The principle of ultrafiltration is also a principle of membrane separation process. Ultrafiltration uses a pressure active membrane to intercept colloids, particles and substances with relatively high molecular weight in water under the action of external driving force (pressure), while water and small solute particles pass through the membrane. Materials with molecular weight of 3x10000-1x10000 can be retained through micropore screening on the membrane surface. When the treated water passes through the membrane surface at a certain flow rate with the help of external pressure, water molecules and solutes with molecular weight less than 300-500 pass through the membrane, while particles and macromolecules larger than the membrane hole are intercepted due to screening, so as to purify the water. In other words, when the water passes through the ultrafiltration membrane, most of the colloidal silicon contained in the water can be removed, and a large amount of organic matter can be removed at the same time.
Commonly used ultrafiltration membranes include cellulose acetate membrane, polysulfone membrane and amide membrane, mainly including plate frame type, tube type, roll type and hollow fiber type.
Main differences between ultrafiltration and reverse osmosis equipment:
1、 The first is the filtering accuracy
The obvious difference between reverse osmosis technology and ultrafiltration membrane technology * lies in the filtration accuracy.
Reverse osmosis: refers to the process of applying external pressure higher than the osmotic pressure of the solution on the water inlet side of the membrane, allowing only water and some components in the solution to selectively penetrate, while other substances cannot penetrate and are retained on the membrane surface. It is referred to as RO for short, and its filtration accuracy is 0.0001 microns.
Ultrafiltration: it is a physical screening process driven by pressure difference, with separation molecular weight ranging from several hundred to several million and membrane pore size of about 0.001 ~ 0.2 microns. It is referred to as UF for short, and its filtration accuracy is 0.001 microns.
2、 Components and operation of the machine
RO machine: booster pump, power supply required, water storage tank, generally five-stage filtration. The first stage is filter element, the second and third stages are activated carbon, the fourth stage is RO reverse osmosis membrane for aerospace technology, and the fifth stage is refined activated carbon, which is mainly used to improve the taste.
Ultrafiltration machine: there is no motor, no power supply, and the filter is driven by water pressure. Most of them use stainless steel tubes as the body. The stainless steel material is resistant to high temperature and corrosion, and can better adapt to the change of environmental temperature difference.
3、 Functional differences
RO machine: it can remove impurities, rust, sediment, colloid, bacteria, viruses, radioactive particles, organics, fluorescent substances and pesticides harmful to human body, as well as water alkali and heavy metals; But it will also remove trace elements beneficial to human body.
Ultrafiltration machine: it can filter out impurities, rust, some bacteria, viruses, colloids, etc. in tap water, and the filtered water retains trace elements beneficial to human body.
What are the application fields of ultrafiltration membrane
1. Urban drinking water purification
Traditional drinking water purification methods can realize the inactivation and purification of microorganisms and fungi, as well as the purification of micron suspended particles. On this basis, ultrafiltration membrane technology can also effectively remove nano particles, so the effluent quality is higher.
2. Seawater desalination
The excellent separation and physicochemical properties of ultrafiltration membrane technology further improve the efficiency of seawater desalination and greatly reduce energy consumption.
3. Treatment of electroplating wastewater
The wastewater produced by the electric industry contains a large number of heavy metals such as hexavalent chromium, copper and nickel, which is very harmful. In practical work, iron oxidation, electrolysis and so on are often used, but it will produce a large amount of sludge, which needs further treatment, and the operation cost is high.
The combination of ultrafiltration membrane technology and reverse osmosis technology can remove most of the heavy metals, organic carbon and some salts in electroplating wastewater, and the use of ultrafiltration membrane can also reduce the pollution of osmotic membrane and improve the service life.
4. Treatment of oily wastewater
The main sources of oily wastewater include crude oil leakage, slaughterhouse wastewater and domestic wastewater. Its main components are floating oil, dispersed oil, emulsified oil and heavy oil. The commonly used oily wastewater treatment device is oil separator, which is often treated by air flotation. Because the emulsified oil molecules are generally large, ultrafiltration membrane technology can be used to make the oily wastewater pass through the ultrafiltration membrane under pressurized conditions, and the emulsified oil and other macromolecular pollutants will be intercepted, with high removal efficiency.
5. Urban sewage reuse
Urban sewage reuse is an important measure to alleviate the pressure of urban water use. The use of ultrafiltration membrane technology can quickly treat urban sewage up to the standard. Due to the good biodegradability of urban sewage, in practical work, in order to improve the effluent quality, cyclic activated sludge process (CASS) and ultrafiltration membrane technology are often used at the same time. Under the condition that the hydraulic action time is 12 hours, the COD removal rate of this method is more than 86%, the ammonia nitrogen removal rate is more than 90%, and the pH value range of the effluent is 7.25-7.89, which meets the reuse standard. After treatment, the urban domestic sewage is used for urban greening.
6. Food industry wastewater recovery
Ultrafiltration membrane technology can not only improve the effluent quality, but also concentrate and recover a large number of useful solid substances. * the typical application is recycling in the field of food industry
A lot of fat, protein, starch, yeast, etc.