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Ultrafiltration device (ultrafilter)
1、 The principle of ultrafiltration membrane device ultrafiltration system is to selectively separate substances through the microporous structure on
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1、 Principle of ultrafiltration membrane device Ultrafiltration system selectively separates substances through the microporous structure on the membrane surface. When a liquid mixture flows through the membrane surface under a certain pressure, small molecule solutes pass through the membrane (called ultrafiltration), while large molecule substances are intercepted, gradually increasing the concentration of large molecules in the original solution (called concentrated solution), thereby achieving the separation, concentration, and purification of large and small molecules. Ultrafiltration is different from all conventional filtration and microporous filtration (both static filtration) in that it has a small separation diameter and can almost intercept all bacteria, viruses, colloidal particles, proteins, and large molecule organic matter in the solution. The second is that the entire filtration process is carried out dynamically, and only a portion of the solvent is separated. The raw material liquid entering the ultrafiltration module, driven by the pressure difference on both sides of the membrane, partially passes through the membrane to become ultrafiltration liquid, while the rest becomes concentrated liquid and continuously flows out, causing limited accumulation of substances that cannot pass through the membrane surface. The filtration rate can reach an equilibrium value in a stable state without continuous attenuation, and the entire process can be sustained for a long time. 2、 Characteristics of ultrafiltration system The characteristics of ultrafiltration equipment include small footprint, large membrane area, compact structure, simple installation and maintenance, low energy consumption, and stable performance. Ultrafiltration is a membrane separation technology, whose main component is ultrafiltration membrane, used for the separation of substances at the molecular level in solution. The ultrafiltration process is powered by the pressure difference on both sides of the membrane and based on the principle of mechanical screening. The pressure used is usually 0.1 Mpa-0, 25 Mpa, and the separation pore size is 1 μ m-0.1 μ m, with a molecular weight cutoff of about 500-1000000. Ultrafiltration is carried out at room temperature and low pressure, with low energy consumption, no need for heating, and no need for medication to achieve the purpose of separation, concentration, separation, purification, and grading. The ultrafiltration device is easy to operate, fast to start, easy to maintain, and easy to control. It can be used alone or as a pre-treatment for reverse osmosis equipment inlet water and as a finishing treatment for high-purity water terminals. Application areas of ultrafiltration systems: filtration of food, beverages, drinking water, and mineral water; Cheese preparation, whey separation, sucrose purification, and plant protein treatment; Pharmaceutical industry process concentration and purification; Separation and extraction of enzyme preparations and microorganisms; Coating, electrophoretic paint, electroplating wastewater treatment, etc. 3、 Compared with traditional separation methods, ultrafiltration technology has the following characteristics: The filtration process is carried out at room temperature, with mild conditions and no component damage, making it particularly suitable for the separation, classification, concentration, and enrichment of heat sensitive substances such as drugs, enzymes, fruit juice, etc. 2 The filtration process does not undergo phase changes, does not require heating, has low energy consumption, does not require the addition of chemical reagents, is pollution-free, and is an energy-saving and environmentally friendly separation technology. 3 Ultrafiltration technology has high separation efficiency and is very effective in recovering trace components from dilute solutions and concentrating low concentration solutions. 4. The ultrafiltration process only uses pressure as the driving force for membrane separation, so the separation device is simple, the process is short, the operation is easy, and it is easy to control and maintain. 5. Ultrafiltration also has certain limitations as it cannot directly obtain dry powder formulations. For protein solutions, typically only a concentration of 10-50% can be obtained. 4、 Introduction to the Application Industry of Ultrafiltration At present, the application of membrane water treatment technology in environmental processes mainly includes methods such as ultrafiltration, reverse osmosis, dialysis, and electrodialysis for treating various industrial wastewater. Ultrafiltration technology has become the main membrane separation technology used in wastewater treatment projects due to its low operating pressure, low energy consumption, high flux, and high separation efficiency. It can recover and reuse useful substances and water, especially with its high flux characteristics. 