Bernard Legube

Catalytic ozonation: a promising advanced oxidation technology for water treatment

Abstract The first part of this paper presents generalities on molecular ozone reactivity. The second part focuses on catalytic ozonation with the objective to evaluate the efficiency of such an AOT versus ozonation alone. The literature data relative to catalytic ozonation concerns either the activation of ozone with metals in solution, or the heterogeneous behavior of solid catalysts. Numerous metals (Fe, Mn, Ni, Co, Zn, Ag, Cr) under various forms (salt of reduced metal, solid oxide, deposited metal on support) were reported to enhance the efficiency of ozone towards the removal (or the conversion) of different organic compounds in aqueous solution. Some years ago, heterogeneous catalytic ozonation has begun to be studied in our group. This paper presents a short synthesis of the main results obtained, illustrated by three different experimental procedures which can be used to test catalytic ozonation. Finally, some hypothesis on reaction mechanisms and prospects are examined.

Chlorination studies of free and combined amino acids

Abstract Nitrogenous organic compounds in raw and treated water are of concern because they may exert high chlorine demand. They are also known as precursors of halogenated compounds. In this study, chlorine demand, TOX and THM formation potentials of 22 free amino acids, and some polypeptides and proteins were determined. Results have shown that the reactivity of free amino acids with chlorine is related to their structure. Experiments conducted with combined amino acids have shown that the amide linkage does not participate significantly in the chlorine demand of polypeptides, and does not seem to be TOX precursor. Specific amino acids that possess reactive side groups such as amino nitrogen, sulfur or activated aromatic ring were defined as the main chlorine consumer and TOX precursor sites of polypeptides. Complementary experiments indicated that sodium sulfite dechlorination can affect, more or less, the determination of amino acids TOXFP.

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).

Liquid chromatography coupled with tandem mass spectrometry method for thirty-three pesticides in natural water and comparison of performance between classical solid phase extraction and passive sampling approaches.

The aim of this study is to propose an analytical method for determining different classes of pesticides in water using LC-ESI-MS/MS. Two techniques of field-sampling and analyte extraction were used: solid phase extraction (SPE) of water samples from active sampling and field exposure of Polar Organic Chemical Integrative Samplers (POCIS). We have worked with thirty-three molecules representing eight pesticide classes: carbamates, chloroacetanilides, dicarboximides, morpholines, organophosphorous, phenylureas, strobilurines and triazines. First, liquid chromatography separation protocols and the optimization of the ESI-MS/MS parameters were developed. Then, the SPE step was optimized to obtain acceptable levels of recovery for the various classes of molecules. The matrix effect that may significantly lower the ionization efficiency with ESI interfaces was evaluated and minimized. The performances (limits of quantification, accuracy and precision) of the SPE and POCIS techniques were evaluated, and a comparison between the active and passive sampling techniques was carried out with a field application.

Atrazine and simazine removal mechanisms by nanofiltration : Influence of natural organic matter concentration

Abstract Experiments on a semi-industrial scale on the removal of atrazine and simazine by nanofiltration have demonstrated the influence of natural organic matter (NOM) on the retention of these two s -triazines. In-depth studies at pilot scale, presenting the advantage of working on a larger range of NOM concentrations (or dissolved organic carbon: DOC), have given a better understanding of the principal phenomena involved in atrazine and simazine retention mechanisms in the presence or absence of NOM. When taken together, the results show that the principal transfer mechanism of the two s -triazines is probably through diffusion. However, their complexation with NOM leads, on the one hand, to an increase in their apparent molecular weight and, on the other, to the appearance of negative charges. As a result, electrostatic repulsion and adsorption are also phenomena to be considered. At pilot scale, atrazine and simazine removal by nanofiltration increases from 50% to 90–100% when the waters NOM content varies from 0.4 to 3.6 mg 1 −1 of DOC.

