Nathalie Karpel Vel Leitner

Degradation of acetic acid with sulfate radical generated by persulfate ions photolysis.

The photolysis of S(2)O(8)(2-) was studied for the removal of acetic acid in aqueous solution and compared with the H(2)O(2)/UV system. The SO(4)(-) radicals generated from the UV irradiation of S(2)O(8)(2-) ions yield a greater mineralization of acetic acid than the ()OH radicals. Acetic acid is oxidized by SO(4)(-) radicals without significant formation of intermediate by-products. Increasing system pH results in the formation of ()OH radicals from SO(4)(-) radicals. Maximum acetic acid degradation occurred at pH 5. The results suggest that above this pH, competitive reactions with the carbon mineralized inhibit the reaction of the solute with SO(4)(-) and also ()OH radicals. Scavenging effects of two naturally occurring ions were tested; in contrast to HCO(3)(-) ions, the presence of Cl(-) ions enhances the efficiency of the S(2)O(8)(2-)/UV process towards the acetate removal. It is attributed to the formation of the Cl() radical and its great reactivity towards acetate.

Kinetic of benzotriazole oxidation by ozone and hydroxyl radical

Ozonation experiments were performed in batch reactors in order to determine the rate constants for the reaction of molecular ozone and OH radicals with benzotriazole (BT) at different pHs. The first group of ozonation experiments was carried out for the determination of the rate constant for the direct reactions between ozone and BT. Two different kinetic models were used for the determination of kinetic rate constants: (i) the log-reduction of BT with ozone in excess, (ii) the competition kinetic model. The second-order rate constants for BT with molecular ozone were determined to be 36.4+/-3.8M(-1) s(-1) and 18.4+/-0.8M(-1) s(-1) at pH 2 from the two methods respectively. With the competition method, the value at pH 5 was found to be 22.0+/-2.0M(-1) s(-1). In a following stage, the reaction of BT with OH radicals was investigated at pH values ranging from 2 to 10.2. Using a method involving two probe compounds during the ozonation, the second-order rate constants of the BT reaction with hydroxyl radicals were determined. The rate constants were found to vary from 6.2x10(9)M(-1) s(-1) at pH 10.2 to 1.7x10(10)M(-1) s(-1) at pH 2.

Mecanisme d'action des radicaux OH sur les acides glycolique, glyoxylique, acetique et oxalique en solution aqueuse: Incidence sur la consammation de peroxyde d'hydrogene dans les systemes H2O2UV et O3H2O2

The aim of this work is to study the mechanism of the reaction of hydroxyl radicals with simple aliphatic acids (acetic, glycolic, glyoxylic and oxalic acids; see Table 1) in aqueous solution. The decomposition of organic acids by hydroxyl radicals has been studied using the photolysis of hydrogen peroxide and the ozone/hydrogen peroxide system.

Effect of persulfate on the oxidation of benzotriazole and humic acid by e-beam irradiation

These days, the use of persulfate in advanced oxidation processes (AOPs) has gained more attention as an emerging clean and efficient technology to degrade the organic pollutants. The objective of this study was to investigate the effect of the addition of persulfate on the oxidation of benzotriazole (BT) and humic acids (HAs) by irradiation. The degradation of BT (3.7 μM) was followed under the influence of persulfate addition (200-500 μM) in combination with a fixed radiation dose (15 Gy) in the absence and presence of HA (5 and 20mg/L) in deionized water. The main results obtained in this study on the degradation of BT in the presence of HA showed a different effect of S(2)O(8)(2-) addition during irradiation, depending on whether HA are oxidized or not-oxidized. (1) An inhibitory effect of S(2)O(8)(2-) was observed in the presence of non-oxidized HA. (2) The removal of BT was generally more important during irradiation in the presence of S(2)O(8)(2-) when HA is pre-oxidized. This could be explained by the different structures of humic acids. These differences of structures of HA were identified by physico-chemical parameters such as the absorbance in the UV (254 nm), the fluorescence and the SUVA measurement.

Levofloxacin oxidation by ozone and hydroxyl radicals: Kinetic study, transformation products and toxicity

This work was carried out to investigate the fate of the antibiotic levofloxacin upon oxidation with ozone and hydroxyl radicals. A kinetic study was conducted at 20 °C for each oxidant. Ozonation experiments were performed using a competitive kinetic method with carbamazepin as competitor. Significant levofloxacin removal was observed during ozonation and a rate constant value of 6.0×10(4) M(-1) s(-1) was obtained at pH 7.2. An H2O2/UV system was used for the formation of hydroxyl radicals HO. The rate constant of HO was determined in the presence of a high H2O2 concentration. The kinetic expressions yielded a [Formula: see text] value of 4.5×10(9) M(-1) s(-1) at pH 6.0 and 5.2×10(9) M(-1) s(-1) at pH 7.2. These results were used to develop a model to predict the efficacy of the ozonation process and pharmaceutical removal was estimated under different ozonation conditions (i.e. oxidant concentrations and contact times). The results showed that levofloxacin was completely degraded by molecular ozone during ozonation of water and that hydroxyl radicals had no effect in real waters conditions. Moreover, LC/MS/MS and toxicity assays using Lumistox test were performed to identify ozonation transformation products. Under these conditions, four transformation products were observed and their chemical structures were proposed. The results showed an increase in toxicity during ozonation, even after degradation of all of the observed transformation products. The formation of other transformation products not identified under our experimental conditions could be responsible for the observed toxicity. These products might be ozone-resistant and more toxic to Vibrio fisheri than levofloxacin.

