title: Towards reducing DBP formation potential of drinking water by favouring direct ozone over hydroxyl radical reactions during ozonation.
abstract: When ozonation is employed in advanced water treatment plants to produce drinking water, dissolved organic matter reacts with ozone (O3) and/or hydroxyl radicals (OH) affecting disinfection byproduct (DBP) formation with subsequently used chlorine-based disinfectants. This study presents the effects of varying exposures of O3 and •OH on DBP concentrations and their associated toxicity generated after subsequent chlorination. DBP formation potential tests and in vitro bioassays were conducted after batch ozonation experiments of coagulated surface water with and without addition of tertiary butanol (t-BuOH, 10 mM) and hydrogen peroxide (H2O2, 1 mg/mg O3), and at different pH (6-8) and transferred ozone doses (0-1 mg/mg TOC). Although ozonation led to a 24-37% decrease in formation of total trihalomethanes, haloacetic acids, haloacetonitriles, and trihaloacetamides, an increase in formation of total trihalonitromethanes, chloral hydrate, and haloketones was observed. This effect however was less pronounced for samples ozonated at conditions favoring molecular ozone (e.g., pH 6 and in the presence of t-BuOH) over •OH reactions (e.g., pH 8 and in the presence of H2O2). Compared to ozonation only, addition of H2O2 consistently enhanced formation of all DBP groups (20-61%) except trihalonitromethanes. This proves that •OH-transformed organic matter is more susceptible to halogen incorporation. Analogously, adsorbable organic halogen (AOX) concentrations increased under conditions that favor •OH reactions. The ratio of unknown to known AOX, however, was greater at conditions that promote direct O3 reactions. Although significant correlation was found between AOX and genotoxicity with the p53 bioassay, toxicity tests using 4 in vitro bioassays showed relatively low absolute differences between various ozonation conditions.
authors.affiliation: The University of Queensland, Advanced Water Management Centre, Queensland, 4072, Australia.
authors.forename: Glen Andrew
authors.initials: GA
authors.lastname: De Vera
authors.affiliation: The University of Queensland, National Research Centre for Environmental Toxicology (Entox), Brisbane, Queensland, 4108, Australia; Swiss Federal Institute of Aquatic Science and Technology (EAWAG), Überlandstrasse 133, Dübendorf, 8600, Switzerland.
authors.forename: Daniel
authors.initials: D
authors.lastname: Stalter
authors.affiliation: The University of Queensland, Advanced Water Management Centre, Queensland, 4072, Australia; ICRA, Catalan Institute for Water Research, Scientific and Technological Park of the University of Girona, H(2)O Building, Emili Grahit 101, 17003, Girona, Spain.
authors.forename: Wolfgang
authors.initials: W
authors.lastname: Gernjak
authors.affiliation: University of North Carolina at Chapel Hill, Department of Environmental Sciences and Engineering, 146A Rosenau Hall, Chapel Hill, NC, 27599, United States.
authors.forename: Howard S
authors.initials: HS
authors.lastname: Weinberg
authors.affiliation: The University of Queensland, Advanced Water Management Centre, Queensland, 4072, Australia.
authors.forename: Jurg
authors.initials: J
authors.lastname: Keller
authors.affiliation: The University of Queensland, Advanced Water Management Centre, Queensland, 4072, Australia; ICRA, Catalan Institute for Water Research, Scientific and Technological Park of the University of Girona, H(2)O Building, Emili Grahit 101, 17003, Girona, Spain. Electronic address: mjfarre@icra.cat.
authors.forename: Maria José
authors.initials: MJ
authors.lastname: Farré
mesh_terms: D004203:Disinfection; D060766:Drinking Water / Q000032:analysis*; D054879:Halogenation; D006846:Hydrocarbons, Halogenated / Q000032:analysis* / Q000633:toxicity; D006861:Hydrogen Peroxide / Q000737:chemistry; D017665:Hydroxyl Radical / Q000737:chemistry*; D010126:Ozone / Q000737:chemistry*; D014874:Water Pollutants, Chemical / Q000032:analysis* / Q000633:toxicity; D018508:Water Purification / Q000379:methods*
chemical_list: D060766:Drinking Water; D006846:Hydrocarbons, Halogenated; D014874:Water Pollutants, Chemical; D017665:Hydroxyl Radical; D010126:Ozone; D006861:Hydrogen Peroxide
keywords: Adsorbable organic halogens; Disinfection byproducts; Hydroxyl radicals; In vitro bioassays; Ozonation