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0. Overview MSBR (Modified Sequencing Batch Reactor) is a modified sequential batch reactor. It is a more ideal sewage treatment system developed by CQYang and others based on the characteristics of SBR technology and combined with traditional activated sludge technology. MSBR does not require a primary sedimentation tank or a secondary sedimentation tank, and can operate when the reactor is fully filled and continuously fed water at a constant liquid level. It adopts a single-tank multi-cell method and combines the advantages of traditional activated sludge method and SBR technology. Not only does it eliminate the need for intermittent flow, it also eliminates the need for more connecting pipes, pumps and valves required for multi-pool processes. Through pilot studies and productive applications, it has been proven that the MSBR method is an economical, effective, reliable, and easy-to-implement computer-controlled sewage treatment process. 1.Basic principles and characteristics of MSBR method 1.1 Basic composition of MSBR The reactor consists of three main parts: Aeration grid and two alternating sequential batch processing grids. The main aeration grid maintains continuous aeration during the entire operation cycle, and during each half cycle, the two sequential batch processing grids alternately serve as SBR and clarifier respectively. 1.2 Operation steps of MSBR In each half operation cycle, the main aeration cell is continuously aerated, one of the sequential batch processing cells is used as a clarifier (equivalent to the secondary sedimentation tank of the ordinary activated sludge method), and the other sequential batch processing cell performs the following series of operation steps. Step 1: The raw water and circulating fluid are mixed and stirred in anoxic condition. At the beginning of this half cycle, the raw water enters the sequence batch processing cell and mixes with the reflux liquid that is controlled back to the main aeration cell. Under conditions of anoxia and abundant nitrifying nitrogen, the facultative denitrifying bacteria in the sequential batch processing grid use nitrate and nitrite as electron acceptors, and use raw water and organic carbon released by endogenous respiration as carbon sources to perform anaerobic respiratory metabolism. Due to the high concentration of MLSS and the high concentration of nitrated nitrogen in the initial batch processing grid, the carbon source becomes the limiting condition for the denitrification rate. With the addition of raw water, the concentration of organic carbon increases, increasing the rate of denitrification. The original nitrate nitrogen from the aeration grid and sequence batch grid is removed through denitrification. In addition, this stage of operation is also a process in which the sludge with a higher concentration in the batch processing grid flows back to the aeration grid to increase the sludge concentration in the aeration grid. Step 2: Part of the raw water and circulating fluid are mixed and stirred in anoxic condition. As the raw water continues to enter in step 1, the concentration of organic matter and ammonia nitrogen in the sequence batch processing grid gradually increases. In order to prevent the excessive increase of organic matter and ammonia nitrogen in the sequential batch processing compartment, raw water flows into the sequential batch processing compartment and the main aeration compartment respectively. Maintain an appropriate organic carbon level in the sequencing batch processing grid to facilitate denitrification. The mixed liquid passes through the circulation and continues to cause the MLSS originally accumulated in the sequence batch processing cell to flow into the main aeration cell. Step 3: The feed of raw water to the sequence batch grid stops, and the circulating liquid continues to be stirred due to lack of oxygen. After that, the raw water entering the sequence batch processing grid is interrupted. The raw water flows directly into the main aeration grid for the rest of the operation. This allows the main aeration compartment to degrade a large amount of organic carbon and weaken the aerobic endogenous respiration of microorganisms. The sequencing batch processing cell uses the residual organic matter in the circulating fluid as an electron donor and nitrated nitrogen as an electron acceptor to continue anoxic denitrification. As organic carbon sources decrease, the rate of anoxic endogenous respiration will increase. The mixed liquor from the main aeration box has lower organic matter and MLSS concentrations. After circulation, the residual organic matter and activated sludge in the sequence batch treatment compartment are pushed into the main aeration compartment, where an aeration reaction is performed to degrade the organic matter and maintain material balance. Step 4: Aerate, and continue circulation. Aeration is carried out to reduce the residual organic carbon, organic nitrogen and ammonia nitrogen in the initial incoming water, as well as the undegraded organic matter from the main aeration grid and the ammonia nitrogen released by endogenous respiration, and to blow off the nitrogen trapped in the mixed liquid produced in the previous anoxic stage. Continuous circulation increases the microbial load in the main aeration compartment, while further reducing the suspended solids in the sequence batch processing compartment and reducing the MLSS concentration, which is beneficial to reducing the amount of sludge and improving the efficiency of the sedimentation tank when it is used as a clarifier in the second half of the cycle. Step 5: Stop circulation and delay aeration. In order to further reduce the concentration of organic matter and nitrogen in the sequencing batch processing grid and reduce remaining nitrogen bubbles, delayed aeration is used. This step is performed in an isolated state with no circulation and no incoming and outgoing traffic. Delayed aeration makes BOD5 and TKN in the sequential