The basic design concept of MBBR is to be able to operate continuously without blockage, without the need for backwashing, with small head loss and a large specific surface area. This can be achieved by growing biofilms on smaller carrier units and allowing the carrier to move freely with water flow in the reactor. In an aerobic reactor, the carrier is pushed to move by aeration; In anaerobic/anaerobic reactors, the carrier is moved by mechanical stirring. To prevent the loss of fillers in the reactor, a porous filter screen can be installed at the outlet of the reactor (Figure 1). MBBR is generally a rectangular or cylindrical structure. The rectangular reactor is evenly divided into several compartments or no compartments along the length direction of the pool using partitions. Overall, the water flow in the reactor is in a push flow state, while in each cell, due to aeration fluidization, the water flow is in a completely mixed state. The proportion of polyethylene or polypropylene suspension fillers with a specific surface area close to water filled in the pool can reach 500m2/m3 on the biofilm attachment surface in the reactor, and the actual specific surface area (inner surface of the filler) can reach 350m2/m3. Perforated aeration pipe is used to aerate on one side, allowing the filling material to circulate in the pool. The bottom of the reactor with a cylindrical structure is equipped with a microporous aeration head. In addition, some reactors not only have aeration devices installed at the bottom of the tank, but also have mixing devices installed. These stirring devices can enable the reactor to be conveniently and flexibly applied in anaerobic conditions. Sometimes, to prevent the stripping and volatilization effects caused by aeration, a lid can be added above the reactor.
In foreign countries, MBBR has been applied for small-scale, pilot, and production studies on the treatment of domestic wastewater and certain industrial wastewater, all of which have achieved good results. Experiments have shown that the mobile bed biofilm wastewater treatment process is suitable for the treatment of small and medium-sized domestic wastewater and industrial organic wastewater. Among them, integrated or buried sewage treatment devices have good prospects for promotion and application in China. However, there are still some issues with the moving bed biofilm reactor, such as uneven movement of the packing in the reactor and varying degrees of dead zones in the pool. How to improve the hydraulic flow characteristics inside the reactor and reduce operational energy consumption is a topic worthy of in-depth exploration in the development of moving bed biofilm reactors. Operating MBBR in the SBR operating mode is an improvement on MBBR technology. This reactor is called the Moving Bed Sequencing Batch Biofilm Reactor (MBSBBR), which combines the advantages of both MBBR and SBR. Another improvement is to circulate the packing material with the water flow in the reactor, which is called a circulating carrier biofilm reactor, which combines the advantages of MBBR and internal circulation reactors.
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