Sterlitech™
Flat Sheet Membranes: Frequently Asked Questions
Q. The Flat Sheet Membranes appear dry in their packaging. How do I pre-wet them? Do I need to do this?
Q. What do I do to store the membranes after I use them?
Q. Do you have any information on the storage of the MX series of membranes?
Q. I have a DK series and wonder if there is a shelf life?
Q. How can I store the membranes?
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 to use 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.
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Q.
What do I do to store the membranes after I use them?
A.
Keep all of the membranes wet once used. Either keep the water fresh (change every couple of days), or add ~0.5 sodium metabisulfite (preferred) to keep the bacteria from growing.
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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.
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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.
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Q. How can I store the membranes?
A. Storage and preserving the membranes:
Keep the membrane wet.
Having said that, we should mention that the membrane will need to have the bio growth controlled.
You can use 0.5% formaldehyde solution (1.5% formalin, the commercial solution of formaldehyde you actually buy), or 0.5% sodium metabisulfite or just plain water and change the water with fresh DI water probably once per week. If you use sodium metabisulfite, change the solution for a new sodium metabisulfite every 3 months or so. It is just not as strong as formaldehyde. But just keeping it in clean DI water in a covered container and replacing the DI water with new DI water every week will probably be fine (may get surface biofilm growth in just water, we suggest a biostat.)
Additionally, formalin would cross-link any proteins on the membrane and we have heard reports that formalin in the presence of Iron Fe++ will make the membrane more brittle.
Cleaning:
What you would use to clean a membrane depends on what it is fouled with. Generally speaking a caustic or oxidant solution for organic fouling and an acid solution for scale or inorganics. The different membranes PA, CA, and PS have different pH tolerances.
There are also different enzyme cleaners and surfactants that again have different tolerances for different membrane and applications.
- PLUS: can we store polyamide membranes e.g.192-HR(PA) in 0.5% Formaldehyde. YES, if the membrane is rinsed fairly well before contact with formaldehyde.
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