Membrane Bioreactor (MBR) is a new and efficient sewage treatment technology combined with membrane separation and biological treatment. Membrane separation technology was first applied in the microbial fermentation industry. With the development of membrane materials and membrane technology, its application fields have been expanding, involving chemical, electronics, light industry, textile, metallurgy, food, petrochemical and sewage treatment. Fields.
1 Research and application of MBR technology in foreign sewage treatment
The application of membrane separation technology in wastewater treatment began in the late 1960s. In 1969, Smith et al. of the United States first combined the activated sludge process with ultrafiltration membrane modules for the treatment of municipal wastewater. It is proposed to replace the secondary settling tank in the conventional activated sludge process by membrane separation technology, and to maintain the high sludge concentration in the bioreactor by using the physical properties of the membrane with high efficiency, and work at a low ratio of F/M. It is possible to make the organic matter get oxidative degradation as much as possible, and improve the removal efficiency of the reactor, which is the initial prototype of the MBR.
In the 1970s, research on MBR was further carried out. In 1970, Hardt et al. used a complete hybrid bioreactor and ultrafiltration membrane combination process to treat domestic sewage, achieving 98% COD removal rate and 100% bacteria removal. result. In 1971, Bemberis et al. conducted an MBR test at a sewage treatment plant and obtained good test results. In 1978, Bhattacharyya et al. used ultrafiltration membranes to treat urban sewage and obtained non-drinking water. In 1978, Grethlein used the anaerobic digestion tank and membrane separation to conduct research on domestic sewage. The removal rates of BOD and TN were 90% and 75%, respectively.
During this period, although scholars from various countries have done a lot of research work on MBR technology and obtained certain research results, due to the small number of membrane modules at that time, the membrane forming process is not very mature, and the membrane life is usually very short. This limits the long-term stable operation of the MBR process, which limits the application of MBR technology in practical engineering.
After the 1980s, with the development of materials science and the improvement of membrane level, the development of membrane bioreactor technology was promoted, and the MBR process was also rapidly developed. Japanese researchers have vigorously developed and researched MBR technology according to the characteristics of their country's small territory and high land price, and have taken the lead in the research and development of MBR technology, making MBR technology begin to practical application.
After the 1990s, MBR technology has been the fastest growing, people are dealing with MBR in domestic sewage treatment! Industrial wastewater
In the last years of the 20th century, people conducted more research on the key issues of membrane bioreactors and achieved some results. The research on membrane bioreactors has gone from laboratory trials to pilot scales to productive trials, and small and medium-sized sewage treatment plants using MBR have also been reported. In early 1998, Europe's first domestic sewage treatment plant with integrated membrane bioreactor was built and operated in Porlock, England, and became a milestone in membrane bioreactor technology in the UK.
At the beginning of this century, research on membrane bioreactors is on the rise, making the technology gradually mature.
2 Research and application of MBR technology in domestic sewage treatment
Although the research on membrane bioreactors in China started late, it has developed rapidly. In 1991, Qi Yunhua reviewed the application of membrane bioreactors and introduced the research status of MBR in Japan. This is an earlier report by Chinese scholars on membrane bioreactors. Subsequently, Jiang Chengyu and others conducted research on the application of hollow fiber ultrafiltration membranes in biotechnology. In 1995, Fan Yaobo used MBR for petrochemical wastewater purification research and developed a laboratory-scale aerobic separation MBR.
Since 1995, China's research work on membrane bioreactor wastewater treatment technology has started in full swing, and many research institutes have carried out research in this area, Tsinghua University, Harbin Institute of Technology, Chinese Academy of Sciences Ecological Environment Research Center, Tianjin University, Tongji University has done a lot of detailed research work on the operational characteristics of membrane bioreactors, the factors affecting membrane flux, and the prevention and cleaning of membrane fouling.
In 2000, Gu Ping used a domestic hollow fiber membrane to conduct a pilot-scale MBR study on domestic sewage. The results showed that the MBR process had zero effluent content, the total number of bacteria was better than the drinking water standard, and the removal rates of COD and ammonia nitrogen were higher. 95%, the water can be directly reused. In 2001, Zhang Liqiu et al. theoretically deduced the main design parameters HRT and SRT for integrated MBR treatment of domestic sewage, provided reference for practical engineering design, and conducted in-depth research on membrane blocking mechanism, and proposed membrane internal organisms. The presence of a blockage.
