Using an advanced oxidation processes (AOP) as a final wastewater treatment step has gained much interest over the past two decades. Typically, AOPs utilize UV light and hydrogen peroxide (H2O2) to photolytically generate the oxidizing hydroxyl radical, which reacts non-selectively to destroy any residual organic contaminants. However, recently there has been an increased interest in using free chlorine, particularly hypochlorite (OCl-), rather than H2O2 in the AOP. This option is more cost-effective, and generally safer, but the addition of hypochlorite/ hypochlorous acid into an AOP results in significantly different thermal and radical chemistry occurring. To properly assess the overall efficiency of a free-chlorine based AOP, this chemistry must be quantitatively elucidated. In this study, we have examined the reactivity of the hypochlorous radical (OCl●), expected to be created from the excess hypochlorite that would be added. Here, we generated this radical by the oxidation of OCl- using either the hydroxyl or sulfate radicals in aqueous solution. By directly monitoring this radical’s absorbance, we determined its reactivity with a small library of low-molecular-weight nitrosamines. Absolute second-order rate constants for these reactions were obtained, demonstrating that this oxyradical has similar reactivity to the chlorine atom for these carcinogens, with both much slower than observed for the hydroxyl radical. These data can now be combined with other performance factors to study the overall AOP efficiency at removing these contaminants.

Investigation of the reaction of the hypochlorite radical with nitrosamines in aqueous solution

255th National Meeting (2018)

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