Advantages of Flat Membranes in Membrane Bioreactors (MBR)

Membrane bioreactor (Membrance Bioreactor (MBR) is a biochemical reaction system that integrates membrane separation technology and biodegradation of bioreactors. Membrane separation technology is a commonly used physical treatment technology in the field of sewage treatment. Its mechanism is mainly the screening effect. According to different membrane surface pore sizes, it can be divided into filtration, microfiltration (MF), ultrafiltration (UF) and nanofiltration ( NF) etc. Microfiltration and ultrafiltration membranes are usually used in membrane bioreactors. The separation mechanism is mainly the screening effect. Due to the different membrane structures, the interception can be roughly divided into mechanical interception, adsorption interception and bridging effect. The traditional activated sludge treatment process includes grids, grit chambers, primary sedimentation tanks, biological reaction tanks, secondary sedimentation tanks and disinfection tanks. Among them, the grille, sand settling and primary settling are all used to remove impurities and larger particles in the influent water, paving the way for subsequent biological reactions. Most of the organic pollutants in the sewage, including COD, BOD, and nitrogen and phosphorus, will be consumed and degraded through the metabolism of the microorganisms in the tank. In order to ensure the treatment efficiency of the biological reaction tank, the activated sludge There are certain requirements for the concentration and state of the product. The effluent from the biological reaction tank also contains a large number of microorganisms, so it needs to flow into the secondary sedimentation tank for mud-water separation to clarify the effluent, and return or dispose of the settled sludge. The intervention point of the membrane bioreactor is to replace the secondary settling tank in the traditional activated sludge process with ultrafiltration or microfiltration membrane modules to achieve mud-water separation. The process has the characteristics of strong processing capacity, high solid-liquid separation efficiency, good effluent quality, small footprint, and simple operation and management. At present, the MBR process technology has achieved outstanding results in the treatment of domestic sewage and industrial wastewater. Membrane modules are the core part of MBR. At present, hollow fiber membrane modules and flat membrane modules are mainly used in engineering applications. Flat membranes and hollow fiber membranes have different characteristics and different scopes of application. Flat membranes have the characteristics of easy control of hydraulic conditions, high flux, strong anti-pollution ability, and easy cleaning and replacement. They can maintain higher sludge concentration conditions. High throughput and stable operation; hollow fiber has the advantages of high packing density and low price. As of 2006, according to incomplete statistics, there were 2259 sets of MBRs in operation around the world, of which flat-panel membrane bioreactors accounted for 68%. However, the degree of engineering application of flat membrane bioreactors in China is still very low, obviously lagging behind hollow fiber membrane bioreactors.

1. Compared with the traditional activated sludge process (CAS), MBR has the following obvious advantages:

(1) High pollutant removal rate and good effluent quality

MBR can be used not only for the treatment of high-concentration, refractory organic industrial wastewater, but also for the purification of domestic sewage and general industrial wastewater. In MBR, because the membrane module has a very good interception effect on the microorganisms in the reaction tank, especially for the nitrifying and denitrifying bacteria with a long generation cycle, and the microorganisms existing in small sludge particles; also due to the existence of the membrane , the activated sludge in the MBR system can be as high as (MLSS) 8000-15000mg/L, which is much higher than the traditional activated sludge method (about 3000-4000mg/L). The removal efficiency of suspended solids (SS) and organic matter is high, the suspended solids (SS) and turbidity of the effluent can be close to zero, and it can remove bacteria, viruses, etc. It can be used as advanced sewage treatment and resource utilization technology. Based on its high-efficiency biological reaction and the good separation and retention of the membrane itself, the removal rates of COD, BOD, and SS of the membrane bioreactor can reach 95%, 98%, and 99% respectively, and the effluent of the membrane bioreactor can be directly reused as reclaimed water.

(2) Strong adaptability to load changes and impact load resistance

Due to the high-efficiency interception effect of the membrane, the membrane bioreactor can completely intercept the activated sludge, so that the sludge concentration in the reactor is very high, and the complete separation of the hydraulic retention time (HRT) and the sludge retention time (SRT) in the reactor is realized. , even if the water inflow suddenly increases, the biological properties inside the entire reactor can also be maintained in a relatively stable state; at the same time, due to the increase in sludge concentration, the adsorption of activated sludge is strengthened; moreover, the interception effect of the membrane Under this condition, the pollutants that are too late to be biodegraded will not be discharged along with the effluent. Based on the above points, the operation control of the whole reactor will be more flexible and stable. Therefore, the membrane bioreactor system overcomes the problems of sludge bulking in traditional water treatment processes when the hydraulic load and organic load of the system change.

