Effects of highly corrosive pipe wall and disinfectant constituent on the chlorine decay behavior in drinking water

In this study, a pilot-scale pipeline reactor and refined total chloramine decay model were employed to study the effects of the highly corrosive pipe wall and three kinds of disinfectant constituents on the chlorine decay behavior. The bulk decay coefficient, kbulk for NaClO, NaClO + NH3·H2O, and NaClO + (NH4)2SO4 were 0.011, 0.004, and 0.004 h−1, respectively. By resorting to the refined total chloramine decay model, the comprehensive wall decay coefficient kwall appeared in the ascending order of NaClO, NaClO + NH3·H2O, and NaClO + (NH4)2SO4. The remarkable contribution of the aged cast iron pipe wall to overall total chlorine residual decay was manifested by the ratio, kwall/kbulk. The pipe wall-induced decay was related to microbe consumption and electrochemical corrosion as indicated by variations in total organic carbon (TOC), NO2−-N, NO3−-N, and Fe residual. The larger kwall for NaClO + NH3·H2O (0.720 h−1) relative to NaClO (0.465 h−1) was mainly attributed to enhanced nitrifier-mediated microbe consumption. The largest kwall for NaClO + (NH4)2SO4 (0.864 h−1) was due to the further promoted microorganism regrowth and metabolization as evidenced by the SO42- declining behaviors. On this basis, it was suggested to minimize extra inorganic salt introduction into treated water to constrain microbial development in drinking water distribution system (DWDS). Temporal-free chlorine disinfection was also recommended for the chloraminated DWDS before the critical temperature. HIGHLIGHTS The new refined total chloramine decay model could well simulate total chlorine residual (TCR) decay behavior and give calibrated kwall.; TCR decay in aged cast iron (CI) pipe is caused by Fe-related corrosion and biotic consumption.; Minimize inorganic salt introduction is recommended to maintain the TCR level in DWDS.;