title: Biodegradability of DBP precursors after drinking water ozonation.
abstract: Ozonation is known to generate biodegradable organic matter, which is typically reduced by biological filtration to avoid bacterial regrowth in distribution systems. Post-chlorination generates halogenated disinfection byproducts (DBPs) but little is known about the biodegradability of their precursors. This study determined the effect of ozonation and biofiltration conditions, specifically ozone exposure and empty bed contact time (EBCT), on the control of DBP formation potentials in drinking water. Ozone exposure was varied through addition of H2O2during ozonation at 1 mgO3/mgDOC followed by biological filtration using either activated carbon (BAC) or anthracite. Ozonation led to a 10% decrease in dissolved organic carbon (DOC), without further improvement from H2O2addition. Raising H2O2concentrations from 0 to 2 mmol/mmolO3resulted in increased DBP formation potentials during post-chlorination of the ozonated water (target Cl2residual after 24 h = 1-2 mg/L) as follows: 4 trihalomethanes (THM4, 37%), 8 haloacetic acids (HAA8, 44%), chloral hydrate (CH, 107%), 2 haloketones (HK2, 97%), 4 haloacetonitriles (HAN4, 33%), trichloroacetamide (TCAM, 43%), and adsorbable organic halogen (AOX, 27%), but a decrease in the concentrations of 2 trihalonitromethanes (THNM2, 43%). Coupling ozonation with biofiltration prior to chlorination effectively lowered the formation potentials of all DBPs including CH, HK2, and THNM2, all of which increased after ozonation. The dynamics of DBP formation potentials during BAC filtration at different EBCTs followed first-order reaction kinetics. Minimum steady-state concentrations were attained at an EBCT of about 10-20 min, depending on the DBP species. The rate of reduction in DBP formation potentials varied among individual species before reaching their minimum concentrations. CH, HK2, and THNM2 had the highest rate constants of between 0.5 and 0.6 min-1followed by HAN4 (0.4 min-1), THM4 (0.3 min-1), HAA8 (0.2 min-1), and AOX (0.1 min-1). At an EBCT of 15 min, the reduction in formation potential for most DBPs was less than 50% but was higher than 70% for CH, HK2, and THNM2. The formation of bromine-containing DBPs increased with increasing EBCT, most likely due to an increase in Br-/DOC ratio. Overall, this study demonstrated that the combination of ozonation and biofiltration is an effective approach to mitigate DBP formation during drinking water treatment.
authors: The University of Queensland, Advanced Water Management Centre, Queensland, 4072, Australia.
authors: Glen Andrew
authors: GA
authors: de Vera
authors: The University of Queensland, Advanced Water Management Centre, Queensland, 4072, Australia.
authors: Jurg
authors: J
authors: Keller
authors: 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; ICREA, Catalan Institute for Research and Advanced Studies, 08010, Barcelona, Spain.
authors: Wolfgang
authors: W
authors: Gernjak
authors: University of North Carolina at Chapel Hill, Department of Environmental Sciences and Engineering, 146A Rosenau Hall, Chapel Hill, NC, 27599, United States.
authors: Howard
authors: H
authors: Weinberg
authors: 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: Maria José
authors: MJ
authors: Farré
mesh_terms: D004203:Disinfection; D060766:Drinking Water; D006861:Hydrogen Peroxide; D010126:Ozone; D022882:Trihalomethanes; D014874:Water Pollutants, Chemical; D018508:Water Purification
chemical_list: D060766:Drinking Water; D022882:Trihalomethanes; D014874:Water Pollutants, Chemical; D010126:Ozone; D006861:Hydrogen Peroxide
keywords: Biofiltration; Disinfection byproducts; Empty bed contact time; Ozonation