Monochloramine Decay for Two Chlorine to Ammonia Ratios in Bulk Water

Abstract

Within the context of the treatment of tap water as a research objective, a bulk model has been developed to describe chloramines decay for chlorine to ammonia ratios of 3:1 and 4:1. The model is based on studies of isolated individual reactions and also concerning the chloramines decay as a whole. The experimental results were used to estimate and verify the model for use in actual drinking water distribution systems under various chloramines conditions. The overall model formulation works reasonably well in describing chloramines decay in bulk water containing natural organic matter (NOM) and nitrite over a variety of reaction conditions. The data show that the auto-decomposition rate of chloramines is faster in the presence of NOM in bulk water for a chlorine to ammonia ratio (C1:N) of 3:1 versus 4:1. In contrast, the decay rate caused by nitrite is independent of the C1:N ratio. The decay rate increases with the NOM and nitrite concentrations and the temperature, but decreases with increasing pH. The effect of higher temperature on chloramines loss was more marked at the 3:1 C1:N ratio. Water Environ. Res., 85, 2194Res., 85, (2013.

Monochloramine Loss Mechanisms in Tap Water

“…It is therefore assumed that although the rapid reactive NOM was consumed during the disinfection process, most of the long-term reactive NOM is still retained in tap water, which subsequently reacted with free chlorine after the treated water entered the drinking water network. Zhou et al (2013) also studied the NH 2 Cl loss in tap water. However, their NOM reaction rate constant is significantly lower than that of this work, as in their study, this reaction rate was assumed to be related only to the concentration of NH 2 Cl itself (a first-order reaction), while in the present study, it was assumed to be related to the concentrations of both reactive DOC and free chlorine (eq 3, second-order reaction).…”

“…Future studies on tap water that contains high concentrations of these compounds (e.g., for some distribution systems that have significant nitrification and/or corrosion and/or bromide contamination), these factors should be considered. Duirk et al, 2005 7.72 3 10 5~4 .95310 5 M À1 h À1 0.68~0.42 Zhou et al, 2013 0.011722~0.014093 h À1 Not determined…”

“…To limit the formation of many chlorinated DBPs, chloramination, an alternative water disinfection technology, has been developed and applied in drinking water systems throughout North America (Chowdhury et al, 2010;Hua and Reckhow, 2008;Minear and Amy, 1996;U.S. EPA, 2012;Wolfe et al, 1984;Zhou et al, 2013). Chloramination has also proven useful for its longlasting residual, with corresponding disinfection effect, in water distribution systems (Brodtmann and Russo, 1979;Mitcham et al, 1983;Norman et al, 1980).…”

“…The NH 2 Cl autodecomposition rate depends markedly on pH, temperature, the Cl/N molar ratio, and the initial NH 2 Cl concentration (Vikesland et al, 2001). Further, chemical compounds existing in drinking water, including natural organic matter (NOM), nitrite, bromide, and ferrous ions can also accelerate NH 2 Cl decomposition (Cowman and Singer, 1995;Vikesland et al, 2001;Zhou et al, 2013). In this research, based on an Edmonton water quality report (EPCOR, 2015) and pre-chemical test results of this study, the concentrations of nitrite, bromide, and ferrous ion in drinking water samples are very low (less than 0.01 mg/L for nitrite and ferrous ion, and not detectable for bromide) and so their effects are not considered independently in this research.…”

“…The modification of source waters through treatment processes before distribution may cause the NOM species in drinking water to differ from those in the source water, with a consequent difference in NH 2 Cl loss processes. Under real drinking water conditions, the only reported work (Zhou et al, 2013)according to Web of Science-built an NH 2 Cl loss model under specific active chlorine to ammonia ratios, but did not study chemical reaction mechanisms.…”