Bioconversion of high-concentration chelatedCdtonano-CdSphotocatalyst by sulfate-reducing bacteria

BACKGROUND Chelated heavy metals have received wide attention due to their adverse effects and difficulty in removal. Sulfate-reducing bacteria (SRB) inducing heavy metals to produce metal sulfide precipitation is an attractive bioremediation technology. It not only reduces heavy metal pollution but also transforms metal contaminants into value-added products. RESULTS The stable ethylenediaminetetraacetic acid (EDTA)-Cd was effectively removed and converted to CdS nanoparticles by SRB. The SRB could resist high concentrations of EDTA-Cd up to 2.5 mmol L-1, while no growth was observed at 1.0 mmol L(-1)of free cadmium ions. The bio-removal efficiencies of EDTA-Cd at initial concentrations of 0.5, 1.0, 1.5, 2.0 and 2.5 mmol L(-1)were 100%, 100%, 95.89%, 67.63% and 26.66%, respectively. Meanwhile, the reduction efficiencies of sulfate by SRB were 45.6% to 24.9%. The products were cadmium sulfide nanoparticles with a mean particle size of 40-80 nm, which were confirmed by X-ray diffraction and scanning electron microscopy analyses. Furthermore, the cadmium sulfide product exhibited a good photocatalytic performance, and the removal efficiency of rhodamine B (RhB) reached 97% within 2 h. CONCLUSION This study demonstrated that EDTA-Cd could be effectively removed by SRB and recovered in the form of high-value cadmium sulfide photocatalyst. The proposed strategy may provide a new solution for the recycling of chelated heavy metal ions. (c) 2020 Society of Chemical Industry