1. According to the form of pollution:

a. Membrane pore blockage: Membrane pore blockage caused by small molecules.

b. Gel layer on the membrane surface: The formation of a gel layer caused by concentration polarization of macromolecules.

c. Sludge filter cake: Deposition of particulate matter.

d. Floating object entanglement:

2. Recoverability of pollution:

a. Reversible pollution/temporary pollution: Generally refers to the sludge layer deposited on the membrane surface, which can be removed by physical cleaning.

b. Irreversible pollution/long-term pollution: Generally refers to the gel layer and membrane pore blockage on the membrane surface, which can be removed by chemical cleaning.

c. Irreversible pollution/long-term pollution: Generally caused by irreversible adsorption, which cannot be removed by any cleaning means.

Membrane cleaning is to remove the covering on the membrane surface, restore and improve the membrane flux, which can be regarded as the reverse process of membrane pollution. Effective cleaning of the membrane can not only ensure the continuous operation of the system, but also avoid the generation of long-term membrane pollution, thereby extending the life of the membrane and reducing operating costs. It should be noted that certain substances in the influent water may react chemically with the membrane surface, causing precipitation and aging of the membrane surface, contaminating the membrane surface or causing the performance of the membrane to deteriorate.