(3) Small amount of sludge discharge

Membrane bioreactor water treatment technology can not only be used as advanced sewage treatment and resource utilization technology, but also can be used as an important technology for sludge reduction and an effective means to avoid the problem of large amount of excess sludge disposal in conventional sewage plants. The sludge discharge of the membrane bioreactor is very small, and even no sludge can be produced. Sludge autodegradation and sludge hydrolysis can reduce the efficiency of traditional water treatment systems, but are very beneficial to membrane bioreactor systems. The traditional activated sludge method usually uses the activated sludge from the end of the stable period to the beginning of the decay period, and due to the high sludge concentration in the membrane bioreactor, a large amount of organic matter is consumed, and a considerable part of it is in the decay period. Microorganisms rely on their own endogenous respiration for metabolic decomposition, while maintaining a low concentration of effluent pollutants, they consume the remainder of the sludge growth process. Membrane separation makes the macromolecular refractory substances in sewage have sufficient residence time in the membrane bioreactor with limited volume, which greatly improves the degradation efficiency of refractory substances. The reactor operates under the conditions of high volume load, low sludge load, and long sludge age, and it is completely possible to achieve no sludge discharge or a small amount of sludge discharge for a long period (such as June or longer), and the remaining sludge discharge The amount is very small, not even muddy.

(4) The process flow is short, the system equipment is simple and compact, and the land occupation is small

Since the membrane bioreactor does not need to produce flocs in the aerobic sludge system for the separation of mud and water in the secondary sedimentation tank, the sludge concentration in the bioreactor can be much higher than that of the traditional process, and the biochemical reaction rate is related to the concentration of the reactants. The higher the reactant concentration, the greater the reaction rate, so the volume load of the membrane bioreactor can be as high as 5kgCOD/(m3d), while the traditional process is usually only 0.4-0.9kgBOD/(m3d), and the hydraulic retention time (HRT) when treating domestic sewage ) can be reduced to 2h, and the volume of the biological reaction tank can be greatly reduced. According to foreign research data, the volume of the aerobic tank of the membrane bioreactor is one-third of the volume of the traditional treatment process aerobic tank for the same scale of sewage. At the same time, the membrane bioreactor saves auxiliary equipment such as secondary sedimentation tank, filter tank and sludge return system, and even sludge treatment equipment and costs. Almost all MBR processes have a good effect on the removal of pathogens. Enteroviruses, total Escherichia coli, fecal streptococcus, and fecal Escherichia coli in the effluent water are all below the detection limit, which indicates that if the MBR effluent is directly discharged or there is no residual chlorine requirement If it is reused, it can even save the disinfection facilities, so the structure of the membrane bioreactor is simple and compact.

(5) Easy to realize automatic control, simple maintenance, saving manpower

In the traditional activated sludge process, due to frequent fluctuations and instability in operation, in order to ensure good effluent quality, a lot of manpower, financial and material resources must be invested in operation management. The membrane bioreactor adopts membrane separation technology to achieve stable effluent water quality, while eliminating the need for mud-water separation facilities. Therefore, it is easy to realize the full automatic control of the membrane bioreactor system from water inflow to effluent with a computer.

(6) The system starts up quickly, and the water quality can quickly meet the treatment requirements

Since the sludge concentration in the water can be well maintained, in the start-up period of the reaction tank, unlike the traditional aeration tank, it is necessary to remove the supernatant through sedimentation to increase the sludge concentration. Due to the complete interception of sludge particles by membrane separation, the sludge concentration in the system can be rapidly increased under the combined action of aeration and nutrients, so that the entire membrane bioreactor system can be quickly started, and the water quality can quickly meet the treatment requirements. .

2. Compared with hollow fiber MBR, flat plate MBR has the following obvious advantages:

(1) Better anti-pollution performance

Compared with hollow fiber membrane bioreactors, flat membrane bioreactors can maintain high flux and stable operation at higher activated sludge concentrations. In the actual use process, although there will be grilles, hair removal machines and other equipment in the pretreatment facility, it is inevitable that some objects such as hair will enter the aerobic pool. These filaments are wound on the membrane filaments. When the sludge concentration reaches a certain level, mud lumps will appear, causing more and more membrane filaments to be entangled together, greatly reducing the effective membrane area of the hollow fiber filaments, causing a sharp drop in membrane flux, and such problems are also very serious. Difficult to repair, usually only replaceable. The applicable activated sludge concentration (MLSS) range of the flat membrane bioreactor is 10000-15000mg/L, which is much higher than that of the hollow fiber membrane bioreactor (about 6000mg/L). The special structure of the flat membrane can realize the The gap between them is controllable, which is convenient for online cleaning of the membrane surface by gas-liquid mixed flow, and has excellent anti-pollution performance. In addition, the flat-panel membrane bioreactor can remove the attachments on the membrane surface very well by adjusting the aeration intensity at the bottom of the module and the scouring effect of the gas-water mixture on the membrane surface, even if it is caused by some unknown factors. In the case of silting, the membrane can also be taken out and removed by flushing with a low-pressure water gun, so that the membrane can operate effectively for a long time, while the hollow fiber cannot be cleaned by this method.

