Commercial RO membranes (based on the poly(m-phenylenediamine trimesic acid), a.k.a. polyamide) chemistry have zero tolerance to free chlorine and will rapidly

Commercial RO membranes (based on the poly(m-phenylenediamine trimesic acid), a.k.a. polyamide) chemistry have zero tolerance to free chlorine and will rapidly degrade under such conditions. The chlorine tolerance is listed as “nil” on many manufacturer’s spec sheets. Even using tap water on a polyamide membrane without some kind of prefilter (like GAC) will cause noticeable reduction in both the permeance and rejection of the membrane. There was a big push towards developing chlorine-resistant chemistries a few years ago, but as far as I can tell, that has fallen into a “researchers don’t know what they’re doing, the plants are already designed around this problem” narrative. Of course, those plants are huge investments, and maybe it’s correct that one wouldn’t be able to take advantage of chlorine-resistant membranes until a new plant was built. Cellulose triacetate RO membranes have chlorine tolerance, but have inferior chemical stability, productivity and selectivity to polyamide membranes, so it is sometimes used where chlorine tolerance is an issue. CTA membranes are also available in hollow fiber format, while polyamide membranes are essentially exclusively found in spiral wound configuration (some operators want fibers for higher fouling/solids feed). CTA is limited to a much smaller pH window (like 4-6 versus 2-12), and are not suitable for more aggressive cleaning methods, so I’m not sure if it overall provides a benefit versus polyamide RO with more aggressive cleaning cycles.