M. Dore

Utilisation du rayonnement ultraviolet dans le traitement des eaux: mesure du flux photonique par actinometrie chimique au peroxyde d'hydrogene

Disinfection of water by u.v. irradiation has known significant technological developments and industrial applications during these last years (Matsuura and Smith, 1970; Jepson, 1973; Severin et al., 1984). More recently, advanced oxidation processes involving the generation of hydroxyl radicals or other reactive entities by the combination of u.v. radiation and a chemical oxidant (ozone or hydrogen peroxide) have been shown to be effective for the degradation of organic micropollutants resistant to classical oxidants (Glaze et al., 1984, 1987; Bourbigot et al., 1985; Sundstrom et al., 1986; Guittonneau et al., 1988). The effectiveness of these oxidation processes depends on some physico-chemical parameters (initial oxidant dosage, pH, concentration of bicarbonate ions ...) and on the conditions of irradiation (exposure time or irradiation dose). Meanwhile, the comparison of the results of photochemical—oxidative degradation rates is difficult because of the great diversity of photochemical reactors used in the studies and of the lack of data about the characteristics of u.v. light sources (photonic fluxes). Therefore, this study describes an experimental procedure for the determination of photonic fluxes at 253.7 nm emitted by low-pressure mercury vapour lamps and for the evaluation of the reflecting power of the internal wall of photochemical reactors.

Hydroxyl radical induced decomposition of aliphatic acids in oxygenated and deoxygenated aqueous solutions

Abstract The aim of this work was to study the oxidation of aliphatic acids by radicals resulting from the protolysis of hydrogen peroxide. Experiments carried out in dilute aqueous solutions (pH = 2.9−3.5) of mono and dicarboxylic acids with 1 to 4 carbon atoms showed (i) the oxidation of the carboxylic group is slow, (ii) the hydroxyl group of hydroxylated acids activates the adjacent Cue5f8H bond and leads, after hydrogen atoms abstraction, O2 addition and HO2 removal, to the carbonyl group, (iii) a Cue5f8C bond cleavage occurs after hydrogen atom abstraction and oxygen addition for unsubstituted dicarboxylic acids. Except for oxalic acid, the mechanism of oxidation into CO2 of the acids studied involves oxygen consumption and O2−/HO2 release.

Constantes Cinetiques de Reaction de L'Ozone Moleculaire et des Radicaux Hydroxyles Sur Quelques Phenyl-Urees et Acetamides Rate Constants for Reactions of Ozone and Hydroxyl Radicals with Several Phenyl-Ureas and Acetamides

Second-order rate constants for the reactions of molecular ozone and of hydroxyl radicals with some nitrogenous herbicides (phenyl-ureas and acetamides) have been measured in water at 20 °C using absolute and relative rate methods. Molecular ozone oxidation was carried out at acidic pH and in the presence of hydroxyl radical scavenger (tert-butanol). Hydroxyl radicals were generated from the aqueous decomposition of ozone by hydroxyde ions or by hydrogen peroxide. The order of kinetic rate constants for molecular ozone with the herbicides was found to be as follows: Isoproturon >> Chlortoluron > Diuron > Linuron ≈ Metolachlor ≈ Alachlor > Propachlor. Rate constants for the reactions of hydroxyl radicals with these herbicides were in the range of 4.3 109 – 5.2 109 l mol−1 s−1.

Ozonation of an Extracted Aquatic Fulvic Acid : Theoretical and Practical Aspects

Abstract A laboratory study was conducted on the ozonation of an aquatic fulvic acid extracted from a forest pond near Poitiers in France. The rate of molecular ozone consumption was fast during the first minutes, and ozonation led to a slight increase of the lower apparent molecular weight, an enhancement of carboxyl content, and aldehyde formation. By ozonation of a bromide-containing solution of fulvic acid, some brominated organics were formed, while ozonation without bromide led to a reduction of the organic halide formation potential of a fulvic acid, especially in the presence of bicarbonate ions. The increase of GAC-filtration efficiency following ozonation was found to be the result of a biodegradability enhancement of fulvic acid by ozone. Manganese oxidation by ozone was partially inhibited by fulvic acid, particularly in the absence of bicarbonate ions.

Modeling the oxidation of atrazine by H2O2/UV. Estimation of kinetic parameters

Abstract A kinetic model for the oxidation of atrazine by H2O2/UV in dilute aqueous solutions ([Atrazine]0 < 2 μM) has been tested in a batch reactor. In this model, direct photolysis and oxidation by hydroxyl radicals are assumed to be the main reactions in the decomposition of atrazine by H2O2/UV. The data showed that the model can be used to predict the effects of some parameters (hydrogen peroxide dose, pH, bicarbonate alkalinity, …) and to estimate values of quantum yield of photolysis, rate constants for the reaction of hydroxyl radicals with atrazine and of the scavenging term (SkiSi) of natural waters.

Etude de l'oxydation de chloroethanes en milieu aqueux dilue par H2O2/u.v.

Resume Cette etude a eu pour but de mieux comprendre linfleunce de certains parametres experimentaux sur lefficacite du procede doxydation radicalaire (H2O2/u.v. vis-a-vis de la degradation de composes organiques en milieu aqueux dilue. Les experiences ont ete effectuees avec des reacteurs photochimiques equipes dune lampe basse pression a vapeur de mercure (emission principale a 253,7 nm) et avec des solutions aqueuses de trichloro et tetrachloroethanes qui sont des composes non degradables par photolyse directe a 253,7 nm dans les conditions employees au cours de ce travail. Les resultats obtenus ont permis de montrer linfluence de la dose doxydant (existence dune dose optimale en H2O2), du pH, de la concentration en pieges a radicaux hydroxyles (ions bicarbonate) ou en composes absorbant a la longueur donde de 253,7 nm (acide fulvique). Les resultats obtenus ont pu etre interpretes a laide dun modele cinetique qui a permis egalement destimer les valeurs des constantes cinetiques de reaction des radicaux hydroxyles sur les chloroethanes (valeurs comprises entre 2 107 et 1,1 108 l mol−1 s−1).

