Impact of pre-oxidation using H2O2 and ultraviolet/H2O2 on disinfection byproducts generated from chlor(am)ination of chloramphenicol

Hydrogen peroxide with and without activation by ultraviolet irradiation (UV/H2O2 and H2O2, respectively) has been investigated to degrade emerging contaminants in drinking water. The antibiotic chloramphenicol (CAP) and its analogues (thiamphenicol and florfenicol), referred to collectively as CAPs, can produce a range of disinfection by-products (DBPs) during chlorination or chloramination (chlor (am)ination). The impact of unactivated and activated H2O2 pre-oxidation on the formation of nitrogenous and carbonaceous DBPs from the chlor(am)ination of CAP model precursors was investigated. A theoretical estimated toxicity evaluation was also carried out based on the DBPs that formed. H2O2 pretreatment alone did not affect organic carbon and nitrogen concentrations, but significantly reduced the formation of trichloromethane (TCM) during chlorination and trichloronitromethane (TCNM) during chloramination, and enhanced dichloroacetonitrile (DCAN) yields during chloramination. These significant changes in DBP yields caused by H2O2 pre-oxidation are attributable to the transformation of the three CAPs into more reactive precursor structures. The three CAPs did not form DCAN and TCNM during chlorination, regardless of whether H2O2 pre-oxidation was used. However, UV/H2O2 pretreatment resulted in the unexpected formation of TCNM during chlorination. Furthermore, UV/H2O2 pre-oxidation increased the formation of DCAN and TCNM, whereas it had little effect on TCM formation during chloramination. A preliminary estimated toxicity evaluation demonstrated that UV/H2O2 pre-oxidation at low doses, followed by chlorination, resulted in the lowest estimated toxicity from a range of DBPs. Conversely, the estimated toxicity evaluation showed that unactivated H2O2 (high dose) was preferable to UV activated H2O2 for overall control of these investigated DBPs during chloramination. (C) 2017 Elsevier B.V. All rights reserved.