Remediation Of Heavy Metals-Contaminated Soil By Combination Of Soil Washing And Sulfate-Reducing Bacteria

In this study,the effects of sulfate-reducing bacteria（SRB）including Shewanella JN01,Clostridium ZG01 and their mixture on the passivation of heavy metals（Cd,Pb,Cu and Zn）in alkaline and acidic soils before and after washing were investigated through soil incubation experiment.The uptake characteristics of heavy metals by Chinese cabbage planted in passivated soil were also discussed.The effects of SRB treatments on soil physicochemical properties and microbial community structure were also explored.The results were shown as follows:（1）SRB treatment increased soil pH and passivation efficiencies of available heavy metals to different extent,and decreased the contents of SO₄^2-and exchangeable heavy metals,resulting in the increase in percentage of stable fractions heavy metals in alkaline and acidic soils.The passivation efficiencies of available heavy metals in the alkaline soils that treated with SRB were greater than 80%,while those in the acidic soils were less than 40%.SRB treatment had a negative effect on microbial richness and slightly increased microbial diversity in alkaline and acidic soils.Clostridium sp.was more viable than Shewanella sp in the washed soils.（2）SRB had a good passivation effect on heavy metal complexes in MC-washed soils.The passivation mechanism was mainly through the use of SRB growth metabolites to first break the heavy metal complexes and then form metal sulfide precipitates.The passivation efficiencies of available heavy metals in MC-washed alkaline soil（13.07%-64.95%）was higher than that in MC-washed acidic soil（0.30%-12.29%）.SRB were able to decrease SO₄^2-content,raise pH,and promote the conversion of soluble heavy metals to the stable fractions,effectively decreasing bioavailability of heavy metals in the MC-washed soil.SRB treatment had a greater effect on the physicochemical properties of the MC-washed acidic soil than the MC-washed alkaline soil,and increased the microbial diversity in the MC-washed alkaline soil.（3）Chinese cabbage could grow in the MC-washed alkaline soil after treatment with SRB,which was unable to grow in the MC-washed acidic soil after treatment with SRB.The SRB treatments significantly increased the SO₄^2-content,and Clostridium sp.treatment had the lowest concentration of heavy metals in aboveground of Chinese cabbage and its highest biomass.After planting Chinese cabbage,SRB treatment had a negative effect on microbial richness,but increased the diversity of microbial genera and biomass of Chinese cabbage in the MC-washed alkaline soil.