1. Recycling of electrophoretic paint The large-scale application of ultrafiltration technology abroad began in the 1970s and was applied in the recycling of electrophoretic paints. The paint in the wastewater accounts for 10% to 50% of the total amount of paint used. Using ultrafiltration technology to treat electrophoretic paint wastewater can not only reduce paint loss and reuse wastewater, but also allow harmful inorganic salts to pass through the ultrafiltration membrane, thereby increasing the specific resistance of electrophoretic paint. Adjusting and controlling the composition of the paint solution ensures the normal operation of electrophoretic paint. In the early 1970s, CA membrane tubular ultrafiltration devices were mainly used to treat anodic electrophoretic paint wastewater. In the late 1970s, frame, roll, and hollow fiber ultrafiltration devices were switched to treat cathodic electrophoretic paint wastewater. Some domestic automobile factories and electrophoretic paint industries also adopt ultrafiltration technology. For example, Changchun Automobile Car Factory introduced a hollow fiber cathode electrophoretic paint special ultrafiltration device from Aomicon Company, which is composed of 30 membrane modules with a diameter of 7.62cm connected in parallel, with a total membrane area of about 75 m2 and a processing capacity of 1.5 t/h. It is equipped with a circulating liquid timed automatic reversing system to reduce membrane pollution and extend the membrane cleaning cycle. After ultrafiltration treatment, the electrophoretic paint ensures that the resistivity of the electrophoretic tank paint solution is greater than 500 Ω/cm, maintaining the stability of the solid content of the electrophoretic paint. The retention rate of the electrophoretic paint is 97%~98%, and the drainage volume is greatly reduced, saving a large amount of deionized water for replenishment. 2. Chemical fiber and textile industry wastewater There are various types of wastewater in the chemical fiber industry that can be treated and recovered by ultrafiltration, such as the recovery of polyvinyl alcohol (PVA). A factory in Japan uses an 8 cm2 tubular ultrafiltration device to concentrate PVA raw material from 0.1% to 10-15 times, with an inlet pressure of 3.92 × 105 Pa, an outlet pressure of 1.96 × 105 Pa, a feed temperature of 55-66 ℃, a membrane water flux of 100-140 L/(cm2 · h), a PVA separation rate of 98.2%, and a daily recovery of about 20 kg of PVA. The operation is good. There are various types and complex compositions of dye wastewater, mainly including colored wastewater containing salt and organic matter; Chlorination and bromination wastewater; Organic wastewater containing trace acids and bases; Colored wastewater containing cations such as copper, lead, chromium, manganese, mercury, etc; Organic wastewater containing sulfur. The amount of wastewater is large, the concentration is high, the color is high, and the toxicity is high, making it one of the most difficult industrial wastewater to treat. Shanghai Printing and Dyeing Factory was the first to use an acetic acid fiber external pressure tube ultrafiltration device to treat dye wastewater and recover dyes successfully. It used polysulfone ultrafiltration membrane tube and hollow fiber devices to treat dye wastewater, with a decolorization rate of 95%~98%, COD removal rate of 60%~90%, and a concentrated solution containing 15-20 g/L of dye. Wool washing wastewater is one of the most polluted wastewater in the textile industry. It contains a large amount of suspended solids, oils, and synthetic detergents, with lanolin being the main pollutant. Lanolin is a raw material for daily chemical and pharmaceutical industries, as well as a good preservative and lubricant, with high economic value. The traditional method of recycling lanolin has a low recovery rate, while the use of ultrafiltration technology to treat wool washing wastewater has achieved good results. Many domestic wool spinning and washing factories use ultrafiltration to treat wool washing wastewater, which includes four systems: pretreatment, ultrafiltration concentration, centrifugal separation, and water reuse. Compared with traditional centrifugal processes, the recovery rate of wool fat is 1-2 times higher, the oil retention rate is 98%~99%, and the COD retention rate is 90%~98%. 3. Paper industry wastewater The papermaking industry consumes a great deal of water, and the wastewater from papermaking mainly comes from processes such as peeling, pulping, washing, bleaching, and papermaking. The use of ultrafiltration technology to treat papermaking wastewater can not only concentrate and recover certain useful components in the wastewater, but also reuse the permeate water. In 1981, Japan built a tubular membrane device with a daily processing capacity of 4000 m3 using the NTU-3508 ultrafiltration module, which is the largest device in the world. China currently has the ability to produce such ultrafiltration and reverse osmosis membrane components and is rapidly promoting them. 4. Banknote printing wastewater The treatment of waste liquid from wiping plates in China's banknote printing industry has always been a long-standing and difficult problem. After ultrafiltration treatment, the clear liquid of the cleaning plate waste liquid passing through the membrane does not contain ink, and the alkali content remains unchanged. The COD removal rate is over 99%, and the solid content of the cleaning plate waste liquid with a solid content of 3% can be concentrated to 12%. The recovery rate of the waste liquid is 75%, and it is more labor-saving and cost-effective than using neutralization method to treat waste liquid. 