Introduction: Ultrafiltration is a rapidly rising separation technology, which is widely used in environmental protection water treatment. This paper briefly introduces the development status of ultrafiltration technology, and summarizes the application of ultrafiltration separation method in wastewater treatment of electrophoretic paint, chemical fiber, textile, paper making, banknote printing, wine making, leather making, petroleum and food industries.
As early as 186 1, Schmidt used bovine pericardium to intercept Arabic gum, which can be used as the first ultrafiltration test in the world. By 1960, under the influence of Loeb and Sourirajan's successful asymmetric reverse osmosis cellulose acetate membranes, Michaels developed asymmetric CA ultrafiltration membranes with different pore sizes in 1963. Due to the limitation of physical and chemical properties of CA membrane, since 1965, new kinds of polymer ultrafiltration membranes have been published and commercialized rapidly. 1965- 1975 is a stage of great development of ultrafiltration technology. The membrane materials have expanded from the initial asymmetric CA membrane to polysulfone (PSF), polyacrylonitrile (PAN) and polyethersulfone (PES). At present, most ultrafiltration membranes are made of polymer materials. With the application and development of ultrafiltration technology in industry, important progress has been made in inorganic membranes such as metal, ceramics, porous silicon and aluminum from the early 1980s to the 1990s. For example, during the period of 1980- 1985, the inorganic membrane with porous carbon as the carrier and coated with ceramic zirconia developed by UCC Company of the United States can be used as an ultrafiltration membrane tube, and the ceramic membrane tube with the trade name Membralox developed by Alcoa/SCT Company of the United States can withstand recoil and can run in cross flow [2]. Inorganic membrane ultrafiltration is more economical and effective than conventional separation technology. At present, almost all inorganic membranes used in industry are porous ceramic membranes or composite membranes supported by porous ceramics. With the development of powder technology, many sintered metal microporous tubes with high quality and low price are put into the market, which has the advantage of easy assembly and processing with metal components. In recent years, a thin layer of TiO2 _ 2 with a pore size of 0. 1 nm was sintered on the inner wall of stainless steel microporous tubes abroad to form Scepter stainless steel film [3].
In recent 30 years, ultrafiltration technology has developed rapidly. Ultrafiltration technology has been widely used in drinking water preparation, food industry, pharmaceutical industry, industrial wastewater treatment, metal processing coatings, biological products processing, petroleum processing and other fields.
1 application of industrial wastewater treatment
At present, the application of membrane technology in environmental processes is mainly ultrafiltration, reverse osmosis, dialysis and electrodialysis to treat various industrial wastewater. Ultrafiltration technology has the characteristics of low operating pressure, low energy consumption, high flux and high separation efficiency. It can recover and reuse useful substances and water, especially Qualcomm, which makes ultrafiltration the main membrane separation technology used in wastewater treatment projects.
1. 1 electrophoretic paint wastewater
The large-scale application of ultrafiltration technology abroad began in the 1970s, when it was mainly used in electrophoretic coating industry. The coating in wastewater accounts for 10%~50% of the total coating consumption. Using ultrafiltration technology to treat electrophoretic paint wastewater can not only reduce the loss of paint and reuse of wastewater, but also make harmful inorganic salts permeate through ultrafiltration membrane, improve the specific resistance of electrophoretic paint, regulate the composition of paint solution and ensure the normal operation of electrophoretic paint. In the early 1970s, CA membrane tube ultrafilter was mainly used to treat anode electrophoretic paint wastewater, and in the late 1970s, frame, roll and hollow fiber ultrafilters were used to treat cathode electrophoretic paint wastewater. Ultrafiltration technology is also applied in some domestic automobile factories and electrophoretic paint industry. For example, the hollow fiber ultrafilter for cathodic electrophoretic paint imported by Changchun Automobile Factory from Omicon Company is composed of 30 membrane modules with a diameter of 7.62cm connected in parallel, with a total membrane area of about 75 cm2 and a treatment capacity of 1.5t/h, and is regularly equipped with an automatic reversing system for circulating liquid to reduce membrane pollution and prolong membrane cleaning cycle. The original discharge of electrophoretic paint wastewater from an automobile factory in Beijing is 200 m3/d, and the amount of paint discharged from the workpiece is19.13l/h. After ultrafiltration, the resistivity of the paint in the electrophoretic tank is ensured to be greater than 500ω/cm, and the solid content of electrophoretic paint remains stable. The retention rate of electrophoretic paint is 97%~98%, and the drainage rate is reduced to 5 m3/h. The Center for Ecological Environment Research of Chinese Academy of Sciences has developed a hollow fiber membrane module with positive ions. The comparative test shows that the effect is good, the performance is equivalent to that of imported membrane, and it can be used in production. Wuxi Ultrafiltration Equipment Factory has developed related ultrafiltration membranes. A positively charged ultrafiltration membrane made of polyacrylonitrile as membrane material, dimethylacetamide as solvent and proper amount of pore-forming agent has high liquid permeability, stable performance, high paint stripping rate and good anti-pollution performance, and has been used in production. Many domestic manufacturers have introduced foreign ultrafiltration devices, and it has become a new goal to replace imported devices with domestic charged ultrafiltration devices with excellent performance.
