Reverse osmosis membrane life?

Equipment in use, in addition to the normal attenuation of performance, due to pollution caused by the attenuation of the performance of more serious equipment. The main pollution are mainly chemical scale, organic and colloidal pollution, microbial contamination. Different contaminants show different symptoms. Different membrane companies have proposed the symptoms of membrane fouling is also a certain difference.
In the project, we found that the length of time pollution is not the same, the symptoms are not the same. Such as: membrane calcium carbonate pollution occurs, the pollution time for a week, mainly for the rapid decline in desalination rate, pressure increases slowly, while the water production changes are not obvious, with citric acid cleaning can fully restore performance. The water flux from the initial 2mg / l increased to 37mg / l (raw water 140mg / l ~ 160mg / l), water production from 230l / h down to 50l / h, After washing with citric acid, salt flux reduced to 7mg / l, water production rose to 210l / h.
Furthermore, pollution is often not a single, the performance of the symptoms there are some differences, making the identification of pollution more difficult.
Identification of pollution types to be integrated raw water quality, design parameters, pollution index, operating records, equipment performance changes and microbial indicators to be judged:
(1) colloidal pollution: colloidal pollution occurs, usually accompanied by the following two characteristics: a. Pre-treatment of micro-filter plug very quickly, especially the pressure increases rapidly, b. Sdi value is usually 2.5 or more.
(2) microbial contamination: the occurrence of microbial contamination, ro equipment through the water and concentrated water, the total number of bacteria are relatively high, usually must not be required for maintenance and disinfection.
To prevent the ultrafiltration ro film performance damage
The new reverse osmosis membrane element is usually infiltrated with 1% nahso3 and 18% glycerol in aqueous solution and stored in a sealed plastic bag. In the case of plastic bags are not broken, storage for 1 year or so, it will not affect its life and performance. When the plastic bag opening, should be used as soon as possible, so as to avoid oxidation due to nahso3 in the air, the components have a negative impact. Therefore, the membrane should be opened before use.
After the test machine equipment, we have adopted two methods to protect the film. The machine is run for two days (15-24 hours) and then maintained with 2% formaldehyde solution. After 2 to 6 hours, it is maintained with 1% aqueous solution of nahso3 (the air in the equipment piping should be exhausted, Do not leak, close all the inlet and outlet valves). Both methods can achieve satisfactory results. The first method is more costly, long idle time, the second method in the idle time is short.
(3) calcium scale: can be based on raw water quality and design parameters to judge. For carbonate-type water, if the recovery rate of 75%, the design of adding a scale inhibitor, the concentration of lsi should be less than 1; do not add anti-scaling agent when the concentration of lsi should be less than zero, generally Does not produce calcium scale.
(4) 1/4 inch pvc plastic tube can be inserted into the component test components in different parts of the performance changes to judge.
(5) according to changes in equipment performance to determine the type of pollution.
(6) can be used acid cleaning (such as citric acid, dilute hcl), according to the cleaning effect and cleaning solution to determine calcium scale, cleaning fluid composition by further confirmation.
(7) chemical analysis of the cleaning solution: take raw water, cleaning stock solution, cleaning solution, three samples of analysis.
After determining the type of contamination, the method in Table 1 can be cleaned, and then disinfected. In the case where the type of contamination can not be determined, the cleaning step (3) + sterilization + 0.1% hcl (ph = 3) is usually used.