| PAH_S(polycyclic aromatic hydrocarbons)are trace persistent pollutants in the environment,which bring serious hazards and safety hazards to the ecological environment.Due to the diversity and complexity of soil contamination,and the increasing situation of compound contamination,which leads to the interaction between organic pollutants and heavy metals in soil through physicochemical and biological processes,this increases the difficulty of remediation.According to the previous investigation,the pyrene content in the polluted soil of Dongguan is at a relatively high level,and the cadmium pollution is also serious,so it is urgent to develop a pollution remediation technology with considerable remediation effect,strong environmental adaptability and no secondary pollution.The combined remediation of biochar and microorganisms is an environmentally friendly technology and is one of the more effective remediation methods for organic pollutants in the environment.In this paper,polluted soil from Wangniudun town of Dongguan was used as the source to screen pyrene dominant degrading bacteria.After optimizing the growth conditions,the bacteria were mixed in a certain ratio to build an artificial composite degradation colony with efficient degradation effect.Then biochar was prepared using different biomass materials.The structure and properties of biochar were analyzed based on the characterization results.The biochar and composite bacteria were combined into a composite bacterial agent by adsorption or encapsulation.Further,the degradation effect of the composite on pyrene under cadmium stress was investigated.After a series of degradation conditions were optimized,soil experiments were conducted to investigate the remediation effect of the composite bacterial agent on pyrene-contaminated soil under cadmium stress.Then,the effect of the composite bacterial agent on the physicochemical properties and enzyme activity of the soil was analyzed.Based on the results,the application effect and potential of remediation technology on pyrene-contaminated soil remediation were comprehensively evaluated.The main research results are as follows:Three pyrene dominant degrading strains PZ1,PZ2 and PZ4 were screened from the contaminated soil in Wangniudun town,it was identified that PZ1 belonged to the Bacillus,PZ2 belonged to the Cytobacillu and PZ4 belonged to the Pseudomonas.Their optimal mixing ratio was 1:1:1,and the colony HHP-3X constructed in this ratio had good degradation effect on pyrene(cadmium stress),with a degradation rate of 86.05%at 7 days,rising to 99.13%after 15 d of incubation.In addition,biochar prepared from maize straw,aubergine stalks and deer manure was used as a carrier for the preparation of a composite bacterial agent by means of adsorption and encapsulation of the coupling colony HHP-3X.The shake flask experiment of degradation showed that 5LF-PH had the best degradation effect on pyrene among all composites,and the degradation rate could reach 95.61%.Meanwhile the number of live bacteria fixed by 5LF-PH is significantly higher than other materials.And it also has a significant reduction effect on cadmium content,the reduction rate can reach about 90.00%.However,the preparation temperature,solution p H,the amount of compound bacterial agent and the initial concentration of cadmium all have some effects on the degradation of pyrene by 5LF-PH under the stress of cadmium.Soil simulation experiments revealed that cadmium stress would have a significant inhibitory effect on the free state bacterial population,but biochar coupled with the composite bacterial agent could reduce this inhibitory effect to a certain extent.In contaminated soils with and without the effect of cadmium stress,the removal effect of pyrene by biochar coupled with the composite bacterial agent was significantly higher than that by using free flora alone and biochar alone.Among them,5LF-PH showed good degradation performance,its degradation rate of pyrene in soil reached 90.08%after 45 d of incubation,and its degradation rate of pyrene remained at 80.14%under the influence of cadmium stress.In addition,analysis of the changes in soil physicochemical properties and enzyme activities revealed that the application of biochar complex to the soil significantly improved soil p H and also increased the contents of soil total nitrogen,total phosphorus and organic matter as well as the amount of cation exchange in the soil,effectively promoting the activities of soil acid phosphatase,soil urease and soil peroxidase,thereby promoting the migration and transformation of organic matter,regulating the carbon and nitrogen cycle and improving However,cadmium stress may have some effects on this mechanism.Overall,the biochar composite bacterial agent had a favourable impact on the remediation of cadmium-pyrene complex contaminated soil,which not only could effectively reduce the content of pyrene contamination under cadmium stress,but also could improve soil acidification and increase soil fertility to a certain extent,which provided a theoretical basis for the intensive application of biochar coupled composite bacterial agent in the remediation of cadmium-pyrene complex contamination. |
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