Frequently Asked Questions about Reverse Osmosis Membranes and Ion Exchange Resins (51-60)

51. How to replace older nanofiltration (NF) membrane elements in a system with larger product water tubing from the newer series NF90-400, NF270-400, and NF200-400 nanofiltration elements?

You can place all the older elements in the same pressure vessel. If you only intend to replace one of the older elements, please order a 1.125”–1.5” element connector. Please contact your nearest Dow representative for machining dimensions.

52. How to remove silica from water?

Silica in water exists in two forms: activated silica (monomer silica) and colloidal silica (multi-component silica):

 Colloidal silica lacks ionic characteristics but is relatively large in size. Colloidal silica can be retained by fine physical filtration processes, such as reverse osmosis, and its content can be reduced through coagulation techniques, such as coagulation clarifiers. However, separation techniques that rely on ionic charge characteristics, such as ion exchange resins and continuous electro-deionization (CDI), have limited effectiveness in removing colloidal silica.

 Activated silica is much smaller than colloidal silica, making it ineffective for most physical filtration techniques such as coagulation clarification, filtration, and flotation. Reverse osmosis, ion exchange, and continuous electrodeionization are the only effective processes for removing activated silica.

53. Can a permeate pressure booster pump and an inter-stage pressure booster pump be installed in ROSA5?

Yes, a permeate pressure booster pump can be installed in the first stage of ROSA5, and an inter-stage pressure booster pump can be installed between the second and third stages. This is a new design feature of ROSA5.

54. Can membrane elements be exposed to direct sunlight?

No, not even in their original packaging. Indoor storage is recommended, and prolonged exposure to direct sunlight, especially through windows, should be avoided. The ambient temperature should not exceed 45°C.

55. How are Dow FILMTEC membrane elements packaged?

For 8” components, Dow's standard packaging is:

1) One corrugated cardboard box (10 inches × 10 inches × 44.5 inches)

2) Two layers of polyethylene bags

3) Two polystyrene end-face protectors

4) If the component is wet, the protective solution in the sealed bag is less than 250 mL.

For 4” components, Dow's standard packaging is:

1) Each component is individually packaged in a plastic bag

2) A large cardboard box containing 70 components individually packaged in plastic bags is used as the outer packaging; no separate corrugated cardboard box is provided*. * This is because many 4” element systems use modular components, and for environmental protection purposes, internal connectors between elements are not provided.

56. How to select the appropriate element when replacing the NF70-400?

The NF70-400 element has been modified. If a similar desalination rate as the NF70-400 is required, replace it with the NF90-400. If greater hardness and other salts are desired to pass through, replace it with the NF270-400.

57. How does pH affect the removal rate, permeate flow rate, and membrane life?

Dow FILMTEC™ brand membrane elements, due to their proprietary fully aromatic, highly cross-linked desalination layer chemical structure, exhibit minimal pH impact on membrane performance within the specified product pH range, typically 2–11. This is a significant characteristic distinguishing them from other membrane products. However, the properties of many ions in water are greatly affected by pH. For example, weak acids like citric acid are primarily non-ionic at low pH conditions, but dissociate into ionic states at high pH values. Since a higher charge level of the same ion results in a higher removal rate, while a lower charge level or no charge leads to a lower removal rate, pH has a substantial impact on the removal rate of certain impurities.

58. How does the inlet mesh (inlet channel) within the membrane element affect fouling formation and cleanability? The function of the feed water mesh (channel) is to provide a pathway for feed water to flow from the feed end of the element to the concentrate end. It must provide turbulence-promoting effects to the membrane surface to prevent concentration polarization and fouling. Wider channels can significantly inhibit fouling formation and improve cleaning performance. This is why many membrane modules used for concentration separation always employ wider and thicker meshes (channels). Some membrane element manufacturers still use outdated but low-investment manufacturing processes, making it impossible to use wide and thick meshes while ensuring the effective membrane area of the element. This results in their membrane products experiencing increasingly severe fouling and low cleaning efficiency after a few months of use. For equivalent elements, Dow membranes have a mesh thickness of 10-20%.

59. In ROSA5, how can I view various design schemes without opening the workbook?

The simplest method is to fill in a description of each design scheme in the Project Information section when designing each scheme, so that it can be quickly browsed when needed. Alternatively, a database can be created to hold one or more projects. In ROSA5, files can only be renamed after actual design calculations.

60. How can I email the calculation results from ROSA5 to someone who doesn't have ROSA5 installed?

The printed result is displayed as an .html file on the screen, which can be sent as an email attachment. Alternatively, you can use Acrobat Writer (a software that converts it to PDF) to create a PDF file, ensuring it displays and prints correctly on any computer. However, this software is not free. When you set Adobe® Acrobat® Writer as the default printer in ROSA5, ROSA5 will automatically generate a PDF file, which you can then send to others.