Role of Sulfate-Reducing Bacteria in the Removal of Hexavalent Chromium by Biosynthetic Iron Sulfides (FeS1+x)

Abstract

The reduction of Cr(VI) by biosynthesis iron sulfides (FeS1+x) under anoxic conditions has been studied extensively. However, the role of sulfate-reducing bacteria (SRB) when FeS1+x containing SRB removes contaminants during in situ remediation still needs further study. The secondary kinetic constant of biosynthetic FeS1+x with the presence of SRB (called BS-FeS1+x) was 1.72 times that of FeS1+x with the absence of SRB (called BNS-FeS1+x) under FeS1+x:Cr(VI) molar ratio = 10:1, indicating that SRB had a promoting effect on the removal of Cr(VI). Additionally, XPS showed that 5.7% of Cr(VI) remained in the solid phase in the BS-FeS1+x system, indicating BS-FeS1+x could not only remove Cr(VI) by reduction but also by adsorption. Meanwhile, the Cr(VI) removal efficiency of BS-FeS1+x was 100% under anoxic conditions with FeS1+x:Cr(VI) molar ratio = 1:1, which was higher than BNS-SRB (93.4%). SRB could enhance the Cr(VI) removal efficiency, which was possibly due to the constant release of S(-II) and the improvement of the stability and dispersion and the buffering effect. This discovery provided an inspiring idea of the application of biosynthetic iron sulfides to in situ remediation.