J. De Laat

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.

Comparative study of the oxidation of atrazine and acetone by H2O2/UV, Fe(III)/UV, Fe(iii)/H2O2/UV and Fe(II) or Fe(III)/H2O2

Abstract In this study, the rates of degradation of organic compounds by several AOPs (H2O2/UV, Fe(III)/UV, Fe(III)/H2O2/UV, Fe(II)/H2O2 and Fe(III)/H2O2) have been compared. Experiments were carried out at pH ≈ 3 (perchloric acid / sodium perchlorate solutions) and with UV reactors equipped with a low-pressure mercury vapour lamp (emission at 253.7 run). The data obtained with atrazine ([Atrazine]o = 100 μg/L) showed that the rate of degradation of atrazine in very dilute aqueous solution is much more rapid with Fe(III)/UV than with H2O2/UV. Photo-Fenton process (Fe(III)/H2O2/UV) was found to be more efficient than H2O2/UV and Fe(II)/H2O2 for the mineralization of acetone ([Acetone]o = 1 mM).

Kinetics of oxidation of chlorobenzenes and phenyl-ureas by Fe(II)/H2O2 and Fe(III)/H2O2. Evidence of reduction and oxidation reactions of intermediates by Fe(II) or Fe(III)

The rates of degradation of 1,2,4-trichlorobenzene (TCB), 2,5-dichloronitrobenzene (DCNB), diuron and isoproturon by Fe(II)/H2O2 and Fe(III)/H2O2 have been investigated in dilute aqueous solution ([Organic compound]0 approximately 1 microM, at 25.0 +/- 0.2 degrees C and pH < or = 3). Using the relative rate method with atrazine as the reference compound, and the Fe(II)/H2O2 (with an excess of Fe(II)) and Fe(III)/H2O2 systems as sources of OH radicals, the rate constants for the reaction of OH* with TCB and DCNB were determined as (6.0 +/- 0.3)10(9) and (1.1 +/- 0.2)10(9) M(-1) s(-1). Relative rates of degradation of diuron and isoproturon by Fe(II)/H2O2 were about two times smaller in the absence of dissolved oxygen than in the presence of oxygen. These data indicate that radical intermediates are reduced back to the parent compound by Fe(II) in the absence of oxygen. Oxidation experiments with Fe(III)/H2O2 showed that the rate of decomposition of atrazine markedly increased in the presence of TCB and this increase has been attributed to a regeneration of Fe(II) by oxidation reactions of intermediates (radical species and dihydroxybenzenes) by Fe(III).

Chloration de composés organiques: demande en chlore et réactivite vis-a-vis de la formation des trihalométhanes. Incidence de l'azote ammoniacal

The purpose of this work is to contribute to knowledge of the condition of formation of volatile and non-volatile organochlorinated compounds during surface water chlorination. With this aim in view, the chlorination of a number of organic substances in diluted aqueous solutions (10−6-10−5 moll −1) and in a neutral medium was studied. Special attention was given to their reactivity in relation to the formation of trihalomethanes. The results obtained show great differences in the reactivity of chlorine towards chemical substances liable to be present in the waters. The high chlorine demands, 5–12 mol of chlorine per mol of compound after a 15 h reaction at pH 7, where obtained with those aromatic compounds having activating groups such as — OH and — NR2 (phenol and aniline derivatives). On the other hand, a number of compounds (alipahitcs in general; acids, aldehydes, alcohols…) are relatively inert towards chlorination. As far as chloroform production is concerned, the study shows that many organic compounds are liable to lead to the production of low quantities of chloroform in a neutral medium (molar yields < 5%). However, only a few specific structures such as metapolyhydroxybenzenes and metachlorophenols constitute good precursors of the haloform reaction. The study of the formation kinetics of chloroform, carried out with some precursors of different reactivity: acetone, acetylacetone, resorcinol, phloroglucinol and 3,5-dichlorophenol allowed us to determine the kinetic constants of chloroform formation at pH 7.5 and 20° C: Acetone v=k[Acetone] k=1,7 x 10-7s-1 Acetylacetone k[Trichloro-l,l,l acetone] k=5,6 X 10-6s-1 Resorcinol v=k[Resorcinol][Chlore] k=(1,5±0,5) x 10 3 | mol-1s-1 Phloroglucinol v=k[Phloroglucinol][Chloro] k=1,5±0.5 | mol-1s-1 Dichloro-3,5 phenol v=k[Dichloro-3,5 phenol][Chlore] k=0,5±0,25 | mol-1s-1 The results obtained during this work also show that the chlorine found in the chloroform produced from a precursor, represents only a small proportion of the chlorine demand. Even with a highly reactive precursor such as resorcinol. It was shown that the liberation of chloroform is accompanied by the formation of trichloroacetic acid (molar yield < 10%) and of monochloromaleic acid (molar yield 60%). Moreover, tetrahalogenated and pentahalogenated hydrocarbons (C3Cl4 and C3 HCl5) resulting from 3,5 -dichlorophenol chlorination were made manifest. As for the chlorin- ation of acetylacetone, a mechanism passing through the formation of 1,1-tri- chloroacetone was proposed. Lastly, in the general framework of the interactions between chlorine, ammonia nitrogen and the organic compounds which are frequently found in surface water chlorination, the study allowed us to show that the chlorination of highly reactive precursors (such as metapolyhydroxybenzenes and metachlorophenols) can lead to the production of important amounts of chloroform before reaching breakpoint. These results compared to the values of the velocities of the various reactions between chlorine and the ammoniacal compounds.

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.

