Note! Pay attention to residue chlorine value of Pure water treatment system

Currently in the extraordinary period, for water treatment system which adopt municipal city water as source water, especially reverse osmosis pure water treatment system and EDI ultra-pure water treatment system, must check the residual chlorine value of source water.

When SARS occurred 17 years ago, we found that some users RO membrane is oxidized and damaged because the great increase of residual chlorine in source water. And now oronavirus is coming, the government and residents will also increase the frequency of and amount of disinfectant used to prevent the virus.The most commonly used disinfectant is 84 disinfectant which main ingredient is sodium hypochlorite. It can effectively kill virus and bacteria in the water but also increase the residual chlorine concentration in wastewater.

Reason analysis

1) The chlorine gas will damage the RO membrane which is made of aromatic polyamide

2) It will cause the corrosion of stainless steel pipes which level lower then SS316L

If the pure water treatment system used normally, suddenly the concentrated water flow rate increase and desalination rate decrease, the RO membrane probably be oxidized by the residual chlorine in the source water.

If can not prove whether the chlorine gas exist in reverse osmosis system, can process chemical determination; if prove that chlorine gas exist, can use sodium bisulfite solution to reduct the residual chlorine or use activated carbon to absord residual chlorine. By using activated carbon to dechlorinate can operate for a long time. In addition, activated carbon can also remove odor, color and organic matter in the water. But after operation for a period, it shall be replaced to restore the adsorption activity.

Excessive residual chlorine will cause the oxidation of the RO membrane, resulting in a reduction in the desalination rate, shortening the service life, and even cause membrane scrap. For reverse osmosis treatment systems that use municipal tap water as source water, please pay attention to the residual chlorine value of it, can consider to increase the frequency of detection. If the residual chlorine value rises, can appropriately reduce the oxidizing fungicide in the pretreatment unit or increase the dosage of reducing agent before the water into RO system to ensure that the residual chlorine value be kept below 0.1ppm, then can avoid the risk of membrane oxidation to ensure the safe operation of system.

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