[Hongjie Water Service]Pollution situation and cleaning method of nanofiltration membrane

Inorganic pollution: CaCO3 scaling is mainly caused by chemical sedimentation, and the calculation of the Languerre index (LSI) also indicates that if the LSI value of the treated water is greater than zero, there is a tendency for scaling. SiO2 colloidal particles are mainly determined by the enrichment of colloids. Overall, it can be considered that the inorganic pollution of the membrane follows a two-step mechanism, namely nucleation and growth.

Organic pollution: The characteristics of membranes, such as surface charge, hydrophobicity, and roughness, have a significant impact on the organic adsorption pollution and blockage of membranes. The adsorption of polar organic compounds on the surface of nanofiltration membranes may occur through hydrogen bonding, dispersion force adsorption, and hydrophobicity. For non-polar organic compounds: firstly, the interaction between hydrophobic organic compounds and water causes these slow diffusion organic compounds to accumulate on the membrane surface; Secondly, the concentration polarization of polymer organic compounds also facilitates their adsorption on the membrane surface; Once again, the interaction between ions (mainly Ca2+) in water and organic functional groups can alter the hydrophobicity and diffusion of these organic molecules.

Microbial pollution: Generally, the TDS (total solid content dissolved in water) of membrane inlet water is about 10 times that of produced water. At the same time, due to boundary layer effects and the formation of biological scale, the inlet water is non-uniformly mixed on the membrane surface, making it easier for organic and inorganic substances in the inlet water to concentrate on the membrane. This special physical, chemical, and nutritional environment on the membrane surface will affect the growth of microorganisms that ultimately reside on the membrane surface.

Cleaning of nanofiltration membranes: Generally, low pH solution is used first and then high pH solution is used for cleaning, which is mainly related to the formation factors of pollutants on the membrane. During the operation of the system, colloidal particles and organic pollutants first deposit and adsorb on the membrane, forming the first layer of scale on the membrane surface; Carbonate and metal oxide scale gradually forms, deposits on colloidal scale, and slowly infiltrates into the colloid. Therefore, first remove the upper dirt with an acidic solution and achieve the effect of loosening the lower colloid; Then clean with alkaline solution to quickly achieve the cleaning effect.