Answers to common questions about reverse osmosis membrane and ion exchange resin (11-20)

11. Why is the pH value of RO product water lower than the pH value of the feed water?

When you understand the balance between CO2, HCO3- and CO3=, you can find the best answer to this question. In a closed system, the relative content of CO2, HCO3- and CO3= changes with the change of pH, Under low pH conditions, CO2 occupies the main part, in the middle pH range, mainly HCO3-, in the high pH range, mainly CO3=.
Because RO membranes can remove soluble ions but not soluble gases, the CO2 content in RO produced water is basically the same as the CO2 content in RO inlet water, but HCO3- and CO3 = can often be reduced by 1 to 2 orders of magnitude In this way, the balance between CO2, HCO3- and CO3= in the incoming water will be broken. In the series of reactions, CO2 will combine with H2O to transfer the reaction equilibrium as follows until a new balance is established.
CO2 + H2O  HCO3- + H+
If the influent contains CO2, the pH of the RO product water will always decrease. For most RO system reverse osmosis, the pH value of the product water will drop by 1 to 2 pH values. When the influent alkalinity and HCO3-high At this time, the pH of the product water drops even more.
There are very few influent waters, containing less CO2, HCO3-or CO3 = so there is less change in the pH value of the produced water. In some countries and regions, there are regulations on the pH value of drinking water, generally 6.5 ~ 9.0, According to our understanding, this is to prevent corrosion of the water pipeline, and drinking low-pH water does not itself cause any health problems. It is well known that many commercial carbonated beverages have a pH between 2 and 4.

12. How do you know which cleaning method should be used to clean your membrane system?

In order to get the best cleaning effect, it is very important to choose the cleaning agents and cleaning steps that can be symptomatic. Incorrect cleaning will actually deteriorate the system performance. Generally speaking, inorganic scale contaminants are recommended to use acidic cleaning fluids, microorganisms or organic For contaminants, alkaline cleaning solution is recommended.

13. Which cleaning agent supplier is recommended by the membrane supplier?

We do not recommend cleaning agent suppliers, but we provide common cleaning solutions on our website or this manual, as well as knowledge on how to determine the compatibility of commercial cleaning formulations and membrane systems.

14. How to find out which membrane elements need to be replaced?

If the water production of a series or a pressure shell in a reverse osmosis or nanofiltration system exhibits an abnormal increase in salt content (conductivity), this clearly shows that there is a leak in the “O” ring or that place Element is defective. The key to determining the fault is that the designed membrane system should be able to easily diagnose and identify any membrane element or system component with abnormal performance: each pressure vessel should be provided with a sampling port, and the device water production should be segmented to facilitate the overall In the product water, the problematic pressure vessel is traced, and each pressure vessel should be allowed to insert a sampling tube from the product pipe to detect the conductivity of the product water to determine the specific location of the fault.
“O” ring leakage is the most common cause of water quality decline, but if a component has been identified as faulty, we recommend that it be dissected to determine the problem, and Dow Chemical also provides various membrane failures Analysis of paid services.

15. When using ROSA software, why is there an error message that “the calculation cannot be completed in 200 iterations”?

Some countries use a comma as the decimal point, and the ROSA software only defaults to the dot as the decimal point. Please change the computer settings to solve this decimal point problem from Start (Start)  Settings (Settings)  Control Panel (Control Panel)  Regional Settings ( Regional Settings)  Number (Number), set the dot to the decimal point symbol.

16. When will the ROSA software be upgraded in the future?

Be aware of the upgraded version of ROSA software in time

17. Does Dow have a membrane analysis service?

Dow has this service, called DIRECTOR Service, you can get an introduction to this service from the Dow Liquid Separation Department website.

18. How to apply membrane to new fields?

For new applications, membrane technology has significant energy savings and may even help develop new products or create a new industry. Sometimes the process of using membranes is very simple, and sometimes it is very complicated. At this time, a small feasibility test should be conducted and the parameters required for the scale-up design should be obtained. For the end user of the membrane system, we recommend that you contact the membrane system supplier and the research institute The institute cooperates in such small but difficult applied research work.

19. Should degassing devices be installed between the first and second stage RO?

Usually no degassing is required. However, for special requirements and water composition, degassing devices should sometimes be used. When it is necessary to reduce the content of CO2 or H2S, it is the main reason for installing a degassing device. When H2S is contained in the water or there is a possibility of flying dust pollution in the surrounding environment, the vacuum degassing method should be adopted.

20. How to wash away iron pollution?

Sodium bisulfite is the most effective method for cleaning iron pollution.

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