Synergistic removal of decabromodiphenyl ether by sulfurized zero-valent iron coupling with microbacterium in the presence of heavy metals: Biochemical degradation process and mechanism

Microorganisms and sulfurized nano zero-valent iron (S-nZVI) were widely used for the remediation of con-taminants in e-waste sites. However, it is elusive whether microorganisms and S-nZVI have a synergistic effect in the removal of heavy metals (HMs) and organic complex pollutants. In this work, the removal performance and mechanisms of HMs-decabromodiphenyl ether combined pollutants (HMs-BDE-209) in Microbacterium Y2 (MY2)/S-nZVI co-incubation system (MY2 @S-nZVI) was investigated. The results showed that simultaneous removal of HMs-BDE-209 by MY2 or S-nZVI alone was difficult. However, the synergistic removal of HMs-BDE-209 was observed in MY2 @S-nZVI system. Specially, Cr(VI) ions significantly inhibited the removal of BDE-209 by MY2 or S-nZVI. Nevertheless, the rapid immobilization of Cr(VI) ions with S-nZVI not only inhibited the generation of ROS induced by S-nZVI, but also reduced the cytotoxicity of Cr(VI) toward MY2, leading to achieving synergistic BDE-209 removal in MY2 @S-nZVI/Cr(VI) system. Unexpectedly, the bio-degradation mainly accounted for 78.8-88.4% removal of BDE-209 in MY2 @S-nZVI system in the presence of Cr(VI). In contrast, the chemical degradation (95% of BDE-209 removal) dominated the degradation of BDE-209 in MY2 @S-nZVI/Ni(II) system due to the fact that Ni(II) could be quickly reduced by S-nZVI to form highly reactive Ni0/ Fe0 bimetals. The findings of this study are conducive to understanding the complicated mechanism in the remediation of HMs and organic combined pollutants by using microorganisms and S-nZVI hybrid technologies.