[Hongjie Water Service] Reverse osmosis membrane lifespan and identification of pollution types

1、 The lifespan of reverse osmosis membranes

During the use of equipment, in addition to normal performance degradation, the degradation of equipment performance caused by pollution is more severe. The common pollutants include chemical scale, organic and colloidal pollution, microbial pollution, etc. The symptoms exhibited by different types of pollution are different. The symptoms of membrane fouling proposed by different membrane companies also vary to a certain extent. In engineering, we found that the duration of pollution varies, and its symptoms also vary.

For example, when calcium carbonate fouling occurs on the membrane and the fouling time is one week, the main manifestation is a rapid decrease in desalination rate, a slow increase in pressure difference, and no significant change in water production. Cleaning with citric acid can fully restore performance. The pollution time was one year (for a certain pure water machine), and the salt flux increased from the initial 2mg/L to 37mg/L (for raw water ranging from 140mg/L to 160mg/L). The water production decreased from 230L/h to 50L/h. After cleaning with citric acid, the salt flux decreased to 7mg/L, and the water production increased to 210L/h. Furthermore, pollution is often not singular, and its symptoms vary, making it more difficult to identify pollution.

2、 Identification of fouling types in reverse osmosis membranes

To identify the type of pollution, it is necessary to comprehensively evalsuate the raw water quality, design parameters, pollution index, operation records, equipment performance changes, and microbial indicators

1. Colloidal pollution: When colloidal pollution occurs, it is usually accompanied by the following two characteristics: A. The microfilter clogs quickly in the pre-treatment, especially the pressure difference increases rapidly. B. The SDI value is usually above 2.5.

2. Microbial contamination: When microbial contamination occurs, the total number of bacteria in the permeate and concentrated water of the RO equipment is relatively high, and maintenance and disinfection are not carried out as required. Prevent damage to the performance of ultrafiltration RO membranes. New reverse osmosis membrane components are usually soaked in 1% NaHSO3 and 18% glycerol aqueous solution and stored in sealed plastic bags. Even if the plastic bag is not broken and stored for about 1 year, it will not affect its lifespan and performance. When the plastic bag is opened, it should be used as soon as possible to avoid adverse effects on the components due to the oxidation of NaHSO3 in the air. Therefore, the membrane should be opened as much as possible before use. After the equipment was tested, we used two methods to protect the film. Test run the equipment for two days (15-24 hours), and then maintain it with a 2% formaldehyde solution; Or after running for 2-6 hours, use a 1% NaHSO3 aqueous solution for maintenance (the air in the equipment pipeline should be drained to ensure that the equipment does not leak, and all inlet and outlet valves should be closed). Both methods can achieve satisfactory results. The first method is more expensive and can be used for long periods of idle time, while the second method can be used for shorter periods of idle time.

3. Calcium scale: can be judged based on the quality of raw water and design parameters. For carbonate water, if the recovery rate is 75% and scale inhibitors are added during the design, the LSI of the concentrated solution should be less than 1; When no scale inhibitor is added, the LSI of the concentrated solution should be less than zero, and generally no calcium scale will be generated.

4. 1/4 inch PVC plastic pipes can be inserted into the component to test the performance changes of different parts of the component for judgment.

5. Determine the type of pollution based on changes in equipment performance.

6. Acid washing (such as citric acid, dilute HCl) can be used to determine calcium deposits based on the cleaning effect and cleaning solution. Further confirmation can be obtained through analysis of the composition of the cleaning solution.

7. Chemical analysis of cleaning solution: Take three samples for analysis: raw water, cleaning solution, and cleaning solution. After determining the type of pollution, it can be cleaned according to the method in 1 and then disinfected for use. When the type of pollution cannot be determined, a cleaning (3)+disinfection+0.1% HCl (pH 3) step is usually used for cleaning.

More information can be found on the official website of Shenzhen Hongjie Water Technology Co., Ltd. www.czhengwei.net. If you need it, you can call the company's hotline for free at 180 3800 0078, and we will be happy to serve you.