Formation of Targeted and Novel Disinfection Byproducts during Chlorine Photolysis in the Presence of Bromide

Bromide leads to elevated disinfectionbyproduct formationduring chlorine photolysis. Chlorine photolysis is an advanced oxidation processthat relieson the combination of direct chlorination by free available chlorine,direct photolysis, and reactive oxidants to transform contaminants.In waters that contain bromide, free available bromine and reactivebromine species can also form. However, little is known about theunderlying mechanisms or formation potential of disinfection byproducts(DBPs) under these conditions. We investigated reactive oxidant generationand DBP formation under dark conditions, chlorine photolysis, andradical-quenched chorine photolysis with variable chlorine (0-10mg-Cl-2/L) and bromide (0-2,000 & mu;g/L) concentrations,as well as with free available bromine. Probe loss rates and ozoneconcentrations increase with chlorine concentration and are minimallyimpacted by bromide. Radical-mediated processes partially contributeto the formation targeted DBPs (i.e., trihalomethanes, haloaceticacids, haloacetonitriles, chlorate, and bromate), which increase withincreasing chlorine concentration. Chlorinated novel DBPs detectedby high-resolution mass spectrometry are attributable to a combinationof dark chlorination, direct halogenation by reactive chlorine species,and transformation of precursors, whereas novel brominated DBPs areprimarily attributable to dark bromination of electron-rich formulas.The formation of targeted and novel DBPs during chlorine photolysisin waters with elevated bromide may limit treatment applications.