Preparation Of Biochar Immobilized Bacteria And Its Removal And Stabilization Of Copper In Water And Soil

With the continuous development of industrialization,copper and its compounds have caused more and more serious pollution to the environment.From the perspective of environmental protection and human health,it is of great significance to alleviate copper pollution in water and soil.In recent years,immobilization technology has been widely used in the field of heavy metal pollution treatment due to its low cost,excellent removal effect and no secondary pollution.Based on the immobilization technology,a Cu-resistant strain was selected as the immobilization strain.Different parts of corn（root,stalk,leaf and cob）were selected as raw materials to prepare biochar as the carrier materials.The most suitable carrier materials were selected by comparing the physical and chemical properties,surface structure and immobilization capability of different biochar.On the basis of determining the optimal carrier,the immobilization conditions were optimized to prepare the best biochar immobilization agents.The removal effect of Cu²⁺in water was further discussed and its removal mechanism was analyzed.Finally,the bacterial agent was used to effectively remediation copper contaminated soil,and the effects on soil physical and chemical properties,available copper content and copper form transformation were studied.This study aims to screen out more efficient biochar immobilized bacterial agent and improve the utilization rate of corn straw waste.The main conclusions are as follows:（1）By comparing the physical and chemical properties of four kinds of corn biochar（root,stalk,leaf and cob）,we can know that stalk biochar has the lowest p H and the highest water quantity,which is more conducive to the growth of microorganisms.Scanning electron microscopy and energy spectrum analysis showed that stalk biochar had more mature pore structure and abundant element distribution,which could provide a good habitat for microorganisms.The biomass on the stalk biochar reached 1300 nmol P·g^-1,much higher than that of the other three biochar.Therefore,considering the physical and chemical properties,structural characterization and immobilization ability of the four kinds of biochar,stalk biochar was selected as the carrier material in the immobilized bacterial agent.（2）Based on stalk biochar as carrier,the optimal immobilization conditions were determined as follows:the proportion of copper-resistant bacteria was 10%,the biochar particle size was 0.074-0.147 mm,and the immobilization time was 24 h through three-level and three-factor orthogonal test.（3）The removal of Cu²⁺by the immobilized bacterial agent was further studied.It was found that the removal effect of the immobilized bacterial agent increased with the increase of p H.When the p H was 4.5,the removal amount and removal rate were 34 mg·g^-1 and 64%,respectively.The removal capacity and removal rate reached the peak value at 30℃,which were 35.5 mg·g^-1 and 68%,respectively.When the dosage of bacterial agent was increased to8 g·L^-1,the maximum removal amount reached 35 mg·g^-1,and the dosage was increased to10 g·L^-1,reaching equilibrium,and the removal rate was 71%at this time.With the increase of the initial concentration of Cu²⁺,the removal amount increased and the removal rate continued to decrease.The best removal effect was obtained when the concentration was 400mg·L^-1.With the advance of removal time,the equilibrium removal amount of 77.8%could be achieved in 30 minutes and reached equilibrium in 90 minutes.（4）Through the comparison of the infrared spectra of biochar,copper-resistant bacteria and immobilized bacterial agent,it can be found that the immobilized bacterial agent not only combine stably,but also collect all the functional groups that are beneficial to the removal of Cu²⁺.By comparing the removal effect before and after inactivation,it was found that the removal mechanism of immobilized bacterial agent was mainly determined by the intracellular enrichment of copper-resistant bacteria and the surface adsorption of biochar,in which copper-resistant bacteria and biochar accounted for 44.5%and 55.5%of the total removal amount,respectively.Meanwhile,C-O,-OH,C=O,C=C and other groups were involved in the reaction process.（5）Four kinds of immobilized microbial agents（1%,2%,3%,4%）were added to copper contaminated soil for 60 days.Compared with CK group,the improvement effect of physical and chemical properties under 3%dosage was significantly different（P<0.05）:soil p H increased by 0.5 unit and SOM increased by 125%.The addition ratio of immobilized bacteria was positively correlated with SOM（P<0.01）and p H（P<0.05）.In the aspect of stabilization and restoration,DTPA-Cu content decreased by 41.9%at the dosage of 3%,and copper morphology mainly changed from unstable state to stable state,in which exchangeable copper content decreased from the initial 3%to 0.8%.This series of phenomena indicated that the immobilized microbial inoculum can effectively improve the physical and chemical properties of soil and has a good stabilization effect on copper,and the immobilized microbial inoculum with 3%dosage ratio has the most practical significance in repairing copper contaminated soil.