Etude comparative de la degradation de quelques molecules aromatiques simples en solution aqueuse par photolyse UV et par photolyse du peroxyde d'hydrogene

Abstract The photooxidation of some chloroaromatic and nitroaromatic compounds (chlorobenzenes, nitrobenzenes) in water by UV radiation and UV radiation in the presence of hydrogen peroxide was studied. Diluted aqueous solutions of organic compounds (10‐4 mol l‐1) were irradiated at pH 7.5 and at 16°C in a closed reactor equiped with a low pressure mercury vapor lamp. The results showed that chlorobenzenes are more rapidly photodecomposed than nitroaromatic compounds and the rates of degradation were greatly increased by addition of hydrogen peroxide (10‐3 mol l‐1). The degradation pathway of aromatic compounds in the presence of hydrogen peroxide and UV light leads to the production of hydroxylated derivatives (phenolic compounds) as intermediates and chloride, nitrate and carbon dioxide as oxidation end‐products. The effects of benzene ring substituents (Cl, NO2, OH) on the oxidation rate of aromatic compounds by H2O2/UV and the influence of the UV absorbance of the irradiated solutions at 253.7 nm on t...

Etude de la degradation des trihalo‐methanes en milieu aqueux dilue par irradiation UV ‐ determination du rendement quantique de photolyse a 253,7 nm 1

Abstract In this study, the degradation of trihalomethanes (THM) by UV irradiation at 253.7 nm was investigated. Experiments were carried out with dilute aqueous solutions of CHCl3, CHCl2Br, CHBr2Cl and CHBr3 (< I0–6 mol 1‐1) at 20°C and pH = 7.5 and with photochemical reactors equipped with a low‐pressure mercury vapour lamp. Under our experimental conditions (irradiation time ≤ 30 minutes), the results showed that only the brominated THMs were photolysed. The quantum yield values for the photolysis of the three brominated THMS which could be determined from the kinetic results were found to be equal to 0.43 ± 0.01 at 253.7 nm and at 20°C. Moreover, ionic chromatography analysis revealed that organic halogen present in CHCl2 Br, CHBr2 Cl and CHBr3 was completely converted into chloride and bromide ions during irradiation.

Phototransformation of diuron in aqueous solution by UV irradiation in the absence and in the presence of H2O2

Abstract The phototransformation of diuron has been studied by photolysis at 253.7 nm, at 20°C, in the absence and in the presence of H2O2. Experiments were conducted in batch and in continuous‐flow reactors. In the absence of H2O2, the value of the quantum yield of photolysis of diuron at 253.7 nm was found to be equal to be 0.0125 ± 0.0005 (using a molar absorption coefficient of 16500 ± 500 M−1 cm−1 at 253.7 nm) and insensitive to pH in the range 2 ‐ 8.5. Oxidation rates of diuron by H2O2/UV could be predicted successfully by a kinetic model including photochemical and OH.‐oxidation reactions using a value of 4.6×109 M−1 s−1 for the rate constant of the reaction of OH. with diuron. The model was verified for the various reactors used and under a wide range of conditions in pure water (pH : 2 ‐ 8, [H2O2] : 0 ‐ 0.1 M) and in the presence of hydrogenocarbonate ions (0 ‐ 35 mM, pH = 8.3 ‐ 8.4). The contribution of the carbonate radicals to the degradation rates of diuron was found to be insignificant under our experimental conditions

Constantes cinétiques de réaction des radicaux hydroxyles sur quelques sous‐ produits d'oxydation de l'atrazine par O3 ou par O3/H2O2

Abstract Rate constants for the reaction of hydroxyl radicals with some oxidation by‐products of atrazine by O3 or O3/H2O2 have been measured using competitive oxidation experiments. Aqueous solutions containing two organic solutes (2 oxidation by‐products or 1 oxidation by‐product + sodium paranitrobenzoate as a competitor) and hydrogen peroxide have been oxidized by O3/H2O2 in a semi‐batch reactor at 20 ± 0,5°C and pH = 7.5 ‐ 8.1. The following second‐order rate constants for the reaction of hydroxyl radicals were obtained: atrazine: kAt = 2.4 109 1 mol‐1 s‐1; desethylatrazine: kDEA = 1.2 109 1 mol‐1 s‐1; desisopropylatrazine: kDIA = 1.9 109 1 mol‐1 s‐1; hydroxyatrazine: kHA = 2.6 109 1 mol‐1 s‐1. Moreover, desethyldesisopropylatrazine (DEIA) and isocyanuric acid (IA) were found to be refractory to the oxidation by OH∗ radicals (kDEIA or KIA ≪5 107 1 mol‐1 s‐1).

Photodecomposition du bioxyde de chlore et des ions chlorite par irradiation U.V. en milieu aqueux—partie I. Sous-produits de reaction

Literature data about the photochemistry of oxychlorine compounds in aqueous solutions (flash photolysis, pulse radiolysis, solar radiation) indicate that the products (ClO, Cl, O, O−,…) generated from the primary photochemical reactions of decomposition of chlorine dioxide and hypochlorite can then initiate complex reactions which lead to the formation of many secondary products (Cl2O2, Cl2O1, ClO−,…) and of chlorate, chloride and molecular oxygen as end-products (Table 1). The aim of this work was to study the photodecomposition of aqueous solutions of chlorine dioxide and chlorite in u.v. reactors equipped with low pressure mercury vapour lamps in order to show the effects of pH and of the initial concentrations on the nature of photoproducts and on the rate of photodecomposition of ClO2 and ClO2−. This paper presents the data obtained for the identification of photoproducts. The kinetics of photodecomposition will be presented in another paper (Part II).