The process in which some solutes are inevitably retained during membrane separation and the retained solutes deposit on the membrane surface or in the membrane pores, leading to a decline in membrane performance, is called membrane fouling.

The main manifestations of membrane fouling are: reducing the membrane flux of the solvent; Reduce or increase the retention rate of solutes. Membrane fouling is an inevitable by-product phenomenon in membrane technology processes. Membrane fouling driven by pressure in membrane processes mainly includes three categories: inorganic fouling, organic fouling and microbial fouling. Inorganic contamination refers to the precipitation of particulate matter and insoluble salts on the membrane surface. Organic pollution refers to the adsorption, clogging and retention of organic substances within the membrane pores, as well as the formation of a gel layer on the membrane surface. Microbial contamination refers to the adhesion, clogging and proliferation of microorganisms on the membrane surface. The synthesis of three types of membrane fouling factors can clog membrane pores or form filter cakes, deteriorating the separation performance indicators of the membrane.

The contamination of porous membranes is mainly caused by organic matter and microbial contamination, with inorganic matter contamination as a secondary factorThe contamination of dense films exists in three forms simultaneously: inorganic matter, organic matter and microbial contamination. When the saturation of insoluble salts exceeds their limit, precipitates will form on the membrane surface. Meanwhile, when organic matter and microorganisms aggregate on the membrane surface and form a gel layer, technical inorganic salts that have not yet reached their saturation concentration will also combine with the gel to form precipitates.