Polyamide-based thin-film composite membranes are critical components of advanced water treatment systems utilizing unconventional water sources. Disinfectants play important roles in suppressing and/or reversing membrane biofouling, but they can also degrade the polyamide layer of the membranes. In this study, we used a novel tool quartz crystal microbalance with dissipation (QCM-D) to investigate the degradation of the polyamide active layer by a conventional disinfectant monochloramine (NH2Cl) as well as a novel wastewater disinfectant peracetic acid (PAA). Polyamide film extracted from commercial reverse osmosis membrane coupons were transferred to gold QCM sensor, and was exposed to 13 mM of NH2Cl or PAA at a flow rate of 50 µLmin-1. Preliminary results have shown that the active layers show a single-stage sorption upon PAA exposure with a maximum sorbed mass of 708 ± 81 ng cm-2. However, no subsequent mass loss is observed in up to 48 h. In contrast, NH2Cl exposure led to a two-stage and much faster sorption behavior, with a three-folder greater mass sorbed (3216 ± 533 ng cm-2). Complete removal of the polyamide films is observed after ~10.5 h of NH2Cl exposure. These results are noteworthy: PAA, a novel disinfectant with much greater bacterial inactivation ability than NH2Cl, resulted in less polyamide degradation than NH2Cl, the disinfectant currently used in the advanced wastewater treatment systems for fouling control. Work is underway to investigate the polyamide degradation pathways using X-ray photoelectron spectroscopy (XPS). This study examines the interaction between disinfectants and polyamide at a molecular length scale; the findings will enable the selection of halogen-free disinfectant to maximize the performance of membrane processes.

Degradation of polyamide active layer by traditional and novel disinfectants: A quartz crystal microbalance study

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