Effect of cobalamin(III) reduction by sulfide on the reductive dechlorination of tetrachloroethene

The objective of this study was to identify the role of sulfide (HS ^-) on the reduction of cobalamin(III) as an electron-transfer mediator in the reductive dechlorination of tetrachloroethene (PCE). HS ^- has a potential to reduce cobalamin(III) (Co(III)) to cobalamin(II) (Co(II)) and cobalamin(I) (Co(I)) in homogeneous (HS ^--Co(III)) and heterogeneous (FeS-Co(III)) systems at pH 8.3. In the HS ^--Co(III) and FeS-Co(III) systems, Co(II) was detected at 410 nm, and Co(I) was detected at 390 nm and 290 nm, respectively. Approximately 80% of PCE was degraded by FeS-Co(III) suspension, while only 20% of PCE was degraded in Co(III)-Gr(SO ₄) suspensions. No significance PCE degradation by FeS and Fe(II)-treated FeS suspensions in 12 hrs at pH 8.3. No significant PCE degradation was observed in HS ^--Co(III) solution in 250 hrs under the same experimental condition. HS ^- concentration decreased in FeS-Co(III) suspensions due to reduction of Co(III) to Co(II) and Co(I). Significant differences in binding energies of Fe(II) and Fe(III) were observed on FeS surfaces due to reduction of Co(III) to Co(II) by Fe-FeS in FeS-Co(III) suspensions. Co(II) was also detected in Gr(SO ₄) suspensions but no further reduction of Co(II) to Co(I) was observed. Formation of Co(I) in FeS-Co(III) suspensions significantly enhances reductive dechlorination of PCE. The results revealed that the dechlorination kinetics of PCE was significantly influenced by the reduced species of cobalamin(III). This study provides basic knowledge on the interaction between HS ^- and biomimetic materials on the reductive dechlorination of chlorinated organic compounds at enhanced natural attenuation processes in soil and groundwater.