Characterization of biofilm and corrosion of cast iron pipes in drinking water distribution system with UV/Cl2 disinfection

• Effects of UV/Cl2 disinfection on the biofilm and corrosion of cast iron pipes were investigated.
• Passivation occurred more rapidly in the AR with UV/Cl2 than that one with Cl2 alone.
• UV/Cl2 induced denitrifying functional bacteria advantage inside corrosion scales.
• Microbial redox cycling of iron was responsible for higher corrosion inhibition.
• The corrosion scale was more stable in the AR with UV/Cl2 than Cl2 alone.

The effect of UV/Cl2 disinfection on the biofilm and corrosion of cast iron pipes in drinking water distribution system were studied using annular reactors (ARs). Passivation occurred more rapidly in the AR with UV/Cl2 than in the one with Cl2 alone, decreasing iron release for higher corrosivity of water. Based on functional gene, pyrosequencing assays and principal component analysis, UV disinfection not only reduced the required initial chlorine dose, but also enhanced denitrifying functional bacteria advantage in the biofilm of corrosion scales. The nitrate-reducing bacteria (NRB) Dechloromonas exhibited the greatest corrosion inhibition by inducing the redox cycling of iron to enhance the precipitation of iron oxides and formation of Fe3O4 in the AR with UV/Cl2, while the rhizobia Bradyrhizobium and Rhizobium, and the NRB Sphingomonas, Brucella producing siderophores had weaker corrosion-inhibition effect by capturing iron in the AR with Cl2. These results indicated that the microbial redox cycling of iron was possibly responsible for higher corrosion inhibition and lower effect of water Larson–Skold Index (LI) changes on corrosion. This finding could be applied toward the control of water quality in drinking water distribution systems.

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