The most common cause of membrane degradation is chemical interaction with organic and inorganic species. Chlorine is often used in pretreatment prior to RO when biofouling is of concern. Use in membrane process applications can change the polymeric structure of the cellulose acetate membrane. A high-chlorine membrane is generally more brittle than a low-chlorine membrane. Low ammonia concentrations lead to formation of free chlorine, which can quickly damage RO membranes, especially those made from aromatic polyamides. Free chlorine destroys polyamide membranes by dissolving the semipermeable layer, creating depressions and holes in the polymer.
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