Impact of chlorine dioxide (ClO₂) on reverse osmosis (RO) membrane integrity: degradation behavior, surface property...

Chlorine dioxide (ClO₂) has attracted considerable attention as an alternative disinfectant for reverse osmosis (RO) pretreatment because of its broad-spectrum antimicrobial activity, effectiveness over a wide pH range, and lower formation of regulated disinfection by-products compared with conventional chlorination. These characteristics make ClO₂ a promising strategy for mitigating microbial growth and supporting biofouling control in RO systems. However, the strong oxidative nature of ClO₂ also presents a significant challenge, as prolonged exposure may induce degradation of the polyamide selective layer, resulting in deterioration of membrane integrity and filtration performance. This study investigated the effects of ClO₂ concentration and solution pH on the degradation behavior and surface property changes of thin-film composite (TFC) polyamide RO membranes, with particular emphasis on their implications for biofouling control. Membrane performance and structural changes were evaluated using permeate flux measurements, scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy (SEM-EDX), and contact angle analysis. The results demonstrated that increasing ClO₂ concentration and alkaline conditions accelerated membrane degradation, as evidenced by increased permeate flux, pronounced surface deformation and cracking, disruption of the selective polyamide layer, changes in surface elemental composition, and significant alterations in wettability. The membrane exposed to 0.5 ppm ClO₂ at pH 6 exhibited the least structural damage and maintained surface characteristics closest to those of the untreated membrane, indicating that this condition provided the most favorable balance between membrane preservation and operational performance. In contrast, exposure to higher ClO₂ concentration and alkaline pH resulted in severe oxidative deterioration, which compromised membrane integrity despite the potential operational benefits associated with oxidant application. Although biofouling was not directly evaluated through microbial adhesion or biofilm formation experiments, the observed changes in membrane morphology, permeability, and wettability provide valuable insight into surface characteristics associated with fouling propensity. Overall, the findings highlight the importance of optimizing ClO₂ dosage and operating pH to minimize oxidative membrane degradation while maintaining its practical advantages as a disinfectant in RO pretreatment, thereby providing guidance for improving membrane durability and supporting sustainable membrane-based water treatment.