Lab-scale accelerated degradation of membranes in the presence of sodium hypochlorite, an oxidant common to fouling prevention, is frequently used to qualify a membrane’s resistance to degradation.  However, the accelerated aging methodology produces various results dependent on the test parameters used.  These issues can often lead to premature performance loss in membranes, requiring frequent membrane replacement.  To better address this issue, a crossflow cell was employed to explore the relationship between performance and exposure to NaOCl solutions of various concentrations.  From this work, it was shown that increased NaOCl concentration resulted in performance drops at lower exposure values than those exposed to lower NaOCl concentrations.<br/>Another potential cause for the deviation between accelerated aging projections and real-life use cases lies in the difference in chemical components present in the feedwater.  The chemical speciation present in real-world applications is often more complex than those used in the lab setting.  In instances such as seawater and brackish water, halides (i.e. bromides and iodides) are present in the feedstock.  These halide ions are capable of reacting with derivatives of sodium hypochlorite to form other oxidative species which in turn may react more aggressively with the membrane.  In this work, crossflow testing has been employed to compare the performance of network polyamide reverse osmosis membranes when exposed to sodium hypochlorite in addition to halide salts.  Early tests show loss in solute rejection occurring at a rate faster for membranes exposed to dilute NaOCl aqueous solutions with added NaBr than those exposed to only NaOCl aqueous solutions of the same concentration.  This suggests that given the addition of halide salts, more aggressive chemical species may evolve, decreasing the performance lifetime of the membrane from what is projected from accelerated aging tests.<br/>

Performance effects of oxidant and halide concentration on aromatic network polyamide membranes

255th National Meeting (2018)

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