1, to prevent damage to the membrane performance of the new reverse osmosis membrane elements are usually infiltrated with 1% NaHSO3 and 18% glycerol aqueous solution stored in a sealed plastic bag. In the case of the plastic bag is not broken, storage for about 1 year, will not affect its life 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 oxidation of NaHSO3 in the air. Therefore the membrane should be opened before use as much as possible. After the equipment test run, we have used two methods to protect the membrane. Equipment test run for two days (15 ~ 24h), and then use 2% of the formaldehyde solution maintenance; or run 2 ~ 6h, with 1% of the NaHSO3 aqueous solution for maintenance (should exhaust the air in the equipment pipeline to ensure that the equipment does not leak, close all the import and export valves). Both methods can get satisfactory results. The first method is more costly and is used when the idle time is long, and the second method is used when the idle time is short.
2, improper operation of the equipment caused by damage to the membrane performance equipment, residual gas in the high-pressure operation, the formation of gas hammer will damage the membrane There are often two cases: A, after the evacuation of the equipment, re-operation, the gas is not exhausted on the rapid increase in pressure operation. Should be in the 2 ~ 4bar pressure will be the remaining air exhaust, and then gradually increase the pressure to run. B, in the pretreatment equipment and high-pressure pumps between the joints of bad sealing or leakage (especially the microfilter and its pipeline leakage) when the pretreatment water supply is not sufficient, such as microfilter clogging occurs in the sealing of the place due to the vacuum will be sucked into part of the air. The microfilter should be cleaned or replaced to ensure that the piping does not leak. In short, the pressure should be gradually increased to run without air bubbles in the flow meter, and air bubbles found during operation should be gradually reduced to check the cause. Incorrect method when shutting down A. Rapid pressure reduction when shutting down without thorough flushing. As the concentration of inorganic salts in the concentrated water side of the membrane is higher than that in the raw water, it is easy to scale and contaminate the membrane.B. Flushing with pretreatment water with chemical reagents. Because the water containing chemical reagents may cause membrane contamination during equipment shutdown. In preparation for shutdown, should stop adding chemical reagents, and gradually reduce the pressure to about 3bar with pretreatment water flushing for 10min, until the TDS of the concentrated water and the TDS of the raw water is very close to so far.
3, disinfection and maintenance of ineffective microbial contamination This is a common problem in the use of composite polyamide membrane, because the polyamide membrane residual chlorine resistance is poor, in the use of chlorine and other disinfectants are not correctly injected, coupled with the user's prevention of microorganisms is not enough attention to microbial contamination is likely to lead to microbial contamination. At present, many manufacturers produce pure water microbial exceeds the standard, is the disinfection, maintenance is not effective caused by. The main manifestations are: factory, RO equipment does not use disinfectant maintenance; equipment installed after the entire pipeline and pretreatment equipment disinfection; intermittent operation does not take disinfection and maintenance measures; no regular disinfection of pretreatment equipment and reverse osmosis equipment; maintenance fluid failure or insufficient concentration. Ineffective monitoring of residual chlorine such as the failure of the pump to inject NaHSO3 or the failure of the liquid, or activated carbon saturation due to residual chlorine damage to the membrane.
4, cleaning is not timely and incorrect cleaning methods resulting in damage to the membrane performance equipment in the process of use, in addition to the performance of the normal attenuation, due to contamination caused by the attenuation of the performance of the equipment is more serious. Usual pollution is mainly chemical scale, organic and colloidal pollution, microbial pollution. Different contaminants show different symptoms. Different membrane companies put forward the symptoms of membrane contamination is also a certain difference. In the project we found that the length of time of pollution is not the same, the symptoms are not the same. Such as: membrane calcium carbonate scale contamination, contamination time for a week, mainly for the rapid decline in the rate of desalination, the differential pressure increases slowly, while the water production changes are not obvious, with citric acid cleaning can fully restore performance. Pollution time for a year (a water purifier), salt flux from the initial 2mg / L rose to 37mg / L (raw water for 140mg / L ~ 160mg / L), water production from 230L / h fell to 50L / h, after cleaning with citric acid, salt flux fell to 7mg / L, the water production rose to 210L / h. Furthermore, the pollution is not always a single, and the symptoms of the performance of a certain degree of Difference, making the identification of pollution more difficult. Identify the type of contamination to be integrated into the raw water quality, design parameters, pollution index, operating records, equipment performance changes and microbiological indicators to determine: (1) colloidal contamination: colloidal contamination occurs, usually accompanied by the following two characteristics: A, pre-treatment in the microfilter clogging very quickly, especially the pressure difference increases very quickly, and B, the SDI value is usually more than 2.5. (2) microbial contamination: when microbial contamination occurs, the total number of bacteria in the RO equipment through the water and the concentrated water are higher, usually must not be maintained and disinfected as required. (3) Calcium scale: can be based on the raw water quality and design parameters to determine. For carbonate-type water, if the recovery rate of 75%, the design added scale inhibitor, concentrate LSI should be less than 1; do not add scale inhibitor concentrate LSI should be less than zero, generally does not produce calcium scale. (4) Available 1/4-inch PVC plastic pipe inserted into the components to test the components of different parts of the performance changes to judge. (5) Judge the type of contamination based on changes in equipment performance. (6) Available acid wash (such as citric acid, dilute HNO3), according to the effect of cleaning and cleaning fluid to determine the calcium scale, further confirmed by cleaning fluid composition analysis. (7) chemical analysis of the cleaning solution: take the raw water, cleaning the original solution, cleaning solution, three sample analysis. After determining the type of contamination, can be cleaned according to the method in Table 1, and then disinfected for use. When the type of contamination cannot be determined, the cleaning (3) + disinfection + 0.1% HCl (pH 3) step is usually used for cleaning. The authors have also had good results with the cleaning solution (1) + cleaning solution (3) + disinfection step.