Final Laboratory Treatability Report for: Emulsified Zero Valent Iron Treatment of Chlorinated Solvent DNAPL Source Areas (Rev 1)

Abstract

Abstract : Significant laboratory and field research has demonstrated that zero-valent metals will reductively dechlorinate dissolved chlorinated solvents such as tetrachloroethene (PCE) and trichloroethene (TCE) to ethene in groundwater. Permeable reactive barriers (PRBs) containing zero-valent iron (ZVI) as the reactive material have been shown to be effective in treating plumes of dissolved chlorinated solvents. PRB technology is passive; however, it relies on dense non-aqueous phase liquid (DNAPL) dissolution and transport of dissolved chlorinated solvents to the PRB for treatment, and therefore PRBs do not reduce the cleanup time for sites where DNAPL is present. Nano-scale ZVI particles (nZVI), either in a water slurry or as particles contained within an oil emulsion droplet (EZVI), have advantages over the conventional PRB applications since they may be injected deeper in the subsurface than is practical for conventional PRBs, and can be injected directly into DNAPL source areas. Laboratory and field tests have demonstrated that treatment of chlorinated ethenes such as TCE with nZVI particles is more rapid than with conventional forms of granular iron (Wang and Zhang, 1997; Lien and Zhang, 2001; Elliott and Zhang, 2001; Lowry et al. 2004). Nano-scale ZVI is significantly more reactive than micro-scale ZVI or iron powders because the smaller particle size gives the nZVI a larger surface area per unit mass. The degradation of chlorinated solvents by ZVI regardless of particle size is believed to occur via both reductive dechlorination and -elimination (Arnold and Roberts, 2000). The dechlorination reactions occur at the iron surface and require excess electrons produced from the corrosion of the ZVI in water. Through this process, the target chemicals undergo sequential dechlorination steps, resulting in the formation of non-chlorinated hydrocarbon products (e.g., ethene and ethane).