Leandro Oscar Conte

Photo-Fenton degradation of the herbicide 2,4-D in aqueous medium at pH conditions close to neutrality

A theoretical and experimental study of the photo-Fenton degradation of the herbicide 2,4-dichlorophenoxyacetic acid (2,4-D) in water is presented. A kinetic model derived from a reaction sequence is proposed using the ferrioxalate complex as iron source for conditions of pH = 5. The kinetic model was employed to predict the concentrations of 2,4-D, 2,4-dichlorophenol (2,4-DCP), hydrogen peroxide (HP) and oxalate (Ox) in a flat plate laboratory reactor irradiated with a solar simulator. Two types of incident irradiation levels were tested by different combinations of attenuation filters. The effects of the oxalate/Fe(+3) molar ratio (Ox/Fe), the reaction temperature (T) and the 2,4-D/HP molar ratio (R) on the photo-Fenton process were also investigated. For low radiation level and operating conditions of R = 50 and T = 50 °C, a 2,4-D conversion of 95.6% was obtained after 180 min. Moreover, the 2,4-D conversion was almost 100% in only 120 min when the system was operated under the same operating conditions and high radiation level. From the proposed model and the experimental data, the corresponding kinetic parameters were estimated applying a nonlinear regression method. A good agreement between the kinetic model and experimental data, for a wide range of simulated solar operating conditions, was observed. For 2,4-D, 2,4-DCP, HP and Ox concentrations, the calculated RMSE were 1.21 × 10(-2), 5.45 × 10(-3), 2.86 × 10(-1) and 2.65 × 10(-2) mM, respectively.

Modelling of Photo-Fenton Solar Reactors for Environmental Applications

A proposal for modelling photo-Fenton reactors for water pollution remediation is presented. Reactor models, based on chemical reaction engineering principles and radiative energy transport fundamentals in homogeneous systems, are derived at both laboratory and solar pilot-plant scales. The proposed methodology is illustrated by presenting an example on the modelling and scaling up of a solar reactor for degradation of a model pollutant in aqueous solution: the herbicide 2,4-dichlorophenoxyacetic acid. Firstly, a kinetic model derived from a reaction sequence is proposed and its kinetic parameters estimated, using an isothermal, well-stirred tank laboratory photoreactor. Afterwards, the kinetic model is employed to predict the reacting species concentrations during the photo-Fenton degradation in a pilot-plant, nonisothermal solar reactor designed to capture the UV/Visible/IR solar radiation. This approach has proved to be appropriate to simulate the behaviour of the photo-Fenton reactor under different experimental conditions.

Photo-Fenton degradation of a herbicide (2,4-D) in groundwater for conditions of natural pH and presence of inorganic anions

The effects of four inorganic anions (Cl-, SO42-, HCO3-, NO3-) usually present in groundwater were investigated on the photo-Fenton degradation of 2,4-dichlorophenoxyacetic acid (2,4-D). A kinetic model derived from a reaction sequence is proposed using the ferrioxalate complex as iron source at pH close to natural conditions (pH = 5). It was demonstrated that oxalate not only maintained iron in solution for the natural groundwater system, but also increased the photochemical activation of the process. Results showed that the minimum conversion of 2,4-D for the simulated groundwater after 180 min was 63.80%. This value was only 14.1% lower than the conversion achieved without anions. However, with all anions together, the consumption of hydrogen peroxide (HP) per mole of herbicide showed an increase with respect to the test without anions. Only one kinetic parameter was estimated for each anion applying a nonlinear regression method. Subsequently, these optimized kinetic constants were used to simulate the system behaviour, considering the influence of all the studied anions together. A good agreement between kinetic model predictions and experimental data was observed, with the following errors: RMSE2,4-D = 3.98 × 10-3 mM, RMSEHP = 1.83 × 10-1 mM, RMSEOX = 1.39 × 10-2 mM, and RMSE2,4-DCP = 5.59 × 10-3  mM.

A Kinetic Study for the Fenton and Photo-Fenton Paracetamol Degradation in a Pilot Plant Reactor

The present study aims at proposing a kinetic model that can capture the complexity and non - linear nature of the Fenton and photo - Fenton processes in the degradation of a model pollutant . Moreover, t he pro posed model is also able to account for the effect of the Local Volumetric Rate of Photon Absorption (LVRPA), depending on the radiation field within the annular photoreactor and consequently including the reactor dimensions and lamp characteristics. Parac etamol (PCT) was selected as model pollutant, because it is widely used as antipyretic and analgesic. Three kinetic parameters, accounting for the Fenton - like reaction and the hydroxyl radical attack to hydrogen peroxide and paracetamol, were estimated. Me an Square Error (MSE) and Root Mean Square Error (RMSE) were calculated to validate the model reliability