Although China has made remarkable achievements in the research and discussion of MBR technology, compared with Japan, the United Kingdom, the United States and other countries, China's research and test level is still relatively backward. Due to the small number of domestic membrane modules, the film quality is poor. The life expectancy is usually short, so there are certain problems in practical applications. Although the membrane bioreactor has been used in China to treat domestic sewage, so far, the well-designed and well-operated domestic sewage treatment plant using membrane bioreactor has not been reported.
3 Classification of MBR processes
Membrane bioreactor is mainly composed of membrane module and bioreactor. According to the combination of membrane module and bioreactor, membrane bioreactor can be divided into the following three types: split membrane bioreactor, integrated membrane Bioreactor and composite membrane bioreactor.
3.1 Separate Membrane Bioreactor
The split membrane bioreactor means that the membrane module and the bioreactor are arranged separately and relatively independent, and the membrane module and the bioreactor are connected by the pump and the pipeline. The process flow of the split membrane bioreactor is shown in FIG. 1 .
The process membrane module and the bioreactor are separated and operated independently, so the mutual interference is small, the adjustment and control are easy, and the membrane module is placed outside the bioreactor, which is easier to clean and replace. The pump provides high pressure, causing high-speed cross-flow on the surface of the membrane and delaying membrane fouling. This is the reason for its high power cost. The energy consumption per ton of effluent is 2~10kWh, which is about 10~ of the energy consumption of traditional activated sludge method. 20 times, the research on integrated membrane bioreactor with lower energy consumption has gradually gained people's attention.
3.2 Integrated Membrane Bioreactor The integrated membrane bioreactor originated in Japan and is mainly used to treat domestic sewage. In recent years, some countries in Europe are also keen on its research and application. The integrated membrane bioreactor is a direct membrane module. Placed inside the bioreactor, sometimes referred to as the Submerged Membrane Bioreactor (SMBR), relying on gravity or pump suction to generate a negative pressure or vacuum pump as the water power. #Integral membrane bioreactor process shown in Figure 2 . The process reduces the footprint of the processing system due to the membrane module being placed in the bioreactor, and the process draws water out with a suction pump or a vacuum pump, and the power consumption cost is much lower than that of the separate membrane bioreactor. The power consumption per ton of water is about 1/10 of the split type. If gravity is used, this part of the cost can be completely saved. However, since the membrane module is immersed in the mixture of the bioreactor, the contamination is faster, and the cleaning is troublesome, and the membrane module needs to be taken out of the reactor.
3.3 Composite Membrane Bioreactor The composite membrane bioreactor also places the membrane module in the bioreactor, and the water is discharged by gravity or negative pressure, but the type of the bioreactor is different. The composite MBR is in the bioreactor. Install packing to form a composite processing system,
There are two purposes for installing packing in the composite membrane bioreactor: one is to improve the impact load of the treatment system and ensure the treatment effect of the system; the other is to reduce the concentration of suspended activated sludge in the reactor and reduce membrane fouling. The degree ensures a high membrane flux.
In the composite membrane bioreactor, due to the large amount of microorganisms adhering to the filler, the system can ensure a high treatment effect and the ability to withstand impact load, and at the same time, the concentration of suspended sludge in the reactor is not too high, affecting Membrane flux.
4 Characteristics of MBR Process 4.1 High removal efficiency of pollutants MBR has a very good removal effect on suspended solids (SS) concentration and turbidity. Since the membrane pore size of the membrane module is very small (0.01~1μm), all the suspended solids and sludge in the bioreactor can be intercepted, and the solid-liquid separation effect is much better than that of the secondary sedimentation tank. The rate is above 99%, even reaching 100%; the removal rate of turbidity is also above 90%, and the effluent turbidity is similar to that of tap water.
Due to the high-efficiency retention of the membrane module, all the activated sludge is trapped in the reactor, so that the sludge concentration in the reactor can reach a high level, up to 40~50g/L. In this way, the sludge load in the bioreactor is greatly reduced, and the removal efficiency of the organic matter by the MBR is improved. The average removal rate of the domestic sewage COD is above 94%, and the average removal rate of the BOD is above 96%.
At the same time, due to the separation of the membrane module, the hydraulic retention time (HRT) and sludge residence time (SRT) in the bioreactor are completely separated, so that microorganisms with slow growth and long generation time (such as nitrification) can be made. Bacteria can also survive in the reactor, ensuring that MBR has good nitrification in addition to its efficient degradation of organic matter. Studies have shown that MBR treatment of domestic sewage, the average removal rate of ammonia nitrogen is above 98%, and the effluent ammonia nitrogen concentration is less than 1mg / L.
