Bromide ion effect on N-nitrosodimethylamine formation by monochloramine

Area of Science:

• Environmental Chemistry
• Water Treatment Chemistry
• Organic Contaminant Formation

Background:

• N-Nitrosodimethylamine (NDMA) is a disinfection byproduct of concern in water treatment.
• Monochloramine is a common disinfectant, and its reactions can lead to NDMA formation.
• The role of bromide ions in NDMA formation during monochloramine disinfection is not fully understood.

Purpose of the Study:

• To investigate the effect of bromide ions on NDMA formation in the presence of monochloramine.
• To elucidate the reaction mechanisms and species responsible for bromide's influence on NDMA formation.
• To compare NDMA formation at different pH levels with and without bromide.

Main Methods:

• NDMA formation experiments were conducted in phosphate buffer solutions.
• Reactions involved monochloramine and varying concentrations of bromide ions at different pH values (6-9).
• UV spectral analysis was used to study reaction intermediates and products.

Main Results:

• At high pH (8-9), bromide ion significantly enhanced NDMA formation after 24 hours.
• At low to neutral pH (6-7), bromide ion resulted in lower NDMA formation compared to bromide-free conditions.
• Bromamines, hypobromous acid, hypobromite ion, and tribromide ion were tested but did not directly explain the enhanced NDMA formation at high pH.

Conclusions:

• The mechanism of bromide's influence on NDMA formation is pH-dependent.
• The enhanced NDMA formation at high pH is not directly caused by bromamines or other tested active bromine species.
• UV spectral data suggest that a mixed dihaloamine, possibly bromochloramine, may be responsible for the observed enhancement of NDMA formation.