Waterguide - Nanofiltration

What is nanofiltration?

Similar to ultrafiltration and reverse osmosis, nanofiltration is a pressure-operated membrane separation process for filtering an impure solution. But unlike reverse osmosis, nanofiltration requires lower pressure values, which is why this method is also known as low pressure reverse osmosis.

In contrast to ultrafiltration, the size of the particles retained is ≥ 1 nm.

What is the process principle of nanofiltration?

Like reverse osmosis, nanofiltration also works on the basis of a membrane. High-pressure (3 to 30 bar) is used to press the liquid against the membrane. Liquid and monovalent ions can pass through the membrane (ion selectivity), but dissolved molecules, heavy metals and small particles are prevented from passing through. The way the substances are carried away is based on the diffusion effect.

The filter cake that forms on the membrane improves the filtration performance. It reduces the size of the pores on the membrane and enables particles that are even smaller than 1 nm to be retained.

In which application areas can nanofiltration be used?

Nanofiltration can be used for lots of different areas in which water or waste water has to be treated.

It can be used for softening and for removing heavy metals during water treatment.

It can also be used to remove humic substances, sulphates, discolouration, chloride, fluoride, bacteria and viruses.

Nanofiltration is also often used in combination with a reverse osmosis unit, with the water that flows through the RO unit being pretreated with nanofiltration. This helps to prevent the membrane in an RO unit from scaling and sustaining biological and inorganic fouling early on.

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