In addition, after selecting a membrane module with a suitable pore size, MBR also has a good removal effect on bacteria and viruses, so that the sterilization process in the conventional treatment process can be omitted, and the process flow is greatly simplified.
In addition, when the DO concentration is low, there is an oxygen-deficient or anaerobic zone inside the fungus mass, which creates conditions for denitrification. Only the aerobic MBR process is used, although the removal efficiency of TP is not high, if it is combined with anaerobic, the removal rate of TP can be greatly improved. Studies have shown that with the A/O composite MBR process, the removal rate of TP can reach more than 70%.
4.2 With greater flexibility and practicability In the treatment of urban sewage or industrial wastewater, the traditional treatment process (grid + grit chamber + primary sedimentation tank + aeration tank + secondary sedimentation tank + disinfection tank) has a long process. The area is large, and the quality of the effluent is not guaranteed. The MBR process (screen filter + MBR) has obvious advantages due to short process, small floor space, flexible water treatment, etc. #MBR's water output is only required to increase or decrease the number of membrane modules according to the actual situation. The water production adjustment can be completed, which is very simple and convenient.
For the sludge expansion phenomenon that occurs in the traditional activated sludge process, the MBR can be easily solved by not using the secondary sedimentation tank for solid-liquid separation. In this way, the complexity of the management operation is greatly reduced, and the high quality and stable effluent is made possible.
At the same time, the MBR process is very easy to implement automatic control, which improves the automation level of sewage treatment.
4.3 Solved the problem of disposal of excess sludge. The problem of disposal of excess sludge is one of the key problems in the operation of sewage treatment plant. In the MBR process, the sludge load is very low, and the nutrient in the reactor is relatively lacking. In the endogenous respiration zone, the sludge yield is low, so that the amount of excess sludge is small, the SRT is prolonged, and the excess sludge concentration is large, so that the sludge can be concentrated without direct concentration, which is greatly Saves on the cost of sludge treatment. Studies have shown that the optimal sludge discharge time of MBR is about 35d when treating domestic sewage.
It can be seen from the above that the superiority of the MBR process is unmatched by other treatment processes. The process is widely used in urban sewage or domestic sewage treatment, high-concentration organic wastewater, refractory organic wastewater, and reuse of water. Application prospects.
1 Research and application of MBR technology in foreign sewage treatment
The application of membrane separation technology in wastewater treatment began in the late 1960s. In 1969, Smith et al. of the United States first combined the activated sludge process with ultrafiltration membrane modules for the treatment of municipal wastewater. It is proposed to replace the secondary settling tank in the conventional activated sludge process by membrane separation technology, and to maintain the high sludge concentration in the bioreactor by using the physical properties of the membrane with high efficiency, and work at a low ratio of F/M. It is possible to make the organic matter get oxidative degradation as much as possible, and improve the removal efficiency of the reactor, which is the initial prototype of the MBR.
In the 1970s, research on MBR was further carried out. In 1970, Hardt et al. used a complete hybrid bioreactor and ultrafiltration membrane combination process to treat domestic sewage, achieving 98% COD removal rate and 100% bacteria removal. result. In 1971, Bemberis et al. conducted an MBR test at a sewage treatment plant and obtained good test results. In 1978, Bhattacharyya et al. used ultrafiltration membranes to treat urban sewage and obtained non-drinking water. In 1978, Grethlein used the anaerobic digestion tank and membrane separation to conduct research on domestic sewage. The removal rates of BOD and TN were 90% and 75%, respectively.
During this period, although scholars from various countries have done a lot of research work on MBR technology and obtained certain research results, due to the small number of membrane modules at that time, the membrane forming process is not very mature, and the membrane life is usually very short. This limits the long-term stable operation of the MBR process, which limits the application of MBR technology in practical engineering.
After the 1980s, with the development of materials science and the improvement of membrane level, the development of membrane bioreactor technology was promoted, and the MBR process was also rapidly developed. Japanese researchers have vigorously developed and researched MBR technology according to the characteristics of their country's small territory and high land price, and have taken the lead in the research and development of MBR technology, making MBR technology begin to practical application.
