

The filtration spectrum below shows that ultrafiltration is succeeded by Nanofiltration. NF is defined by a pore size of approximately 1nm (0.001μm) and a cut-off of 150 to 500 Dalton. In comparison, the pore size of PB membranes is approximately 10 and 20 nanometres (0.01-0.02μm).

Nanofiltration can occur in the following forms;

• Hollow fibre
• Tubular
• Spiral wound
• Capillary membrane
• Flat plate form

The term cut-off was mentioned in the first paragraph. The cut-off of a membrane indicates the extent to which the membrane can capture molecules and is expressed in Dalton. An NF membrane thus stops all molecules larger than 150 to 500 Dalton. PB UF membranes have a cut-off of 100-150 kDa, which converts to 100,000-150,000 Dalton.

Nanofiltration is therefore capable of removing molecules, dissolved particles. This includes, for example, some of the salts, minerals and hardness (Ca and Mg). Nanofiltration is also very suitable for capturing the complete range of humic acids. Ultrafiltration can capture part of the humic acids, so this has everything to do with the molecular size of the humic acids per location.

Nanofiltration is a technique that is becoming increasingly popular, and the following applications can be considered;

• Wastewater treatment
• RO pre-treatment
• Reduction of colour, turbidity and tannins
• Demineralisation
• Process water

Nanofiltration has very small pores, which means that relatively high pressure is required. NF quickly requires a minimum pressure of 6 bar. Besides MF and UF, PB can also deliver custom-made NF modules.

Please contact our sales team to get information on the type of hollow fibre nanofiltration that PB can offer for your application.