The Difference Between Reverse Osmosis Membrane and Nanofiltration Membrane

2022-04-07


Reverse osmosis and nanofiltration membrane technology are widely regarded as one of the most effective and economical separation processes. Reverse osmosis membrane has been widely used in industrial or civil water treatment, but many users know little about nanofiltration membrane. So what's the difference between them?

 

Ⅰ. Working Principle

1. Reverse Osmosis Membrane

Operating pressure is applied to the inlet (concentrated solution) side to overcome the natural osmotic pressure. When the operating pressure higher than the natural osmotic pressure is applied to the concentrated solution side, the flowing direction of natural permeation of water molecules will be reversed, and some water molecules in the inlet (concentrated solution) will pass through the membrane to become purified water produced on the dilute solution side. The ideal Reverse Osmosis Membrane Manufacturer requires a high water flux and does not allow salt to penetrate at all.

2. Nanofiltration Membrane

Nanofiltration Membrane 8040 is a special and promising separation membrane. There was a popular saying in the market that nanofiltration is a loose reverse osmosis. Actually, this is a misleading technical concept. The nanofiltration with the real separation concept is a filtration membrane that satisfies the Dow-Nan effect and has selective retention of ions, a membrane whose sodium chloride permeability is proportional to the concentration of sodium chloride, and the ratio is greater than 0.4.

 

II. Filtering Accuracy

  1. Reverse Osmosis Membrane

Reverse osmosis is the most sophisticated membrane liquid separation technology. It can block all soluble salts and organic substances with molecular weight greater than 100, but allow water molecules to penetrate. The desalination rate of cellulose acetate reverse osmosis membrane is generally greater than 95%, and that of Reverse Osmosis Composite Membrane 4040 is generally greater than 98%.

2. Nanofiltration Membrane

The filtration accuracy of nanofiltration membrane is between that of reverse osmosis membrane and ultrafiltration membrane. It can intercept the molecular weight of organic matter about 200~400, and its ability to intercept soluble salt is between 20~98%. The removal rate of monovalent anion salt solution is lower than that of high-priced anion salt solution, such as sodium chloride and calcium chloride, which are 20~80%, and magnesium sulfate and sodium sulfate, which are 90~98%.

 

III. Operating Pressure

1. Reverse Osmosis Membrane

The operating pressure of reverse osmosis membrane is generally greater than 5bar when the inlet water is brackish water, and lower than 84bar when the inlet water is seawater.

2. Nanofiltration Membrane

Because monovalent salt can freely penetrate nanofiltration membrane, the osmotic pressure caused by different ion concentrations on both sides of the membrane is much lower than that of reverse osmosis membrane. Therefore, the operating pressure of nanofiltration membrane is far lower than that of Reverse Osmosis Membrane, and the operating pressure is generally 3.5~16bar.

 

IV. Application

1. Reverse Osmosis Membrane

Reverse osmosis membrane is widely used in desalination of seawater and brackish water, boiler feed water, preparation of industrial pure water and electronic grade ultrapure water, production of drinking pure water, wastewater treatment and special separation, etc. Using reverse osmosis before ion exchange can greatly reduce operating costs and wastewater discharge.

2. Nanofiltration Membrane

Nanofiltration Membrane is generally used in the fields of concentration purification of drinking water, water softening, desalination and concentration of organic and bioactive substances, removal of trihalogenated precursors in water, classification and concentration of organic substances with different molecular weights, decolorization of wastewater, removal of hardness and radioactive radium from well water, concentration of food and separation of useful substances in medicines, etc.