The UV photolysis of chlorinated compounds as a potential Advanced Oxidation Process (AOP) treatment is of interest to many U.S. water utilities that maintain a chloramine residual in their wastewater treatment systems. Rapid quenching of free chlorine with ammonia limits the risk of NOM chlorination, and provides a stable residual disinfectant. In some wastewater treatment and water reuse systems chloramines are deliberately added before the reverse osmosis (RO) process to control membrane biofouling. However, these chloramines can readily pass through the RO membranes and thus could impact a downstream UV/H2O2 AOP. The generation of chloramines through addition of hypochlorite to wastewaters containing ammonia forms a mixture of monochloramine (NH2Cl), dichloramine (NHCl2), and trichloramine (NCl3). The photolytically-induced chemistry of these chloramines within a UV/H2O2 AOP is complex. Measured absorbance and quantum yields for chloramine species suggest that they are a major competitor for UV photons as compared to added H2O2. Both the direct photolysis and indirect reaction of produced HO? radicals with mono- and dichloramine with will produce NHCl?, NCl2?, and Cl? radicals. In addition, it has been observed that a significant amount of the prototypical contaminant 1,4-dioxane removal by UV/AOP in the absence of H2O2 still occurs when there are chloramines present. Literature studies suggest that the chloroamine radical does not yield much oxidizing power, which implicates the chlorine radical as the primary oxidant under these conditions. As a full understanding of the role the Cl? radical play is important to the understanding the chemical dynamics and the optimization of any photolysis-based AOP, in this study we have measured the reaction kinetics of this species with a variety of important wastewater constituent species.

Reactivity of chlorine radicals with wastewater constituents in support of UV-based AOPs

248th National Meeting (2014)

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