Bisulfite reduction of soil iron for the reductive degradation of trichloroethylene

Abstract

This study explored the potential reactivities of various reductants in inducing subsurface TCE degradation in natural soils. It was found that bisulfite (HSO₃^-) exhibited the ability to induce reduction in soil iron minerals, and increase the degradation of TCE in the soil slurry system; however, no TCE degradation occurred in the aqueous system. The role of TCE degradation by soil constituents, such as major soil mineral elements, Fe and humic acid (HA) on HSO₃^-, was examined in aqueous phase. It was seen that by themselves, the presence of Fe³⁺, HA, Fe₂O₃, FeOOH, and Fe₃O₄ did not result in substantial TCE removals. However, the presence of HSO₃^- can significantly induce iron reduction, producing a reducing condition that can result in complete TCE degradation. Furthermore, the reductive pathway was identified as the dominant degradation route via electron scavenging with periodate ion. To demonstrate the applicability of HSO₃^- reduction enhancement, a HSO₃^-/TCE mixed solution was flushed through a soil column, with gradually increased HSO₃^- concentrations, at a fixed flow rate, and also with varied flushing rates at a fixed HSO₃^- concentration. Based on our study, a 10 mM HSO₃^- solution may be effective for some environmental sites; however, each site requires specific evaluation based on contaminant concentrations and subsurface conditions.

Keywords: Bisulfite; Chlorinated solvent; In situ chemical reduction (ISCR); Soil column; Soil iron minerals; Trichloroethylene (TCE).