Efficiency Optimization And Mechanism Of Fe²⁺/Na₂S₂O₈-Enterobacter Himalayensis GZ6 In Remediation Of Phenanthrene/anthracene Contaminated Soil

Polycyclic aromatic hydrocarbons（PAHs）,a series of persistent organic pollutant,produced in petroleum processing and coal chemical production are known for their carcinogenicity,mutagenicity,and toxicity to humans.In situ chemical oxidation（ISCO）before microbial remediation can not only reduce the toxicity and improve biodegradability of pollutants,but also mitigate the emergency risk to the ecosystem in the early stage of severe contamination.Oxidation leads to a decrease in p H and an increase in salt content,which is not conducive to natural attenuation and limits the efficiency of bioremediation.Based on the stress of temperature,p H value and salinity of oxidized soil,targeted screening of functional bacteria is expected to break through the restriction of bioremediation by harsh environmental conditions.The high dosage of oxidants not only leads to high remediation costs,but also damages soil quality,which damages soil ecosystems and ecological functions.Based on the oxidation mechanism,it is particularly important to optimize the effectiveness of oxidants and functional bacteria in synergistic remediation of organic contaminated soil.However,the relationship among oxidation,key degrading bacteria and their functions,environmental factors,and key degrading enzyme genes and metabolic pathways is complex.The relationship between soil oxidation and ecological function is not simply positive or negative.The coupling mechanism between oxidants and functional bacteria for remediation of contaminated soil has not yet been explored.In view of the above problems,this study obtained a functional bacterium through targeted domestication screening.The response relationship between different soil physicochemical parameters and microbial survival metabolism was analyzed.The efficiency of persulfate（PS）and functional bacteria in remediation of phenanthrene/anthracene contaminated soil was optimized,and its engineering application prospects were verified.The coupling mechanism of PS and functional bacteria in the remediation of different phenanthrene/anthracene contaminated soils has been revealed.The main results are as follows:（1）One gram-negative bacteria,Enterobacter himalayensis GZ6 was screened from the petrochemical contaminated soil under temperature of 12℃based on the“pyrocatechol-phenanthrene/anthracene”acclimation model.After 9 days of remediation,while p H ranged from 3 to 6,the removal of phenanthrene was 88-100%.The removal of phenanthrene and anthracene by Enterobacter himalayensis GZ6 were both 20%at 12℃,and were 100%and 77%at 28-35℃.Adding 20 mmol/L Na₂SO₄could promote the growth and the PAHs degradation performance of Enterobacter himalayensis GZ6,with the removal of phenanthrene reached 62%.The experimental results of Enterobacter himalayensis GZ6 involved in the remediation of acid-contaminated soil with high SOM and alkaline-contaminated soil with medium and low SOM showed that the abundance of degradation genes such as nah H,HPD,nah G,xln E,cat A,lig A,nag G,ant A,nah C increased significantly,which stimulated a variety of enzymes to induce parallel metabolic pathways and synergistically repaired phenanthrene/anthracene contaminated soil with indigenous bacteria.As a result,Enterobacter himalayensis GZ6 could break through the harsh environmental restrictions of bioremediation such as low p H value and high salinity after oxidation.（2）Remediation of phenanthrene/anthracene contaminated alkaline soil under low temperature by Fe²⁺/PS-Enterobacter himalayensis GZ6 showed that after 7 weeks of combined remediation,the dominant genera of two types of soil community were both Achromobacter,Paenibacillus and Microbacterium;the abundance of protocatechuic acid 3,4-dioxygenase,catechol 1,2-dioxygenase,salicylic acid 5-hydroxylase,protocatechuic acid 4,5-dioxygenase and other functional genes in the soil increased significantly,among which salicylic acid 5-hydroxylase was the highest.Fe²⁺/PS-Enterobacter himalayensis GZ6 enhanced the metabolic pathways of protocatechuic acid and salicylic acid,especially the salicylic acid pathway.（3）Based on the rebound effect and final remediation effect of pollutants in different soils,an in-situ remediation strategy for PS-Enterobacter himalayensis GZ6in complex environments was established.0.24%PS-Enterobacter himalayensis GZ6was used to restore low to medium SOM alkaline soil,and high SOM acidic soil could be repaired by 0.24%PS,inoculating Enterobacter himalayensis GZ6 and 0.48%PS-Enterobacter himalayensis GZ6 separately.Field remediation experiments quantified the effects of indigenous bacteria and abiotic environmental parameters on the remediation performance of PS-Enterobacter himalayensis GZ6.Both C10-C17 and C18-C30 were oxidized and biodegradable,with PS mainly oxidizing C18-C30 and microorganisms mainly degrading C10-C17,and C30-C40 could only be removed by biodegradation.After 103 days of combined remediation,the degradation rate of petroleum hydrocarbons（TPH）was 15%higher than that of PS-indigenous bacteria（71%）and single bioremediation（71%）.Enterobacter himalayensis GZ6 made an important contribution in the middle stage of remediation,and its solution activated indigenous dominant bacteria,such as archaea Nitrosopumilales archaeon and bacteria Acinetobacter indicus,Porticoccaceae-bacrerium,Nocardioidesiriomotensis and Solirubrobacterales bactenium and so on.（4）The coupling mechanism of Fe²⁺/PS-Enterobacter himalayensis GZ6remediation of phenanthrene/anthracene contaminated soil was revealed.The determination of free radicals,soil physical and chemical properties,biological enzyme activity and microbial diversity showed that the alkaline environment produced more SO₄·^-and·OH than the acidic environment and was rapidly consumed.Besides,quinone intermediates produced by microorganisms can act as electron transport carriers in PAHs oxidation,reducing Fe³⁺to Fe²⁺to promote PS activation.The driving force of Fe²⁺/PS-Enterobacter himalayensis GZ6 on soil bioremediation is mainly through the two ways.At first,0.24-0.48%PS decomposes and oxidizes SOM to release nutrients such as sulfate,total available nitrogen,phosphate and iron,and it converts S₂O₈^2-/SO₄·^-into the electron acceptor SO₄^2-.The increase of nutrients and electron acceptors can increase soil microbial species richness,promote the recovery of species diversity,and strengthen biodegradation.Second,Laccase and other enzymes can depolymerize phenolic and non-phenolic lignin polymers through SO₄·^-and·OH as well as the comparable low molecular weight free radicals produced by Fe²⁺activated PS,so that insoluble lignin is mineralized.And herewith soil microorganisms are stimulated by K01897 and K06994 to produce soil urease,polyphenol oxidase,phosphatase,peroxidase,etc.,which indirectly promotes the further degradation of soil PAHs.In summary,this study provided a reliable inoculation source for the combined remediation of PAHs contaminated soil by chemistry and microorganisms,optimized the synergistic remediation efficiency of Fe²⁺/PS-Enterobacter himalayensis GZ6 and verified the engineering application effect,reveald the coupling mechanism of Fe²⁺/PS-Enterobacter himalayensis GZ6 in remediation of phenanthrene/anthracene contaminated soil.The results provided theoretical and technical support for in situ remediation of PAHs contaminated sites.