During the entire application process of reverse osmosis membranes, in addition to all normal attenuation coefficients of performance, the degradation coefficient of machine equipment performance caused by pollution is more severe. For example, when the membrane produces calcium bicarbonate fouling and the fouling time is one week, it is manifested as a rapid decrease in desalination rate, slow expansion of pressure difference, and insignificant change in water production rate. Cleaning with sodium citrate can completely restore performance. The pollution time was one year (for a certain water purifier), and the salt diffusion coefficient increased from the initial two mg/L to 37mg/L (for raw water ranging from 140Mg/L to 160Mg/L). The water production rate decreased from 230L/h to 50L/h. After cleaning with sodium citrate, the salt diffusion coefficient decreased to 4mg/L, and the water production rate increased to 210L/h. The length of time for reverse osmosis membrane fouling varies, and its symptoms also vary.

The key to general pollution include organic chemical scale, organic compound and colloidal solution pollution, microbial contamination, etc. The main symptoms of different types of pollution are different. The specific symptoms of membrane fouling proposed by different membrane companies also have certain differences. Secondly, pollution is usually not singular, and its main symptoms also have certain differences, making it more difficult to distinguish pollution.

To distinguish the types of pollution, it is necessary to comprehensively consider the raw water body, main parameters of the design plan, pollution index values, operation records, performance changes of machinery and equipment, and microbial species index values

Colloidal solution pollution: When colloidal solution pollution occurs, there are generally two characteristics: A. The blockage of small and medium-sized filtration devices is quickly resolved, especially the rapid expansion of pressure difference, B. The SDI value is generally above 2.5.

Microbial contamination: When microbial contamination occurs, the number of bacteria in the water and concentrated water of the RO machine equipment is relatively high, and maintenance, disinfection, and sterilization are not carried out as required.

Calcium scale: It can be distinguished based on the main parameters of the original water body and design scheme. For sulfide type water, if the utilization rate is 75% and reverse osmosis scale inhibitor is added in the design scheme, the LSI of the extraction solution should be less than 1; When no reverse osmosis scale inhibitor is added, the LSI of the extracted liquid should be below zero, which is generally not easy to cause calcium scale.

D can be distinguished by inserting a 1/4 inch PVC plastic pipe into the component to detect performance changes in different positions of the component.

Distinguish the types of pollution based on the performance changes of machine equipment.

F can be passivated by acid washing (such as sodium citrate, dilute HNO3), and calcium deposits can be distinguished based on the actual cleaning effect and cleaning solution. Further confirmation can be made by analyzing the chemical composition of the cleaning solution.

Perform chemical composition analysis on the cleaning solution: take three samples of raw water, cleaning source solution, and cleaning solution for analysis.

After identifying the type of pollution, it is possible to clean the reverse osmosis membrane and then apply disinfection and sterilization. When the type of pollution cannot be clearly identified, the general process of cleaning (3)+disinfection and sterilization+0.1% HCl (pH 3) is used for cleaning.

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