The serious contamination of cadmium (Cd) in sediments has become an urgent environmental problem. Quinones mediated dissimilatory iron and manganese reduction widely occurs in sediments, this process may enhance Cd immobilization by promoting production of secondary minerals. Nevertheless, the enhancing effect of Cd immobilization is still poorly understood. Here, 9,10-anthraquinone-2,6-disulfonic acid (AQDS) was used to facilitate the microbial reduction of iron and manganese oxides by Geobacter metallireducens GS-15, and its effects on Cd species was investigated. Compared to goethite (FeOOH), microorganisms preferentially reduced birnessite (MnO 2 ) due to more dramatic interfacial electron transfer between birnessite and AQDS. AQDS thus significantly enhanced microbial reduction of iron and manganese coexisted minerals as well as Cd 2+ immobilization. After 80 days, an impressive 83% of reducible-Cd appeared in the FeOOH–MnO 2 -AQDS group, demonstrating the most effective Cd immobilization. Furthermore, XANES results suggested that AQDS promoted the increase of vivianite-Cd in secondary minerals in MnO 2 -AQDS and FeOOH–MnO 2 -AQDS groups. Based on the structural equation model, HCl-extracted Fe(II) indirectly affected the increase of reducible-Cd mainly through vivianite-Cd. The AQDS enhancement on microbial reduction of iron and manganese oxides promotes the recrystallization of secondary minerals and the immobilization of Cd, offering a promising strategy for the remediation of Cd-contaminated sediments.
Gongting Wang,Wenqing Luo,Zedong Teng,Xin Zhao,Yuxin Cheng,Yanzhong Wang,Bin Liu,Mengnan Lu,Min Li
Cadmium (Cd) pollution in sediments has become an urgent environmental problem. Humus mediated dissimilatory iron reduction and phosphorus solubilizing bacteria (PSB) were widely used for Cd immobilization. Here, we utilized humic acid (HA) and fulvic acid (FA) to promote the efficiency of iron reduction by Geobacter metallireducens GS-15 to immobilize Cd with the involvement of PSB. The results showed that both HA and FA can facilitate the reduction of Fe(III) and the release of P in ferric phosphate minerals, and then the immobilization of Cd. The immobilization of dissolved Cd 2 + in HA, FA and BCK groups were 76.25 %, 65.25 % and 63.58 %, respectively. HA and FA promoted the growth of PSB and the secretion of acetic acid, high concentration of acetic acid provided sufficient nutrients for the growth of iron-reducing bacteria. Thereby, high concentration of Fe(II) facilitated the recrystallization, which effectively immobilized Cd 2+ . Compared to the CK group, the HA and the FA groups increased the proportion of exchanged Cd converted to combined Cd in secondary minerals by 25.32 % and 19.16 %, respectively. The findings reveal that enhanced effect of HA on microbial iron reduction coupled with PSB can facilitate the immobilization of Cd, providing a promising strategy for the remediation of Cd-contaminated sediments.
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