Effects Of Bacillus And Citric Acid Enhanced Phytoremediation In Pb,Zn And Cd Contaminated Soil

Phytoremediation is considered as the most potential and clean soil heavy metal pollution remediation technology due to its low cost,no secondary pollution,environmental friendliness and other advantages.But it also has some restrictions in the practical application because the plant biomass is small and the absorption of heavy metals is not as good as expected.Therefore,the application of chelating agents and microbial enhanced phytoremediation has become one of the hot spots of soil heavy metal remediation,it could theoretically be able to have better results than individual chelator or microbial enhanced phytoremediation.In this paper,the effects of different concentration Bacillus subtilis and citric acid treatments enhanced phytoremediation were studied by using Indian mustard in Pb,Zn and Cd contaminated soil.In this study,the effects of chelating agents and microorganisms on the enrichment of heavy metals in Cd,Pb and Zn contaminated soil were studied,and proposed the appropriate amount of chelating agent and microbial combination.It also provided experimental guidance and technical support for the phytoremediation of heavy metals enhanced by the combination of chelating agents and microbes.The main results are as follows:(1)Bacillus and citric acid promoted the growth of Brassica juncea in Cd,Pb and Zn contaminated soil,and significantly increased the contents of Pb,Zn and Cd in plants,the BCF and the removal rate of heavy metals of Brassica juncea.The sorting of the heavy metal increase concentration and the removal rate in three kinds of heavy metals in Indian mustard were Cd>Pb>Zn,while the sorting of BCF was Cd>Zn>Pb.The treatment of 109 cfu/kg Bacillus megaterium and 30 mmol/kg citric acid showed the best at the removal rate of Zn,Pb and Cd in all treatments,and then it was determined as the best treatment.However,the combined treatment of Bacillus cereus and citric acid is better than the combination treatment of Bacillus megaterium and citric acid in promoting plant growth,the extraction of heavy metals,the BCF and theremoval rate.(2)The morphological changes of heavy metals in the soil were mainly showed at the increase of the acidic fraction and the decrease of the residual fraction after the addition of Bacillus suspension and citric acid.The changes of oxidizable and residual fraction varied of heavy metal species,microbial species and the addition amounts.The application of Bacillus subtilis and citric acid significantly reduced soil pH and increased the contents of tartaric acid and citric acid in the rhizosphere soil,which might be the reason for the change of heavy metal in soil.(3)The activity of soil urease,alkaline phosphatase and catalase increased significantly after adding Bacillus suspension and citric acid conditioner in the soil.It indicated that Bacillus suspension and citric acid could increase soil enzyme activities,improve soil quality,and which is conducive to the promotion of plant growth.(4)The addition of Bacillus and citric acid affected the population and quantity of microbes in the soil.It mainly showed at a significant decrease of Actinomycetes and a significant increase of Proteobacteria.The combined remediation of Bacillus and citric acid had a certain selectivity to rhizosphere microorganisms.The mixed treatment of Bacillus megaterium and citric acid had the most significant effect on the diversity of microbial populations,which caused the disappearance of the population which was detrimental to the activation of heavy metals in the soil,and the increase of microbial populations was favorable for plant growth and heavy metal activation.The results showed that citric acid could cause the formation of special populations of soil microbes and lead to the generation of stable genetic phenomena,and the difference of soil microbial population diversity caused by citric acid was more significant compared with the treatment of adding Bacillus suspension.