The Orange County Water District (OCWD) utilizes chloramines (NHxCly) as an alternative disinfectant to free chlorine in their wastewater treatment system due to the fewer disinfectant by-products formed by these reactions. Monochloramine, dichloramine, and trichloramine (NH2Cl, NHCl2, and NCl3 respectively) are deliberately generated before the final stages of their remediation process to prevent bio-fouling of the reverse osmosis (RO) membranes. The final stage of OCWD’s treatment is an Advanced Oxidation Process (AOP) in which they combine hydrogen peroxide and UV light to generate the highly reactive hydroxyl radical (●OH). The ●OH is used to mineralize any harmful chemical contaminants remaining in the partially treated water. However, the chloramines generated before the RO system continue through the membrane and flow into the AOP, which can significantly decrease the efficiency for the production and reactivity of ●OH with desired chemical contaminants. Understanding the impact of the chloramines in the AOP is essential for its optimal operation. In this study, the absolute second-order kinetics of these three chloramines with the ●OH radical have been quantified. Decreasing ●OH radical reactivity with increasing chlorine substitution was observed, however, all three chloramines reacted quickly (k = 1-5 x 108 M-1 s-1). The temperature dependence of these reactions has been studied to determine Arrhenius activation energies. These data will be combined with other performance factors to study the overall effects these chloramines have on the efficiency of the AOP.

Investigation of radical chloramine reaction kinetics and thermodynamics under advanced oxidation processes

253rd National Meeting (2017)

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