Aqueous chlorination of levofloxacin: Kinetic and mechanistic study, transformation product identification and toxicity

The aim of this study was to gain further insight into the fate of levofloxacin during the chlorination process. First, a kinetic study was thus performed at pH 7.2, 20 °C and in the presence of an excess of total chlorine. A slower apparent removal of levofloxacin (k ~ 26 M(-1) s(-1)) was noted when sodium thiosulfate was used to stop the chlorination reaction compared to the degradation observed without using a reducing agent (k ~ 4400 M(-1) s(-1)). The formation of a chlorammonium intermediate which could be converted back into the parent compound through a reaction with thiosulfate was thus expected. This intermediate would result from an initial chlorine attack on the tertiary amine function of levofloxacin. Secondly, four chlorination transformation products were detected by LC/UV/MS analysis. The chemical structures of two of them are proposed. It was suggested that these compounds could come from a secondary reaction of the chlorammonium intermediate on levofloxacin. A reactional pathway is then proposed. Finally, a bioassay using Vibrio fisheri was carried out to study the toxicity pattern during levofloxacin chlorination. An increase in toxicity was observed during chlorination suggesting that the first transformations products formed were more toxic than the parent compound.

Influence of persulfate ions on the removal of phenol in aqueous solution using electron beam irradiation.

The removal of phenol (Co = 100 μM) during electron beam irradiation was studied in pure water and in the presence of HCO(3)(-) and Br(-) ions. It was found that the introduction of S(2)O(8)(2-) ions (1mM), by generating SO(4)(-) radicals increases the radiation yield of phenol removal. 90% removal of phenol was obtained with radiation doses 600 and 1200 Gy with and without S(2)O(8)(2-) ions respectively. This system induced smaller oxygen consumption with smaller concentration of catechol and hydroquinone found in the solution. HCO(3)(-) and Br(-) have an inhibiting effect in the presence as in the absence of S(2)O(8)(2-). In most cases, the introduction of S(2)O(8)(2-) ions in water radiolysis system can advantageously increase the yield of organic compounds removal by oxidation.

Catalytic ozonation of chlorinated carboxylic acids with Ru/CeO2–TiO2 catalyst in the aqueous system

The catalytic mineralization of chloroacetic acid (CAA) and chlorosuccinic acid (CSA) by ozone with Ru/CeO2–TiO2 solid catalyst in aqueous systems was studied. The catalyst significantly improves the oxidation and degradation at acidic pH. More than 80 to 90% of the converted CAA and CSA are mineralized during the reaction. The chloride is nearly completely released along with the decomposition of CAA and CSA. The catalytic oxidation of CAA and CSA and conversion of total organic carbon can be simply simulated with a pseudo-first-order behavior with little dependence on the concentration of the dissolved ozone in the aqueous systems, which is maintained in sufficient quantity during the reaction. The catalytic ozonation displays a higher ozone use efficiency than ozonation alone. CSA is apparently easier to degrade than CAA. The chloride ion in the solution has little detrimental influence on the catalytic effects under our experimental conditions. The oxidation of 2 mM CAA is apparently stopped after about 50 min when the CAA concentration decreases to about 0.6 mM and the pH value of the system is lower than the pKa of CAA. The explanation is that in very dilute systems with pH values lower than the pKa, the low-concentration of CAA ions slows the adsorption and reaction rates. The near-total elimination of CAA at low concentrations can be achieved only if the pH value is increased above the pKa. The results demonstrate that catalytic ozonation is an effective and promising method for the oxidation and elimination of chlorocarboxylic acids.

Kinetics of Chlorination of Benzophenone-3 in the Presence of Bromide and Ammonia

The aim of this study was to assess the impact of chlorination on the degradation of one of the most commonly used UV filters (benzophenone-3 (BP-3)) and the effects of bromide and ammonia on the kinetics of BP-3 elimination. Bromide and ammonia are rapidly converted to bromine and chloramines during chlorination. At first, the rate constants of chlorine, bromine and monochloramine with BP-3 were determined at various pH levels. BP-3 was found to react rapidly with chlorine and bromine, with values of apparent second order rate constants equal to 1.25(±0.14) × 10(3) M(-1)·s(-1) and 4.04(±0.54) × 10(6) M(-1)·s(-1) at pH 8.5 for kChlorine/BP-3 and kBromine/BP-3, respectively, whereas low monochloramine reactivity was observed (kNH2Cl/BP-3 = 0.112 M(-1)·s(-1)). To assess the impact of the inorganic content of water on BP-3 degradation, chlorination experiments with different added concentrations of bromide and/or ammonia were conducted. Under these conditions, BP-3 degradation was found to be enhanced in the presence of bromide due to the formation of bromine, whereas it was inhibited in the presence of ammonia. However, the results obtained were pH dependent. Finally, a kinetic model considering 18 reactions was developed using Copasi to estimate BP-3 degradation during chlorination in the presence of bromide and ammonia.

Identification and control of a wastewater treatment pilot by catalytic ozonation

This paper deals with the control of a wastewater treatment pilot by catalytic ozonation. In general, catalytic ozonation processes operate with a deliberate ozone overproduction to obtain a treated water which respects the discharge standards. But, in this case, the oxygen consumption is not optimal and the operating costs are important. The objective of this study focuses on the optimization of the catalytic ozonation pilot. A continuous-time transfer function model is identified to represent the pilot behavior, and an internal model control is proposed to obtain a significant abatement of the pollutant. In this application, the pollutant abatement is represented by the absorbance.