Corrosion Characteristics of Iron Pipe in Reclaimed Water Disinfected by UV/NaClO

The use of reclaimed water is a crucial strategy for water conservation. However, the quality of reclaimed water may induce corrosion in pipelines. Although UV (Ultraviolet) irradiation is a highly effective physical disinfection method that requires no chemical additives, it must be used in conjunction with NaClO (Sodium hypochlorite) disinfection because UV alone cannot provide continuous control of bacterial growth. This study monitored the concentrations of Cl− and SO42− in water samples collected from an annular biofilm coupon reactor, as well as the corrosion rate of cast iron coupons, to explore the corrosion characteristics of reclaimed water pipelines under different disinfection modes. The results showed that, when using NaClO as the sole disinfectant, the corrosion rate of the pipeline was the lowest at a NaClO dosage of 7 mg/L (corrosion rate: 0.85 mm/a at 72 h). For the UV-NaClO-combined disinfection, the optimal parameters were a UV dose of 120 mJ/cm2 and a NaClO dosage of 5 mg/L, with a minimum corrosion rate of 0.62 mm/a at 72 h. The scanning electron microscopy (SEM) and X-ray diffraction (XRD) analyses revealed that a protective CaCO3 layer forms on the pipe surface in the early corrosion stage, which effectively protects the metal pipeline. This study innovatively clarifies the synergistic effect of UV and NaClO on pipeline corrosion and identifies the optimal disinfection parameters, filling the research gap in the correlation between combined disinfection and cast iron pipe corrosion in reclaimed water systems.