The Nanofiltration (NF) is a pressure-driven membrane process of the Membrane filtrationbetween the Ultrafiltration (UF) and the Reverse osmosis (RO) is located. It is used for Separation of dissolved substances - especially small organic molecules and polyvalent ions - from liquids. The pore size of nanofiltration membranes is typically in the range of 1 to 10 nanometerswhat a Molecular mass limit of around 200 to 1,000 Daltons corresponds.
Functional principle
In nanofiltration, the medium to be separated is mixed with moderate pressure (usually between 5 and 40 bar) is led past a semi-permeable membrane.
- Water and small, uncharged molecules can pass through the membrane (permeate).
- Organic molecules of medium size, polyvalent ions and Macromolecules are retained (retentate).
The separation performance of nanofiltration is based on both Sieve effect (size exclusion) as well as on electrostatic repulsion (Donnan effect). This allows specific groups of substances to be separated while others can pass through - an advantage over the Reverse osmosiswhich retains almost all dissolved substances.
Properties of nanofiltration membranes
Nanofiltration membranes often consist of Polyamide composite systemsbut increasingly also from inorganic materials like Ceramics.
Typical properties are
- Selective retention of divalent ions (e.g. Ca²⁺, SO₄²-), with partial permeability for monovalent ions (Na⁺, Cl-)
- Efficient removal organic substances, colorants and micropollutants
- High water permeability at moderate operating pressure
- Good durability against many chemical and biological influences
Areas of application
Nanofiltration is used in numerous industrial and municipal areas, including:
- Drinking water treatment (hardener reduction, pesticide removal, disinfection by-products)
- Food industry (decolorization of sugar solutions, fruit juice concentration, whey processing)
- Chemical and pharmaceutical industry (product concentration, solvent recovery)
- Waste water and process water treatment (removal of heavy metals, organic trace substances)
Summary
Nanofiltration represents a Energy-efficient and selective membrane process which represents a Finely graduated separation between ultrafiltration and Reverse osmosis made possible. Thanks to their precise ion selectivity and high flow rates it is ideally suited for applications in which High purity and Resource efficiency are required.
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