Removal Of Hexavalent Chromium By Ramie Biochar Loaded With Zero-valent Iron Nanoparticles And Synergistic Microbial Mechanism

Nanometer zero-valent iron(nZ?)has large specific surface area with the advantages of strong reduction potential,but also has the disadvantages of easy agglomeration and passivation.The agglomeration problem of nZ? can be effectively overcome by biochar modification,which can enhance the removal of Cr(?)from the environment.We prepared ramie biochar-loaded nano-zero-valent iron(RBC-nZ?)composites to investigate their effects on the removal of Cr(?)from water and soil;a composite system of nZ? and chromium reducing bacteria(Cr RB)was constructed to remove Cr(?)from water,and the synergistic mechanism of nZ? + Cr RB was explored.The main results are as follows.(1)Study on the removal of Cr(?)from water by RBC-nZ?: The best removal of Cr(?)was achieved with ramie biochar prepared at a pyrolysis temperature of 600 ?,a particle size of < 150 ?m,and an iron to carbon ratio = 1:1.Thus,this treatment of biochar was termed as RBC600.The removal rate of Cr(?)by RBC600-nZ?(100 %)was much higher than that of RBC600(12.42 %)and nZ?(58.26 %).Among them,the Cr(?)removal efficiency was affected by the temperature,p H,material addition and the initial concentration of Cr(?)in the system.Combined with SEM,FTIR,XPS and XRD characterization analysis,the main mechanisms of Cr(?)removal by RBC600-nZ? were adsorption,reduction and co-precipitation,which accomplished by the loading of nZ? by RBC600 causing the increases in the specific surface area and adsorption active sites of the composite.(2)Study on the removal of Cr(?)from soil by RBC-nZ?: The addition of 1.0 %RBC600-nZ? was able to remove 86.55 % of Cr(?)from the soil after 15 days of remediation,which was much higher than that of RBC600(50.64 %)and nZ?(60.63 %).The exchangeable state in the restored soil was transformed into the Fe-Mn oxidation state as well as the residual state.The addition of RBC600-nZ? not only increased the p H,soluble organic carbon,but also the effective iron content,which increased the bind.This reduced the biotoxic concentration of Cr(?)and increased the abundance and diversity of indigenous bacteria.(3)Study of Cr(?)removal from water by nZ? and Cr RB: In the combined system of nZ? + Cr RB,the removal rate of Cr(?)reached 100 % within 3 days.Among them,the Cr(?)removal efficiency was influenced by the p H in the system,the amount of nZ? added,the amount of Cr RB inoculation,and the initial concentration of Cr(?).The characterization analysis,high-throughput sequencing and fluorescence quantitative PCR results showed that Cr RB and its derived extracellular polymer had the reduction potential and complexation for Cr(?),which promoted the dissolution of the passivated layer on the surface of nZ?,and enhanced the reaction efficiency of nZ? with Cr(?).In addition,the nZ? provided a favorable living environment for Cr RB and thus improved the community richness and diversity of Cr RB.