FAQ: Flat Sheet Discoloration Exposed

If you've ever worked with a Polyamide flat sheet membrane, there's a good probability that you may have noticed some slight discoloration on the active layer side of the filter, as seen below:  And additionally, this may have caused some uneasy speculation; is it mold? contamination? time to purchase a new membrane? The good folks at Toray Membranes were able to shed some light on this common concern... literally. Brown discoloration can be due to small amounts of residual amine from the manufacturing process.  The amine, (one of the building block compounds used to create the polymer constituting  the polyamide membrane family),  can turn brown with exposure to direct light. This effect doesn't make for a pretty membrane,  but it does not affect the performance of the membrane in any way. Note: if it is in fact mold that you're seeing, you can try irrigating the area with dechlorinated water with a laboratory wash bottle to see if it lifts off.  Any rubbing of the membrane surface should be kept to an absolute minimum, as there is the possibility to scratch or damage the integrity of the membrane layer. And again, while not pretty, the mold shouldn't affect the integrity of the membrane.