Injection of nanoscale zero-valent iron (nZVI) into the subsurface can be a promising approach for the in situ remediation of aquifers contaminated by toxic pollutants, including chlorinated hydrocarbons (CHCs). This study compares the efficacy of sulfidated vs. unsulfidated nZVI in degrading selected CHCs. Our results show that nZVI pre-treated with bisulfide increases the kinetics of dechlorination of carbon tetrachloride (CT), chloroform (CF), and 1,1,1-trichloroethane (1,1,1-TCA) in comparison to that by unsulfidated nZVI. The focus of this research was to characterize degradation kinetics and reaction byproduct distributions of CT, CF and 1,1,1-TCA by nZVI treated with bisulfide, termed as nZVI/FeS. Carboxymethylcellulose (CMC) was used as a stabilizer in all experiments to prevent agglomeration of nZVI. Results indicated that the nZVI/FeS system was faster and produced less toxic byproducts than nZVI for all CHCs studied. α-elimination in nZVI/FeS system appear to be an important degradation pathway for CF and 1,l,1-TCA; which can produce reactive carbene intermediates capable of degrading into benign products such as methane, ethane, and ethene. Regardless of CHC, the rate constant of their degradation increased with increasing bisulfide loading, reaching the highest value at 1 wt% bisulfide, and then declined at higher bisulfide. The study further indicated that nZVI/FeS particles exhibited a rapid power function decline in its reactivity with time. Increasing the amount of borohydride during nZVI/FeS synthesis improved reactivity by 43%. The addition of CMC optimized at 4.0 g/L showed a 3-fold increase in nZVI/FeS reactivity.

Degradation of chlorinated hydrocarbons by nanoscale zero-valent Iron treated with bisulfide and stabilized with carboxymethylcellulose

253rd National Meeting (2017)

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