(2) Good mechanical stability, no broken wire

In the actual use process, the hollow fiber membrane module will inevitably have broken filaments, including two reasons, one is the uneven wall thickness caused by defects in the spinning process, of course, this situation is relatively rare, and It can be further avoided by purchasing high-quality products; the second is the root fracture caused by the fatigue of spinning materials. We know that due to aeration, the hollow fiber will always be in a relatively large vibration phenomenon under working conditions. It causes material fatigue, and once the broken wires caused by this material fatigue occur, it is often large-scale, and this is fatal to the membrane bioreactor, making the effluent water quality worse. The material strength of the flat membrane is much higher than that of the hollow fiber, and there will be no similar phenomenon at all, which can completely guarantee the high-quality effluent water quality.

(3) The cleaning method is more convenient and the cleaning cycle is longer.

The flat membrane bioreactor can effectively scour the membrane by controlling the aeration rate of the aeration system at the bottom of the module, and control the pollution of the membrane surface during operation, while the chemical cleaning of the flat membrane module (On-line cleaning) is also simpler. You only need to pour the prepared agent back into the membrane from the suction port and soak for a period of time. Unlike hollow fiber membrane modules, the membrane modules need to be taken out frequently for backwashing. At the same time, compared with the hollow fiber-membrane bioreactor, the cleaning cycle of the flat membrane bioreactor is longer, and the cleaning cycle can reach more than 3 months, and if the working pressure is always in a relatively low state, it may not even be cleaned. The flat membrane module can also restore the membrane flux through physical cleaning, which is almost impossible for the hollow fiber membrane.

(4) Long life and low operating cost

According to incomplete statistics, the average lifespan of hollow fiber membranes on the market is about 2 years, which means that there will be a large membrane replacement rate in 2 years. However, the average service life of flat membranes on the market is 5-7 years, without frequent replacement of membranes, relatively speaking, the operating costs are greatly reduced, and good operating conditions are guaranteed. The flat membrane has a high-strength support body, the membrane is less damaged, and the replacement rate is low; at the same time, the flat membrane can be replaced in a single sheet, and the replacement cost is relatively low.

(5) The diaphragm replacement process is simple

Due to the unique design of the flat membrane module, the membranes can be replaced one by one during the replacement of the membrane damage, without the need to replace the bracket. If the number of broken intermediate fiber membranes reaches a certain level, the entire module will be scrapped, and the entire membrane module needs to be replaced, which will greatly increase the cost.

3. Brief introduction of Shanghai Snap Membrane Separation Technology Co., Ltd. (SINAP)

Shanghai Snap Membrane Separation Technology Co., Ltd. is a membrane separation technology company jointly established by Shanghai Filter Co., Ltd. and Shanghai Institute of Applied Physics in 2008. The New Technology Center of the Shanghai Institute of Applied Physics started the research and product development of ultrafiltration membrane technology in 1980. It is one of the major membrane separation technology research units in China. The development and production of large-scale and small-scale laboratory ultrafiltration equipment are leading domestically, and the products have independent intellectual property rights. Our company produced the first flat film in China in 2002, and obtained the Chinese patent authorization in 2005. After two years of improvement and hard work, our company successively launched the second and third generation flat film in 2007 and 2008, and passed the ISO9001-2000 quality system certification in 2009.

Since 2002, with the support of Shanghai Municipal Science and Technology Commission, rapid progress has been made in the research and development of MBR products. The key component of the MBR flat membrane element is the flat membrane. The PVDF microfiltration membrane produced by the company has a pore size of 0.1 micron and a large pore size. The performance has reached the international level. At present, it has an annual production capacity of 200,000 square meters. Secondly, the company has successfully developed the third-generation MBR flat-sheet filter membrane elements produced by the international advanced level of ultrasonic heat welding and sealing technology. Four production lines have been put into production, with an annual production capacity of 100,000 pieces of MBR150 membranes. . (Note: With one piece of MBR150 membrane, the filter area is 1.5 square meters, and the daily sewage treatment volume is 0.8 cubic meters, which can treat 80,000 cubic meters of sewage per day.)

The Snap Technology R&D Center is led by well-known domestic membrane technology experts from the Shanghai Institute of Applied Physics, Chinese Academy of Sciences, and consists of a research and development team composed of doctors and masters. It is equipped with scanning electron microscopes, atomic force microscopes, gel chromatographs, total organic carbon analyzers, Multifunctional water quality analyzer, dissolved oxygen analyzer, chemical aerobic oxygen (COD), biochemical oxygen demand (BOD), ammonia nitrogen analyzer, contact angle analyzer, melting point microscope, ultraviolet spectrophotometer and other advanced equipment .

Over the past few years, Shanghai Snap Membrane Separation Technology Co., Ltd. has successively established cooperative relations with dozens of environmental engineering companies. MBR flat membrane products have been successfully used in a number of sewage treatment and reclaimed water reuse projects. These projects involve steel mills Emulsified oil wastewater, landfill leachate, washing wastewater, pharmaceutical wastewater, food processing wastewater, hotels, villas, schools, hospitals and other domestic sewage, the early engineering applications have been in normal operation for four years.

We SINAP people are confident to make SINAP flat film a banner of Chinese flat film, and SINAP to become a well-known domestic and even international film brand.