Esther Chamarro

Use of Fenton reagent to improve organic chemical biodegradability.

Fenton reagent has been used to test the degradation of different organic compounds (formic acid, phenol, 4-chlorophenol, 2,4-dichlorophenol and nitrobenzene) in aqueous solution. A stoichiometric coefficient for the Fenton reaction was found to be 0.5 mol of organic compound/mol of hydrogen peroxide, except for the formic acid where a value of approximately one was obtained (due to the direct formation of carbon dioxide). The treatment eliminates the toxic substances and increases the biodegradability of the treated water (measured as the ratio BOD5/COD). Biodegradability is attained when the initial compound is removed.

Influence of H2O2 and Fe(III) in the photodegradation of nitrobenzene

Abstract The influence of H 2 O 2 and Fe(III) in the degradation of nitrobenzene in aqueous solutions combined with UV radiation has been studied. A major efficiency is achieved when UV is combined with H 2 O 2 or Fe(III). Likewise, H 2 O 2 and Fe(III) concentration has an important effect on the degradation. Nitrophenol isomers are detected as the major intermediate products.

Rate equation for the degradation of nitrobenzene by ‘Fenton-like’ reagent

Abstract This paper describes the effect of temperature and initial concentration of H 2 O 2 , Fe(II), PhNO 2 and dissolved oxygen on the degradation rate of PhNO 2 in homogeneous aqueous solution by ‘Fenton-like’ reagent ([H 2 O 2 ] o ≫[Fe(II)] o ). The oxidation products o -, m - and p -nitrophenol were found as intermediates in the ratio 1:1.3–2.8:1.4–2.7 as compared with PhNO 2 when conversion of the latter was less than 25%. This fact suggests that hydroxylation of PhNO 2 was promoted by HO radicals. The reaction was investigated in a completely mixed-batch reactor under a wide range of experimental conditions: pH ∼3.0; 278–318 K; 1.5 2 O 2 ] o o 2 ] o 2 ] o 2 was determined to be 59.7 kJ mol −1 . The degradation rate of PhNO 2 follows pseudo-first-order kinetics. The results of this study demonstrate that the degradation rate of PhNO 2 in the ‘Fenton-like’ system could be predicted with sufficient precision by the equation R D =1.05×10 11 exp(−59.7/ RT )[H 2 O 2 ] o 0.68 [Fe(II)] o 1.67 [PhNO 2 ] o −0.32 . The second-order rate constant for the overall rate of H 2 O 2 decomposition by Fe(III) was found to be 0.83 M −1 s −1 at 298 K. The value of the steady-state HO radical concentration in the ‘Fenton-like’ reaction was found to be ∼10 −13 M, as estimated by two independent methods.

PHOTOCHEMICAL DEGRADATION OF PARATHION IN AQUEOUS SOLUTIONS

Abstract The photodegradation of O,O′-diethyl O-4-nitrophenyl phosphorothioate (common name parathion or ethyl parathion) in aqueous solutions has been studied by using u.v. radiation at different pH values. According to the experimental results it was observed that the dark reactions were negligible and the reaction rate increased as the pH increased. Finally, assuming a simple mechanism for the parathion photodegradation at initial times, the quantum yield (molecules degraded/photon absorbed) in the wavelength of parathion absorption was determined.

Kinetics of the UV degradation of atrazine in aqueous solution in the presence of hydrogen peroxide

Abstract The kinetics of degradation of atrazine were studied using UV radiation in combination with hydrogen peroxide at different pH values. The influence of the initial concentration was also considered. The dark reactions were negligible. The kinetic constants were determined following a proposed first-order kinetic model. The photochemical treatment of water contaminated with atrazine is conditioned by the toxicity of the decomposition products, since the treatment is unable to degrade all of these products.

Simple Models for the Control of Photo-Fenton by Monitoring H2O2

Abstract It has been demonstrated that Photo-Fenton process is feasible for the remediation of wastewater containing multiple organic pollutants. In order to promote its industrialization, control strategies have to be defined and tested. The objective of the present work is to describe a mathematical equation that fits the amount of COD abated regarding the dose of H2O2. UVA Laboratory-scaled and solar up-scaled experiments are compared. Also two H2O2 supply strategies are compared; one in which H2O2 is added at the beginning of an experiment; the second, H2O2 is added in doses through an experiment. According to the results, simple equations have been found to fit experimental COD degraded depending on the amount of H2O2 supplied. There is also a ratio of COD degraded per amount of H2O2 consumed that fits a wide range of operating conditions. The ratio is estimated to be 0.51 (mg O2/mg H2O2) which can be considered as a stoichiometry of Photo-Fenton process in the current conditions.

Photochemical degradation of malathion in aqueous solutions

Abstract The photodegradation of diethyl(dimethoxythiophosphorylthio)succinate (common name malathion) in aqueous solutions has been studied by using ultraviolet radiation alone and with hydrogen peroxide. The effect of pH on the photodecomposition rate of malathion was examined. It was observed that the dark reactions were negligible. The kinetic parameters were determined assuming first order with respect to the absorbed radiation.