Reverse Osmosis Membrane Technology and Principles

Introduction.

Membrane separation technology refers to the selective separation of mixtures of molecules of different particle sizes at the molecular level when they pass through a semi-permeable membrane. 

Semi-permeable membranes, also known as separation membranes or filtration membranes, have walls full of small pores and can be classified according to their pore size: ultrafiltration (UF), nanofiltration (NF), reverse osmosis (RO), etc. Membrane separation uses staggered flow filtration.

Membrane separation technology is characterised by normal temperature operation, no phase change, high efficiency and energy saving, and no pollution during the production process. 

Therefore, it is widely used in drinking water purification, industrial water treatment, food and beverage water purification, sterilization, bioactive material recovery and refinement, etc., and is rapidly spreading to various fields such as textile, chemical, electric power, food, metallurgy, petroleum, machinery, biology, pharmaceutical, fermentation, etc. 

Due to its unique structure and performance, the separation membrane has emerged as a leader in environmental protection and water reclamation, and has a wide application prospect in environmental engineering, especially in wastewater treatment and water reuse.

Service industries.

1. Metallurgical industry: boiler make-up water, cooling circulating water, production process water, industrial wastewater treatment

2. Electric power industry: boiler make-up water, cooling circulating water, industrial wastewater treatment

3. Chemical industry: boiler make-up water, cooling circulating water, production process water, industrial wastewater treatment

4. Electronics industry: ultra-pure water for process, heavy metal-containing wastewater treatment

5. Biopharmaceutical industry: water for injection, special process treatment, pharmaceutical organic wastewater treatment

6. Food and beverage: drinking water, water for production process

1.Reverse Osmosis Membrane (RO)

RO is the abbreviation of Reverse Osmosis. The general flow of water is from low concentration to high concentration, once the water is pressurized, it will flow from high concentration to low concentration, which is also known as the principle of reverse osmosis. 

As the pore size of an RO membrane is one millionth of a hair (0.0001 micron), it is generally invisible to the naked eye, and bacteria and viruses are 5,000 times larger than it. Only water molecules and some mineral ions can pass through (the ions that pass through have no beneficial orientation), other impurities and heavy metals are discharged by the waste pipe. 

All seawater desalination processes, as well as astronaut wastewater recycling treatment are used in this method, so RO membrane is also known as the in vitro high-tech "artificial kidney". At present, domestic and foreign, medical military civil field, are taken top RO membrane for polymer filtration.

Learn more about reverse osmosis membrane products

2.Ultra-filtration membrane (UF)

Ultrafiltration membrane pore size of only a few nanometers to tens of nanometers, that is, only a hair of 1 ‰! The ultrafiltration membrane is driven by the pressure difference between the two sides, with the ultrafiltration membrane as the filtration medium. 

Under a certain pressure, when the original liquid flows over the surface of the membrane, the many tiny pores on the surface of the ultrafiltration membrane only allow water and small molecules to pass through and become the permeate, while the substances in the original liquid that are larger than the pore size on the surface of the membrane are trapped on the inlet side of the membrane and become the concentrate, thus achieving the purpose of purification, separation and concentration of the original liquid.

The pore size only allows water molecules, beneficial minerals and trace elements in water to pass through, while the volume of the smallest bacteria are above 0.02 microns, so bacteria and much larger than the volume of bacteria colloids, rust, suspended matter, sediment, macromolecular organic matter, etc. can be retained by the ultrafiltration membrane, thus achieving the purification process.

3.Nanofiltration membrane (NF)

Nanofiltration is a pressure-driven membrane separation process between reverse osmosis and ultrafiltration, with the pore size of the nanofiltration membrane ranging from a few nanometres or so. 

Compared to other pressure-driven membrane separation processes, it emerged relatively late. Its emergence can be traced back to J.E. Cadotte's NS-3 0 0 membrane research in the late 1970s, after which nanofiltration developed rapidly and membrane units were commercialised in the mid-1980s.

Nanofiltration membranes are mostly derived from reverse osmosis membranes, such as CA and CTA membranes, aromatic polyamide composite membranes and sulfonated polyethersulfone membranes. 

Nanofiltration (NF) is used to separate substances with small relative molecular masses, such as inorganic salts or small organic molecules such as glucose and sucrose, from solvents. 

Nanofiltration, also known as low-pressure reverse osmosis, is an emerging field of membrane separation technology with separation performance between reverse osmosis and ultrafiltration, allowing some inorganic salts and certain solvents to pass through the membrane, thereby achieving separation.