Chemical And Microbial Remediation Of Heavy Metal Contaminated-soils And It's Follow Up Effects On Plants

Soil heavy metal pollution is one of the important environmental problems in the world agriculture sustainable development.In this paper two types of soil heavy metal pollution has been studied.Chemical remediation method is adopted,study the factors of leaching agents,soil particle size,temperature,leaching time,leaching solution pH on the heavy metals removal rate,and the effect of fermentation liquid on the heavy metal leaching rate was also studied for the first time.By index analysis of soil enzyme activity,plant biomass to evaluate the effects of chemical leaching on soil physicochemical,properties and plant growth.The recovery function of soil was studied to provide a theoretical basis for the application of chemical leaching remediation technology.The main results are as follows.Using the method of oscillation extraction,Compared artificial chelators,organic acid and inorganic acid on the heavy metals leaching rate.The result showed that when the leaching solution pH=2,soil and water ratio= 10:1,25? shaker oscillation for 24 hours,10(?)mmol L-1 EDDS leaching rate of Cu reached 80.2%,10 mmol L-1 EDTA leaching rate of Pb reached 48.2%,0.1 mol L-1 critic acid leaching rate of Zn reached 35.1%.Analysis the forms of heavy metal in soil before and after leaching,the results showed that,soil and water ratio 10:1,after 0.1 mol·L-1 critic acid leaching,total copper content decreased by 35.3%.The oxidation state of iron and manganese,the residue state,the organic combination and the carbonate bound state were decreased by 22.9%,9.8%,3.9%and 1.1%respectively,but the ion exchange state increased by 2.5%.after 10 mmol·L-1 Na2EDTA leaching,total copper content decreased by 64.2%,The oxidation state of iron and manganese,the residue state,the organic combination,the carbonate bound state and the ion exchange state decreased by 34.2%,17.7%,4.7%,3.9%and 3.8%.after 10 mmol·L-1 Na2EDTA leaching,total copper content decreased by 78.1%,the carbonate bound state and the ion exchange state decreased by 40.8%,25.1%,4.8%,3.7%and 3.6%.It is suggested that EDDS has the best extraction effect for copper contaminated soil,EDDS and EDTA are mainly dissolved in the residual state and the iron manganese oxide state,while the citric acid is mainly dissolved in the iron manganese oxide copper.The effect of compound addition of SDS on the heavy metals leaching rate of Na2EDTA was compared.The result showed that when soil and water ratio 10:1,SDS in low concentration,SDS have synergistic effect on the heavy metals leaching rate of Na2EDTA,when the concentration of SDS at 10 mmol·L-1,the leaching rate of Cu increased from 66.5%to 83.9%,and Pb increased from 49.3%to 74.3%,and Zn increased from 44.9%to 58.1%.With the increase of SDS concentration,SDS has antagonistic effect on the heavy metals leaching rate of Na2EDTA.The effect of 45 kinds fungus fermentation liquor on heavy metals leaching rate was compared.The results showed that Fermentation broth of fungal Zjj2 and fungal K11 has good effect on the leaching rate of Cu,reached 22.1%and 17.4%respectively.Fermentation broth of fungal Zj6 and fungal Zj27 leaching rate of Zn reached 25.4%and 29.8%respectively.Fermentation broth of fungus X16 has better extraction rate of Pb,the leaching rate of Pb reached 8.3%.Fermentation broth of fungus Zj15 have good leaching rate of Cu,Pb and Zn,reached 11.9%,7.1%and 28.5%respectively.By using the method of column washing,using Na2EDTA as the eluent,the results showed that in the same quality of Na2EDTA,different volume ratio have different effect on heavy metal leaching rate.With the increase of the volume,heavy metal leaching rate is on the increase.when soil and water ratio was 20:1,Na2EDTA on heavy metal leaching rate is 39.2%,the soil and water ratio reached 40:1,Na2EDTA on heavy metal leaching rate reached maximum,44.3%.Using Na2EDTA/water as eluent,the results showed that water can also leaching large amount of heavy metals.it means that after Na2EDTA column washing,Soil contained large amount free state heavy metal.Precipitation of heavy metals in the leachate by Na2S and recycling leaching liquid was studied.The results showed that,when Na2S concentration reached 50 mmol·L-1,The contents of Cu,Pb and Zn were decreased by 96.8%,80.5%and 90.9%respectively.The eluent again leaching,when soil and water ratio was 14:1,the leaching rate of Cu reached equilibrium,at this time,the leaching rate of Cu was 23.4%.The eluent will influence physicochemical property of soil,thus undermining the normal function of the soil.Compared with no leaching of soil,after 10 mmol L-1 Na2EDTA leaching soil urease,catalase and transforming enzyme were decreased by 32.7%,20.8%and 16.6%respectively.Soil actinomycetes,bacteria and fungi were also decreased by 50%,35.1%and 57.5%respectively.The growth status of pea and ryegrass was compared and analyzed in different eluent leaching soil.The results showed that after Na2EDTA leaching peas dry weight and plant height were decreased by 43.7%,25.5%,ryegrass dry weight and plant height were decreased by 30.9%and 13.4%respectively.The improvement effect of earthworm fertilizer,soil nutrient and soil leaching solution on soil was studied.The results showed that,After adding 5%nutrient soil,Pea plant height and biomass were the highest.After adding 5%earthworm fertilizer,Ryegrass plant height and biomass were the highest.