Interaction between abiotic and biotic reactions on reductive dechlorination of chlorinated organics

Abstract

Roles of geo-biochemical interactions on reductive degradation of chlorinated organics were investigated in this Ph. D. dissertation to provide better understanding of contaminant fate in sub-surface environment. Especially, effect of interactions on the degradation of chlorinated organics was investigated using nano-sized zero-valent iron (nZVI), reactive iron-bearing soil minerals (IBSMs), iron reducing bacteria (IRB), and electron transfer mediators (ETMs). The reductive degradation of 1,1,1-trichloethane (1,1,1-TCA) by interaction of nZVI and magnetite (FeII1III2O4) was investigated as the nZVI/IBSMs/contaminant interaction. A remarkable reductive degradation of 1,1,1-TCA (0.289 hr-1) was observed in nZVI (0.01 g/24 mL) suspension in 5 h, while the degradation was not significant in nZVI (0.01 g)/magnetite (0.5 g) suspension in 80 h. This indicated that magnetite can inhibit the reactivity of nZVI for 1,1,1-TCA degradation. No significant difference in the inhibition of nZVI reactivity by magnetite was observed in the pH range of 6 to 9. The result of X-ray photoelectron spectroscopy revealed that magnetite surface was reduced by an electron transfer from nZVI. The results showed that electrons from nZVI were used for the reduction of magnetite surface rather than the reduction of 1,1,1-TCA, leading to the decrease of 1,1,1-TCA degradation in this study. The effect of ETMs on biotransformation of lepidocrocite (γ-FeIIIOOH) by Shewanella putrefaciens CN32 (CN32) was investigated as the IRB/IBSMs/ETMs interaction. In PIPES buffer without phosphate, green rust ([Fe4IIFe2III(OH)12][A2- o 6H2O]) formation was observed with fast Fe(II) production rate (0.44-0.56 mM d-1) during the bioreduction of lepidocrocite with exogenous ETMs (quinones). In contrast, goethite (α-FeIIIOOH) formed at slow Fe(II) production rate (0.24-0.29 mM d-1) with endogenous ETMs (flavins). In the presence of phosphate, formation of green rust and vivianite (FeII3(PO4)2o8H2O) was observe...