Volatile organic chloramines formation during ClO₂ treatment

Area of Science:

• Environmental Chemistry
• Water Treatment Technologies
• Disinfection Byproducts

Background:

• Chlorination and chloramination produce volatile organic chloramines (VOCs) as disinfection byproducts (DBPs).
• Chlorine dioxide (ClO2) is an alternative disinfectant, but its potential to form halogenated amines was unexplored.
• Dye pollutants are common contaminants in water sources.

Purpose of the Study:

• To investigate the formation of volatile organic chloramines during ClO2 disinfection of dye pollutants.
• To identify the specific VOCs produced and the reaction mechanisms involved.
• To assess the significance of these findings for ClO2 water treatment.

Main Methods:

• Reaction of ClO2 with four azo dyes (Methyl Orange, Methyl Red, Methylene Blue, Malachite Green).
• Identification and quantification of volatile organic chloramines using analytical techniques.
• Investigation of the role of hypochlorous acid (HOCl) in the formation pathway.

Main Results:

• Volatile organic chloramines, including N,N-dimethylchloramine ((CH3)2NCl) and N-chloromethylamine (CH3NCl2), were generated.
• (CH3)2NCl was the dominant DBP, with yields up to 38.5% at a ClO2/precursor ratio of 10.
• Hypochlorous acid (HOCl) was identified as the reactive species, indicating a combined ClO2/HOCl oxidation mechanism.
• ppb-level concentrations of (CH3)2NCl were observed in treated real water samples containing dyes.

Conclusions:

• Azo dyes act as precursors for HOCl formation during ClO2 treatment.
• Organic chloramines are significant DBPs in ClO2 disinfection chemistry.
• Water treatment strategies using ClO2 must account for potential organic chloramine formation from dye contaminants.