Modeling chloramine stability and disinfection byproduct formation in groundwater high in bromide

Abstract

Bromide can promote monochloramine decomposition and disinfection byproduct (DBP) formation. Monochloramine and total chlorine stability as well as total trihalomethane and haloacetic acid formation were examined in groundwater with high bromide levels (300–1700 μg/L) following chlorine or KMnO₄ preoxidation. An N,N-Diethyl-p-phenylenediamine (DPD)-based total chlorine method detected chloramines and brominated amines (e.g., NH₂Br, NHBrCl). An indophenol-based monochloramine method showed minimal interference from brominated amines. Differences between these methods' measurements likely indicated brominated amine concentrations. Substantial total chlorine demands (up to ~3.5 mg/L in 4 days) following chlorine preoxidation were observed due to the presence of brominated amines. Total chlorine measurements were more stable and DBP formation was limited following KMnO₄ preoxidation because ammonia was dosed before chlorine, which inhibited brominated amine formation. A kinetic model developed elsewhere for dissolved organic matter (DOM)-free water generally tracked with experimental results but some deviations occurred possibly because DOM consumed bromochloramine or its reaction intermediates.