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.