Sulfidation Doses of Nanoscale Zerovalent Iron Particles Need to Be Tuned to Achieve High Reactivity to Different Chlorinated Solvent Compounds

The sulfur content in sulfidated nanoscale iron (S-nZVI) alters the degradation efficiency of trichloroethene (TCE), a common groundwater contaminant, but its impact on other chlorinated hydrocarbon contaminants (CHCs) has not been characterized. In this study, the anaerobic degradation of carbon tetrachloride (CT), chloroform (CF), trichloroethane (1,1,1-TCA) and TCE was assessed using S-nZVI at seven S loadings ([S/Fe] = 0.01-0.303). S-nZVI_0.01 yielded the highest degradation rate constants for CT, 1,1,1-TCA, and CF, which were 1.77-10.9 times higher than those of nZVI and other S-nZVI. In contrast, S-nZVI_0.075 yielded the highest rate constant for TCE. S-nZVI_0.01 provides the most rapid electron release, and because CT, 1,1,1-TCA, and CF have higher electron affinity than water, their degradation is the quickest at this [S/Fe]. TCE degradation was faster only at higher [S/Fe], where S-nZVI reactivity to water was diminished and S-nZVI_0.075 provided a 20-fold enhancement in electron selectivity to TCE over H₂O. Although TCE was completely dechlorinated, the other CHCs were only partially dechlorinated. The degradation products dichloromethane and 1,1-dichloroethane were dechlorinated in the presence of their parent CHCs and at specific [S/Fe], although they were not dechlorinated as sole compounds. The results demonstrate that dechlorination rates and extents of CHCs can be optimized by tuning the sulfidation dose.