Free chlorine formation in the process of the chlorine dioxide oxidation of aliphatic amines.Water Res. 2022 Jun 15; 217:118399.WR
Chlorine dioxide (ClO2) is commonly used as an alternative disinfectant to chlorine because it has a high bactericidal effect and may produce limited concentrations of halogenated disinfection byproducts (DBPs). However, previous studies have reported that free available chlorine (FAC) was produced when ClO2 reacted with some compounds, such as phenol, leading to the formation of halogenated DBPs. In this study aliphatic amines was found to react rapidly with ClO2 to form significant amount of FAC and its related DBPs. This study investigated the formation of FAC when ClO2 reacts with six model aliphatic amines (including primary amines, secondary amines and tertiary amines). FAC was formed immediately as ClO2 was added to the precursor solution. The maximum yield of FAC even reached 45% (based on consumed ClO2) when ClO2 reacted with 20 μM methylamine at a dose of 10 μM, which is close to a realistic maximum dose (about 0.8 mg/L) in the U.S.. The reactivity of amines to result FAC follows the sequence tertiary amines < secondary amines < primary amines. It was verified that the addition of aliphatic amines may enhance the formation of FAC during ClO2 oxidation in actual water samples. Organic chloramines and other chlorinated DBPs, such as cyanogen chloride, were detected when ClO2 was used as the sole oxidant of real water samples. This study demonstrated that chlorine-related byproducts may also be formed in the presence of organic amines during ClO2 treatment.