Study On The Removal Of Cu²⁺ In Water By Biochar-loaded Bacillus Subtilis In Dandelion Chinese Medicine Residue

In recent years,China’s industrialization and urbanization process has been accelerating,and heavy metal pollution has become one of the pollutants with greater impact in environmental pollution.Immobilized microbial technology has become a research hotspot for the treatment of heavy metal pollution due to its advantages of high treatment rate,simple operation,environmental safety and low cost.In this study,Dandelion Chinese medicine residue biochar prepared under three different conditions was obtained by comparing the physical and chemical properties,structural characterization,ability to fix microorganisms and ability to remove Cu²⁺of different biochars.The conditions for the immobilization of the fungicide were optimized by orthogonal experiments to prepare the optimal immobilized bacteriological agent.The influencing factors and mechanisms of Cu²⁺removal by immobilized bacteria agents were also explored.The main findings are as follows:（1）Using Bacillus subtilis as the test strain,the medium of Bacillus subtilis was selected,and the growth curves of the strains at different Cu²⁺concentrations were drawn,and the results showed that the most suitable medium for Bacillus subtilis was LB medium.Bacillus subtilis has a strong tolerance to Cu²⁺.（2）By analyzing the physical and chemical properties and structural characterization（crystal structure,specific surface area and pores,thermogravity）of biochar fired at 300°C,500°C and 700°C,it is found that biochar fired at 500°C has the best water absorption performance,has a more developed pore structure,good thermal stability,and is more conducive to the fixation and growth of Bacillus subtilis.Compared with the biochar fired at300°C（DBCM-300,DBCM-700）,the immobilized bacteria prepared by biochar fired at 500°C（DBCM-500）fixed more microbial amount,about 1414 nmol P/g,and the removal rate of Cu²⁺by DBCM-500 reached 70.87%after 6 h,which was higher than that of the other two biochar agents.Therefore,dandelion biochar pyrolyzed at 500°C was selected as the immobilization carrier for subsequent research.（3）The optimal conditions for DBCM-500 preparation were determined by three-factor three-level orthogonal experiments:the particle size of biochar was 0.25-0.5 mm,the immobilization time was 24 h,and the fixed ratio of charcoal bacteria was 5 g/L.The influencing factors of the removal of Cu²⁺by the immobilized bacteriological agent DBCM-500were analyzed and the p H of the solution was 5.0,the initial Cu²⁺concentration was 100 mg/L,the reaction temperature was 30℃,the amount of immobilized bacteriological agent was 4 g/L,and the reaction time was 6 h,the removal rate of Cu²⁺reached the maximum,reaching 83.43%.The adsorption effect of Pb²⁺and Cd²⁺metal interference ions on Cu²⁺was studied,and the results showed that when Pb²⁺and Cd²⁺existed as interfering ions,the adsorption of Cu²⁺was inhibited,and the inhibition of Pb²⁺was greater than that of Cd²⁺,and the inhibition of both ions was greater than that of a single interfering ion.（4）The adsorption isothermal model was used to fit the process of Cu²⁺adsorption by immobilized bacteria,and the results showed that the process of removing Cu²⁺by DBCM-500adsorption could be well described by Freundlich isothermal model,and the adsorption process was mainly physical adsorption of multimolecular layers.The fitting analysis of the adsorption kinetic model shows that the adsorption process conforms to the quasi-secondary kinetic model,and the adsorption amount calculated in the quasi-secondary kinetic model at equilibrium is closer to the adsorption amount when the adsorption reaches equilibrium in this experiment.The infrared spectra of biochar DBC-500,the copper-tolerant Bacillus subtilis and the immobilized bacterium DBCM-500 were analyzed,and the results showed that DBCM-500 contained favorable functional groups of biochar and Bacillus subtilis,among which O-H,C=O,C-H and other functional groups participated in the removal of Cu²⁺.Through the control test before and after inactivation,it was found that the removal mechanism of Cu²⁺by DBCM-500 was jointly determined by Bacillus subtilis and biochar DBC-500,accounting for 23.12%and 76.88%of the removal,respectively.The results of this study will provide a reference for the treatment of copper contamination with immobilized bacteria in actual production.