In situ chemical reduction (ISCR) technologies: Significance of low Eh reactions

Zero valent iron (ZVI; Fe(0)) has been successfully employed for the transformation and subsequent detoxification of a wide range of environmental contaminants, including chlorinated organics, heavy metals, nitroaromatics and, to some degree, perchlorate. The combined use of ZVI plus controlled release carbon has been shown to generate environmental conditions defined herein as in situ chemical reduction (ISCR) that facilitate the microbiological, chemical and/or physical destruction of various contaminants. In this context, the salient features of ISCR are: (i) its low redox potential; and (ii) its propensity to produce H2. In this paper we discuss the thermodynamics of these characteristics (with special emphasis on ZVI reactions) and provide representative case studies documenting the safe and effective use of ISCR technology to rapidly remove halogenated organics from impacted subsurface environments.