The three major contaminants of membranes and the phenomenon of concentration polarization all have a cumulative process. During the normal operation of the membrane system, regular hydraulic flushing plays an important role in reducing and alleviating membrane fouling. For medium and small-sized systems with relatively simple pretreatment processes, the effect of hydraulic flushing is particularly obvious.

The normal membrane process of the so-called hydraulic Chinese and Western stop system is carried out, and a special membrane flushing procedure is performed. Hydraulic flushing can be divided into two methods: forward flushing and reverse flushing. Forward flushing (referred to as forward washing for short) is a process that uses the original liquid to wash away contaminants in a low-pressure and high-flow manner, to polarize the concentration difference, remove contaminants on the membrane surface and the filter cake layer. Reverse washing (referred to as backwashing for short) is a process that uses the permeate to flush the contaminated membrane pores at high pressure and large flow rate, thereby polarizing the concentration difference, removing contaminants from the membrane pores and the filter cake layer. The forward washing process is simple and has low consumption and loss, but the rinsing effect is poor. The backwashing process is complex. The loss is large, but the flushing effect is good.

For mild membrane fouling, hydraulic flushing can be adopted. In the hydraulic flushing process, there are also flushing process parameters such as flushing frequency, time, pressure and flow rate. Flow rate is the main parameter during forward washing, while pressure is the main parameter during backwashing. Frequent forward and reverse washing of the pore membrane under the full filtration operation mode is indispensable. Under the cross-flow filtration operation mode, the forward and reverse washing frequencies of the porous membrane are relatively low. The duration and effect of flushing directly affect the working efficiency of the system, and the main factor determining the flushing frequency is the quality of the system's feed water. The operation mode of the system and factors such as system operation parameters. The flushing water in the cross-flow operation mode can be reused, while the flushing water in the full filtration operation mode is generally discharged.

During the cleaning process of porous membranes such as ultrafiltration and microfiltration, a positive air pressure can be applied to the membrane in the forward direction before backwashing, and then a reverse water pressure can be applied to facilitate the large-scale stripping of the filter cake layer from the membrane surface. This process is called "positive pressure air flushing". Due to the weak connection between the composite layer of the composite membrane and the base layer, the composite membrane structure is generally not suitable for backwashing.