1. The life of the reverse osmosis membrane of the reverse osmosis membrane
In the process of using the equipment, in addition to the normal attenuation of performance, the attenuation of equipment performance caused by pollution is more serious. The usual pollution mainly includes chemical scale, organic matter and colloidal pollution, microbial pollution, etc. Different pollution exhibits different symptoms. The symptoms of membrane fouling proposed by different membrane companies are also different. In the project, we found that the length of the pollution time is different, and the symptoms are also different.
For example, when the membrane is polluted with calcium carbonate scale, and the pollution time is one week, it is mainly manifested as a rapid decrease in the desalination rate, a slow increase in the pressure difference, and no obvious change in water production, and the performance can be fully restored by cleaning with citric acid. The pollution time is one year (a water purifier), the salt flux increases from the initial 2mg/L to 37mg/L (raw water is 140mg/L~160mg/L), the water yield decreases from 230L/h to 50L/h, and after cleaning with citric acid, the salt flux decreases to 7mg/L, and the water yield rises to 210L/h. In addition, pollution is often not singular, and its symptoms are also different, making it more difficult to identify pollution.
2. Identification of pollution types of reverse osmosis membranes
To identify the type of pollution, it is necessary to judge 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 is blocked very quickly in the pretreatment, especially the pressure difference increases quickly. B. The SDI value is usually above 2.5.
（2） Microbial pollution: When microbial contamination occurs, the total number of bacteria in the permeable water and concentrated water of the RO equipment is relatively high, and it must not be maintained and disinfected as required. Prevent damage to the performance of ultrafiltration RO membranes. New reverse osmosis membrane elements are typically soaked with 1% NaHSO3 and 18% glycerol in aqueous solution and stored in a sealed plastic bag. In the case that the plastic bag is not broken, it will be stored for about 1 year, and its life and performance will not be affected. When the plastic bag is opened, it should be used as soon as possible to avoid the adverse effects on the components due to the oxidation of NaHSO3 in the air. Therefore, the film should be opened as much as possible before use. After the equipment was tested, we used two methods to protect the film. The equipment was put into trial operation for two days (15~24h), and then maintained with 2% formaldehyde solution; Or after running for 2~6h, use 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 is used when there is a long idle time, and the second method is used when the idle time is shorter.
（3） Calcium scale: It can be judged according to the quality of raw water and design parameters. For carbonate water, if the recovery rate is 75%, the LSI of the concentrate should be less than 1 if the antiscalant is added to the design; The LSI of the concentrate should be less than zero when the antiscalant is not added, and calcium scale will generally not be generated.
（4） You can use 1/4 inch PVC plastic pipe inserted into the assembly to test the performance changes of different parts of the component to judge.
（5） Judge the type of pollution according to the change of equipment performance.
