Formation of chloroform during chlorination of alanine in drinking water

Currently, dissolved nitrogenous organic matters in water, important precursors of disinfection by-products (DBPs), are of significant concern. This study was to explore the formation of chloroform (CF) during chlorination of alanine (Ala), an important nitrogenous organic compound commonly present in water sources. Our results indicated that the CF yield reached a maximum value of 0.143% at the molar ratio of chlorine atom to nitrogen atom (Cl/N) = 1.0 over a Cl/N range of 0.2-5.0 (pH = 7.0, reaction time = 5 d, and initial Ala = 0.1 mM). At an acidic-neutral condition (pH 4-7), the formation of CF was suppressed. However, the highest CF yield (0.227%) occurred at weakly alkaline condition (pH 8.0) (initial Ala = 0.1 mM, and Cl/N = 1.0). The increase of Br− in water can increase total trihalomethanes (THMs) and bromo-THMs. However, the bromo-THMs level reached a plateau at Br−/Cl > 0.04. Finally, based on the computation of frontier electron density and identification and measurement of key intermediates during Ala chlorination, we proposed a formation pathway of CF from Ala chlorination: Ala → monochloro-N-alanine (MC-N-Ala) → acetaldehyde (AAld) → monochloroacetaldehyde acetaldehyde (MCAld) → dichloroacetaldehyde (DCAld) → trichloroacetaldehyde (TCAld) → CF.