Study On The Remediation Of Lead Contaminated Soil By Immobilized Microorganism

Soil contamination has become increasingly prominent,especially the heavy metal pollution with the accelerating process of industrialization.Therefore,the heavy metal pollution has attracted extensive attention of researchers.Due to its advantages of cleanliness,economy and safety,microorganism remediation has become a research hotspot for heavy metal contaminated soil.However,the dissociated microorganisms remediation has disadvantages such as low microbial activity,low density and poor adaptability to heavy polluted soil environment.In this study,phosphate solubilizing bacteria 20-3,resistant to lead and highly capable of phosphorus solubility,was isolated from the soil contaminated.Choosing biochar of wheat straw,corn cobs,saw dust and activated sludge,immobilized microorganisms were conducted.The best immobilized carrier was selected according to the adsorption capacity of the immobilized microorganisms prepared with different biochar as the carrier.The effects of immobilized microorganisms on soil remediation,soil enzyme activity and soil physical and chemical properties were studied by pot experiment.The remediation mechanism of lead contaminated soil by immobilized microorganisms was studied.The strain 20-3 was identified as Acinetobacter calcoaceticus by morphological analysis and16S rDNA identification.The phosphorus solubility of strain 20-3 reached the maximum value of 531.28 mg/L on the eighth day,and the medium pH was 5.01.There was a significant negative correlation between phosphate solubilization capacity and pH(r=-0.994,P<0.01).It was found that 20-3 showed strong resistance to penicillin and chloramphenicol.The yield,ash content and pH of biochar were determin.The surface functional groups,surface morphology and crystal structure of biochar were characterized by FTIR,XRD and SEM.The results showed that the yield showed a downward trend,ash content increased gradually,and pH value increased gradually.Meanwhile,the pH range of biochar was7.27¹0.07,which was generally alkaline.FTIR analysis showed that the surface functional groups of wheat straw biochar were more abundant and the degree of aromatization increased with the increase of temperature.XRD analysis showed that the contents of Si,SiO₂ and Al₂O₃gradually increase,namely the ash content of biochar gradually increase with increasing of pyrolysis temperature.SEM analysis showed that,with increasing of pyrolysis temperature,the micropores of wheat straw biochar developed gradually,the pore wall became thinner and the pore structure became more developed.The immobilization conditions such as time,biochar content,solution pH and temperature were optimized through the single factor experiment.Meanwhile,the effects of heavy metal concentration and adsorption time on the adsorption Pb²⁺of IBWS700 were studied.The results showed that IBWS700 had the highest equilibrium adsorption capacity of Pb²⁺,reaching 89.39 mg/g.IBWS700 best preparation conditions as follows:biochar content is 0.2g,pH of 8,the temperature of 30?,time of 18 h,,under the condition of the preparation of IBWS700 to Pb²⁺equilibrium adsorption quantity can reach 94.71 mg/g.The adsorption of Pb²⁺by IBWS700 conforms to the quasi-second-order kinetic model of adsorption kinetics.the adsorption process was controlled by both external diffusion and internal diffusion through the particle internal diffusion equation.IBWS700 adsorption of Pb²⁺conforms to the Langumir isotherm model.Immobilized microorganism could significantly increase soil enzyme activity,such as urease,catalase,sucrase,cellulase and alkaline phosphatase.It showed that immobilized microorganism can significantly improve the soil microbial community structure and soil environment.At the same time,the increase of the heavy metals concentration in general would restrain soil enzyme activity.Adding immobilized microorganism to significantly improve the content of the soil available phosphorus,available potassium,organic matter and soil cation exchange capacity,improve the level of soil fertility,improve soil environment.The mechanism,repairing lead contaminated soil by IBWS700,was found that it mainly includes two parts:adsorption and precipitation.The adsorption was mainly through the adsorption of biochar and microorganisms to lead.The precipitation effect is mainly the soluble phosphate ions decomposed by the dissolving effect of phosphorus bacteria on the insoluble phosphate in the soil,and the phosphate ions react with the lead in the soil to generate lead phosphate ore and other substances.So that to reduce the content of soluble lead in the soil and repair the lead contaminated soil.