1.2 chemical fiber and textile industry wastewater
There are many kinds of wastewater from chemical fiber industry, which can be treated and recovered by ultrafiltration. For example, recycled polyvinyl alcohol (PVA) has been used in the production of many foreign factories. A factory in Japan concentrated PVA stock solution from 0. 1% to 10~ 15 times with 8 cm2 tubular ultrafilter. The inlet pressure was 3.92× 105 Pa, the outlet pressure was 1.96× 105 Pa, and the feed temperature was 55~66℃.
Dye wastewater has many kinds and complex components, mainly including colored wastewater containing salt and organic matter; Chlorination and bromination wastewater; Organic wastewater containing weak acid and weak base; Colored wastewater containing cations such as copper, lead, chromium, manganese and mercury; Sulfur-containing organic wastewater. Because of its large quantity, high concentration, high chroma and high toxicity, it is one of the most difficult industrial wastewater to treat. Shanghai Printing and Dyeing Factory took the lead in treating vat dye wastewater by using acetate fiber external pressure tube ultrafiltration device and successfully recovered dye. The Institute of Environmental Chemistry of Chinese Academy of Sciences has also completed the field experiment of treating dye wastewater with polysulfone ultrafiltration membrane tube and hollow fiber device. The decolorization rate is 95%~98%, the COD removal rate is 60%~90%, and the concentrated solution contains 65,438+0.5 ~ 20 g/L, which has been cited by printing and dyeing plants in production [6].
Wool washing wastewater is one of the most polluted wastewater in textile industry. Wool washing wastewater contains a large number of suspended solids, oils and synthetic detergents, of which lanolin is the main pollutant. Lanolin is a raw material for daily chemical and pharmaceutical industries, and it is also a good preservative and lubricant with high economic value. The recovery rate of traditional lanolin recovery method is low, while ultrafiltration technology has achieved good results in treating wool washing wastewater. Many wool mills and wool washing factories in China use ultrafiltration to treat wool washing wastewater, including pretreatment, ultrafiltration concentration, centrifugal separation and water reuse. Compared with the traditional centrifugal method, the recovery rate of lanolin is increased by 1~2 times. The specific operating conditions are [7]: feed temperature 50℃, operating pressure 0. 12~0.35 MPa, membrane surface velocity 3 m/s, average membrane water flux 40 L/(cm2 h), and concentration multiple 3~6 times. As a result, the rejection rate of oil is 98%~99%, and the rejection rate of COD is 90% ~ 99%.
