Suspension filtration has three methods: filter residue layer filtration, deep filtration and sieve filtration.
① Filtration in the filter residue layer: In 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 initial filter residue layer is formed, the filter residue layer plays a major role in filtration. At this time, large and small particles are trapped, such as the filtration of the plate and frame filter press.
②Deep filtration: the filter medium is thicker, the suspension contains less solid particles, and the particles are smaller than the pores of the filter medium. When filtering, the particles are absorbed in the pores after entering, such as the filtration of porous plastic tube filters and sand filters.
③ Sieve filtering: The solid particles retained by the filter are larger than the pores of the filter medium, and the solid particles are not adsorbed inside the filter medium. For example, the rotary drum filter screen filters out the coarse impurities in the sewage. In the actual filtration process, the three methods often appear simultaneously or sequentially.