Answers to common questions about reverse osmosis membrane and ion exchange resin (101-110)

101. What is the maximum allowable silica concentration in the reverse osmosis membrane inlet water?

The maximum allowable concentration of silica depends on temperature, pH value and scale inhibitor. Generally, the maximum allowable concentration in concentrated water end is 100ppm when no scale inhibitor is added, some scale inhibitors can allow the highest silica concentration in concentrated water For 240ppm, please consult the scale inhibitor supplier.

102. How does chromium affect RO membranes?

Some heavy metals such as chromium will catalyze the oxidation of chlorine, which in turn causes the irreversible performance of the diaphragm to decay. This is because Cr6+ is less stable than Cr3+ in water. It seems that the oxidation of metal ions with high valences is more damaging. Therefore, the concentration of chromium should be reduced in the pretreatment section or at least Cr6+ should be reduced to Cr3+.

103. How to dechlorinate from water?

The preferred method is to add sodium bisulfite. The other common method is to use activated carbon for adsorption, but it should be noted that activated carbon will be dechlorinated while powdering occurs. In some industrial applications, ammonium bisulfite is used for dechlorination.

104. What kind of pretreatment is generally required for RO systems?

The general pretreatment system consists of the following: coarse filtration (~80 microns) to remove large particles, adding oxidants such as sodium hypochlorite, then precision filtration through a multi-media filter or clarifier, and then adding sodium bisulfite to reduce oxidants such as residual chlorine, Finally, install a security filter before the high-pressure pump inlet. As the name implies, the role of the security filter is to act as the ultimate insurance measure to prevent the accidental large particles from damaging the impeller and membrane elements of the high-pressure pump. Water sources with more particulate suspended matter usually require a higher degree of pretreatment to meet the specified influent requirements; for water sources with high hardness content, it is recommended to use softening or adding acid and scale inhibitors. For microbial and organic content High water source also requires the use of activated carbon or anti-fouling membrane elements.

105. How is Dow FILMTEC membrane element manufactured?

It consists of two steps: the first step is to manufacture Dow FILMTEC™ FT30 flat film diaphragm; the second step is to roll the diaphragm and other materials into rolled membrane elements as required, and the highly automated advanced fully automatic production line of the Dow production process Each step is controlled by a special computer diagnostic system, making FILMTEC components a well-known brand with more consistent performance, more reliable performance and longer life span in the membrane industry worldwide.

106. How big should the pore size of the security filter element in the RO system be?

In most cases, a filter element with a filter accuracy of 5m is selected. However, when the colloid and silicon content is high, it is recommended to use a filter element with a smaller pore size. Please refer to the detailed description in the relevant chapters of this manual.

107. What is unique about Dow FILMTEC membrane elements?

Each membrane element uses Dow FILMTEC™ FT30 membrane, which is recognized by the world membrane industry as having the widest operating pH range (2~11) and the widest cleaning pH range (1~12). Firm, showing extremely high separation performance for a long time;
The membrane blades constituting the membrane element are shorter, which greatly reduces the unevenness of the water pressure of the membrane leaf from the inside to the outside, making the water flux values ​​throughout the membrane leaf more uniform, and improving the anti-pollution of the element;
Adopt fully automatic bonding technology to obtain a precise, accurate and uniform sealing line and improve the physical integrity of the membrane element;
The precise blade assembly technology can accurately insert more blades, and the effective membrane area is higher. At the same time, it ensures that any membrane element has a consistent membrane area. A wider inlet flow channel is adopted without sacrificing the effective membrane area. .
All the above-mentioned characteristics make the system with Dow membrane components have the lowest failure rate, the most stable performance, and the least maintenance service, and achieve “at the lowest cost, get the highest water quality.”

108. How about the warranty of Dow FILMTEC membrane elements?

We provide a three-year global limited warranty.

109. Can trihalomethane (THM), carbon tetrachloride (CTC) and other low molecular weight chlorine-containing compounds be removed by Dow FILMTEC membranes?

Compounds containing the above halogens such as THM, CTC, etc. are common in wastewater, some contaminated groundwater, and disinfected water sources such as chlorine. They have been proven to be a health threat. They are medium-molecular-weight organic compounds, Dow FILMTEC ™ RO membrane has a very high removal rate for them, and Dow FILMTEC NF membrane has a very high removal rate for them.

110. How is pressure drop defined, and why is there a problem with high pressure drop?

The pressure drop is defined as the pressure loss between the inlet and concentrated water of the component or pressure vessel. Under normal operating conditions, the pressure drop of each Dow FILMTEC™ element itself is 4 to 5 psi (0.3 bar).
With the accumulation of pollution in the component, the pressure drop will gradually increase. High pressure drop is a problem that must be paid attention to because it can cause telescope phenomena and reduce the operating efficiency and performance of the system. The maximum allowable pressure drop of the case with 6-core components is 60psi ( 4.2bar).

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