The co-exposure to UV irradiation and free chlorine may occur in certain water and wastewater treatment systems. When combined UV/chlorine is applied, the disinfection by-product (DBP) formation potential will likely differ from that under UV alone or chlorine alone because the formation and transformation mechanisms of precursors and DBPs can differ significantly under the more complex UV/chlorine conditions. This presentation will discuss two cases in which the chlorinated DBP formation could be enhanced under combined low-pressure ultraviolet irradiation and free chlorination compared to free chlorination alone: (1) formation of trichloronitromethane (or chloropicrin) from polyamine, dimethylamine, and methylamine; and (2) formation of chloroform from triclosan, under disinfection to advanced oxidation conditions. The enhancement effect on the DBP formation was influenced by UV irradiance, chlorine dose, water pH, and reaction time. The effects of combined UV/chlorine conditions on the degradation of precursors and the formation of DBPs, respectively, will be discussed from the reaction mechanism perspectives. Insights obtained in this study are useful for reducing chlorinated DBP formation during water treatment when both UV and chlorine will be encountered.

Effects of combined UV and chlorine treatment on the formation mechanisms of disinfection by-products: Cases of trichloronitromethane and chloroform

248th National Meeting (2014)

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