Frequently Asked Questions about Reverse Osmosis Membranes and Ion Exchange Resins (21-30)

21. Can the membrane element be exposed to temperatures below freezing?

Yes. However, this must be avoided if possible. If the membrane element accidentally freezes, it must be thawed slowly before use, and this will void the warranty.

22. How can I find product images?

Product, application, and test images are available on the Dow Liquid Separation website, or contact a Dow representative.

23. Is boron in drinking water a problem, and how can it be removed?

Animal studies have shown that boron can cause male infertility. In 1993, the World Health Organization recommended that the boron content in drinking water should be below 0.3 ppm. Boron has also been found to be harmful to some plants at levels above 0.2–0.5 ppm. The boron content in seawater is around 5 mg/L, and boron is also present in some polluted water, introduced into the water by boron-containing soaps or detergents.

Traditional drinking water treatment processes and municipal wastewater treatment processes cannot effectively remove boron. Dow FILMTEC™ membranes can be used for boron removal in drinking water. The boron removal capacity of a membrane depends primarily on the pH value and the type of membrane. Dow DOWEX* resin can also be used for boron removal.

24. How to shut down a membrane system?

For shutdown procedures and storage conditions, please refer to the relevant sections of this manual.

25. What is DIRECTOR Service?

DIRECTOR Service is a comprehensive service provided by Dow Chemical Company to users of Dow FILMTEC™ membranes and DOWEX* resins. It provides effective advice to ensure optimal system performance, including:

 Membrane analysis

 Ion exchange resin analysis

 Online technical support

 Training

Detailed information can be found on the Dow Liquid Separation website: http://www.dow.com/liquidseps/

26. Can membrane elements be stored in ethanol or other alcohols?

Storing membrane elements in alcohol solutions is not recommended.

27. Why does ROSA version 5.0 not include standardized software and a technical manual?

ROSA 5.0 and later versions are only used as design software. Standardized software FTNORM and technical information on Dow membranes can be found on the Dow Liquid Separation website, www.filmtec.com.

28. How effective is the FT30 membrane at removing weak acids such as boric acid, arsenic acid, carbonic acid, or phenol?

The removal rate of these weak acids depends on the pH of the solution and their dissociation constant pK. Generally, the higher the pH, the higher the degree of dissociation. In this case, the trend of the removal rate can be estimated based on the degree of dissociation and pH.

29. How is the bactericide DBNPA used?

There are two dosing methods: intermittent dosing and continuous dosing. Intermittent dosing depends on the severity of biofouling. When the water's biofouling sensitivity is low, use a solution containing 20% of the active ingredient at 50–170 ppm, administered once every 5 days for 30 minutes to 3 hours each time.

However, when the total bacterial count in the water exceeds 10² CFU/mL, or in systems with known biofouling, use a solution containing 20% of the active ingredient at 170 ppm, administered once every 5 days for 3 hours each time. Once the biofouling in the system disappears, continuous dosing should be adopted, using the aforementioned 20% solution at a continuous dosage of 10–15 ppm. The dosage can be adjusted according to fluctuations in bacterial content. The main function of DBNPA is to inhibit bacterial content in the influent to extremely low levels, preventing biofouling.

30. How to select a membrane for different water types and applications?

Many factors can influence the selection of membrane models. Please refer to this manual or consult a representative from Dow Liquid Separation.