Reverse osmosis equipment is bound to encounter various problems during long-term operation, and some of these problems are caused by improper operation by users. This article summarizes and analyzes equipment failures caused by improper operation.

Improper operation of reverse osmosis equipment can cause damage to membrane performance

1Residual gas in reverse osmosis equipment operates under high pressure, forming air hammers that can damage the membrane

There are often two situations that occurAAfter the equipment is emptied, when it is restarted, the pressure is rapidly increased before all the gas is completely discharged. Should be2～4barAfter expelling the remaining air under the pressure, gradually increase the pressure for operation.BWhen the joint between the pretreatment equipment and the high-pressure pump is not well sealed or leaks water(Especially the leakage of the microfilter and the pipeline behind it)When the pre-treatment water supply is insufficient, such as when the microfilter gets clogged, in poorly sealed areas, some air will be drawn in due to vacuum. The microfilter should be cleaned or replaced to ensure that the pipeline does not leak. In conclusion, the flowmeter should be operated under gradually increased pressure when there are no bubbles in it. If bubbles are found during operation, the pressure should be gradually reduced to check the cause.

2The method of shutting down the reverse osmosis equipment is incorrect

AWhen shutting down, the voltage was rapidly reduced without thorough flushing. Because the concentration of inorganic salts on the concentrated water side of the membrane is higher than that of the raw water, it is prone to scaling and membrane contamination.BRinse with pre-treated water containing chemical reagents. Water containing chemical reagents may cause membrane fouling during the equipment's shutdown period.

When the reverse osmosis water treatment equipment is about to be shut down, the addition of chemical reagents should be stopped and the pressure should be gradually reduced3barRinse both sides with pre-treated water10minDirectly concentrated waterTDSWith the original waterTDSStop when it's very close.

3Microbial contamination is caused by poor maintenance of reverse osmosis equipment

This is a common problem in the use of composite polyamide membranes. Due to the poor residual chlorine resistance of polyamide membranes, if chlorine and other agents are not added correctly during use, and users do not pay enough attention to the prevention of microorganisms, it is easy to cause microbial contamination. Many manufacturers produce pure water with excessive microorganisms, which is caused by poor maintenance.

The main manifestations are: at the time of leaving the factory,ROThe equipment was not maintained with liquid. After the equipment was installed, the entire pipeline and pretreatment equipment were not inspected. Intermittent operation without taking maintenance measures; There is no regular maintenance of the pretreatment equipment and reverse osmosis equipment. The maintenance fluid has expired or its concentration is insufficient.

4The residual chlorine monitoring of reverse osmosis equipment is inadequate

If addedNaHSO3The pump malfunctions or the liquid medicine becomes ineffective, or the membrane is damaged due to residual chlorine when the activated carbon is saturated.

Second, damage to membrane performance caused by untimely cleaning and incorrect cleaning methods

During the operation of the equipment, apart from the normal performance degradation, the performance degradation caused by contamination is even more severe.EDIThe common contamination of high-purity water equipment mainly includes chemical scale, organic matter and colloidal contamination, microbial contamination, etc. Different types of pollution present different symptoms. The symptoms of membrane fouling proposed by different membrane companies also have certain differences.

In engineering, we have found that the symptoms vary with the duration of pollution. When the membrane is contaminated by calcium carbonate scale and the contamination lasts for one week, the main manifestations are a rapid decline in desalination rate, a slow increase in pressure difference, while the change in water production is not obvious. Cleaning with citric acid can restore performance. The pollution period is one year(A certain pure water machine)The salt flux changes from the initial2mg/LRise to37mg/L(The raw water is140mg/L～160mg/L)The water production volume is determined by230L/hDecrease to50L/hAfter cleaning with citric acid, the salt flux dropped to7mg/LThe water production has increased210L/h.

Furthermore, pollution is often not singular, and the symptoms it presents also vary to some extent, making the identification of pollution even more difficult.

To identify the type of pollution, a comprehensive judgment should be made based on the quality of the raw water, design parameters, pollution index, operation records, changes in equipment performance and microbial indicators, etc.

(1)Colloidal contamination: When colloidal contamination occurs, it is usually accompanied by the following two characteristics:AThe microfilters in the pretreatment process get clogged very quickly, especially as the pressure difference increases rapidly.B,SDIThe value is usually in2.5That's all.

(2)Microbial contamination: When microbial contamination occurs,ROThe total amount of permeate water and concentrated water in the equipment is relatively high. It is certain that maintenance has not been carried out as required on a regular basis.

(3)Calcium scale: It can be determined based on the quality of the raw water and the design parameters. For carbonate-type water, if the recovery rate is75%At that time, a scale inhibitor and concentrated liquid were added during the designLSIShould be less than1; The concentrated solution without adding scale inhibitorsLSIIt should be less than zero and generally will not produce calcium scale.

(4)Available1/4In inchesPVCThe plastic pipe is inserted into the component to test the performance changes at different parts of the component for judgment.

(5)Determine the type of pollution based on the changes in equipment performance.

(6)Can be acid-washed(Such as citric acid, diluteHNO3)Calcium scale is determined based on the cleaning effect and the cleaning solution, and further confirmed through the analysis of the cleaning solution composition.

(7)Chemical analysis of the cleaning solution: Take three samples, namely raw water, cleaning raw solution and cleaning solution, for analysis.

After determining the type of pollution, the table can be followed1Clean it by the method in the middle and then use it. When the type of contamination cannot be determined, cleaning is usually adopted(3)0.1%HCl(pHfor3)The steps for cleaning.

Iii. Prevent damage to membrane performance

New reverse osmosis membrane elements are usually impregnated1%NaHSO3and18%Store it in a sealed plastic bag after obtaining a glycerol aqueous solution. Store when the plastic bag is not broken1It will take about a year and will not affect its lifespan or performance. Once the plastic bag is opened, it should be used as soon as possible to avoid any inconvenienceNaHSO3Oxidation in the air has adverse effects on components. Therefore, the film should be opened as much as possible before use.

After the trial operation of the reverse osmosis equipment, we adopted two methods to protect the membrane. The equipment has been in trial operation for two days(15～24h)Then adopt2%Formaldehyde solution maintenance; Or run2～6hAfter that,1%theNaHSO3Maintain it with a water solution(All the air in the equipment pipeline should be completely expelled to ensure that the equipment does not leak, and all the inlet and outlet valves should be closed). Both methods can achieve satisfactory results. One method is more costly and is used when the idle time is long, while the other is used when the idle time is short.