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Nanofiltration System

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Nanofiltration like other membrane separation processes uses membranes to separate different fluids or ions. Organic semipermeable membrane, forms a separation layer where the filtration process takes place. Once the pressure difference between the feed (retentate) and the filtrate (permeate) is created, the separation process starts. Membrane, because of its selectivity, retain one or many components of a dissolved mixture whereas water and substances having a molecular weight < 200 D are able to permeate the semipermeable separation layer. The most important aspect of nanofiltration membrane is that, monovalent ions pass the membrane whereas divalent and multivalent ions are rejected.

Nanofiltration uses cellulosic acetate and aromatic polyamide type Membranes which can reject salts from 95% for divalent salts to 40% for monovalent salts. The membrane used by Nanofiltration have pores that are typically much larger than the membrane pores that are used in reverse osmosis. The rejection rate of divalent and multivalent cations especially calcium and magnesium is higher in nanofiltration due to this, it is used extensively in industrial water softening applications as well as pre-treatment for reverse osmosis. Nanofiltration can operate at lower pressure and is capable of passing some of the inorganic salts hence they can be used where high organic removal and moderate inorganic removals are desired.

Nanofiltration Versus Reverse Osmosis
The membrane pore structure of nanofiltration is larger than reverse osmosis membrane. That is why it is also sometimes referred to as "loose" RO. More salt is allowed to pass in nanofiltration as compared to reverse osmosis. NF can operate at higher recoveries as compared to reverse osmosis, which enables the conservation of water usage because of lower concentrate stream flow rate.

The other main difference between reverse osmosis and the NF lies in the removal of monovalent ions such as chlorides. The monovalent ion level removed by the RO is 98-99% level at 200 psi. But in case of NF membrane's removal of monovalent ions ranges between 50% to 90%. The removal of monovalent ion by NF depends on the material and manufacture of the membrane due to this, there is a variety of Nanofiltration membranes available. Nanofiltration uses less fine membrane hence the feed pressure required in the system is lower as compared to RO systems. The fouling rate in NF system as compared to RO system is also lower.

Application of Nanofiltration

Food

Whey demineralization
Sugar solution demineralization
Nutrient recycling in fermentation processes
Separates sunflower oil from solvent
Treating Effluent
Recovers regenerated liquid from decolourized resins in sugar industry
Organic acid Purification

Textile

Separation of amino acid
Dye removal from wastewater

Chemical

Bleaching solution Recovery
Bromide Preparation
Recovers caustic solutions in cellulose and viscose production
Precipitation of CaSO4

Water production

Recovering LiOH while treating battery waste
Removes degreasing agents from water
Removes hardness in water
Natural organic matter is removed
Pesticide removal · Heavy metals like (As, Pb), Fe, Cu, Zn and silica is removed
Treats brackish water

Landfills

Phosphate, sulphate, nitrate and fluoride removal

Agriculture

Toxins like algal is removed

Clothing and leather

Salts and water recovery from wastewater

Paper and graphical

Chromium(III) and Chromium(II) recovery and reuse
Water recovery from wastewater or wastewater treatment effluent
Landfill leachate Purification
Selenium removal from drainage water

Others

Desalination of slightly brackish water
Food and pharmaceutical applications
Demineralization
Can concentrate sugars, divalent salts, particles, bacteria, proteins, dyes, and constituents that have molecular weight above 1000 daltons.

Tags:- Nanofiltration System For Wastewater Treatment, Nanofiltration System For Water Softening

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