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Reverse Osmosis Membranes Questions & Answers

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Is it possible to recover an old membrane after a long time of inactivity?

Will Purging  with N2 harm the Membrane?


Is it possible to recover an old membrane after a long time of inactivity and without water (dry)? If it is possible, how we clean it and with which product ?

Most likely the membrane is damaged and will not work. You may try cleaning with AM-11. 

We are considering charging N2 thru the permeate of an RO array  in an attempt to reduce overall Delta by killing organic growth from the surface of the membranes. To some degree we do reduce the delta by 10-12 lbs. But does this harm conventional Thin Film membranes if this procedure is done frequently over time?

As long as there is no shock to the membranes, such as sudden pressurization and depressurization, there is no adverse effect on the membranes.

Can a membrane be flushed with a water temp of 80 degrees C? If not, what is the maximum temp. possible?

The elements of a membrane cannot withstand temperatures above the rated maximum of 45 degrees C. Anything higher than the maximum would destroy the elements of the membrane. If a higher temperature is needed, we recommend Filmtec's "Heat Sanitizable" membrane.

How can I remove the black growth on the unused Cellulose Acetate membranes?

The black growth at the end sections of the unused membrane elements is MOLD. The mold can be removed by soaking the membrane in water solution containing 0.2 weight percent Glutaraldehyde. Adjust pH to 5.5 for a period of 30 minutes.

What is the lifetime of a M-T1812A50 Membrane? Can we use AM-11 to clean our filter?

AM-11 is generally used for cleaning larger membranes but some companies use them also to clean smaller residential membranes. It is difficult to predict the effectiveness of these chemicals, because each fouling situation is different. You will have to try these for your situation to determine the economic viability of cleaning small membranes.

Is it possible to store filmtec 8040 membranes in formaldehyde after pulling them out of our RO unit that will be down for a long period of time?

As long as formaldehyde is not used in the first 24 hours of running the elements, storing these elements in formaldehyde is acceptable. A solution of 0.5% is recommended. No other aldehyde is acceptable for this purpose.

Will membranes operate at a temp. greater than 45C (113F)?

Thin Film Membrane Elements are not designed to support the temperature higher than 45C (113F). It does not mean that the elements cannot exceed the maximum temperature limit of 45C. However, a greater potential for element damage exists as the temperature increases above 45C, and the warranty is void. In order to operate or clean at high temperatures, high-temperature or heat-sanitizable elements with different materials of construction are recommended. We currently offer FilmTec heat-sanitizable elements that can be heat-sanitized up to 85C (185F).

How long can I expect commercial membranes to last in my system?

Membrane life is a function of feed water source, pretreatment, frequency of cleaning, system design, and operating conditions. For economic analysis, a 5 year life is normally used.

What is the difference between Thin Film & CTA Membranes?

CTA (Cellulose Triacetate) membrane is a paper by-product membrane bonded to a synthetic layer. CTA membranes are made to allow contact with chlorine in the water. These require a small amount of chlorine in the water source to prevent bacteria from forming on it. CTA membranes have a rejection rate of 85-95%.

TFC (Thin Film Composite) membrane is made of a a synthetic material, and requires chlorine to be removed before the water enters the membrane. Chlorine will cause irreversible damage to a thin film membrane element - for this reason, carbon filters are used as pre-treatment in all residential reverse osmosis systems using TFC membranes. A Thin film membrane has a higher rejection (95-98%) and longer life than the CTA membrane.

How Often is Membrane Cleaning Recommended?

For commercial membranes (2"Dia. and Larger): Generally, it is recommended to clean an RO plant when a 10% decrease in normalized flux can be observed. For orientation, cleaning frequency can be in the range of 4/year with an SDI of less than 3. With an SDI of 5, the cleaning frequency could double. However, cleaning frequency will depend on the specific situation.

Residential membranes (1.8" Diameter and Smaller) are typically not cleaned, as the cost of cleaning is greater than the cost of replacement.

Can Thin Film RO membranes tolerate chlorine?

Chlorine will oxidize the surface of thin film composite polyamide membranes, causing the membrane to lose its ability to repel or reject salts.

Thin film membranes can tolerate up to 1000 ppm-hours of chlorine. Traces of metals will accelerate oxidation. Therefore chlorine should be removed from the RO feed water.

What is the difference between tap & brackish water membranes?

There is no difference in the membrane material. Brackish water membranes have an outer shell of fiberglass whereas Tap water have a tape wrap. The construction allows Brackish water membranes to be operated at higher pressures required to treat brackish water.

What are the differences of different types of membranes? Are all membranes of the same type (e.g. TFC) from different manufacturers the same? (example: an oil filter by Toyota is different from that of Mitsubishi).

You are right. These are very similar in construction and performance. Like other products, the main difference is in the reputation and reliability of the manufacturer.  However, because there are different manufacturers, membranes do come in several end type configurations depending on the manufacturer.  When ordering vessels, you will need to specify what brand of membrane you plan on using so the appropriate end adapters can be built in.  When replacing membranes with a different brand, you should check the membrane specifications to make sure the end configuration is compatible for direct replacement. 

Why is the performance different in different flow rated residential membranes? (24 gpd, 36 gpd, 100 gpd, etc.) The membranes look the same even the number of times rolled up.

The useful area of the membrane material is different in the two sizes. They look the same because of the difference in membrane area is made up by other fabrics.

What is the difference between dry and wet membranes?

When the thin-film membranes manufactured they are dry. These dry membranes have an indefinite shelf life, when stored properly. Membranes become wet when they are flushed or tested with water. Once wet, the membranes can not be dried. The wet membranes must be preserved to prevent the growth of micro-organisms on them. This is done usually by using a 1-2% solution of sodium metabisulfite. For more details look for information on storing membranes.

What are the proper storage conditions & shelf-life for membranes?

Membrane Storage
Store membranes in a cool area out of direct sunlight. Membrane storage temperature limits are 22F-113F (-5.5C to 45C)

Preserve in a solution of 2% AM-88 Membrane Preservative, and 20% AM-225 Glycerine. This will not prevent freezing below 32F, but the crystals are soft and the membrane is not damaged.

Keep new elements in original packaging.

Examine the preservative in preserved elements every 3 months. If not clear, remove and re-preserve. The pH of the preservative should not drop below 3.

Storage time for preserved elements is 6 months to 1 year.

Storage time for dry (new) elements is unlimited, and these can withstand temperatures below 22F.

Membrane Shipping
Preserve the element in the plastic bag using the recommended procedure. Make sure the plastic bag does not leak and the element is properly identified.

Make sure the preservative solution is correctly labeled.

Protect the element package from physical damage.

System Shut-Down
Clean the membranes in the system using the cleaning procedure.

Circulate the preservative solution.

Shut down the system and close valves to prevent air entering the system.

Check preservative once a month.


Do the CTA wet elements have the same shelf life as the TF wet elements?  What is the shelf life?

All CTA elements are wet, whereas most TF elements (other than sea water) are dry. The wet elements have a shorter shelf life of 6 months. The dry elements are good for 2 years. These are approximate numbers NOT guaranteed values. Factors such as heat, exposure to sunlight can reduce shelf life of all elements.





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All Content on this site is  intended for informational purposes for experienced water treatment professionals only.  Applied Membranes, Inc. does not assume any liability for any damages caused by the misapplication or misinterpretation of any of the information contained on this website.
Applied Membranes, Inc. 2007