MembraneBioreactor (MembraneBioreactor, abbreviated as MBR), is a new and highly efficient wastewater treatment technology by the combination of membrane separation and biological treatment. Membrane separation technology was first used in the microbial fermentation industry, with the development of membrane materials and membrane technology, its application areas are constantly expanding, has been involved in the chemical industry, electronics, light industry, textile, metallurgy, food, petrochemical and sewage treatment and other fields.
1, MBR technology in foreign sewage treatment research and application
Membrane separation technology in wastewater treatment began in the late 1960s # 1969 Smith et al. for the first time in the United States will be the activated sludge method combined with ultrafiltration membrane components for the treatment of municipal wastewater treatment process research, the process boldly put forward the membrane separation technology to replace conventional Activated sludge method in the second sedimentation tank, the use of membrane has a high efficient retention of physical properties, so that the bioreactor to maintain a high concentration of sludge in the low ratio of F / M work, so that organic matter as much as possible to get oxidative degradation, improve the removal efficiency of the reactor, which is the initial prototype of MBR.
Entering the 1970s, the research on MBR was further carried out#1970, Hardt et al. used a complete hybrid bioreactor and ultrafiltration membrane combination process to treat domestic wastewater, obtaining 98% COD removal and 100% removal of bacteria.1971, Bemberis et al. carried out a MBR test in a wastewater treatment plant. In 1978, Bhattacharyya et al. used ultrafiltration membranes for the treatment of municipal wastewater and obtained non-potable reuse water.In 1978, Grethlein carried out a study on the treatment of domestic wastewater using anaerobic digesters with membrane separation, and 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 process and obtained certain research results, but due to the few types of membrane modules at that time, the membrane production process is not very mature, the life of the membrane is usually very short, which restricts the stable operation of MBR process for a long period of time, thus restricting the popularization and application of MBR technology in the actual engineering.
Entering the 1980s, with the development of materials science and the improvement of membrane production level, promoting the forward development of membrane bioreactor technology, MBR process has also been rapidly developed. Japanese researchers according to the country's small size! The characteristics of the high land price of MBR technology has been vigorously developed and studied, and in the research and development of MBR technology in the forefront, so that MBR technology began to move towards practical applications.
After the 1990s, MBR technology has been the most rapid development of MBR technology, people on MBR in domestic sewage treatment! Industrial wastewater treatment! Industrial wastewater treatment! Drinking water treatment and other aspects of the application of research, MBR has entered the stage of practical application, and has been rapidly promoted.
In the last few years of the 20th century, people have conducted more research around the key issues of membrane bioreactors and achieved some results. Research on membrane bioreactors from the laboratory pilot! In early 1998, Europe's first application of integrated membrane bioreactor domestic wastewater treatment plant in the United Kingdom's Porlock was completed and operated, becoming a milestone in the British membrane bioreactor technology.
The beginning of this century, people on the membrane bioreactor research in the ascendant, so that the technology is gradually mature.
2, MBR technology in the domestic sewage treatment research and application
China's research on membrane bioreactor, although a late start, but the development rate is very fast. 1991, baicalin yunhua on the application of membrane bioreactor for a review of the MBR research situation in Japan, which is our scholars on the membrane bioreactor to do the earlier reports. Subsequently, Jiang Chengzhang and others conducted research on the application of hollow fiber ultrafiltration membranes in biotechnology. 1995, Fan Yaobo used MBR for petrochemical wastewater purification research, developed a set of laboratory-scale aerobic separation MBR.
