How to Extend the Life of Reverse Osmosis Membrane
Reverse osmosis membrane is a common and important component in water treatment equipment, which can effectively filter out impurities in water and make the outlet water reach the goal of pure water.
Usually, the service life of reverse osmosis membrane element is 3-5 years. After this service life, the reverse osmosis membrane element should be replaced and treated. Of course, the service life of the membrane element is not fixed. If certain protection methods are adopted and some usage precautions are taken, the service life of the membrane element can be extended.
How to Prevent Damage to Reverse Osmosis Membrane Performance
New reverse osmosis membrane elements are usually soaked in a 1% sodium bisulfite and 18% glycerol aqueous solution and stored in sealed plastic bags. After storing for about a year in the plastic bag without breaking, it will not affect its service life and performance.
After the plastic bag is opened, it should be used as soon as possible to avoid the oxidation of sodium bisulfite in the air and its adverse effect on the element.
After the reverse osmosis equipment is tested, the membrane can be protected by using one of the following two methods. After the equipment is tested and run for two days (15-24 hours), it can be maintained by using a 2% formaldehyde solution. After running for 2-6 hours, it can be maintained by using a 1% sodium bisulfite aqueous solution (the air in the equipment's pipelines should be exhausted, and the equipment should not leak, and all inlet and outlet valves should be closed).
Both methods can achieve satisfactory results. The first method has a slightly higher cost and should be used when the equipment is idle for a long time. The second method should be used when the equipment is idle for a short time.
How to Extend the Life of Reverse Osmosis Membrane
The performance of the reverse osmosis membrane may be damaged due to improper operation of the equipment, failure to clean in time or improper cleaning. The following will analyze the causes of the above two cases and solutions, so as to extend the service life of the reverse osmosis membrane.
First, the membrane performance damage caused by improper operation
01 The residual gas runs under high pressure to form a gas hammer
Reverse osmosis equipment has residual gas operating under high pressure, forming a gas hammer will damage the membrane. Two things often happen:
A, after the equipment is emptied, when it is re-run, the gas is not exhausted and the pressure is quickly boosted. The remaining air should be drained at a pressure of 2 to 4bar, and then gradually increase the pressure operation.
B, when the joint between the pretreatment equipment and the high pressure pump is not sealed or leaked (especially the microfilter and the pipeline leakage after it), when the pre-treatment water supply is insufficient, such as the microfilter is blocked, the vacuum in the place where the seal is not good will suck in some air, the microfilter should be cleaned or replaced to ensure that the pipeline does not leak.
In short, the pressure should be gradually increased in the flow meter without bubbles, and the bubbles found in the operation should be gradually reduced to check the cause.
02 The shutdown method is incorrect
A, The membrane is not thoroughly washed due to the rapid depressurization when shutdown. Because the concentration of inorganic salts in the concentrated water side of the membrane is higher than that of raw water, it is easy to scale and pollute the membrane.
B. Rinse with pretreatment water with added chemical reagents. Water containing chemical reagents may cause membrane contamination during equipment outage.
When the reverse osmosis equipment is ready to shut down, the chemical reagent should be stopped, the pressure should be gradually reduced to about 3bar, and the pre-treated water should be washed for 10min until the TDS of the concentrated water is very close to the TDS of the raw water.
03 Poor disinfection and maintenance lead to microbial contamination
Poor 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 has poor residual chlorine resistance, the disinfectant such as chlorine is not correctly added in use, and the user does not pay enough attention to the prevention of microorganisms, which is easy to lead to microbial pollution.
At present, the pure water produced by many manufacturers exceeds the standard of microorganisms, which is caused by poor disinfection and maintenance.
The main performance is: RO equipment did not use disinfectant maintenance when leaving the factory; Failure to disinfect the entire pipeline and pretreatment equipment after installation; Discontinuous operation without taking disinfection and maintenance measures; Failure to disinfect pretreatment equipment and reverse osmosis equipment regularly; Maintenance solution failure or insufficient concentration.
04 Poor monitoring of residual chlorine in reverse osmosis equipment
For example, if the pump for adding NaHSO3 fails or the solution is ineffective, or when the activated carbon is saturated due to chlorine damage to the membrane.
II. Damage to membrane performance caused by improper cleaning
In addition to the normal performance degradation of the equipment during use, the performance degradation caused by pollution is more serious. The main types of pollution are chemical scale, organic pollution, and colloidal pollution, microbial pollution, etc. The symptoms of different pollution are different.
The symptoms are different depending on the length of pollution time. For example, when the membrane is polluted by calcium carbonate scale, the desalination rate will drop rapidly within a week, and the pressure difference will increase slowly, while the water production will change little. It can be fully restored by cleaning with citric acid.
Pollution is not always of a single type, and the symptoms it exhibits are also different, making pollution identification more difficult.
The type of pollution should be determined by comprehensively judging the original water quality, design parameters, pollution index, operation records, changes in equipment performance, and microbial indicators.
(1) Colloidal pollution: When colloidal pollution occurs, the following two characteristics are usually accompanied: A, the microfiltration unit upstream of the pretreatment quickly clogs, especially the pressure difference increases rapidly; B, the SDI value is usually above 2.5.
(2) Microbiological pollution: When microbial pollution occurs, the bacterial count in the RO device's product water and concentrate is high, and it must not have been properly maintained and disinfected in the past.
(3) Calcite Scale: It can be judged according to the original water quality and design parameters. For carbonate water, if the recovery rate is 75%, the LSI of the scale inhibitor concentrate added during the design should be less than 1; when no scale inhibitor is added, the LSI of the concentrate should be less than zero, and calcium scale is generally not produced.
(4) The performance changes of the components at different locations can be judged by inserting a 1/4-inch PVC plastic pipe into the components for testing.
(5) The type of pollution can be judged by changes in the equipment's performance.
(6) Calcite scale can be judged by acid washing (such as citric acid, dilute HNO3), based on the cleaning effect and cleaning solution. The analysis of the cleaning solution further confirms it.
(7) Chemical analysis of the cleaning solution: Take three samples of original water, cleaning original solution, and cleaning solution for analysis.
After determining the type of pollution, the above method can be used for cleaning, and then disinfection and use. When the type of pollution cannot be determined, the usual method is to clean, disinfect, and clean with 0.1% HCI.
