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

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.