Since 1995, China's research on the membrane bioreactor wastewater treatment technology has begun to carry out comprehensive research work, a number of scientific research institutes carried out research in this area, Tsinghua University, Halvar University, Harvard University, and the University of California at Los Angeles. Research in this area, Tsinghua University, Harbin Institute of Technology, the Chinese Academy of Sciences Ecological Environment Research Center, Tianjin University, Tongji University, etc. on the operational characteristics of membrane bioreactors, membrane flux factors affecting the prevention of membrane contamination and cleaning and other aspects of the research work done a lot of detailed research work.2000, Gu Ping domestic hollow fiber membranes used in domestic sewage to do a pilot scale MBR research, the results show that: MBR process effluent suspended solids is zero, the total number of bacteria is better than the drinking water standard, the removal rate of COD and ammonia nitrogen is higher than 95%, and the effluent can be directly reused. 2001, Zhang Liqiu and others carried out the theoretical derivation of the main design parameters HRT, SRT, etc., of the integrated MBR treatment of domestic wastewater, which provided a reference for the actual engineering design, and carried out an in-depth research to explore the mechanism of membrane plugging, and proposed the membrane The existence of internal biological clogging.
Although, China has made remarkable achievements in the research and discussion of MBR technology, but compared with Japan, the United Kingdom, the United States and other countries, China's research and testing level is still relatively backward, due to the fewer types of domestically produced membrane modules, the membrane quality is poorer, and the life expectancy is usually shorter, so that there are certain problems in the practical application. Although the membrane bioreactor for domestic wastewater treatment in China has been applied, but so far, the well-designed and well-run domestic wastewater treatment plant with the application of membrane bioreactor has not been reported.
3, MBR process classification
Membrane bioreactor is mainly composed of membrane components and bioreactor two parts # According to the combination of membrane components and bioreactors can be divided into the following three types of membrane bioreactors: sub-displacement membrane bioreactors, integrated membrane bioreactors and composite membrane bioreactors.
3.1 Displaced membrane bioreactor
Displaced membrane bioreactor refers to the membrane module and bioreactor are set up separately, relatively independent, the membrane module and the bioreactor are connected through the pump and pipeline # Displaced membrane bioreactor process flow is shown in Figure 1.
The process of membrane module and bioreactor are separated, independent operation, thus less mutual interference, easy to regulate and control, and, the membrane module is placed outside the bioreactor, it is easier to clean and replace#But its power consumption is larger, the pressurized pump provides higher pressure, resulting in high-speed mis-flow on the membrane surface, to delay the membrane contamination, which is the reason for the power cost is large, and the energy consumption of each ton of effluent water is 2~10kWh, which is about the same as that of the traditional membrane bioreactor. 10kWh, about 10 to 20 times the energy consumption of the traditional activated sludge method, so the research of the integrated membrane bioreactor with lower energy consumption has gradually gained attention.
3.2 Integral membrane bioreactor
Integral membrane bioreactor originated in Japan, mainly used for the treatment of domestic wastewater, in recent years, some countries in Europe are also keen on its research and application#Integral membrane bioreactor is the membrane module is directly placed in the interior of the bioreactor, sometimes also known as submerged membrane bioreactor (SMBR), relying on gravity or pumping to generate negative pressure or vacuum. The negative pressure generated by gravity or pumping or vacuum pumping is used as the effluent power # The integrated membrane bioreactor process flow is shown in Figure 2. The process as a result of the membrane module placed in the bioreactor, reducing the footprint of the treatment system, and the process with suction pumps or vacuum pumps suction water, power consumption costs are much lower than the split-type membrane bioreactor, per ton of water power consumption is about 1/10 of the split-type. If the use of gravity water, you can completely save the cost of this part. However, because the membrane module is submerged in the mixture of the bioreactor, the contamination is faster, and the cleaning is more troublesome, the membrane module needs to be removed from the reactor.
3.3 Composite Membrane Bioreactor
Composite membrane bioreactor is also the membrane module placed in the bioreactor, through gravity or negative pressure out of the water, but the bioreactor type is different # composite MBR, is installed in the bioreactor packing, the formation of a composite treatment system.
The purpose of installing packing in the composite membrane bioreactor is twofold: one is to improve the shock load of the treatment system to ensure that the treatment effect of the system; the second is to reduce the concentration of suspended activated sludge in the reactor, reduce the degree of membrane contamination, to ensure a high membrane flux.
