① Filter slag layer filtration: at the initial stage of filtration, the filter medium can only retain large solid particles, and small particles pass through the filter medium with the filtrate. After the formation of the initial filter layer, the filter layer plays a major role in filtration, when large and small particles are trapped, such as the filtration of the plate and frame filter press.

② Deep filtration: the filtration medium is thicker, the suspension contains fewer solid particles, and the particles are smaller than the pores of the filtration medium. During filtration, the particles are adsorbed in the pore after entering, such as the filtration of porous plastic pipe filters and sand filters.

③ Screening: The solid particles trapped by the filter are greater than the pores of the filter medium, and the solid particles are not adsorbed inside the filter medium, such as the rotary drum filter to filter the coarse impurities in the sewage. In the actual filtration process, the three methods often appear simultaneously or successively.