Effects of natural organic matter, anthropogenic surfactants, and model quinones on the reduction of contaminants by zero-valent iron

Recent studies of contaminant reduction by zero-valent iron metal (Fe-0) ha ve highlighted the role of iron oxides at the metal water interface and the effect that sorption has at the oxide water interface on contaminant reduc tion kinetics. The results suggest that a variety of organic surface-active substances might enhance or inhibit contaminant degradation, depending on the degree to which they promote solubilization, sorption, and/or reaction. Of particular interest is the effect of natural organic matter (NOM), beca use of its ubiquitous presence in natural waters and amphiphilic properties ; anthropogenic surfactants, because of their use in groundwater remediatio n; and certain quinones, which represent the redox-active functional groups associated with NOM. In this study, no well-defined effects of these subst ances were found on the reduction of nitro benzene by Fe-0, but the reducti on of carbon tetrachloride and trichloroethylene (TCE) was inhibited by NOM . Results with carbon tetrachloride showed that the inhibitory effect of hu mic acids was greater than fulvic acids, but that several quinonoid NOM mod el compounds (juglone, lawsone, and anthraquinone disulfonate) increased th e rate of reduction by Fe-0. Isotherms for adsorption of TCE and NOM onto F e-0 showed evidence of competition for surface sites. (C) 2001 Elsevier Sci ence Ltd. All rights reserved.