Do you know how you can extend the life of reverse osmosis membranes?

How to prevent reverse osmosis membrane performance damage

New reverse osmosis membrane elements are usually impregnated with an aqueous solution of 1% NaHSO3 and 18% glycerin and stored in a sealed plastic bag. If the plastic bag is not broken, it can be stored for about 1 year without affecting its life and performance.
When the plastic bag open, should be used as soon as possible, so as not to oxidize NaHSO3 in the air, the components have adverse effects.
Reverse osmosis equipment test run after the completion of the following two methods can be used to protect the membrane. Equipment test run for two days (15~24h), can be used 2% formaldehyde solution maintenance; running 2~6h, available 1% NaHSO3 water 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 valve).
Both methods can get satisfactory results, the first method is slightly higher cost, in the long idle time to use, the second method in the short idle time to use.

How to extend the service life of reverse osmosis membrane
Reverse osmosis equipment in operation may be due to improper operation of the equipment, cleaning is not timely or cleaning is not correct and lead to damage to the membrane performance, the following will analyze the causes of the above two situations and the solution to extend the service life of reverse osmosis membrane

First, improper operation caused by membrane performance damage


01 Residual gas running at high pressure, the formation of air hammer

Reverse osmosis equipment in the residual gas running at high pressure, the formation of air hammer will damage the membrane. There are two common situations:
A. When the equipment is emptied and re-run, the gas is not discharged and the pressure is quickly increased. 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 insufficient, such as microfilter clogging occurs, in the sealing of the place due to the vacuum will be sucked into the part of the air, should be cleaned or replace the microfilter, to ensure that the pipeline does not leak.
In short, there should be no air bubbles in the flowmeter under the circumstances of gradual increase in pressure to run, the operation of air bubbles found should be gradually reduced to check the cause.

02 shutdown method is not correct

A, shutdown when the rapid depressurization did not carry out a thorough flushing. As the concentration of inorganic salts in the concentrated water side of the membrane is higher than that of the raw water, it is easy to scale and contaminate the membrane.
B. Flushing with pre-treatment water with chemical reagents. Because the water containing chemical reagents may cause membrane contamination during the equipment shutdown.

Reverse osmosis equipment in preparation for shutdown, should stop adding chemical reagents, and gradually reduce the pressure to about 3 bar with pretreatment water flushing 10min, until the TDS of the concentrated water and the TDS of the raw water is very close to so far.

03 Poor disinfection and maintenance leads to microbial contamination

Ineffective disinfection and maintenance of reverse osmosis equipment leads to microbial contamination. This is a common problem in the use of composite polyamide membrane, because the polyamide membrane is poor in residual chlorine resistance, in the use of chlorine and other disinfectants are not correctly injected, coupled with the user's prevention of microorganisms do not pay enough attention to the 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 performance is: factory RO equipment does not use disinfectant maintenance;
Equipment installed without disinfection of the entire pipeline and pretreatment equipment;
Intermittent operation without taking disinfection and maintenance measures;
No regular disinfection of pretreatment equipment and reverse osmosis equipment;
Failure or insufficient concentration of maintenance solution.

04 Ineffective monitoring of residual chlorine in reverse osmosis equipment
If the pump for dosing NaHSO3 fails or the liquid fails, or the membrane is damaged by residual chlorine when the activated carbon is saturated.

Second, improperly cleaned membrane performance damage

Equipment in the process of use, in addition to the normal attenuation of performance, due to contamination caused by the attenuation of equipment performance is more serious. Usual pollution is mainly chemical scale, organic and colloidal pollution, microbial pollution. Different pollution symptoms are different.
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 when the main performance of 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 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 down to 50L / h, after cleaning with citric acid, the salt flux fell to 7mg / L, the water production rose to 210L / h.
Furthermore, pollution is often not a single, the symptoms of its performance also have some differences, making the identification of pollution more difficult.

Identify the type of pollution to be integrated into the raw water quality, design parameters, pollution index, operating records, equipment performance changes and microbiological indicators to determine.
(1) colloidal pollution: colloidal pollution occurs, usually accompanied by the following two characteristics:
A, pre-treatment in the microfilter clogging very quickly, especially the pressure difference increases very quickly;
B, SDI value is usually above 2.5.

(2) Microbial contamination: When microbial contamination occurs, the total number of bacteria in the produced water and concentrated water of RO equipment is high, and the usual maintenance and disinfection must not have been carried out 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 of the concentrate with scale inhibitor 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 washing (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 samples analyzed. After determining the type of contamination, can be cleaned according to the above methods, and then disinfected for use. When the type of contamination cannot be determined, the steps of cleaning + disinfection + 0.1% HCI are usually used for cleaning.