A new process for simultaneous nitrogen and cadmium(Cd(II)) removal using iron-reducing bacterial immobilization system

The effect of two iron-reducing bacteria on simultaneous denitrification and Cd(II) removal process were researched in the bacterial immobilized reactors. Furthermore, effects of HRT (6 h, 8 h and 10 h), influent Fe(III) concentration (10 mg/L, 30 mg/L and 50 mg/L) and influent Cd(II) concentration (10 mg/L, 20 mg/L and 30 mg/L) on simultaneously removal of nitrate and Cd(II) were investigated during the operation of the reactors. Experimental results indicated that the highest nitrate removal efficiency of 100% (1.31 mg/L/h) and Cd(II) removal efficiency of 95.09% (0.79 mg/L/h) were obtained under the conditions of HRT of 12 h, influnt Fe(III) concentration of 50 mg/L and the influent Cd(II) concentration of 10 mg/L in reactor added with Fe₃O₄ powder. Moreover, gas chromatography (GC) and fluorescence spectroscopy experiments showed that nitrogen was the final product of bacterial denitrification process, and EPS (protein) was produced in bacterial metabolism. Finally, high-throughput sequencing results demonstrated that Cupriavidus sp. CC1 played a primarily role in the process of nitrate and Cd(II) removal. This study lays the foundation for practical application of wastewater treatment.