1.3 paper industry wastewater
The papermaking industry consumes a lot of water, and papermaking wastewater mainly comes from peeling, pulping, washing, bleaching, papermaking and other processes. Using ultrafiltration technology to treat papermaking wastewater can not only concentrate and recover some useful components in wastewater, but also reuse the permeated water. Kaishantun Chemical Fiber Pulp Factory is the first large-scale ultrafiltration equipment imported from domestic pulp and paper industry with international advanced level, and it has been successfully used to treat sulfite pulping waste liquid. On this basis, the self-made polysulfone membrane was used to replace the imported membrane, and the experiment proved that it reached the level of FSN6 1PP ultrafiltration membrane produced by DDS company. The process is as follows: preheat the waste liquid to 50~70℃, open the feed valve, and the waste liquid enters the storage tank through the filter. Ultrafiltration always controls the inlet pressure of 0.6 MPa, the outlet pressure of 0.3 MPa, the membrane working temperature of 60~65℃ and the membrane working area of 2.25 cm2. Results The concentration of lignosulfonic acid in the finished product was more than 95%, the removal rate of reducing agent was more than 85%, and the solid content was more than 30%, which achieved the purpose of effective separation, purification and concentration of polymer lignosulfonic acid in waste liquid. 198 1 year, Japan built a tubular membrane device with a daily output of 4000 m3 by using NTU-3508 ultrafiltration module, which is the largest device in the world at present. At present, China has the ability to produce such ultrafiltration and reverse osmosis membrane modules, and it has been rapidly promoted [8].
1.4 banknote printing wastewater
The treatment of printing waste liquid in China's banknote printing industry has always been a long-standing problem that puzzles the banknote printing industry. Shanghai Institute of Nuclear Research of China Academy of Sciences cooperates with Shanghai Banknote Printing Factory, Nanchang Banknote Printing Factory and Xi 'an Banknote Printing Factory. Since 1993, the plate ultrafilter has been used to treat the plate washing wastewater, and the original HPL-II (A) ultrafilter has been improved, and the HPL-II (B) plate ultrafilter suitable for treating the plate washing wastewater has been successfully developed. After ultrafiltration, the clear liquid passing through the membrane does not contain ink, and the alkali content remains unchanged. The removal rate of COD is over 99%, the waste liquid with solid content of 3% can be concentrated to 12%, and the recovery rate of waste liquid is 75%, which saves labor and a lot of money compared with neutralization method.
1.5 Brewing industrial wastewater
Monosodium glutamate waste liquid is a viscous liquid containing a large number of bacteria and other organic substances and chlorides, and its COD is as high as 70 000 mg/L. The discharge of waste liquid has caused serious pollution to the environment, and it also contains some valuable metabolic by-products. Monosodium glutamate factory uses ultrafiltration membranes such as CA, PS and PVC to treat monosodium glutamate wastewater. The operating conditions are: operating pressure 0.25MPa, operating temperature 25℃, and ultrafiltration concentration multiple 5~6 times. The treatment results show that the permeate is clear and transparent, and the cell removal rate is over 98%. The permeate is input into a soy sauce factory through a pipeline to produce monosodium glutamate soy sauce; Ultrafiltration of concentrated solution can obtain valuable metabolic by-products such as protein, fat and nucleic acid. Ultrafiltration of glutamic acid fermentation broth can improve the purity and extraction rate of glutamic acid [9].
1.6 treatment of oily wastewater
Emulsified oil wastewater is a common industrial wastewater, and ultrafiltration has been used to treat emulsified oil wastewater for more than 20 years. 1979 west Germany uses more than 250 ultrafiltration devices to concentrate emulsified oil, and the membrane modules used are tubular, coiled and plate. 1989, the membrane production plant was upgraded to a series of membrane plants capable of treating emulsified oil wastewater. Emulsified oil wastewater containing sodium hydroxide, phosphate, sodium carbonate, sodium borate, sodium nitrite and nonionic or anionic surfactant was treated by charged hollow fiber membrane. When the temperature was 50℃, the inlet pressure was 0. 12 MPa and the outlet pressure was 0. 10 MPa, the permeation flux reached 25 ~ 33 L/(cm2 h), and the oil content of the permeate was only a dozen mg. The permeate containing sodium hydroxide, salt and some surfactants can be reused for degreasing with a little adjustment. The concentrated solution enters the oil-water separator, and the separated oil can be recovered to form a non-discharge system. At present, Shanghai Baosteel uses Abcor tubular membrane ultrafiltration equipment to treat emulsified oil wastewater. PSF 100 ultrafiltration membrane was selected by Shanghai Institute of Nuclear Research, China Academy of Sciences. Three HPM baffles are connected in parallel to form a plate ultrafilter. Under the operating conditions of feed flow rate of 65438 0.6m/s, average pressure of 0.3 MPa and natural temperature rise, the concentration operation was carried out twice continuously. The results show that the oil retention rate is above 99%, the COD removal rate reaches 95%, the volume concentration ratio is high, and the average ultrafiltration flux is 10%.
