Iron-mediated trichloroethene reduction within nonaqueous phase liquid

Aqueous slurries or suspensions containing reactive iron nanoparticles are increasingly suggested as a potential means for remediating chlorinated solvent nonaqueous phase liquid (NAPL) source zones. Aqueous-based treatment approaches, however, may be limited by contaminant dissolution from the NAPL and the subsequent contaminant transport to the reactive nanoparticles. Reactions occurring within (or at the interface) of the NAPL may alleviate these potential limitations, but this approach has received scant attention due to concerns associated with the reactivity of iron within nonaqueous phases. Results presented herein suggest that iron nanoparticles are reactive with TCE–NAPL and exhibit dechlorination rates proportional to the concentration of (soluble) water present within the NAPL. Reactivity was assessed over a 12-day period for five water contents ranging from 0.31 M to 4.3 M, with n-butanol used to enhance water solubility in the NAPL. Rates of dechlorination were generally slower than those reported for aqueous-phase dechlorination, but were not observed to slow over the course of the 12-day period. The lack of observed deactivation may indicate the potential that highly efficient (with respect to utilization of available electrons) dechlorination reactions can be engineered to occur within nonaqueous liquids. These results suggest a need for subsequent investigations which focus on understanding the mechanisms of the reactions occurring within NAPL, as well as those assessing the utility of controlling both the iron and water content within a NAPL source zone.