Frequently Asked Questions about Reverse Osmosis Membranes and Ion Exchange Resins (1-10)

1. How to choose the right product?

The Dow Chemical Liquid Separation Division website provides an interactive product selection guide to assist in selecting DOWEX* ion exchange resins and FILMTEC™ membrane elements.

Additionally, users can also select by application, product type, or product size on the product information page of the Liquid Separation Division website.

Users familiar with DOWEX and Dow FILMTEC products can directly click on the Dow FILMTEC membrane element or Dow DOWEX resin product specification table on any page of the Liquid Separation Division website.

2. What are the typical removal rates for certain ions when selecting Dow FILMTEC membrane elements?

Please refer to the membrane element product specification table. For the removal rates of uncommon ions, please refer to the typical removal rate data table for Dow FILMTEC™ FT30 in this manual.

3. Comparison of ROSA4 and ROSA5 design software: What are the changes and new features?

ROSA5 includes design calculations for Dow FILMTEC™ NF270 and NF200 nanofiltration elements. The calculation software engine is more professional, employing a database approach to process documents. Product manuals and standardized software are separated from the ROSA software for easier download of the design software.

4. What are the feed water requirements for RO membrane elements and IX ion exchange resin?

Theoretically, the water entering the RO and IX systems should not contain the following impurities:

• Suspended solids

• Colloids
  

• Calcium sulfate
  

• Algae
  

• Bacteria
  

• Oxidizing agents, such as residual chlorine
  

• Oils or lipids (must be below the instrument's detection limit)
  

• Organic matter and iron-organic complexes
  

• Metal oxides such as iron, copper, and aluminum corrosion products
  

The quality of the feed water will have a significant impact on the lifespan and performance of RO elements and IX resin.

5. Is Dow FILMTEC FT30 chlorine-resistant?

All ultrathin polyamide composite membranes will have their surface oxidized by active chlorine, leading to a decrease in the membrane element's ability to remove salt. Dow FILMTEC™ FT30 membranes, due to their highly cross-linked, fully aromatic chemical composition, can withstand residual chlorine oxidation attacks of 1000 ppm•hr. Trace amounts of metals can accelerate this oxidation process; therefore, RO feed water should be dechlorinated. Please refer to the section on "Dechlorination from Reverse Osmosis Feed Water" in this manual.

6. What impurities can RO membranes remove?

RO membranes are excellent at removing ions and organic matter. Reverse osmosis membranes have a higher removal rate than nanofiltration membranes. Reverse osmosis typically removes 99% of the salt in the feed water, and the removal rate of organic matter in the feed water is ≥99%.

7. How to perform ROSA design calculations for mixed water sources?

For some water sources, the type of raw water cannot be clearly determined in ROSA design. This includes mixed water sources (such as well water mixed with tertiary treated effluent) and influent with uncertain water quality (such as wastewater treated by ultrafiltration). Generally, surface water design calculation guidelines can be used for calculations.

8. Under the same arrangement conditions, the calculation results for SW30-4040 in ROSA4 differ from those in ROSA5. What is the reason for this?

ROSA5 calculation results are correct because current SW30-4040 membrane elements have improved effective membrane area and membrane performance due to the adoption of automated manufacturing technology. ROSA4 fails to reflect this change.

9. Does Dow FilmTec sell pressure housings, element adapters (commonly known as "grenades"), and element connectors?

We do not sell pressure housings. The element-to-housing adapters (commonly known as "grenades") are a component of the pressure housing and are provided by the pressure housing manufacturer. The element connector is a component of the membrane element and is included in each Dow FILMTEC™ 8″ membrane element package. For 2.5″ and 4″ elements, they must be purchased separately. Element connectors or O-rings can also be purchased separately from FilmTec as spare parts.

10. Can ozone (O3) be used as a compatible oxidant and disinfectant for Dow FILMTEC FT30?

While ozone can be used in the pretreatment of RO feed water, special measures should be taken to remove residual ozone before it enters the membrane element. UV radiation can successfully decompose ozone (O3), but activated carbon or sodium bisulfite are better options. For disinfection, consider using the newer, highly effective, non-oxidizing disinfectant DBNPA instead of ozone.