Reverse Osmosis (RO) Membrane

Q. The Flat Sheet Membranes appear dry in their packaging. How do I pre-wet them? Do I need to do this?

A. Yes, you need to pre-wet the membranes. The best procedure is to place them in a dry holder and allow them to wet from the inlet side first. It may be best to perform this operation with water or a buffer, then dispose of the first rinse, and introduce the process fluid. This prevents any wetting agents or preservatives from mixing with the process solution.

Q. What do I do to store the membranes after I use them?

A. Most importantly, flat sheet membranes should be kept wet after use. Control biological growth by adding 0.5% solution of formaldehyde, sodium metabisulfite, or use deionized water and change it out at least once a week. If you use sodium metabisulfite we recommend changing it out every three months since it is a little weaker than formaldehyde.

Q. Do you have any information on the storage of the MX series of membranes?

A. The MX series of membranes were dried from solutions of glycerol in ethanol. Thus, strictly speaking, the "dried" membrane is wet with glycerol which acts as a plasticizer and humectant. In this form, MX membrane products exhibit remarkable stability (>1 year). It is suggested that the membranes be stored refrigerated (not frozen). The same advice would be supplied if the material were, say, a protein.

To remove this storage glycerol, we soak the membranes in several (3-4) changes of excess d.i. water.

Bisulfite is an interesting material for MX membranes. In the quantities typical for storage, only small but measurable amounts may react with the N-methylol groups which constitute the MX's surface chemistry. Parenthetically, I would advise that a serious study of these membranes includes examination of their chemical nature.

Q. I have a DK series and wonder if there is a shelf life?

A. Yes, the shelf life for the DK and DL series is 6 months.

Q. How can I clean the membranes?

A. Determining which solution to use to clean a flat sheet membrane depends on the substance it is fouled with. As a general rule, you can use a caustic or oxidant solution for organic fouling and an acidic solution for inorganic causes. Please remember that different membranes polymers have different pH tolerances.