Nano filtrationand Reverse Osmosis are both techniques to bring into action univalent and bivalent ions.
Nano filtration is a technique that has prospered over the past few years. Today, nano filtration is mainly applied in drinking water purification process steps, such as water softening decolouring and micro pollutant removal.
During industrial processes nano filtration is applied for the removal of specific components, such as colouring agents.
Nano filtration is a pressure related process, during which separation takes place, based on molecule size. Membranes bring about the separation. The technique is mainly applied for the removal of organic substances, such as micro pollutants and multivalent ions. Nano filtration membranes have a moderate retention for univalent salts.
Other applications of nano filtration are:
· The removal of pesticides from groundwater
· The removal of heavy metals from wastewater
· Wastewater recycling in laundries
· Water softening
· Nitrates removal
Reverse Osmosis (RO)
Reverse Osmosisis based upon the fundamental pursuit for balance. Two fluids containing different concentrations of dissolved solids that come in contact with each other will mix until the concentration is uniform. When these two fluids are separated by a semi permeable membrane (which lets the fluid flow through, while dissolved solids stay behind), a fluid containing a lower concentration will move through the membrane into the fluids containing a higher concentration of dissolved solids. (Binnie e.a., 2002)
After a while the water level will be higher on one side of the membrane. The difference in height is called the osmotic pressure.
By pursuing pressure upon the fluid column, which exceeds the osmotic pressure, one will get a reversed effect. Fluids are pressed back through the membrane, while dissolved solids stay behind in the column.
Using this technique, a larger part the salt content of the water can be removed.
Dear Prem and Valek,
Thank you very much for your valuable comments.
With my best regards
Prof. Bachir ACHOUR
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