Article

Oxidative Degradation of Organic Compounds Using Zero-Valent Iron in the Presence of Natural Organic Matter Serving as an Electron Shuttle

School of Environmental Science and Engineering, Pohang University of Science and Technology, Pohang 790-784, Korea.
Environmental Science and Technology (Impact Factor: 5.33). 03/2009; 43(3):878-83. DOI: 10.1021/es801705f
Source: PubMed

ABSTRACT

This study aims to understand the oxidative degradation of organic compounds utilizing zerovalent iron (ZVI) which is further promoted by the presence of natural organic matters (NOMs) (as humic acid (HA) or fulvic acid (FA)) working as electron shuttle mediators. The main target substrate used was 4-chlorophenol. Both HA and FA can mediate the electron transfer from the ZVI surface to O2, while enhancing the production of Fe2+ and H2O2 that subsequently initiates the OH radical-mediated oxidation of organic compoundsthrough Fenton reaction. The electron transfer-mediating role of NOMs was supported by the observation that higher concentrations of H2O2 and ferrous ion were generated in the presence of NOM. The NOM-induced enhancement in oxidation was observed with NOM concentrations ranging 0.1-10 ppm. Since the reactive sites responsible for the electron transfer action are likely to be the quinone moieties of NOMs, benzoquinone that was tested as a proxy of NOM also enhanced the oxidative degradation of 4-chlorophenol in the ZVI suspension. The NOM-mediated oxidation reaction on ZVI was completely inhibited in the presence of methanol, an OH radical scavenger, and in the absence of dissolved oxygen.

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Available from: Wonyong Choi, Feb 01, 2015
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    • "With regard to NOM, some studies have shown that ZVI could remove NOM through adsorption and coprecipitation with iron corrosion products (Chiu, 2013;Wei et al., 2011). Fenton-like reactions were also reported on the ZVI surface, which may oxidise NOM (Kang and Choi, 2009;Keenan and Sedlak, 2008). A recent review summarised the general limitations and countermeasures of the ZVI technology (Guan et al., 2015). "
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    ABSTRACT: Former studies have shown that adding granular activated carbon (GAC) cathodes could enhance the overall performance of the zero valent iron (ZVI) process for organics removal. The present study evaluates for the first time the performance of such an enhanced ZVI process to remove natural organic matter (NOM), an important water quality parameter in drinking water. Lab-scale batch tests were conducted with surface reservoir feed water from a drinking water plant. In the GAC enhanced ZVI process dissolved organic carbon (DOC) and UV254 were reduced by 61±3% and 70±2%, respectively, during 24h treatment corresponding to 1.8min empty bed contact time. The process was superior to ZVI alone, particularly during the earlier stages of the process due to the synergistically increased iron dissolution rate. Besides GAC, graphite and anthracite also prove to be suitable and potentially more cost-effective options as cathode materials for the enhanced ZVI process, whereby electrically conductive graphite clearly outperformed anthracite. The dominant mechanisms in terms of NOM removal from surface water were found to be coagulation following iron dissolution and adsorption in the case of employing GAC. Oxidation was also occurring to a lesser degree, converting some non-biodegradable into biodegradable DOC.
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    • "HSs are the main component of natural organic matter, one of the most abundant materials in the world. Natural organic matter is part of soils, coal, peat or surface and groundwater [24]. HSs form polydispersions, with a nonstoichiometric elemental composition and a molecular structure that is very complicated, irregular and heterogeneous [25]. "
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    ABSTRACT: Zero-valent iron nanoparticles (nZVI) are a relatively new option for the treatment of contaminated soil and groundwater. However, because of their apparent toxicity, nZVI in high concentrations are known to interfere with many autochthonous microorganisms and, thus, impact their participation in the remediation process. The effect of two commercially available nZVI products, Nanofer 25 (non-stabilized) and Nanofer 25S (stabilized), was examined. Considerable toxicity to the soil yeast Trichosporon cutaneum was observed. Two chemically different humic substances (HS) were studied as a possible protection agent that mitigates nZVI toxicity: oxidised oxyhumolite X6 and humic acid X3A. The effect of addition of HSs was studied in different phases of the experiment to establish the effect on cells and nZVI. SEM and TEM images revealed an ability of both types of nZVI and humic substances to adsorb on surface of the cells. Changes in cell surface properties were also observed by zeta potential measurements. Our results indicate that humic substances can act as an electrosteric barrier, which hinders mutual interaction between nZVI and treated cell. Thus, the application of humic substance seems to be a promising solution to mitigating the toxic action of nZVI.
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    • "These reactions are mostly reductive and proceed with several types of reducing species generated during iron corrosion (Reddy, 2010; Kang and Choi, 2008). The mechanism involved in ZVI catalyzed reactions is similar to that found for iron mineral catalysis reactions (Kang and Choi, 2008). As mentioned before, the classic Fenton reaction has some limitations. "
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    ABSTRACT: Magnetite, a naturally occurring mineral of iron oxide, and zero-valent iron (ZVI) were used to catalyze hydrogen peroxide and initiate a dark Fenton-like reaction of diesel-contaminated loamy sand in a batch system at circumneutral pH. The effects of hydrogen peroxide concentration and catalyst content on the removal efficiency of total petroleum hydrocarbons (TPHs) were studied. A central composite rotatable design was applied and the derived equation for magnetite and ZVI were linear and quadratic, respectively. In both equations, the factor of hydrogen peroxide concentration was more significant than catalyst content. At optimum conditions (4.27 wt% of catalyst content and 2.17 mol/L of hydrogen peroxide), 57% and 67% of TPH removal were achieved by magnetite and ZVI, respectively. The obtained results suggest the potential of ZVI and magnetite to catalyze a heterogeneous Fenton-like reaction at circumneutral pH. It seems that using ZVI, rather than magnetite, as a catalyst may result in slightly more TPH mineralization; however, since magnetite is a naturally occurring mineral, it may be able to compete economically with ZVI.
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