Reverse osmosis equipment in long-term operation will inevitably have such and such problems, and some of these problems are caused by improper operation of the user. This paper summarizes and analyzes the equipment failure caused by improper operation.
Operation of reverse osmosis equipment caused by improper membrane performance damage
1, reverse osmosis equipment in the residual gas in the high-pressure operation, the formation of gas hammer will damage the membrane
Often there are two cases: A, after the evacuation of the equipment, re-run, 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 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 part of the air sucked in. Should be cleaned or replaced microfilter, to ensure that the pipeline does not leak. In short, there should be no air bubbles in the flow meter to gradually increase the pressure to run, the operation of the bubble should be gradually found to check the cause of the pressure drop.
2, reverse osmosis equipment shutdown method is incorrect
A, shutdown rapid pressure reduction without thorough flushing. As the concentration of inorganic salts in the concentrated water side of the membrane is higher than the raw water, easy to scale and contaminate the membrane. b, with the addition of chemical reagents in the pretreatment water rinse. Because of the chemical reagent containing water in the equipment shutdown period may cause membrane contamination.
Reverse osmosis water treatment equipment in preparation for shutdown, should stop adding chemical reagents, gradually lower the pressure to 3bar or so with the pretreatment water flushing 10min, until the TDS of the concentrated water and the TDS of the raw water is very close to the end.
3, reverse osmosis equipment disinfection and maintenance of ineffective microbial contamination
This is a composite polyamide membrane in the use of common problems, 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 of microbial prevention of insufficient attention to microbial contamination is likely to lead to microbial contamination. Many manufacturers produce pure water microbial exceeds the standard, is the disinfection, maintenance is not effective.
The main performance: factory, RO equipment does not use disinfectant maintenance; equipment installed without 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 of liquid failure or insufficient concentration.
4, reverse osmosis equipment residual chlorine monitoring ineffective
such as adding NaHSO3 pump failure or liquid failure, or activated carbon saturation due to residual chlorine damage to the membrane.
Two, cleaning is not timely and cleaning method is incorrect, resulting in damage to the membrane performance
Equipment in the use of the process, in addition to the performance of the normal attenuation, due to contamination caused by the performance of the equipment is more serious attenuation of the EDI high-purity water equipment is usually contaminated with chemical scales, organic and colloidal pollution, microbial contamination, etc. Different symptoms of pollution. Different pollution symptoms are different. 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, the main performance for the rapid decline in the rate of desalination, differential pressure slowly increase, and water production changes are not obvious, with citric acid cleaning can be fully restored 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, with citric acid cleaning, salt flux fell to 7mg / L, water production rose to 210L / h.
Recurrently, pollution is often not a single, and the performance of the Symptoms also have some differences, making the identification of pollution more difficult.
To identify the type of contamination should be integrated into the raw water quality, design parameters, pollution index, operating records, changes in equipment performance 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 quickly, B, SDI value is usually more than 2.5.
(2) microbial contamination: microbial contamination occurs, RO equipment through the water and the total number of bacteria in the concentrated water are relatively high, usually must not be in accordance with the requirements of maintenance and disinfection.
(3) calcium scale: can be based on the raw water quality and design parameters to determine. Carbonate water, if the recovery rate of 75%, the design of the cast scale inhibitor, concentrate LSI should be less than 1; do not cast scale inhibitor concentrate LSI should be less than zero, generally does not produce calcium scale.
(4) 1/4-inch PVC plastic pipe can be inserted into the components to test the components of different parts of the performance changes to judge.
(5) According to the changes in equipment performance to determine the type of contamination.
(6) Available acid cleaning (such as citric acid, dilute HNO3), according to the effect of cleaning and cleaning solution to determine the calcium scale, through the cleaning solution composition analysis to further confirm.
(7) chemical analysis of the cleaning fluid: take raw water, cleaning fluid, cleaning fluid, three samples analyzed.
After determining the type of contamination, can be cleaned according to the method in Table 1, and then disinfected for use. In can not determine the type of contamination, usually using cleaning (3) disinfection 0.1% HCl (pH 3) step cleaning.
Three, to prevent damage to membrane performance
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 the oxidation of NaHSO3 in the air, which may have adverse effects on the components. Therefore, the membrane should be opened as much as possible before use.
Reverse osmosis equipment after the test machine, 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 pipeline equipment to ensure that the equipment does not leak, close all the import and export valve). Both methods can get satisfactory results. The first method is more costly, in the long idle time to use, the second method in the short idle time to use.