5. Brewing wastewater Monosodium glutamate waste liquid is a viscous liquid containing a large amount of organic matter such as bacteria and chlorides, with a COD of up to 70000 mg/L. The discharge of waste liquid causes serious pollution to the environment, and also contains some valuable metabolic by-products. The monosodium glutamate factory uses CA, PS, PVC and other ultrafiltration membranes to treat monosodium glutamate waste liquid, and the permeate is clear and transparent, with a bacterial removal rate of over 98%. Transported through a pipeline into a soy sauce factory for the production of monosodium glutamate soy sauce; Ultrafiltration of concentrated solution can yield valuable metabolic byproducts containing proteins, fats, and nucleic acids; Ultrafiltration of glutamic acid fermentation broth, with clear and transparent permeate, can greatly improve purity and extraction rate when used to extract glutamic acid. 6. Treatment of oily wastewater Emulsified oil wastewater is a common industrial wastewater, and ultrafiltration treatment of emulsified oil wastewater has been applied for more than 20 years. The oil retention rate can exceed 99%, the COD removal rate reaches 95%, the volume concentration ratio is high, and the average ultrafiltration flux is 30 L/(cm2 · h). The treatment effect of emulsified oil waste liquid is very good. The oil content in oily wastewater is usually 100-1000 mg/L, exceeding the national discharge standard (10 mg/L), so oil removal treatment must be carried out before discharge. Hollow fiber ultrafiltration membrane modules and ultrafiltration equipment can be used, with an operating pressure of 0.10 MPa, wastewater temperature of 40 ℃, and a membrane permeability rate of 60-120 L/(cm2 · h). It can treat wastewater containing 100-1000 mg/L crude oil to meet the environmental discharge standard of less than 10 mg/L, and the treated water quality meets the water injection standard of low-permeability oil fields. A large amount of wastewater containing cutting oil, suspended solids, and detergents is generated during metal processing, which must be treated before discharge. Ultrafiltration treatment can separate wastewater into two parts: the concentrate contains oil and suspended particles, while the permeate contains almost no oil. By combining ultrafiltration and microfiltration, the oil is first concentrated to 10% using microfiltration. The permeability of the microfiltration membrane is 250 L/(cm2 · h), and then ultrafiltration treatment is carried out to recover 85% of the cleaning agent. The combination of ultrafiltration and reverse osmosis (or nanofiltration) can be used in membrane separators for oil fields to treat oily wastewater generated from oil extraction. Firstly, the separated water enters the hollow fiber ultrafiltration membrane, and then the permeate enters the reverse osmosis membrane (or nanofiltration membrane), which not only removes suspended solids but also removes dissolved salts and oils to meet the requirements of special water quality. 7. Leather wastewater The main raw materials used for hair removal in the leather industry are Na2S and lime, which account for about 10% of the total leather wastewater. They are highly toxic, with sulfide content ranging from 2000 to 4000 mg/L. The suspended solids and turbidity values are also high, making them the most polluted wastewater in the leather industry. When treating wastewater, ultrafiltration is used to separate proteins, and sulfonated polysulfone membranes are used for ultrafiltration to increase the concentration of leachate by 5-10 times. The membrane will not clog, and its treatment effect is better than general purification technologies. Ultrafiltration can recover 40% Na2S, 20% lime, and 68%~70% liquid, and recover a large amount of protein. It is estimated that 30-40 kg of keratin can be obtained per ton of salted skin, thus having good economic benefits [13]. 8. Food industry wastewater The production of soy protein isolate generates a large amount of high concentration organic wastewater. Using ultrafiltration to treat the wastewater can not only recover soluble proteins and oligosaccharides with high economic value, but also solve environmental problems. Compared with traditional treatment methods, it has low operating costs, high output efficiency, stable product quality, and easy operation. The organic content of the waste liquid from potato starch production is high, and the COD is usually around 10000 mg/L. Abroad, ultrafiltration technology is applied to remove COD from potato starch discharge wastewater and concentrate and recover soluble proteins. The COD value of the wastewater is reduced from 8175 mg/L to 3610 mg/L, and the COD removal rate is 55.8%. After membrane fouling, cleaning with NaOH solution at 40 ℃ and 0.1 mol/L resulted in a recovery rate of around 90%. In addition, ultrafiltration technology is also used for the treatment of wastewater such as photography wastewater and radioactive wastewater. |
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