| Chlorpyrifos has been widely used in agricultural production since 1960s.It has a long half-life in soil.How to solve the problem of its residue in soil has been widely concerned.It is an environmentally friendly and economical method to remove chlorpyrifos from soil by using microorganisms that can effectively reduce and detoxify chlorpyrifos.The vicious competition and complex environment of indigenous microorganisms in soil can weaken the viability and competitiveness of chlorpyrifos degrading microorganisms,and more and more attention has been paid to the immobilization technology which can improve the survival rate and removal effect of microorganisms.In this study,chlorpyrifos degradation bacteria H27 was screened in the laboratory,and rice husk biochar was used as immobilized carrier to prepare immobilized degradation bacteria to remove chlorpyrifos.By optimizing the preparation conditions,the removal efficiency of immobilized degradation bacteria was improved,and the influence of environmental factors on the immobilized degradation bacteria was analyzed.Through indoor simulation conditions to explore the actual remediation effect of immobilized degradation bacteria on polluted soil.Through this study,we hope to provide some scientific basis for the practical application of immobilized degradation bacteria.Specific research contents are as follows:?1?Optimization of the immobilization conditions of chlorpyrifos degradation bacteria and study on the removal characteristics of chlorpyrifos poisoning in culture medium:first adsorption and fixation of the degradation bacteria with biochar,and optimization of the fixation conditions with response surface analysis,in order to find the best immobilization conditions.The results showed that the immobilized degrading bacteria had the highest removal rate of chlorpyrifos when 10%of the original bacteria solution was added to the liquid medium of biochar with a particle size of 0.109 mm.In the study on the removal of chlorpyrifos by immobilized degrading bacteria,it was found that when the initial concentration of chlorpyrifos was 25 mg·L-1,the removal rate of the immobilized degrading bacteria was as high as 97.4%after 7 days of culture.?2?Analysis of removal effect of immobilized degradation bacteria on chlorpyrifos poisoning in soil.The results showed that the removal rate of chlorpyrifos in all treatment groups increased rapidly in the first 5 days,and the removal rate of immobilized bacteria group was the highest in all sampling days.The removal rate of biochar group did not change again in the remaining sampling days,and remained stable at 25-30%.The removal rate of free bacteria group also tended to flatten after the 10th day without greater improve-ment.However,the removal rate of the immobilized bacteria group in the residual sampling test still increased slowly,and the upward trend was maintained until the end of the experiment.At the end of the 25 d experiment,the removal rate of the immobilized treatment group was the highest,with the removal rate of 87.6%significantly higher than that of other treatment groups.?3?Study on the effect of immobilized degradation bacteria on soil microorganism:First,through the Biolog test,it was found that all indexes of CK group were the highest,and there was no significant difference between immobilization control group and CK group in all indexes.Each index of the four groups was significantly lower than CK group,and immobilization group was the closest to CK.Second In the experiment of terminal restriction fragment length polymorphism?T-RFLP?,it was found that the relative content of bacterial population in four groups was significantly changed.Similar to the previous four treatments,immobilization group was closer to CK group than other groups,but there was no significant difference between immobilization control group and CK group.Last,in the real-time quantitative PCR?RT-PCR?experiment,it was found that the effect of each treatment group on AOB was greater than that of AOA.In each treatment group,the copy number of AOA amoA gene was larger than AOB,about one order of magnitude higher,but the inhibition of chlorpyrifos pollution on AOB was significantly higher than AOA.However,only the four groups with immobilized degradation bacteria were closer to the control group,and the values were higher than other groups.However,there was no significant difference in AOB copy number between immobilization control group and CK group,and AOA showed activation. |
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