Column study of Cd(II) removal and longevity by nitrate-mediated zero-valent iron with mixed anaerobic microorganisms

In this study, hydrogen-autotrophic microorganisms and zero-valent iron (Fe-0) were filled into columns to investigate hydrogenotrophic denitrification effect on cadmium (Cd(II)) removal and column life-span with sand, microorgan-isms, Fe-0 and bio-Fe-0 columns as controls. In terms of the experiment results, the nitrate-mediated bio-Fe-0 column showed a slow Cd(II) migration rate of 0.04 cm/PV, while the values in the bio-Fe-0 and Fe-0 columns were 0.06 cm/ PV and 0.14 cm/PV respectively, indicating much higher Cd(II) removal efficiency and longer service life of the nitrate-mediated bio-Fe-0 column. The XRD and SEM-EDX results implied that this improvement was attributed to hydrogenotrophic denitrification that caused more serious iron corrosion and larger amount of secondary mineral gen-eration (e.g., green rust, lepidocrocite and goethite). These active minerals provided more reaction sites for Cd(II) ad-sorption and further immobilization. In addition, the decrease of Cd(II) migration front and the increase of removal capacity along the bio-Fe-0 column mediated by nitrate presented an uneven distribution in reactive zone. The latter half part was identified to be a more active region for Cd(II) immobilization. The above results indicate that the intro-duction of nitrate and microorganisms will improve the performance of iron-based permeable reactive barriers for the remediation of Cd(II)-containing groundwater.

Automated summary

This study investigated the effect of hydrogenotrophic denitrification on cadmium (Cd(II)) removal and column life-span using hydrogen-autotrophic microorganisms and zero-valent iron (Fe-0) filled columns. The results showed that the nitrate-mediated bio-Fe-0 column had a higher Cd(II) removal efficiency and longer service life compared to the bio-Fe-0 and Fe-0 columns. This improvement was attributed to hydrogenotrophic denitrification, which caused more iron corrosion and more secondary mineral generation, providing more reaction sites for Cd(II) adsorption and immobilization. The distribution of reactive zone along the bio-Fe-0 column mediated by nitrate was found to be uneven, with the latter half part identified as a more active region for Cd(II) immobilization.