Summary of common problems with reverse osmosis equipment

Author: Hongjie Water

1. Why does the sealing ring in reverse osmosis equipment experience expansion?

In water treatment equipment, reverse osmosis equipment requires three types of sealing rubber rings in the membrane shell to achieve sealing and isolation of each section in the membrane shell. To reduce installation resistance, clean water or glycerin should be applied to the surface of each sealing ring during system installation.

It should be noted that lubricants should be used with caution, such as Vaseline or other petroleum grease lubricants, otherwise it will cause cracking of the fresh water pipe, especially the expansion of the sealing ring. The expansion of the rubber ring generally does not directly affect the operating effect of the system, but it will affect the system's unloading and reloading, making it difficult for the expanded rubber ring to enter the slot during loading.

2. Is the water production capacity of each component of the reverse osmosis equipment process consistent?

In the reverse osmosis equipment, because there is a pressure difference between the water supply end and the concentrated water end of the membrane element, that is, the pressure drop of the membrane, and because the salt content of the concentrated water of each element is higher than the salt content of the feed water, the feed water osmotic pressure of each element keeps rising along the system process.

If the fresh water back pressure and osmotic pressure are ignored, the water yield of each membrane element along the system flow will be proportional to the difference between their respective working pressure and osmotic pressure, that is, the water yield of each membrane element will gradually decrease.

3. Will pH have an impact on the removal rate and lifespan of reverse osmosis membranes?

Reverse osmosis equipment is the main filtration process in water treatment equipment. When raw water enters the reverse osmosis membrane, will the pH value of the raw water cause harm to the reverse osmosis membrane? Generally speaking, the material of the reverse osmosis membrane is mostly composite membrane material. If this membrane material is used within the specified pH range of the product, usually 2-11, then the harm and impact of the pH value on the membrane itself are relatively small.

As for the effect of pH on the desalination rate of reverse osmosis, generally speaking, the pH value during normal operation should be close to neutral, that is, around 7. This is due to (1) the high desalination rate of the reverse osmosis membrane at 7.5-7.8. (2) The equilibrium relationship of carbonate systems.

It can be seen that pH still has a significant impact on the desalination rate of certain impurities. Similarly, if the CO2 removal rate of the reverse osmosis membrane is zero, increasing the pH value of the raw water allows CO2 to be converted into CO32-, then the reverse osmosis membrane can effectively desalinate. However, special attention should be paid to the scaling problem of the reverse osmosis membrane at this time.

4. How should reverse osmosis equipment be operated for the first time?

Using low pressure and low flow methods to drive away the air in the pipeline, only when the air in the pipeline is not present can the equipment operate normally. Firstly, the pressure should be maintained between 0.2~0.4MPa. When using low-pressure flushing and exhaust, the generated concentrated water and produced water should be discharged into the sewer.

If there is air in the membrane element during rapid pressure rise during operation, it will generate water flow and radial impact force. In this case, it may cause the outer foreskin of the membrane to rupture, resulting in an irreparable situation for the reverse osmosis membrane.

When using it for the first time, it is necessary to adjust the pressure of the membrane operation to 0.2~0.4MPa for flushing, and ensure that the reverse osmosis system will automatically flush the reverse osmosis membrane function at low pressure every time it is started.

5. How to replace the security filter element in reverse osmosis equipment?

After using the security filter for a period of time, the treated water quality may vary. At this point, there will be a situation of filter fouling and blockage. Replacing the filter element should be based on the pressure difference before and after the filter. When the pressure difference is greater than 0.03MPa, replacement should be considered.

Replacement method: Turn off the reverse osmosis system. Remove the pressure and press the button on the pressure relief valve on the device until the indication on the pressure gauge is zero. Use a professional wrench to rotate and open the filter bottle of the filter. Extract the old filter element and replace it with a new one. Use a professional wrench to rotate and tighten the filter bottle of the filter.

6. How to clean and disinfect the reverse osmosis system?

Generally, professional technicians are required to clean the reverse osmosis system, and customers are not allowed to clean themselves. If the reverse osmosis system needs to be cleaned, professional manufacturer personnel should be contacted to complete it. The following conditions are prerequisites for chemical cleaning, and if they occur, they can be cleaned.

The prerequisite for chemical cleaning is that the water production of the system is reduced by 5% -10% compared to the initial or previous cleaning operation. When the desalination rate of the system decreases by 2.5% -5% compared to the initial or last cleaning run. When the pressure difference between each section of the system is 1-2 times that of the initial or previous cleaning operation. When the system needs to be shut down for a long time, use a protective solution for protection.

Note: Water production and desalination rate are influenced by water temperature, so the test results should be obtained under the same water temperature. 

7. Is the fluoride removal effect of reverse osmosis equipment good?

If people use perfluorinated water, it can cause harm to the human body. To avoid the harm of fluoride in their daily lives, reverse osmosis equipment can be used for fluoride removal. Most of the fluoride ions in groundwater come from the erosion and dissolution of surrounding rocks, and the water also contains a large amount of soluble ions. When removing fluoride, it is necessary to consider the impact of fluoride on other molecules. The removal rate of fluoride in groundwater with excessive salt content using reverse osmosis equipment is not too high. However, compared with other methods, the reverse osmosis method is simple to operate and has good treatment effects.