Understanding the types of RO membrane elements is the first step to choosing the right element for your system — tap water TW elements, brackish water BW elements, fouling-resistant FR versions, and full-fit designs all look similar from the outside but differ completely in wrapping, pressure capability, and application. This guide compares the types of RO membrane elements, explains how FILMTEC elements are manufactured, and covers the replacement, disposal, and installation questions that come up in every plant.
Types of RO Membrane Elements: TW, BW, FR, and Full-Fit Designs
The types of RO membrane elements available today fall into four families distinguished by their outer wrapping and design:
| Type | Wrapping / Structure | Pressure Capability | Typical Use |
| TW (tap water) | Tape-wrapped | Lower | Low-pressure applications, single elements |
| BW (brackish water) | FRP-wrapped | Higher | Multi-element vessels, high pressure difference |
| FR (fouling resistant) | FRP-wrapped, anti-fouling chemistry | Higher | Wastewater, polluted or complex feed water |
| Full-fit | Rigid polypropylene grid, no outer wrap | Varies | Hygienic applications, dead-water-free design |
All of them share the same spiral-wound working principle — the wrapping and grid are engineering choices that trade pressure capability against cleanability and hygiene.
TW vs BW Components: Tape-Wrapped vs FRP-Wrapped
Both TW and BW components have the same exterior dimensions; the primary difference lies in their outer sheathing:
- BW (brackish water) — these components are wrapped with fiberglass reinforced plastic (FRP), making them suitable for use in pressure vessels with multiple components connected in series and where there is a significant pressure difference between the inlet and outlet.
- TW (tap water) — these components are wrapped with tape, making them ideal for applications with less demanding pressure requirements.
For a low-pressure point-of-use system, a TW element is adequate; for a multi-vessel industrial train, choose BW so the wrap withstands the differential pressure across the train.
BW30-365 Series: Standard and Fouling-Resistant FR Elements
The external dimensions of the BW30-365 family are identical; the distinctions are in the membrane chemistry:
- BW30-365 — standard brackish water RO element.
- BW30-365FR1 and BW30-365FR2 — anti-fouling versions (fouling resistance, FR) designed for treating complex and more polluted water sources, including wastewater recycling. Both FR1 and FR2 utilize advanced anti-fouling membrane technology and have been unified under the FR series.
An FR element is the first line of defense when the feed water carries organic or biological foulants — combine it with the fouling prevention practices to keep cleaning frequency low.
Full-Fit Components: Design and Hygienic Applications
A full-fit component is a structural design in which the membrane element has no outer tape or FRP wrapping. Instead, it features a rigid polypropylene grid that eliminates the need for a brine seal ring and minimizes the retention layer between the membrane and the pressure vessel.
- Hygienic design — this design is particularly useful in hygienic applications, allowing some bypass flow to reduce dead water areas and prevent microbial growth.
- Flow requirement — full-fit components require higher water flow to reduce concentration polarization effectively.
- No brine seal — the rigid grid seals against the vessel wall, removing the brine seal ring and its maintenance.
Full-fit elements are a specialized choice — most standard installations remain with TW/BW designs, as covered in the RO membrane maintenance guide.
How FILMTEC Membrane Elements Are Manufactured
Dow FILMTEC membrane elements are meticulously manufactured using advanced technologies and high-quality materials:
- Membrane structure — a highly cross-linked, fully aromatic polyamide separation layer supported by a microporous polysulfone intermediate layer and a high-strength polyester non-woven fabric.
- Manufacturing process — precise, automated systems control every aspect of production; the membranes undergo rigorous inspections, including vacuum tests and water production and desalination efficiency assessments.
- Innovations — dry component production technology simplifies installation and enhances storage stability, complemented by short membrane leaf structures in 8-inch elements that improve separation efficiency and reduce contamination risks.
FILMTEC components are known for high reliability and consistent performance, offering superior salt and organic matter removal rates, lower operating pressures, and extended operational life.
Replacement, Disposal, and Installation Practicalities
Practical questions complete the picture:
- Replacing NF255-400 — the most suitable replacement is the NF270-400, offering similar performance with updated features; see our nanofiltration membrane replacement guide for the full model logic.
- Wet components — wet components can be purchased, but most FILMTEC elements are supplied dry; contact your supplier for wet-component availability.
- Disposal — FILMTEC components do not contain toxic or regulated materials and can generally be disposed of as non-hazardous waste. If the elements treated solutions with harmful impurities, they may be enriched with toxic substances — consult the relevant local or national environmental protection agencies for appropriate disposal.
- Installation lubrication — use glycerin as the lubricant when installing components in a pressure vessel; if glycerin is not available, pre-treated, qualified water can be used to moisten the components. Avoid other chemical reagents and industrial or household detergents due to unknown physical and chemical properties.
- ROSA5 transfer and warranty — transfer ROSA5 calculations by copying the wtdata.mdb file (default directory c: osa5\data\) to the new computer; warranty information is available on the DIRECTOR Service webpage and in the product manual.
Conclusion
Choosing among the types of RO membrane elements — TW, BW, FR, and full-fit — comes down to pressure requirements, feed water quality, and hygiene needs. FR elements handle polluted feed, BW elements carry multi-vessel pressure, TW suits low-pressure duty, and full-fit serves hygienic applications. Pair the right type with proper installation, disposal, and maintenance, and the train delivers its rated life.
CHIWATEC supplies Daltonen, Dupont, Toray, CSM, Nitto, LG, and Vontron RO membranes with more than ten years of export experience. Contact us at [email protected], [email protected], or [email protected] for element selection and technical support.
FAQ:
What are the types of RO membrane elements?
The main types of RO membrane elements are TW (tap water, tape-wrapped), BW (brackish water, FRP-wrapped), FR (fouling-resistant, for polluted feed water), and full-fit (rigid polypropylene grid, no outer wrap, for hygienic applications).
What is the difference between TW and BW membrane elements?
TW and BW elements have identical external dimensions but different outer sheathing: BW elements are wrapped with fiberglass reinforced plastic for multi-element pressure vessels with significant inlet-outlet pressure differences, while TW elements are tape-wrapped for less demanding, low-pressure applications.
What is a full-fit RO membrane element?
A full-fit element has no outer tape or FRP wrapping — a rigid polypropylene grid replaces them, eliminating the brine seal ring. It is designed for hygienic applications, allowing some bypass flow to reduce dead water areas and prevent microbial growth, and requires higher water flow to control concentration polarization.
What lubricant should be used when installing RO membrane elements?
Use glycerin as the lubricant when installing components in a pressure vessel. If glycerin is unavailable, moisten the components with pre-treated, qualified water. Never use other chemical reagents or industrial and household detergents, which may damage the system.
Xi’an CHIWATEC Water Treatment Technology provide the RO membrane to clients both inland and oversea with more than 10years experience. We manufacture our own brand Daltonen RO membrane and we are also the official distributor of Dupont, Toray, CSM, Nitto, LG and Vontron RO membrane. Whatever product you need, we cold meet your requirement.
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