Analysis of reverse osmosis membrane pollution and maintenance methods

1. The pollution types of reverse osmosis membrane

1) Particulate pollution: sediment, fines of pre-treatment filter materials, etc.

2) Biological pollution: bacteria, viruses, algae, etc.

3) Organic pollution: iron, aluminum oxide, etc.

4) Inorganic pollution: carbonate scale, sulfate scale, fluorine, silica scale, etc.

One situation is that the effect is not obvious after washing, and the other is that the effect is not bad at the time after washing, but it returns to the original situation soon after operation. The reason is that the cleaning agent only loosens the scale but fails to dissolve it. Thus after operation for a while it will be blocked again.

That is why the reverse osmosis membrane system operation pressure still high after general cleaning, it is because of the composite scale. It may be that the colloid or protein produced by the body of the organism adsorbs the small particles and adheres to the surface, may also be that the pretreatment flocculant and the scale inhibitor are excessively added and accumulated on the screen in the pores, scaling occurs over time, which affects the product water capacity and desalination rate.

In summary, due to different pollution conditions, one or a few simple methods and cleaning agents cannot solve the pollution problem well. If using the wrong cleaning agent or method, it will lead to irreparable losses. For example, the cleaning of carbonate-type scale and sulfate-type scale is completely different. If you use the reverse, the cleaned membrane will no longer restore the original performance index. Therefore, the premise of selecting the correct cleaning agent and method is to analyze and understand the nature, type and degree of dirt correctly. This work is difficult for non-professional cleaning teams.

2. If following situations occur need to clean reverse osmosis membrane

1) The pressure difference between the feed water and the concentrated water has increased by 15% compared to the base condition, and the pressure difference in each section has increased by 15%

2) As a routine maintenance, generally after 3-6 months of normal operation

3) Under normalfeed water pressure, the product water capacity will drop by 10-15% from the normal value

4) The quality of product water is reduced by 10-15%, and the salt permeability is increased by 10-15%

5) The feed water pressure is increased by 10-15%;

6) The pressure difference between the various sections of the system has increased significantly

Regularly monitoring the overall performance of the reverse osmosis membrane system is the basic method to confirm whether the membrane element has been contaminated. The impact of pollution on membrane elements is gradual, and the extent of the impact depends on the nature of the pollution. The cleaning cycle of the contaminated reverse osmosis membrane depends on the actual situation on site, normal cycle is once every 3-12 months.

3. During the operation of the reverse osmosis membrane system, pollution and cleaning are always a dynamic balancing process. Each cleaning must maintain the maximum cleanliness to make the membrane run more efficiently.

After a period of operation, a large number of pollutants adsorbed and deposited on the membrane need to be removed. If the system operate again under the not enough cleaning situation, the pollution will further accumulate to block surface of membrane. At the same time, due to the long-term operation under pressure, the contaminants will be densely realized, which will make the cleaning and recovery of the membrane extremely difficult, and ultimately lead to the scrap of the membrane. Therefore, the reverse osmosis membrane should be cleaned regularly to ensure the quality of product water and the performance of the membrane.

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