There is significant environmental concern about chlorinated organic compounds (COCs) in wastewater, surface water, and groundwater due to their low biodegradability and high persistence. In this work, 1,2,4-trichlorobenzene (124-TCB) was selected as a model compound to study its abatement using wet peroxide oxidation at neutral pH with goethite as a heterogeneous catalyst, which was enhanced with visible monochromatic light-emitting diode (LED) light (470 nm). A systematic study of the main operating variables (oxidant and catalyst concentration and irradiance) was accomplished to investigate their influence in the abatement of 124-TCB in water. The reaction was carried out in a well-mixed reactor of glass irradiated by a visible LED light. The hydrogen peroxide concentration was tested from 0 to 18 mM, the goethite concentration within the range 0.1–1.0 g·L−1 and the irradiance from 0.10 to 0.24 W·cm−2 at neutral pH. It was found that this oxidation method is a very efficient technique to abate 124-TCB, reaching a pollutant conversion of 0.9 when using 0.1 g·L−1 of goethite, 18 mM of H2O2, and 0.24 of W·cm−2. Moreover, the system performance was evaluated using the photonic efficiency (ratio of the moles of 124-TCB abated and the moles of photons arriving at the reactor window). The maximum photonic efficiencies were obtained using the lowest lamp powers and moderate to high catalyst loads.
A kinetic model describing Fenton and photo-Fenton degradation of paracetamol (PCT) and consumption of hydrogen peroxide (HO) was proposed. A set of Fenton and photo-Fenton experiments (18 runs in total) was performed by fixing the initial concentration of PCT to 40 mg L and varying the initial concentrations of HO and ferrous ion, Fe. The experimental set-up was a well-stirred annular photoreactor equipped with an actinic BL TL-DK 36 W/10 1SL lamp. Experimental results highlighted that PCT is no more detected by HPLC analysis within a minimum reaction time of 2.5 and a maximum reaction time of 15.0 min. Besides, a maximum conversion of total organic carbon (TOC) of 68.5% was observed after 75 min of reaction in case of using UV radiation and the highest concentrations of the Fenton reagents. The experimental data were used to fit the kinetic model. The radiation field inside the reactor was taken into account through the local volumetric rate of photon absorption, evaluated by assuming a line source model with spherical and isotropic emission. The kinetic parameters were estimated by using a non-linear least-squares regression procedure and root mean square errors (RMSE) were calculated in order to validate the feasibility of the proposed model. A good agreement between experimental and predicted data was observed and the lowest values of RMSE resulted in 5.84 and 9.59% for PCT and HO normalized concentrations, respectively.
A theoretical and experimental study of a pilot-plant
solar reactor
for the photo-Fenton degradation of the herbicide 2,4-dichlorophenoxyacetic
acid (2,4-D) in aqueous solution is presented. Initially, a kinetic
model is proposed to obtain the reaction rates of 2,4-D, the main
intermediate (2,4-dichlorophenol), and the hydrogen peroxide. The
kinetic study was performed in a well-stirred tank laboratory reactor.
The effects of ferric salt initial concentrations, hydrogen peroxide
to 2,4-D initial concentration ratios, reaction temperatures, and
radiation levels are studied. The proposed kinetic model and the experimental
data are used to estimate the kinetic parameters, applying a nonlinear
regression procedure. Afterward, the kinetic model is used to predict
the reactant concentrations during the photo-Fenton degradation in
a pilot-plant solar reactor designed to capture the UV/visible/IR
solar radiation. The solar reactor was able to reach a complete degradation
of the 2,4-D and 2,4-dichlorophenol after 60 min, and a total organic
carbon conversion of 98.9% after 210 min.
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