1. Q:What is the difference between Thin Film & CTA Membranes?
A: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.

2.Q:Can Thin Film RO membranes tolerate chlorine?
A: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.

3.Q: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 ?
A:Most likely the membrane is damaged and will not work. You may try cleaning with AM-11.

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

5.Q:How long can I expect commercial membranes to last in my system? 
A: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.

6.Q:Is it possible to store GL- 4040-ULP membranes in formaldehyde after pulling them out of our RO unit that will be down for a long period of time?
A: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.
Q:Will membranes operate at a temp. greater than 45°C (113°F)? 

7.Q:How Often is Membrane Cleaning Recommended?
A: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.

8.Q:What is the difference between tap & brackish water membranes?
A: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.

9.Q: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.
A: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.

10.Q:What is the difference between dry and wet membranes?
A: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.