The odor problems in drinking water derived from chlor(am)ine disinfection cannot be ignored. After chlor(am)ination, the residual chlorine in drinking water exists in several species. Compared with free chlorine and NH₂Cl, NHCl₂ and NCl₃ have lower odor thresholds. In water supply system, NH₂Cl can be gradually converted to NHCl₂, leading to the increase in odorous intensity (FPA values), and it is obviously affected by pH, temperature and Cl₂/N ratio. Besides, in the presence of dissolved organic matter (DOM), organic chloramines can be produced, and then the FPA values of drinking water increase obviously. These organic chloramines not only have a high odor risk, but also have weak sterilization ability, which will lead to the overestimation of effective chlorine residue in finished water. Meanwhile, these formed organic chloramines will continuously react with disinfectants to produce highly toxic N-DBPs. Among these organic chloramines, N-chloroaldimines were identified as typical odorous compounds (odor threshold: 200-250 ng/L). After a long-term investigation, the total concentration of N-chloroaldimines in finished and tap water in SH city, China ranged from 200 to 750 ng/L, which faced a high risk of odor problem. In addition, in the presence of DOM and halogen ions, other odorous compounds can also be derived from chlor(am)ine disinfectant. For instances, the haloanisoles with lower odor thresholds (0.03-4 ng/L) can be detected as 0-9 ng/L in drinking water. The iodo-trihalomethanes produced after chlor(am)ination have both strong medicinal odor and high toxicity, and their total yield can exceed their odor thresholds by a maximum of 130 times during seawater intrusion. Therefore, how to reduce such odor problem by optimizing disinfection methods will be an important direction for the improvement of drinking water quality in the future.

Tianyang Zhang

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