Influence du developpement bacterien au sein des filtres de charbon actif en grains sur l'elimination de composés organiques biodegradables et non biodegradables

Resume Letude a eu pour but de montrer linfluence de lactivite bacterienne au sein des filtres de charbon actif en grains sur lelimination de la matiere organique. Pour atteindre cet objectif, des filtrations sur des mini-colonnes de charbon actif ont ete effectuees dans des conditions steriles et non steriles, afin de distinguer les parts respectives dues a ladsorption et a la biodegradation dans lenlevement de la matiere organique. Les experiences ont ete realisees a 20°C avec diverses fractions granulometriques de charbon actif CHEMVIRON F 400 et avec des solutions synthetiques diluees de produits organiques tamponnees a pH 8. Les solutions etudiees ont ete, soit des melanges renfermant un produit organique biodegradable et un compose non biodegradable (melanges acide salicylique/acide chloro-4 benzoique et nitro-4 phenol/methyl-2 dinitro-4,6 phenol), soit des solutions pures dun de ces composes. Dans les conditions steriles de filtration, les capacites dadsorption obtenues sont pratiquement egales aux valeurs determinees a partir des isothermes dadsorption fournies par des experiences en statique avec du charbon en poudre. De plus, les resultats obtenus avec des melanges permettent de montrer linfluence des phenomenes de competition sur ladsorbabilite des composes et sur lallure des courbes depuisement. Dans les conditions non steriles, les proprietes adsorbantes du charbon actif permettent de retenir la micropollution organique biodegradable et non biodegradable au cours de la phase dadaptation des souches bacteriennes. Par la suite, le demarrage de la phase de biodegradation qui peut etre caracterise par une augmentation de la consommation doxygene et de la production danhydride carbonique conduit progressivement a une elimination de la matiere organique, grâce a une mineralisation des substances biodegradables (acide salicylique et nitro-4 phenol) ainsi qua une regeneration partielle de ladsorbant par voie biologique. Grâce a son action sur la matiere organique biodegradable, lactivite bacterienne conduit a une augmentation des capacites dadsorption du charbon actif vis-a-vis des produits organiques non biodegradables (acide chloro-4 benzoique et methyl-2 dinitro-4,6 phenol).

Kinetics and mechanisms of the photolytic and OH° radical induced oxidation of fluorinated aromatic compounds in aqueous solutions

Abstract Laboratory experiments with H 2 O 2 /UV oxidation processes and photolysis at 253.7 nm wavelength have been carried out on dilute aqueous solutions (C o = 0.1 to 3.0 mM) of trifluorobenzene derivatives (1,3,5-trifluorobenzene, 1,2,3 and 1,2,4-trifluorobenzene) and of α,α,α-trifluorotoluene in the presence and in the absence of dissolved oxygen. The analyses of fluoride ions content during the oxidation experiments showed that the first steps lead to the production of about 2 mol of F-/mol of trifluorobenzene decomposed and of 1 mol of F − /mol of trifluorotoluene decomposed. Kinetic studies lead to the determination of the quantum yield for the photolysis of 1,3,5-trifluorobenzene, 1,2,3 and 1,2,4-trifluorobenzene ( Φ = 0.011, 0.010 and 0.015 respectively), and of trifluorotoluene ( Φ = 0.015). The rate constants for the reaction of hydroxyl radicals with these molecules, determined under specific experimental conditions, were found to range from 3.7 10 9 to 4.9 10 9 M −1 .s −1 ). GC/MS analyses carried out on extracts at different irradiation time (UV, H 2 O 2 /UV) lead to the identification of numerous by-products from trifluorobenzene and trifluorotoluene. They consist mostly in hydroxylated and dehalogenated compounds. Dimers have also been observed during photolysis. Moreover, experiments carried out under oxygen limiting conditions revealed the formation of other compounds. For each case studied, a detailed mechanism involving radical intermediates and the different reaction sequences is proposed.

Ozonation of selected molecules constituting cellular matter

Ozonation of purine and pyrimidine bases and of carbohydrates was studies in laboratory experiments. The results showed that nucleobases are much more reactive with molecular ozone in aqueous solution than carbohydrates. Second order rate constants for direct reaction of ozone on purines (adenine and guanine) and on pyrimidines (cytosine, thymine and uracil) ranged from 0.76 × 103 to 6.8 × 103 M-1s-1at 2°C. The difference of reactivity between these solutes may be attributed to their substituents. As far as carbohydrates are concerned, direct reactions of ozone are very slow k03 ≍ 0.1 – 0.3 M-1s-1 at 20°C, and the results indicated that free radical reactions are predominant in the degradation pathway of carbohydrates by ozone. Some ozonation by-products of monosaccharides (glucose, xylose) and disaccharides (cellobiose) also were identified in this study by means of GC/MS analyses.

Ozonation of Amino Acids: Ozone Demand and Aldehyde Formation

Abstract This study is related to the ozonation of free and combined amino acids, which present a high reactivity with ozone. Amino acids reactivities studied in the presence or absence of tert-butyl alcohol as radical scavenger were found to be related to their structures. Amino acid side chains seem to be the main sites that are responsible for the high ozone reactivity in polypeptide structures. Ozonation of amino acids led to the formation of aldehydes such as formaldehyde, acetaldehyde, glyoxal and glyoxal derivatives. The direct ozone reaction has been shown to favor aldehyde production.