batch processing grid reach the required level for processing. Step 6: Leave to settle. After the delayed aeration stops, it starts to settle in an isolation state to effectively separate the activated sludge from the supernatant and prepare for the clarification tank effluent in the second half of the cycle. When precipitation begins, since there is still residual dissolved oxygen, the nitrifying bacteria in the settled sludge continue to nitrify the remaining ammonia, while the aerobic microorganisms continue to perform aerobic endogenous respiration. When the oxygen in the mixed solution is reduced to a certain extent, facultative bacteria begin to use nitrated nitrogen as an electron acceptor to perform anoxic endogenous respiration and perform denitrification to a low degree. During the entire half-cycle, the concentrations of BOD, TKN, ammonia, nitrate, and nitrite in the supernatant in this sequence of batch cells are the lowest, and the total amount of suspended solids is also the least. Therefore, this sequence of batch cells serves as a sedimentation tank in the second half of the cycle, and its effluent quality is reliable. At this step, the remaining sludge can be discharged from the alternating sequence batch processing grid. second half cycle: The end of step 6 marks the beginning of the second half of the processing run. Through two half cycles, the operation form of the alternating order batch grid is changed. The second half-cycle has the same six operating steps as the first half-cycle. 2. The main operating characteristics of the MSBR method (1) The MSBR system can be designed and operated with different configurations to achieve different processing purposes. (2) In each half operation cycle, the number of steps and the time required for each step depend on the characteristics of the raw water and the requirements of the effluent. Six operational steps are described here, but the total number of steps required can be chosen by the system designer. It can often be reduced in actual operation to simplify the operation process. For example, steps 1 and 2 can be combined into one by extending the time for step 1 and reducing the time for step 2. Increasing the time of step 1 will increase the amount of organic carbon in the sequencing batch processing grid, which requires a longer anoxic mixing time without adding raw water to balance step 3. It is also possible to add steps and perform more anoxic and aerobic sequential batch operations to treat raw water with higher concentrations of organic matter and ammonia nitrogen to achieve lower total nitrogen requirements in the effluent. (3) In each half cycle, raw water enters the main aeration grid most of the time. Then part or all of the sewage enters the sequencer and batch processing compartment of the SBR. Most of the oxidation of organic carbon, organic nitrogen and ammonia nitrogen is completed in the main aeration chamber. In addition, the main aeration grid is continuously aerated in a completely mixed state, creating a stable biological reaction environment. This enables the entire device to withstand the effects of shock loads. (4) The circulating flow from the sequencing batch processing compartment to the main aeration compartment causes the suspended solids accumulated in the former to be transported to the latter. The cycle also transports the oxidized nitrate nitrogen in the main aeration cell to the sequential batch processing cell which is in anoxic stirring state during most of the half cycle to achieve the purpose of denitrification. (5) The sludge layer, as a sludge filter, plays an important role in improving effluent quality and denitrification through anoxic endogenous respiration. 3. Application and development of MSBR method MSBR technology has been applied in several sewage treatment plants. The Estevan Wastewater Treatment Plant in Saskatchewan, Canada, is an example. Although there were some freezing problems due to the severe cold, the sewage plant achieved quite good treatment efficiency. The average temperature is 13℃. Practice shows that MSBR is a sewage treatment process that can continuously feed water and is simple, small in volume, and single tank. Easy to realize computer automatic control. With low investment and operating costs, it can effectively remove sewage containing high concentrations of BOD5, TSS, nitrogen and phosphorus. In short, the system has excellent processing capabilities under low HRT, low MLSS and low temperature conditions. The research and development directions of MSBR technology are as follows: (1) The further development of MSBR technology is biological phosphorus removal or simultaneous nitrogen and phosphorus removal. At present, the School of Environmental Science and Engineering of Tongji University is conducting further research on this and has achieved research results with important theoretical significance and application value. (2) MSBR systems can have various configurations, such as ditch (canal) forms, and are currently under development and research. (3) Research on the kinetic model of MSBR biological treatment to provide a universal basis for design and operation. (4) Research on intelligent control of MSBR operation process to achieve adaptability and optimal control of each operation process of the system. Since each grid of the system is interconnected and operates alternately, and the operation can be controlled by selecting, combining and discarding operation steps, and adjusting the time of each operation step, the operation process is relatively complex. In addition, if the incoming water quality changes, the operating process of the MSBR method is more nonlinear, time-varying and fuzzy, making it difficult to use mathematical models to effectively control based on traditional control theory. Therefore, online fuzzy control of complex systems such as the MSBR method will achieve satisfactory control effects that cannot be achieved by other control methods. This is also an important research direction of the MSBR method.