The Remediation Of Chromium Contaminated Soil By The Combinantion Of Zero Valent Iron And Microorganisms

Recnetly,the unreasonable discharge of chromium-containing wastewater and the percolation of chromium-containing slag and sludge has caused serious chromium pollution in surrounding soil.Zero valent iron(Fe~0) has been widely used in the remediation of Cr contaminated soil on account of its advantages of small particle size,large specific surface area and strong reducing power.However,the easy passivation and deactivation of Fe~0 in remediating chromium-contaminated soil limited its application.Considering the release of hydrogen by Fe~0 under anoxic condition,this study try to introduce microorganisms into Fe~0 to enhance its remediation through the improvement of iron corrosion by biological effects,and investigate the mechanism and control method of reducing the chromium transfer from soil to plant by the biotic Fe~0 system.The experimental results of the remediation by the biotic Fe~0 system showed that more active iron minerals with high specific surface area and reactivity,such as green rust,lepidocrocite and magnetite,were produced in the biotic Fe~0 system,which provided sufficient amount of reactive sites for the removal of Cr(?).Thus,the biotic Fe~0 system has better removal efficiency of Cr(?)in soil than the single system.The Cr(?)removal efficiency in biotic Fe~0 system was 85.6%,which was 2.9 times and 2.2 times higher than that of abiotic Fe~0 system and microbial system,respectively.After remediated by the biotic Fe~0 system,57.0% of total chromium was stabilized in soil by converting the easily available total chromium species into less available total chromium species,which greatly reduced the biological and environmental hazards of chromium in the soil.In addition,the low pH and increasing Fe~0 dosage were beneficial to the remediation of chromium-contaminated soil.Batch experiments were conducted to investigate the influence of soil common environmental factors on the removal of chromium in the biotic Fe~0 system.The experimental results showed that additional substrates such as sodium acetate and humic acid were found to be effective for the biotic Fe~0 system to remove Cr(?)since microorganisms were able to gain extra reducing capacity from substrates.However,the effects of oxygen,nitrate and sulfate on the remediation of Cr contaminated soil were different.Oxygen and nitrate acted as electron acceptor were easy to compete with Cr(?)for electrons released by Fe~0,resulting in a drop of Cr(?)removal in the biotic Fe~0 system.Sulfate can compete with Cr(?)for electrons released by Fe~0 as well.But microorganisms induced the production of iron rective menirals such as tetragonal pyrite in Fe~0 surface during the biological reduction of sulfate,which enhanced the reduction of Cr(?)in the biotic Fe~0 system.Pot experiments demonstrated that the biotic Fe~0 system can effectively reduce the toxicity of chromium to swamp cabbage.After remediation by the biotic Fe~0 system,the absorption of chromium by swamp cabbage was reduced by 69.1%,which was two times of that of the abiotic Fe~0 system,indicating the bioavailability of chromium was significantly reduced.Moreover,since Cr(?)was effectively removed,and many Fe(?) existed in a form of iron active minerals in the biotic Fe~0 system,the absorption of iron by swamp cabbage in the biotic Fe~0 system was lower than that in the abiotic Fe~0 system,and almost return to an uncontaminated level.In summary,the biotic Fe~0 system of Fe~0 and microorganisms can effectively enhance the removal of Cr(?)in soil and reduce its migration and bioavailability,which is expected to become a feasible technology for the remediation of chromium-contaminated soil.