Decontamination of 1,2-Dichloroethane DNAPL in Contaminated Groundwater by Polymer-Modified Zero-Valent Iron Nanoparticles

Abstract

Remediation of dense non-aqueous phase liquids (DNAPLs) contaminants in groundwater has received considerable attention in the environmental field. Generally, DNAPLs can flow with groundwater and further infiltrate down to deeper aquitard zone that is difficult to be removed by pumping. The DNAPLs may also contaminate the soil and groundwater concurrently in the duration of flowing with groundwater slowly. In this study, remediation of 1,2-dichloroethane (1,2-DCE) in DNAPL contaminated groundwater was studied by a reductive reaction with polyethylenimine (PEI) surface-modified zero-valent iron nanoparticles (PEI-nZVI). The prepared PEI-nZVI was injected into upstream wells and reach the plume of DNAPLs down with the flowing groundwater. Moreover, nZVI was further characterized after field injection and 1-day reaction with the contaminants to assess its effectiveness for the on-site reduction of 1,2-DCE. After direct injection of PEI-nZVI into the contaminated plume, the concentrations of 1,2-DCE was significantly reduced. Moreover, the plume was decontaminated to nontoxic species onto the highly active nZVI. By using resistivity image profiling (RIP), the conductivity data of modified nZVI solution and sampled groundwater were similar. In addition, RIP can reveal complex subsurface DNAPLs structures by dense sampling of resistivity variation at shallow depth. Additionally, X-ray absorption near edge structure (XANES) and extended X-ray absorption fine structure (EXAFS) spectroscopy studies indicated that after the reductive reaction, nZVI and PEI-nZVI were oxidized to Fe3O4. The interatomic distances for the reacted samples were 1.95 A and 1.93 A, respectively. The combined technique of floating surface-modified nZVI and RIP method would be economically and environmentally attractive.