Fe-Mn oxide, microbe and biochar composite for remediation of Cd and As co-contaminated water and soil

The novel Fe-Mn oxide, microbe and biochar composite (FM-DB) synthesized by mixing Fe-Mn oxide, Cd(II)-resistant microbe inoculated biochar, was to simultaneously remediate the co-contamination of Cd and As. The adsorption behaviour and mechanism of Cd(II) and As(III) were studied by using adsorption experiments: the effects of the initial pH of solution, initial concentration of heavy metal, and addition order of Cd(II) and As(III) solutes on adsorption of FM-DB. The adsorption capacity for Cd and As was 59.27 and 84.73 mg·kg⁻¹, respectively. The results showed both antagonism and synergistic interaction behaviour of Cd(II) and As(III) adsorption. Synergistic effects was primarily governed by electrostatic interaction, biochemistry/specific adsorption and Cd-As co-precipitation. To investigate the FM-DB stabilization ability of heavy metal in two paddy soils, a 60-days soil incubation experiment was carried out. The pH of SY was significantly increased by 0.39–1.21 units with FM-DB addition, and the pH of FS remained relatively stable throughout the incubation periods. FM-DB significantly increased the DOC of the two soils by 40.57% and 18.16%, respectively. The BCR extraction was employed in this study to assess the transformation of unstable Cd and As into residual fractions. FM-DB significantly decreased the concentration of available Cd and As by 6.7%–20.4% and 8.7%–24.3%, respectively in SY, and by 4%–8% and 5.4%–25.2%, respectively in FS (p <.05). Thus, it is feasible to apply FM-DB to alleviate the Cd and As pollution in the environment.