Impact of brominated amines on monochloramine stability during in-line and pre-formed chloramination assessed by kinetic modelling

Sébastien Allard; Keith Cadee; Rachel Tung; Jean-Philippe Croué

doi:10.1016/j.scitotenv.2017.09.281

Impact of brominated amines on monochloramine stability during in-line and pre-formed chloramination assessed by kinetic modelling

Sci Total Environ. 2018 Mar 15:618:1431-1439. doi: 10.1016/j.scitotenv.2017.09.281. Epub 2017 Nov 7.

Authors

Sébastien Allard¹, Keith Cadee², Rachel Tung², Jean-Philippe Croué²

Affiliations

¹ Curtin Water Quality Research Centre, Department of Chemistry, Curtin University, GPO Box U1987, Perth, WA 6845, Australia. Electronic address: s.allard@curtin.edu.au.
² Curtin Water Quality Research Centre, Department of Chemistry, Curtin University, GPO Box U1987, Perth, WA 6845, Australia.

PMID: 29122349
DOI: 10.1016/j.scitotenv.2017.09.281

Abstract

In this study, a comprehensive kinetic model was developed and validated to predict the stability of monochloramine (NH₂Cl) in presence of iodide and bromide for both pre-formed and in-line chloramination application in absence of organic matter. pH had the greatest influence on the stability of NH₂Cl in waters containing bromide. For in-line chloramination, the NH₂Cl decay over 3days was only 10% for pH9 and 58% for pH7 (400μgBr^-/L and 3 mgCl₂/L). Bromide also greatly affected the stability of NH₂Cl by influencing the formation and speciation of the halamines produced during chloramination. In-line chloramination is commonly used since the pre-chlorination oxidises iodide to the non-toxic iodate. During pre-chlorination, brominated organics are formed from reaction between bromine and dissolved organic matter (DOM). In the case of the Colorado River DOM, 26% of the bromine was sequestered in only 4min, and therefore not available to form brominated amines during chloramination. Following ammonia addition, an immediate loss of oxidant was observed in water containing bromide at pH7 and 8. This is due to the reaction between NHBrCl and NHBr₂, and the auto-decomposition of NHBr₂ formed from NH₂Br. Once NHBr₂ was consumed, NHBrCl accumulated and then slowly decayed. Thereafter, the total oxidant concentration decayed slowly due to the auto-decomposition of NHCl₂ and the reaction between NHBrCl and NHBr_2. In the presence of DOM, the CHBr₃ concentration increased, while the CHCl₃ concentration (formed during pre-chlorination) was constant during chloramination, indicating that brominated-amines may continue to form disinfection by-products (DBPs).

Keywords: Bromamine; Bromide; Bromochloramine; Chloramine; Disinfection; Kinetic modelling.