将一定量粒径较小的粒状滤料装在滤池中，由于滤料表面生长着高活性的生物膜，因此在滤池内能够曝气，当污水经过时，就能给利用滤料氧化降解作用达到快速净化污水的效果，这就是生物氧化降解过程。同时，流经污水时，由于滤料呈现压实状态，因此，利用滤料粒径小以及生物膜絮凝作用可以截流污水中的悬浮物，从而保证脱落的生物膜不会随水漂出，此为截留作用。运行～ 段时间后，随着水头损失的增加，为了释放截留的悬浮物和更新生物膜，要对滤池进行反冲洗，这就是反冲洗过程。
A certain amount of granular filter material with smaller particle size is installed in the filter tank, because the surface of the filter material grows a highly active biofilm, so it can be aerated in the filter tank, when the sewage passes through, it can be used to achieve the effect of rapid purification of sewage by the oxidation and degradation of the filter material, which is the process of biological oxidation and degradation. At the same time, when flowing through the sewage, due to the compaction of the filter material, the use of small filter material particle size and biofilm flocculation can intercept the suspended solids in the sewage, so as to ensure that the falling biofilm will not float out with the water, which is the interception effect. In order to release the suspended solids and renew the biofilm, it is necessary to backwash the filter with the increase of head loss.