Remediation of trichloroethylene by xanthan gum-coated microscale zero valent iron (XG-mZVI) in groundwater: Effects of geochemical constituents

Abstract

Xanthan gum-coated microscale zero valent iron (XG-mZVI) is potentially an inexpensive and effective material to promote the degradation of environmental contaminants. The effects of geochemical constituents (humic acid (HA), Ca2+/Mg2+-HCO3-,Na+-Cl-) on trichloroethylene (TCE) removal using XG-mZVI were investigated using batch experiments to evaluate the potential performance of XG-mZVI in field treatments. TCE was removed from groundwater by adsorption and chemical reduction. In the co-presence of geochemical constituents, TCE adsorption was not significantly impacted, while its reduction rate was increased by the presence of HA (5–20mgL−1), inhibited with increasing Ca(HCO3)2 and Mg(HCO3)2 concentrations (0.4–2mM) and unaffected by NaCl in the range of 10–100mM. The promotional effect of HA on TCE reduction was primarily due to the Fe-humate complexes in solution that delayed the formation of passivated precipitates. However, the presence of Ca(HCO3)2 and Mg(HCO3)2 exerted an opposite effect on TCE reduction by facilitating the formation of passivated precipitates, such as green iron rust. These findings provide insight into the impact mechanism of XG-mZVI reactivity by organic and inorganic geochemical constituents with particular implications for the XG-mZVI degradation of TCE in real groundwater.