The difference between Micro-filtration, ultra-filtration, Nanofiltration and Reverse Osmosis

Micro-filtration (MF)
The filtering precision ranges between 0.1 and 50 microns. Micro-filtration includes different PP filter elements, activated carbon filter elements, ceramic filter elements, and so forth. Removes dangerous elements from water, like microorganisms. The filter element is often not washable and is a one-time filter material that must be replaced on a regular basis.

①PP cotton core: generally only used for coarse filtration with low requirements to remove large particles such as sediment and rust in water.

②Activated carbon: It can eliminate the different colors and odors in the water, but it cannot remove the bacteria in the water, and the removal effect of sediment and rust is also very poor.

③Ceramic filter element: The small filtration precision is only 0.1 micron, and the flow rate is usually small, which is not easy to clean.

Ultra-filtration Membrane (UF)
A microporous filter membrane has a rated pore size range of 0.001-0.02 microns and consistent pore size standards. Ultra-filtration membrane filtration is a membrane filtration process that employs an Ultra-filtration membrane with pressure difference as the driving force. The majority of ultrafiltration membranes are constructed of acetate fibers or polymer materials with comparable characteristics. It is appropriate for the separation and concentration of solutes in treatment solutions, and it is also often used for the separation of colloidal suspensions that are difficult to finish using other separation techniques, and its application domains are continually growing.

Membrane ultrafiltration based on pressure difference is classified into three types: ultrafiltration membrane filtration, microporous membrane filtration, and reverse osmosis membrane filtration. They are distinguished by the tiny particle size or molecular weight that the membrane layer may maintain. When the rated pore size range of the membrane is used as the distinguishing standard, the microporous membrane (MF) has a rated pore size range of 0.02-10 m, the ultra-filtration membrane (UF) has a rated pore size range of 0.001-0.02 m, and the reverse osmosis membrane (RO) has a rated pore size range of 0.0001-0.001 m. There are several control elements for pores, such as ultra-filtration membranes with varying pore sizes, and pore size distributions may be generated based on the type and concentration of the solution, as well as evaporation and coagulation conditions during membrane production.

Ultra-filtration physical map
Ultra-filtration membranes are usually polymer separation membranes, with the polymer materials utilized for ultra-filtration membranes mostly consisting of cellulose derivatives, polysulfone, polyacrylonitrile, polyamide, and polycarbonate. Ultra-filtration membranes are widely utilized in the pharmaceutical, food, and environmental industries, and can be formed into flat membranes, roll membranes, tubular membranes, or hollow fiber membranes.

The ultra-filtration membrane was one of the first polymer separation membranes to be invented, and ultra-filtration machines were manufactured in the 1960s. Ultrafiltration membranes are widely utilized in industry and have emerged as a new chemical unit operation. It is employed in the separation, concentration, and purification of biological products, pharmaceutical goods, and food items, as well as terminal treatment devices in blood treatment, wastewater treatment, and ultrapure water preparation.

The filtration precision of nanofiltration (NF) is between that of ultrafiltration and that of reverse osmosis, and the desalination rate is lower than that of reverse osmosis. In the market, there was a widespread saying: nanofiltration is sloppy reverse osmosis. Actually, this is a deceptive technical idea.
Physical map of nanofiltration
In the actual separation concept, nanofiltration is a filter membrane that satisfies the Daunan effect and has selective ion rejection, a membrane whose sodium chloride permeability is proportional to the sodium chloride concentration and is more than 0.4. Its primary applications are desalination and the concentration of various input liquids. 0% NaCl rejection observed using nanofiltration membranes at 30,000 ppm NaCl combined with other ions. 

Reverse osmosis (RO): The filtration accuracy is around 0.0001 microns, and it is an ultra-high-precision membrane separation method developed in the United States in the early 1960s employing differential pressure. It can filter out practically all contaminants (both harmful and helpful) in water, leaving just water molecules. In most cases, it is employed in the production of pure water, industrial ultrapure water, and medical ultrapure water. Pressurization and energy are required for reverse osmosis technology.

RO is the abbreviation of Reverse Osmosis membrane in English. Since the pore size of RO membrane is five millionths of a hair (0.0001 microns), it is generally invisible to the naked eye, and bacteria and viruses are its 5000 Therefore, only water molecules and some mineral ions that are beneficial to the human body can pass through, and other impurities and heavy metals are discharged from the waste water pipe.

The principle of reverse osmosis:
First and foremost, we must comprehend the idea of “osmosis.” Osmosis is a physical process. When two types of water with differing salts are separated, such as by a semi-permeable barrier, the water on the side with less salt will be found to permeate. The membrane enters the water with high salt content, but the salt does not permeate, causing the salt concentration on both sides to progressively fuse until they are equal. However, it takes a long time to complete this process, which is also known as osmotic pressure.

Reverse osmosis physical map
However, if you try to put a pressure on the water side with a large salt content, the consequence might also limit the aforementioned penetration, and this pressure is known as osmotic pressure. If the pressure is raised, the infiltration can be reversed, and the salt will stay. As a result, the principle of reverse osmosis desalination is to apply a pressure greater than the natural osmotic pressure in salty water (such as raw water), so that osmosis proceeds in the opposite direction, and the water molecules in the raw water are pressed to the other side of the membrane, resulting in clean water, in order to achieve the goal of removing impurities and salts from the water.

The origin of RO reverse osmosis:

An American scientist, found by accident in 1950 that seagulls sucked a huge mouthful of seawater off the sea surface when flying at sea. They vomited up a little mouthful of seawater after a few seconds, which raised concerns because animals on land breathe via their lungs. High-salt salt water cannot be consumed. After dissection, it was discovered that the seagull’s body has a thin layer. The film is really exact. The seagull inhales saltwater, which is subsequently compressed, and the water molecules pass through the film due to the effect of pressure.

It is turned into fresh water, and the contaminants and extremely concentrated salt in the sea water are spit out of the mouth. This is the fundamental theoretical underpinning of the reverse osmosis process, which was first applied to desalination equipment in 1953 by the University of Florida. Dr.S.Sidney Lode, a UCLA University School of Medicine professor, collaborated with Dr.S.Soirirajan to begin research on reverse osmosis membranes in 2009, with the support of a US federal government project, and invested approximately $400 million US dollars per year in research to apply it to astronauts.

Post time: Mar-31-2022


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