Disinfection byproduct formation kinetics of a water treatment plant on Kinmen Island

Chloramine has often been used as a chlorine alternative for trihalomethane (THM) and haloacetic acid (HAA) control. However, nitrogenous disinfection byproduct (N-DBP) formation and nitrification in distribution have always been major concerns in chloramination practices. On Kinmen Island, the high organic nitrogen content in raw water may increase the nitrogenous DBP formation. Simulated distribution system tests were conducted to explore the DBP formation kinetics in the distribution system. Lower haloacetonitrile (HAN₄) formation (0.26 μg L⁻¹) with chloramination than with chlorination (10.48 μg L⁻¹) was observed from the 24 hours of reaction time. The nitrogen sources contributing to the dichloroacetonitrile (DCAN) formation kinetics were explored with ¹⁵N-chloramination. The results showed that nitrogen sourced from organic nitrogen was more dominant in DCAN formation with low chloramine dosage. This suggests that chloramine contributes to less DCAN formation in practice, especially for short distribution systems. In summary, the results provide evidence that simultaneous post-chloramination and pre-chlorination would be a feasible disinfection strategy applied to control regulated THM and HAA formation on Kinmen Island.