Constructing the Active Surface Soil Layer with Zvi-Biochar Amendment for Simultaneous Immobilization of as and Zn in Both Contaminated Soil and Groundwater: Continuous Versus Intermittent Infiltration Mode

Abstract

Zero valent iron-biochar composite (ZVI-BC) was applied to construct an active surface soil layer for the simultaneous remediation of As-Zn contaminated soil and groundwater, focusing on the influence of the infiltration mode of pumped-up groundwater into soil. The active surface soil treated more contaminated groundwater for As than that for Zn under two infiltration modes. The As(V) in the active soil layer was reduced to As(III) accompanied by Fe(0) oxidation and transformed into As(V)/As(III)-Fe coprecipitates. The intermittent infiltration mode was enriched by the Sphingomonas with arsenate reductase genes, which promoted more reduction and coprecipitation of As(V). The Mn oxide determined the sorption of Zn in the active soil layer, where the Hyphomicrobium, one type of manganese oxidizing bacteria, was much higher under the continuous infiltration mode, which accounted for the more Zn immobilization. After the remediation, both As and Zn immobilized in the active surface soil showed high stability, with the downward migration rate of only 0.21-0.36 cm year -1 within 20-year rainfall exposure. Our findings indicate that this active surface soil layer is applicable for simultaneous immobilization of As and Zn in both contaminated soil and groundwater, and the groundwater intermittent infiltration could be a better option.

Keywords: Active soil layer, Groundwater, Heavy Metals, Immobilization, soil