Composite membrane bioreactor, because the filler attached to the growth of a large number of microorganisms, to ensure that the system has a high treatment effect and have the ability to resist the shock load, while not making the reactor suspended sludge concentration is too high, affecting the membrane flux.
4, MBR process characteristics
4.1 high removal efficiency of pollutants
MBR has a very good removal of suspended solids (SS) concentration and turbidity. Due to the membrane module of the membrane pore size is very small (0.01 ~ 1μm), the bioreactor can be all the suspended solids and sludge are retained, the solid-liquid separation effect is far better than the secondary sedimentation tank, MBR on the removal of SS more than 99%, or even reach 100%; turbidity removal rate is also more than 90%, the effluent turbidity is similar to the tap water.
Because of the high efficiency of the membrane module retention effect, all the activated sludge are retained in the reactor, so that the sludge concentration in the reactor can reach a high level, up to 40 ~ 50g / L. This greatly reduces the sludge load in the bioreactor, improves the removal efficiency of the MBR of organic matter, the average removal rate of COD of domestic sewage is more than 94%, the average BOD removal rate is more than 96%, the average removal rate is more than 96%. The average removal rate of domestic wastewater COD is more than 94%, and the average removal rate of BOD is more than 96%.
At the same time, due to the separation effect of the membrane module, the hydraulic residence time (HRT) and sludge residence time (SRT) in the bioreactor are completely separated, which can make the microorganisms (such as nitrifying bacteria) that grow slowly and have a long generation time also survive in the reactor, and ensure that the MBR, in addition to having a high efficiency in degrading the organic matter, also has a good Nitrification. Research shows that MBR in the treatment of domestic sewage, the average removal rate of ammonia nitrogen in more than 98%, the effluent concentration of ammonia nitrogen is less than 1mg / L.
In addition, the selection of the appropriate pore size of the membrane module, the MBR also has a better removal of bacteria and viruses, which can be eliminated from the traditional treatment process of disinfection process, greatly simplifies the process flow.
In addition, at low DO concentration, there is an anoxic or anaerobic zone inside the bacterial colloid, creating conditions for denitrification. Only aerobic MBR process, although the removal efficiency of TP is not high, but if it is combined with anaerobic, the removal rate of TP can be greatly improved. Studies have shown that the removal rate of TP can be more than 70% by using A/O combined MBR process.
4.2 Greater flexibility and practicality
In municipal wastewater or industrial wastewater treatment, the traditional treatment process (grid + sand sedimentation tank + primary sedimentation tank + aeration tank + secondary sedimentation tank + disinfection tank) process is long, covers a large area, and the quality of effluent water can not be guaranteed. The MBR process (screen filtration + MBR) is due to the short process, covers an area of small! Processing water volume flexibility and other characteristics, and presents obvious advantages # MBR water output according to the actual situation, only need to increase or decrease the number of pieces of membrane module can be completed to adjust the amount of water production, very simple and convenient.
For the traditional activated sludge process in the sludge expansion phenomenon, MBR due to the solid-liquid separation without the second sedimentation tank, can be easily resolved. This greatly reduces the complexity of management operations and makes high quality! Stable effluent becomes possible.
At the same time, MBR process is very easy to realize automatic control, improve the automation level of sewage treatment.
4.3 Solve the problem of difficult disposal of residual sludge
The disposal of residual sludge is one of the key problems of good or bad operation of sewage treatment plant #MBR process, sludge load is very low, the reactor is relatively lacking in nutrients, microorganisms are in endogenous respiration zone, sludge yield is low, thus making the production of residual sludge is very small, the SRT has been prolonged, the excluded The concentration of residual sludge is so large that it can be dewatered directly without sludge thickening, which greatly saves the cost of sludge treatment. Some studies have concluded that the optimal sludge discharge time for MBR is around 35d when treating domestic wastewater.
From the above, it can be seen that the MBR process has the superiority of the current other treatment processes can not be compared # The process in the municipal wastewater or domestic sewage treatment! High concentration of organic wastewater, difficult to degrade organic wastewater and water reuse have broad application prospects.
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