Cleaning of reverse osmosis membranes, although the feed liquid undergoes various pretreatment measures, long-term use may still lead to deposits and scaling on the membrane surface, causing membrane pores to clog and reducing water production. Therefore, regular cleaning of contaminated membranes is necessary. However, the reverse osmosis membrane system should not wait until contamination is severe before cleaning, as this will increase the difficulty of cleaning, extend the cleaning steps, and prolong the cleaning time. It is essential to correctly grasp the timing of cleaning and promptly remove contaminants. Cleaning principle: Understand local water quality characteristics, conduct chemical analysis of pollutants, and select better cleaning agents and methods based on the analysis results, providing a basis for finding optimal methods under specific water supply conditions. Cleaning conditions: a. Product water volume decreases by 5%-10% compared to normal. b. To ensure product water volume, the temperature-corrected water supply pressure increases by 10%-15%. c. The conductivity of permeate water (salt content increase) increases by 5%-10%. d. For multi-stage RO systems, the pressure drop across different stages increases significantly. Cleaning methods: First, perform system backwashing; then conduct negative pressure cleaning; if necessary, perform mechanical cleaning; followed by chemical cleaning. Since chemical cleaning is more effective, other methods may be less practical. Although the names and usage methods of agents provided by different suppliers vary, their principles are generally similar. Cleaning steps: Cleaning a single-stage system: (1) Prepare cleaning solution; (2) Input cleaning solution at low flow rate; (3) Circulate; (4) Soak; (5) High-flow pump circulation; (6) Rinse; (7) Restart the system. Special contaminant cleaning includes: cleaning salt scale, cleaning carbonate scale, cleaning iron and manganese contamination, cleaning organic contamination, etc. The service life of reverse osmosis membranes in Nantong reverse osmosis ultrapure water equipment depends on the membrane's chemical stability, physical stability, water source, pretreatment, cleaning frequency, and operational management level.

Reverse osmosis membrane contamination is the main cause of reduced water production flow. This includes increased membrane filtration resistance due to clogging of membrane pores and macromolecular solutes; adsorption of solutes on the inner walls of pores; and the formation of a gel layer on the membrane surface, increasing mass transfer resistance. The deposition of components in membrane pores reduces or even blocks the pores, effectively decreasing the membrane's effective area. The additional resistance caused by the contamination layer formed by component deposition on the membrane surface may far exceed the membrane's inherent resistance, making the permeation flow independent of the membrane's permeability. This effect is irreversible. The degree of contamination is related to the membrane material, solvent in the retentate, concentration and properties of macromolecular solutes, solution pH, ionic strength, charge composition, temperature, and operating pressure. Severe contamination can reduce membrane flux by more than 80%. In system operation, membrane contamination is a very challenging issue. Its occurrence significantly reduces the removal rate, water permeation, and membrane flux of reverse osmosis equipment, while increasing the operating pressure at various stages, raising operational and maintenance costs, and severely affecting the membrane's service life. Pure water refers to water from which electrolytes (such as SiO2, CO2, etc.) dissolved in water have been removed or reduced to a certain extent. Its conductivity is generally: 1.0–0.1 μs/cm.