Ozone and hydroxyl radicals induced oxidation of glycine

The study of the oxidation of glycine by ozone and hydroxyl radicals has been undertaken. Different experimental procedures involving the H2O2/UV process or ozone in the presence of hydrogen peroxide on one hand, and ozone alone on the other hand allowed to distinguish between the two oxidation pathways. It has been shown that nitrites and nitrates are observed byproducts resulting from molecular ozonation whereas ammonium ions constitute the only inorganic nitrogen species from hydroxyl radicals induced decomposition of glycine. Therefore, the ozonation process promoting radical pathways will favor ammonia production vs. nitrates. Among the organic compounds resulting from oxidation by hydroxyl radicals, oxalic acid was the major byproduct detected in the presence of oxygen. Oxamic acid and formic acid were also observed. In addition, the nitrogen mass balance indicated the formation of unidentified nitrogen byproducts derived from glycine. These nitrogen compounds could result from the interaction of oxygen with nitrogen radical, but, mainly, with α-amino radical of glycine. This reaction is very different from the molecular ozonation which directs the attack on the nitrogen functional group before the C–N bond cleavage of the amino acid molecule.

The ozonation of organic halide precursors: effect of bicarbonate

A laboratory study of the effect of bicarbonate on the ozonation of organic halide precursors in fulvic acid solutions and in a raw drinking water was conducted. The experimental variables were bicarbonate concentration, ozone dose and pH of chlorination. Results are expressed in terms of trihalomethane (THM), total organic halide (TOX), trichloracetic acid, dichloroacetic acid, trichloroacetone and dichloroacetonitrile precursor concentrations. Kinetic studies showed that bicarbonate slowed the decomposition of ozone in the presence of fulvic acid, and thereby, led to a greater degree of destruction of u.v.-absorbing substances. Similarly, precursor destruction increased with increasing bicarbonate concentrations in the range of 10−4spd 10−2 M. Precursor destruction was greatest when chlorination was performed at low pH. At high pHs of chlorination, some precursor enhancement was noted, especially in the absence of bicarbonate. Results are interpreted both from a mechanistic standpoint and with respect to their applicability to water treatment practice.

Aqueous chlorination of diclofenac: Kinetic study and transformation products identification

Diclofenac reactivity and fate during water chlorination was investigated in this work. In the first step, chlorination kinetic of diclofenac (DCF) was studied in the pH range of 4-10 at 20 ± 2 °C and in the presence of an excess of total chlorine. A second-order reaction (first-order relative to DCF concentration and first-order relative to free chlorine concentration) was shown with rate constant about 3.89 ± 1.17 M(-1) s(-1) at pH 7. The elementary reactions (i.e. reactions of hypochlorous acid (HOCl) with neutral and ionized forms of DCF, and acid-catalysed reaction of HOCl with neutral and ionized forms of DCF) were proposed to explain the pH-dependence of the rate constants and intrinsic constant of each of them were calculated. In the second step, several degradation products formed during chlorination of DCF were identified. These compounds could come from an initial chlorine electrophilic attack on aromatic ring or amine function of DCF. Some of these chlorinated derivatives seem to accumulate in solution in the presence of an excess of chlorine.

Ozonation of Aqueous Solutions of Nitrogen Heterocyclic Compounds : Benzotriazoles, Atrazine and Amitrole

Abstract Study of the ozonation of aqueous solutions of four heterocyclic nitrogen compounds, at slightly acidic pH in a heterogeneous gas-liquid system, showed that the reactivities of these compounds are different. Amitrole, a five-membered ring heterocycle, has been found to be a highly reactive compound, while atrazine, a six-membered ring heterocycle, has been found to be a poorly reactive compound. The benzotriazoles, benz-fused five-membered ring heterocycles, present intermediate reactivities. Moreovoer, the chemical natures of the ozonation by-products have been found to be different between amitrole and atrazine. With atrazine, ozone did not open the heterocyclic ring, and led to the formation of a trioxotriazine. With amitrole, ozone broke the heterocyclic ring and formed mainly formamide.

Experimental and theoretical studies of the mechanism of the initial attack of ozone on some aromatics in aqueous medium

Abstract An experimental study showing the selectivity of the direct reaction of ozone on some aromatics in aqueous medium is presented. The mechanism of the initial attack of ozone on phenol, benzaldehyde and acetophenone is discussed. Molecular orbital calculations are used to study the possible reaction paths for the ozonation of phenol. The changes in relative reactivity of phenol, benzaldehyde and acetophenone are discussed in terms of charges and frontier orbitals.