The pH of the water produced by RO membrane water treatment is too low
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Dear experts, have you ever encountered a situation where the pH of water treated by RO membranes for aquaculture is below 5? Adding sodium hydroxide before the security filter can lead to the formation of sodium chloride, which in turn can damage the RO membranes. Do you know any ways to address this issue?
This post was last edited by qugd on 2019-6-22 at 11:03. This may be due to the anionic properties of the water passing through the RO membrane, or it may be due to the characteristics of the membrane itself. You should ask the manufacturer of the membrane; they should have test results for different types of water available for your reference. Or carry out targeted treatment on the raw water, such as removing a portion of the anions in advance.
Check what the pH of the water entering the system is. In normal cases, the pH of the first-stage produced water is acidic; therefore, the second-stage RO system should be designed to add sodium hydroxide in order to raise the pH to 8.2, thereby converting molecular CO2 into ionic bicarbonate ions, which facilitates removal by the membrane. For adding alkali, the locations are: first, in the primary RO product water; second, before the secondary high-pressure pump. However, attention should be paid to ensuring proper mixing. Where does sodium chloride come from? Is it from liquid caustic? Please use ion-exchange membrane caustic of grade one or higher.