Reaction Mechanism and Kinetic Modeling of DEET Degradation by Flow-Through Anodic Fenton Treatment (FAFT)

Cornell University, Итак, New York, United States
Environmental Science and Technology (Impact Factor: 5.33). 08/2006; 40(14):4488-94. DOI: 10.1021/es060515b
Source: PubMed


The previously developed batch anodic Fenton treatment (AFT) technology has been successfully applied to degrade various pesticides in aqueous solution. The goal of this work is the development of a flow-through AFT system (FAFT) which is critical to bringing this technology into practical general use in the field. For this purpose, the degradation of DEET (N,N-diethyl-3-methylbenzamide), an insect repellent, and nine model amides was studied. Oxidation products of these compounds in FAFT were identified by GC/MS, and the results revealed that various -OH additions (most likely on the aromatic ring), quinone/keto product formation, and dimerization/bimolecular disproportionation are the major reaction pathways. This proposed overall reaction mechanism was then combined with the basic Fenton's mechanism to model the kinetics of various active species in FAFT including DEET, Fe2+, H2O2, and total iron under different reaction conditions. In addition, both initial and steady-state hydroxyl radical concentrations were measured in FAFT using benzoic acid as a chemical probe; the measured *OH concentrations were best-fitted exponentially. On the basis of the obtained [*OH] trend and the mass balance of the FAFT system, a simple FAFT model was developed to fit all of the degradation data of DEET and the model amides.

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    ABSTRACT: A flow-through anodic Fenton treatment (FAFT) system based on the batch AFT technology was previously developed to degrade pesticides in aqueous solution. As one of a series of benchtop and pilot-scale studies in process optimization, the goal of the reported work is to evaluate the performance of the FAFT system under various operating conditions, which is critical to bringing this technology into practical general use in the field. For this purpose, the removal efficiency of the parent pesticide and the concentration of the hydroxyl radical in FAFT were calculated on the basis of a previously developed FAFT kinetic model and used for the evaluation. N,N-Diethyl-3-methylbenzamide (DEET), an insect repellent, was used as a chemical probe. Experimental data showed that the key to a high treatment efficiency is to operate the FAFT system to achieve a maximum *OH production with a minimum input of energy and chemicals. For the anodic half-cell, the system should be operated under flow-through conditions with a self-developed optimum pH of 3.0, a relatively high flow rate, and the initial effluent recycled within 6-10 min to the FAFT system for further treatment; for the cathodic half-cell, it should have a fixed volume and be entirely replaced by another batch of cathodic solution only when the pH reaches a very high value. The delivery rate of the ferrous iron should be maintained at an electrolytic current between 0.01 and 0.02 A; the ratio of H2O2/Fe2+ should be between 5:1 and 10:1. NaCl was found to be the best electrolyte, with concentrations of 0.01-0.02 and 0.08 M in the anodic and cathodic half-cells, respectively. The FAFT system was successfully applied to degrade various model amide compounds and DEET formulations, which suggests the likelihood of extending this approach to other pesticide-containing wastewaters.
    No preview · Article · Jun 2007 · Journal of Agricultural and Food Chemistry
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    ABSTRACT: Degradation products of the dye extracted from turmeric and the turmeric dyed textiles were examined by using GC-MS after 100 oven (OV) and (PER) treatments for up to 28 days. Throughout the OV degradation times, 2-propenoic acid, 3-(2-hydroxyphenyl)- was found consistently, while isovanillin, and vanillic acid were newly detected. In 28 day PER degradation sample, feruloylmethane, 2-propenoic acid, 3-(2-hydroxyphenyl)-, benzoic acid, and vanillic acid were detected as well as isovanillin. Feruloylrnethane, and 2-propenoic acid, 3-(2-hydroxyphenyl)- were detected from the degraded fabric samples. With the absence of curcuminoids in the GC-MS result, the decreasing pattern of 2-propenoic acid, 3-(2-hydrokyphenyl)- reflect the degradation of curcuminoids in turmeric extraction with the progression of OV degradation times. It is suggested that isovanillin, feruloylmethane, 2-propenoic acid,3-(2-hydroxyphenyl)-, and vanillic acid are the probable fingerprint products for determining the turmeric dye from the badly faded archaeological textiles.
    Preview · Article · Jun 2007
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    ABSTRACT: The corrosion of zero-valent iron (Fe0(s)) by oxygen (O2) can lead to the oxidation of organic compounds. To gain insight into the reaction mechanism and to assess the nature of the oxidant, the oxidation of methanol, ethanol, 2-propanol, and benzoic acid by the reaction of nanoparticulate zero-valent iron (nZVI) or ferrous iron (Fe[II]) with O2 in the absence of ligands was studied. At pH values below 5, Fe0(s) nanoparticles were oxidized by O2 within 30 min with a stoichiometry of approximately two Fe0(s) oxidized per O2 consumed. The yield of methanol and ethanol oxidation products increased from 1% at acidic pH to 6% at pH 7, relative to nZVI added. Product yields from 2-propanol and benzoic acid were highest under acidic conditions, with little oxidation observed at neutral pH. At pH values below 5, product formation was attributable to hydroxyl radical (OH.) production through the Fenton reaction, involving hydrogen peroxide and Fe(II) produced during nZVI oxidation. At higher pH values, the oxidation of Fe(II), the initial product of nZVI oxidation, by oxygen is responsible for most of the oxidant production. Product yields at circumneutral pH values were consistent with a different oxidant, such as the ferryl ion (Fe[IV]).
    Full-text · Article · Mar 2008 · Environmental Science and Technology
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