The oil content of wastewater containing crude oil is usually 100~ 1000 mg/L, which exceeds the national discharge standard (1000 mg/L), and oil must be removed before discharge. Hollow fiber ultrafiltration membrane modules and ultrafiltration equipment can be used. Under the conditions of operating pressure of 0. 10 MPa and wastewater temperature of 40℃, the water permeability of the membrane can reach 60 ~120 l/(cm2 h), which can treat wastewater containing crude oil 100~ 1000 mg/L and achieve environmental discharge.
A large amount of wastewater containing cutting oil, suspended matter and detergent will be produced during metal processing, and these wastewater must be treated before it can be discharged. Ultrafiltration can separate wastewater into two parts: concentrated solution containing oil and suspended particles, and permeate containing almost no oil. Treatment of oil by combining ultrafiltration and microfiltration. Firstly, the oil was concentrated to 10% by microfiltration, and the water permeability of the microfiltration membrane was 250 L/(cm2 h). After ultrafiltration, 85% of the cleaning agent can be recovered. During ultrafiltration treatment of calendering oily wastewater in cold pressing workshop of iron and steel plant, it is filtered with 80 mesh screen first, then the oily wastewater enters the circulating pool, then the ultrafiltration membrane, and the ultrafiltration concentrated solution enters the oil-water separator. The separated oil has an oil content of over 90% and can be burned, and the separated water is returned to the circulating tank for ultrafiltration treatment. Ultrafiltration permeate can be recycled, and the water permeability and oil concentration of permeate are very stable during ultrafiltration, which is not affected by the oil concentration in make-up water.
Membrane separators used in oil fields can be combined with ultrafiltration and reverse osmosis (or nanofiltration) to treat oily wastewater produced by oil exploitation. The separated water first 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 dissolved oil, thus meeting the requirements of special water quality.
The development of treating emulsified oil wastewater by ultrafiltration is still going on, and the separation efficiency has been basically solved, but the difficulties to be overcome are membrane pollution and cleaning [12].
1.7 tannery wastewater
The raw materials for hair removal in leather industry are mainly Na2S and lime, and its wastewater accounts for about 65,438+00% of the total leather wastewater, which is highly toxic, with sulfide content of 2,000 ~ 4,000 mg/L and high suspended solids and turbidity, making it the most polluted wastewater in leather industry. When treating wastewater, protein was separated by ultrafiltration and ultrafiltration by sulfonated polysulfone membrane, which increased the concentration of waste liquor from liming by 5~ 10 times. The membrane will not be blocked, and the treatment effect is better than the general purification technology.
Ultrafiltration can recover 40% Na2S, 20% lime, 68%~70% liquid and a lot of protein. It is estimated that 30~40 kilograms of keratin can be obtained per ton of salt skin, which has good economic benefits [13].
1.8 food industry wastewater
A large number of high concentration organic wastewater will be produced in the production of soybean protein isolate. Using ultrafiltration technology to treat wastewater can not only recover soluble protein and oligosaccharides with high economic value, but also solve environmental problems. Compared with the traditional treatment method, it has the advantages of low operating cost, high output benefit, stable quality of recovered products and simple operation.
The organic content of waste liquid from potato starch production is high, and the COD is usually around 65,438+00,000 mg/L. In foreign countries, ultrafiltration technology is used to remove COD from wastewater discharged from potato starch and concentrate and recover soluble protein. In China, experiments were also carried out with polysulfone (PS) and polyacrylonitrile (PAN) hollow fiber ultrafiltration membrane modules. The process conditions are: operating pressure 0. 10 MPa, feed flow 70 L/h, room temperature. The experimental results show that the ultrafiltration effect is good, the COD value of wastewater is reduced from 8 175 mg/L to 3 6 10mg/L, and the COD removal rate is 55.8%. After the membrane was polluted, it was washed with 0. 1 mol/L NaOH solution at 40℃, and the recovery rate was about 90% [14].
For more information about project/service/procurement bidding, and to improve the winning rate, please click on the bottom of official website Customer Service for free consultation:/#/? source=bdzd