title: Chlorination of natural organic matter: kinetics of chlorination and of THM formation.
abstract: The kinetics of the formation of trihalomethanes (THMs) and of chlorine consumption for the chlorination of natural organic matter with an excess of chlorine (50 microM > [Cl2]o >210 microM) was investigated. THM precursors could be divided into a fast and a slowly reacting fraction. Long term chlorine demand and the formation of THM could be described by second order kinetics. Rate constants were between 0.01 and 0.03 M(-1) s(-1) in the pH range 7-9 for surface waters and humic materials extracted from surface waters. A groundwater gave a higher rate constant of 0.124 M(-1) s(-1). Resorcinol-type structures were tested with respect to kinetics and yield of THM formation. They could possibly be responsible for the fast reacting THM precursors. which represent 15-30% of the THM precursors of natural waters. Additional classes of compounds that might contribute to the initial THM formation include readily enolizable compounds such as beta-diketones and beta-ketoacids. Experiments with phenol showed that slowly reacting THM precursors may consist of phenolic compounds. The influence of pretreatments (UV/visible irradiation, ozone and chlorine dioxide) on chlorine demand and THM formation from NOM was also studied: UV/visible irradiation does not alter THM formation but leads to a higher chlorine demand. Preoxidation with ozone leads to a lower THM formation with an unaltered chlorine demand and preoxidation with chlorine dioxide reduces THM formation and the chlorine demand.
authors.affiliation: Swiss Federal Institute for Environmental Science and Technolocy (EAWAG), Dübendorf.
authors.forename: Hervé
authors.initials: H
authors.lastname: Gallard
authors.forename: Gunten Urs
authors.initials: GU
authors.lastname: von
mesh_terms: D017606:Chlorine Compounds / Q000737:chemistry*; D007700:Kinetics; D008962:Models, Theoretical; D010083:Oxidants, Photochemical / Q000737:chemistry; D010084:Oxidation-Reduction; D010126:Ozone / Q000737:chemistry; D012989:Soil Pollutants; D022882:Trihalomethanes / Q000737:chemistry*; D014466:Ultraviolet Rays; D014874:Water Pollutants, Chemical / Q000032:analysis; D018508:Water Purification
chemical_list: D017606:Chlorine Compounds; D010083:Oxidants, Photochemical; D012989:Soil Pollutants; D022882:Trihalomethanes; D014874:Water Pollutants, Chemical; D010126:Ozone