The commonly used method for advanced treatment of secondary treated effluent is filtration, and sand filter or composite filter material filter can be used. According to the filtration rate, it can be divided into slow sand filter and fast filter. The filtration rate of general single-layer sand filter is 8 ~ 12m/h. Sieve filtration is the most widely used method in pretreatment. Its main function is to separate coarse dispersed suspended solids from sewage. The equipment used is a grid and a grid screen. Grille intercepts coarse suspended solids, and its function is to protect water pump and subsequent treatment equipment. There are fixed screens, rotating screens and vibrating screens commonly used in food industry sewage, and the most commonly used aperture of the grid screen is 11-41 mesh. Precipitation is used to remove inorganic solid and organic solid in raw sewage, and to separate solid phase and liquid phase in biological treatment process. Removing inorganic solids in raw sewage by a grit chamber; Removing organic solids in raw sewage by a primary sedimentation tank; The secondary sedimentation tank is used to separate the biological phase and the liquid phase in the biological treatment process, and the grit chamber is generally located behind the grid and grid screen. In order to remove the organic matter on the surface of inorganic solids in sewage and avoid the organic solids in sewage from precipitating in the grit chamber, aeration grit chamber can be used. Using the primary sedimentation tank can reduce the load of the subsequent process. The effect of removing suspended solids in the primary sedimentation tank is related to the processed raw materials and products. According to the direction of water flow in the pool, it is divided into advection sedimentation tank, vertical sedimentation tank and radial sedimentation tank. In order to improve the sedimentation efficiency of the sedimentation tank, parallel inclined plates or inclined tubes can be arranged in the sedimentation tank to form an inclined plate (tube) sedimentation tank. Generally, the precipitation time is 1.5-2.1h..