Remediation Of Chromium Contaminated Soil By Zero-valent Iron Loaded On Black Carbon Coupled To Chromium Reducing Bacteria

With the development of social modernization,soil pollution has become increasingly prominent in China.Chromium has high mobility which caused serious harm to the environment and human health.Microorganisms can use their own active substances to adsorb or redox heavy metal pollutants.Zero-valent iron is a strong reductant with strong surface reactivity and relatively low price.Using biochar as carrier can not only overcome the shortcomings of free microorganisms vulnerable to environmental factors and weak biological stability,but also overcome the disadvantage of zero-valent iron oxidation and poor dispersion.In this paper,zero-valent iron loaded on black carbon and chromium reducing bacteria were used to form a coupling system,and the three were mutually reinforcing to remediate chromium-contaminated soil.Black carbon（BC）and zero-valent iron loaded on black carbon（BF）were prepared from corn straw by direct pyrolysis and carbothermal reduction.The effects of BC and BF on the stabilization and morphological changes of chromium in chromium-contaminated soils were investigated through soil stabilization culture experiments.The results showed that soil pH increased with BC addition,while decreased with BF.After 30 days of treatment,the removal efficiencies of TCLP-Cr_totalotal and TCLP-Cr（VI）by BF were close to100%.Morphological analysis showed that BF was superior to BC in stabilization and transformation of chromium in contaminated soil.Bacillus cereus were screened and purified as chromium reducing bacteria.The removal of Cr（VI）by zero-valent iron loaded on black carbon coupled chromium reducing bacteria showed that high concentration of chromium could inhibit the growth of bacteria.The chromium-reducing bacteria immobilized by BF were highly concentrated,and the stability and toxicity of microorganisms were enhanced.It is most suitable for the growth of the strain and with a high removal efficiency when the initial pH is 7.It is shown that microorganisms can reduce Fe（III）to Fe（II）,which enhancing the effect of removing Cr（VI）in the coupling system.After 30 days of soil remediation,zero-valent iron loaded on black carbon and chromium reducing bacteria reduced the acid-soluble fractions by 23.58%,increased the reducible and oxidizable fractions by 9.09%and 10.16%,and increased the residual fractions by 4.33%.The adsorption,reduction and co-precipitation of soil chromium by BF-A were better than treatments alone.High-throughput sequencing technique was used to analyze the microbial community structure of each group for 7 and 30 days.The results showed that the coupling system increased the species richness of microbial community and enriched the diversity of microbial community.By analyzing the changes of microbial community structure in chromium contaminated soil,it can be showed that Bacillus is the dominant bacteria in chromium environment as well as the composition and structure of bacterial community changed in each treatment group.