After the 1990s, MBR technology has been the fastest growing, people are dealing with MBR in domestic sewage treatment! Industrial wastewater
In the last years of the 20th century, people conducted more research on the key issues of membrane bioreactors and achieved some results. The research on membrane bioreactors has gone from laboratory trials to pilot scales to productive trials, and small and medium-sized sewage treatment plants using MBR have also been reported. In early 1998, Europe's first domestic sewage treatment plant with integrated membrane bioreactor was built and operated in Porlock, England, and became a milestone in membrane bioreactor technology in the UK.
At the beginning of this century, research on membrane bioreactors is on the rise, making the technology gradually mature.
2 Research and application of MBR technology in domestic sewage treatment
Although the research on membrane bioreactors in China started late, it has developed rapidly. In 1991, Qi Yunhua reviewed the application of membrane bioreactors and introduced the research status of MBR in Japan. This is an earlier report by Chinese scholars on membrane bioreactors. Subsequently, Jiang Chengyu and others conducted research on the application of hollow fiber ultrafiltration membranes in biotechnology. In 1995, Fan Yaobo used MBR for petrochemical wastewater purification research and developed a laboratory-scale aerobic separation MBR.
Since 1995, China's research work on membrane bioreactor wastewater treatment technology has started in full swing, and many research institutes have carried out research in this area, Tsinghua University, Harbin Institute of Technology, Chinese Academy of Sciences Ecological Environment Research Center, Tianjin University, Tongji University has done a lot of detailed research work on the operational characteristics of membrane bioreactors, the factors affecting membrane flux, and the prevention and cleaning of membrane fouling.
In 2000, Gu Ping used a domestic hollow fiber membrane to conduct a pilot-scale MBR study on domestic sewage. The results showed that the MBR process had zero effluent content, the total number of bacteria was better than the drinking water standard, and the removal rates of COD and ammonia nitrogen were higher. 95%, the water can be directly reused. In 2001, Zhang Liqiu et al. theoretically deduced the main design parameters HRT and SRT for integrated MBR treatment of domestic sewage, provided reference for practical engineering design, and conducted in-depth research on membrane blocking mechanism, and proposed membrane internal organisms. The presence of a blockage.
Although China has made remarkable achievements in the research and discussion of MBR technology, compared with Japan, the United Kingdom, the United States and other countries, China's research and test level is still relatively backward. Due to the small number of domestic membrane modules, the film quality is poor. The life expectancy is usually short, so there are certain problems in practical applications. Although the membrane bioreactor has been used in China to treat domestic sewage, so far, the well-designed and well-operated domestic sewage treatment plant using membrane bioreactor has not been reported.
3 Classification of MBR processes
Membrane bioreactor is mainly composed of membrane module and bioreactor. According to the combination of membrane module and bioreactor, membrane bioreactor can be divided into the following three types: split membrane bioreactor, integrated membrane Bioreactor and composite membrane bioreactor.
3.1 Separate Membrane Bioreactor
The split membrane bioreactor means that the membrane module and the bioreactor are arranged separately and relatively independent, and the membrane module and the bioreactor are connected by the pump and the pipeline. The process flow of the split membrane bioreactor is shown in FIG. 1 .
The process membrane module and the bioreactor are separated and operated independently, so the mutual interference is small, the adjustment and control are easy, and the membrane module is placed outside the bioreactor, which is easier to clean and replace. The pump provides high pressure, causing high-speed cross-flow on the surface of the membrane and delaying membrane fouling. This is the reason for its high power cost. The energy consumption per ton of effluent is 2~10kWh, which is about 10~ of the energy consumption of traditional activated sludge method. 20 times, the research on integrated membrane bioreactor with lower energy consumption has gradually gained people's attention.
3.2 Integrated Membrane Bioreactor The integrated membrane bioreactor originated in Japan and is mainly used to treat domestic sewage. In recent years, some countries in Europe are also keen on its research and application. The integrated membrane bioreactor is a direct membrane module. Placed inside the bioreactor, sometimes referred to as the Submerged Membrane Bioreactor (SMBR), relying on gravity or pump suction to generate a negative pressure or vacuum pump as the water power. #Integral membrane bioreactor process shown in Figure 2 . The process reduces the footprint of the processing system due to the membrane module being placed in the bioreactor, and the process draws water out with a suction pump or a vacuum pump, and the power consumption cost is much lower than that of the separate membrane bioreactor. The power consumption per ton of water is about 1/10 of the split type. If gravity is used, this part of the cost can be completely saved. However, since the membrane module is immersed in the mixture of the bioreactor, the contamination is faster, and the cleaning is troublesome, and the membrane module needs to be taken out of the reactor.
