The use of pressure-driven membrane processes, particularly reverse osmosis (RO) processes, has grown significantly over the past few decades in water treatment and reuse applications to safeguard water supplies against harmful pathogens and impurities. A common type of RO membranes is the thin film aromatic polyamide based membranes. Although polyamide RO membranes have been successfully utilized in desalination and water reuse applications, they are prone to chemical oxidation by chlorinated disinfectants, such as free chlorine, chloramine, and chlorine dioxide. Chlorinated disinfectants (if present in or introduced to the feed water) attack the aromatic ring in polyamide chains, causing conformational changes of the membrane polymer, and subsequently creating membrane integrity breach. In the presence of membrane integrity breaches, nanosize pathogens (e.g., enteric viruses) can potentially pass through the membrane and contaminate the product water stream, thereby posing a potential hazard, especially for drinking water production. Although there have been extensive studies concerning the polyamide degradation mechanism, a systematic evaluation that clarifies the independent effects of chlorine exposure period, concentration and hydrodynamic conditions on degradation of RO membrane integrity is lacking. Accordingly, a study was undertaken of the impact of polyamide membrane oxidation, due to exposure under various chlorine exposure conditions (i.e., concentration and exposure time) and concentration polarization (CP), on membrane integrity.
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