Frequently Asked Questions about Reverse Osmosis Membranes and Ion Exchange Resins (60-70)

61. Which product should I choose when replacing an NF255-400?

NF270-400 is the most suitable.

62. Can I buy Dow wet membrane elements?

Yes, but most Dow FILMTEC elements are dry membrane elements. It's still possible to purchase wet membrane elements by contacting a Dow representative.

63. How do I transfer all ROSA5 calculations to another computer?

The ROSA5 software contains a subdirectory containing wtdata.mdb. Copy this to the corresponding subdirectory of the ROSA5 software on another computer. The typical ROSA5 home directory is c:\rosa5\data\.

64. How should I dispose of old Dow FILMTEC elements?

Since the elements themselves do not contain toxic or regulated materials, Dow FILMTEC™ elements do not have special disposal requirements and can be disposed of as harmless waste through landfill. However, if the elements are used to process solutions containing harmful impurities, toxic substances may accumulate within the membrane elements. In this case, consult the relevant local or national environmental protection authorities for appropriate disposal procedures.

65. Where can I find warranty information for Dow FILMTEC?

Warranty information for Dow FILMTEC™ membrane elements can be found on the DIRECTOR Service website for the Liquid Separation section, or refer to the relevant section of this manual.

66. How are Dow FILMTEC membrane elements manufactured?

Dow FILMTEC™ elements have a spiral wound structure and utilize a highly cross-linked, fully aromatic polyamide and polypiperazine ultrathin composite membrane sheet invented by FilmTec, a wholly owned subsidiary of Dow Chemical.

The Dow FILMTEC ultrathin composite membrane sheet consists of three layers: an ultrathin, highly cross-linked aromatic polyamide separation layer, a finely porous polysulfone intermediate support layer, and a high-strength polyester-reinforced nonwoven fabric. This nonwoven fabric provides structural strength, the polyamide functional layer offers high water production, optimal salt and silica removal rates, and unparalleled chemical stability, while the thick, porous polysulfone support layer provides high porosity and rigidity, resisting compaction under membrane operating conditions.

Dow FilmTec was among the first companies to achieve ISO 9002 certification. Dow FilmTec elements utilize the industry's most advanced precision manufacturing technology, ensuring consistently high product quality and performance. Membrane production is entirely controlled by an automated diagnostic computer system. Each batch of proprietary FT30 membranes undergoes rigorous online inspection and quality recording before entering the element assembly stage.

The assembly of Dow FilmTec elements is the only process using a dedicated computer-controlled winding process to control deviations. The highly automated assembly line ensures uniform winding tension and spacing between membrane blades. All adhesive seals are straight and narrow to guarantee effective membrane area, and all critical connections are reinforced with ultrasonic welding for strength and durability.

After assembly, Dow FilmTec elements undergo further quality and performance testing to ensure they meet our high product standards. This includes vacuum testing of adhesive seals and random water flow tests to check permeate flow and desalination rates. To ensure the performance of Dow FilmTec membrane elements remains unaffected, each element is packaged in an oxygen-barrier plastic bag to prevent any microbial contamination. Selecting components with highly consistent performance allows for accurate prediction of system performance, ensuring long-term, trouble-free operation.

One of the major innovations in Dow FilmTec's manufacturing process is the precision assembly of its components. Dow FilmTec's ability to manufacture membrane elements with such precise tolerances allows its component design engineers to employ a unique "short leaf" element structure. By using more and shorter membrane leaves within an 8" element, separation efficiency is further improved, permeate flow is increased, the effective membrane area is better utilized, operating pressure is lower, permeate flux is more uniform per leaf area, and fouling susceptibility is reduced.

Dow FilmTec's manufacturing breakthrough is also reflected in its unique dry element production technology. Dry elements are faster and easier to install because no pre-installation flushing solution is required. Although the manufacturing technology and equipment for dry elements are complex, they are lightweight, resulting in lower transportation costs. Furthermore, dry elements are easier to store and transport because they do not freeze, offering a longer shelf life than wet elements.

Dow FILMTEC reverse osmosis and nanofiltration elements are used and applied more extensively than any other brand, and their high consistency and reliability have been widely verified in field use for decades. Dow FILMTEC elements have been tested in various water sources worldwide, demonstrating outstanding removal rates of dissolved salts and organic matter. They can operate efficiently at lower pressures, exhibiting higher chemical structure and pH stability, the lowest system failure rate, the most stable performance, and minimal maintenance, achieving "the highest quality permeate at the lowest cost." They offer better system operating economy than other traditional membrane elements.

67. What is the difference between TW and BW elements?

Both are identical in external dimensions. The only difference is that BW's outer sheath is made of wound fiberglass, while TW's is wrapped with adhesive tape. BW is suitable for pressure vessels containing multiple elements in series, where the pressure difference between the inlet and outlet of the element is large.

68. What is the difference between Dow FILMTEC BW30-365, BW30-365FR1, and FILMTEC BW30-365FR2? What?

They are identical in size. FR stands for Fouling Resistance, and as the name suggests, it is particularly suitable for wastewater recycling or treating complex, heavily polluted water sources. It utilizes Dow's leading proprietary antifouling membrane technology. FR1 and FR2 have been upgraded and merged into a unified FR.

69. What is a full-fit element?

Dow's full-fit design refers to a type of element structure, still a spiral wound structure, but its outer sheath no longer uses tape or fiberglass wrapping. Instead, it uses a highly rigid polypropylene mesh, which reduces or even eliminates the stagnant layer between the membrane element and the pressure vessel wall. Therefore, this type of element does not require a brine seal ring. In applications with sanitary requirements, the full-fit design intentionally allows a certain amount of bypass flow around the element to reduce dead zones and prevent microbial growth. While this process promotes the growth of pollutants, a higher feed water flow rate is required to effectively reduce concentration polarization at the membrane surface. All standard membrane elements use brine seals to prevent feed water from bypassing the outer layer of the element and the inner wall of the pressure vessel. Although a water stagnation layer (dead water zone) exists, it ensures that all feed water flows across the membrane surface, resulting in a lower feed water flow rate required to effectively reduce concentration polarization.

70. What solution should be used to lubricate the pressure vessel during element installation?

Glycerin. If glycerin is unavailable, pretreated qualified water may be used for wetting. No other chemical reagents or industrial or domestic detergents with unknown physicochemical properties should be used.