3.3 Composite Membrane Bioreactor The composite membrane bioreactor also places the membrane module in the bioreactor, and the water is discharged by gravity or negative pressure, but the type of the bioreactor is different. The composite MBR is in the bioreactor. Install packing to form a composite processing system,
There are two purposes for installing packing in the composite membrane bioreactor: one is to improve the impact load of the treatment system and ensure the treatment effect of the system; the other is to reduce the concentration of suspended activated sludge in the reactor and reduce membrane fouling. The degree ensures a high membrane flux.
In the composite membrane bioreactor, due to the large amount of microorganisms adhering to the filler, the system can ensure a high treatment effect and the ability to withstand impact load, and at the same time, the concentration of suspended sludge in the reactor is not too high, affecting Membrane flux.
4 Characteristics of MBR Process 4.1 High removal efficiency of pollutants MBR has a very good removal effect on suspended solids (SS) concentration and turbidity. Since the membrane pore size of the membrane module is very small (0.01~1μm), all the suspended solids and sludge in the bioreactor can be intercepted, and the solid-liquid separation effect is much better than that of the secondary sedimentation tank. The rate is above 99%, even reaching 100%; the removal rate of turbidity is also above 90%, and the effluent turbidity is similar to that of tap water.
Due to the high-efficiency retention of the membrane module, all the activated sludge is trapped in the reactor, so that the sludge concentration in the reactor can reach a high level, up to 40~50g/L. In this way, the sludge load in the bioreactor is greatly reduced, and the removal efficiency of the organic matter by the MBR is improved. The average removal rate of the domestic sewage COD is above 94%, and the average removal rate of the BOD is above 96%.
At the same time, due to the separation of the membrane module, the hydraulic retention time (HRT) and sludge residence time (SRT) in the bioreactor are completely separated, so that microorganisms with slow growth and long generation time (such as nitrification) can be made. Bacteria can also survive in the reactor, ensuring that MBR has good nitrification in addition to its efficient degradation of organic matter. Studies have shown that MBR treatment of domestic sewage, the average removal rate of ammonia nitrogen is above 98%, and the effluent ammonia nitrogen concentration is less than 1mg / L.
In addition, after selecting a membrane module with a suitable pore size, MBR also has a good removal effect on bacteria and viruses, so that the sterilization process in the conventional treatment process can be omitted, and the process flow is greatly simplified.
In addition, when the DO concentration is low, there is an oxygen-deficient or anaerobic zone inside the fungus mass, which creates conditions for denitrification. Only the aerobic MBR process is used, although the removal efficiency of TP is not high, if it is combined with anaerobic, the removal rate of TP can be greatly improved. Studies have shown that with the A/O composite MBR process, the removal rate of TP can reach more than 70%.
4.2 With greater flexibility and practicability In the treatment of urban sewage or industrial wastewater, the traditional treatment process (grid + grit chamber + primary sedimentation tank + aeration tank + secondary sedimentation tank + disinfection tank) has a long process. The area is large, and the quality of the effluent is not guaranteed. The MBR process (screen filter + MBR) has obvious advantages due to short process, small floor space, flexible water treatment, etc. #MBR's water output is only required to increase or decrease the number of membrane modules according to the actual situation. The water production adjustment can be completed, which is very simple and convenient.
For the sludge expansion phenomenon that occurs in the traditional activated sludge process, the MBR can be easily solved by not using the secondary sedimentation tank for solid-liquid separation. In this way, the complexity of the management operation is greatly reduced, and the high quality and stable effluent is made possible.
At the same time, the MBR process is very easy to implement automatic control, which improves the automation level of sewage treatment.
4.3 Solved the problem of disposal of excess sludge. The problem of disposal of excess sludge is one of the key problems in the operation of sewage treatment plant. In the MBR process, the sludge load is very low, and the nutrient in the reactor is relatively lacking. In the endogenous respiration zone, the sludge yield is low, so that the amount of excess sludge is small, the SRT is prolonged, and the excess sludge concentration is large, so that the sludge can be concentrated without direct concentration, which is greatly Saves on the cost of sludge treatment. Studies have shown that the optimal sludge discharge time of MBR is about 35d when treating domestic sewage.
It can be seen from the above that the superiority of the MBR process is unmatched by other treatment processes. The process is widely used in urban sewage or domestic sewage treatment, high-concentration organic wastewater, refractory organic wastewater, and reuse of water. Application prospects.
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